[PATCH v5 00/15] livepatch: hybrid consistency model

[PATCH v5 00/15] livepatch: hybrid consistency model

[Josh Poimboeuf]

Here's v5 of the consistency model, targeted for 4.12.  Only a few minor
changes this time.

I would very much appreciate reviews/acks from the following:

- Michael Ellerman for the powerpc changes in patch 5.

- Heiko Carstens for the s390 changes in patches 6 & 7.

- Peter Zijlstra/Ingo Molnar for the use of task_rq_lock() and the
  modification of do_idle() in patch 13.

Thanks!

Based on linux-next/master (20170213).

v5:
- return -EINVAL in __save_stack_trace_reliable()
- only call show_stack() once
- add save_stack_trace_tsk_reliable() define for !CONFIG_STACKTRACE
- update kernel version and date in ABI doc
- make suggested improvements to livepatch.txt
- update barrier comments
- remove klp_try_complete_transition() call from klp_start_transition()
- move end of klp_try_complete_transition() into klp_complete_transition()
- fix __klp_enable_patch() error path
- check for transition in klp_module_going()

v4:
- add warnings for "impossible" scenarios in __save_stack_trace_reliable()
- sort _TIF_ALLWORK_MASK flags
- move klp_transition_work to transition.c.  This resulted in the following 
  related changes:
  - klp_mutex is now visible to transition.c
  - klp_start_transition() now calls klp_try_complete_transition()
  - klp_try_complete_transition() now sets up the work
  - rearrange code in transition.c accordingly
- klp_reverse_transition(): clear TIF flags and call synchronize_rcu()
- klp_try_complete_transition(): do synchronize_rcu() only when unpatching
- klp_start_transition(): only set TIF flags when necessary
- klp_complete_transition(): add synchronize_rcu() when patching
- klp_ftrace_handler(): put WARN_ON_ONCE back in and add comment
- use for_each_possible_cpu() to patch offline idle tasks
- add warnings to sample module when setting patch.immediate
- don't use pr_debug() with the task rq lock
- add documentation about porting consistency model to other arches
- move klp_patch_pending() to patch 13
- improve several comments and commit messages

v3:
- rebase on new x86 unwinder
- force !HAVE_RELIABLE_STACKTRACE arches to use patch->immediate for
  now, because we don't have a way to transition kthreads otherwise
- rebase s390 TIF_PATCH_PENDING patch onto latest entry code
- update barrier comments and move barrier from the end of
  klp_init_transition() to its callers
- "klp_work" -> "klp_transition_work"
- "klp_patch_task()" -> "klp_update_patch_state()"
- explicit _TIF_ALLWORK_MASK
- change klp_reverse_transition() to not try to complete transition.
  instead modify the work queue delay to zero.
- get rid of klp_schedule_work() in favor of calling
  schedule_delayed_work() directly with a KLP_TRANSITION_DELAY
- initialize klp_target_state to KLP_UNDEFINED
- move klp_target_state assignment to before patch->immediate check in
  klp_init_transition()
- rcu_read_lock() in klp_update_patch_state(), test the thread flag in
  patch task, synchronize_rcu() in klp_complete_transition()
- use kstrtobool() in enabled_store()
- change task_rq_lock() argument type to struct rq_flags
- add several WARN_ON_ONCE assertions for klp_target_state and
  task->patch_state

v2:
- "universe" -> "patch state"
- rename klp_update_task_universe() -> klp_patch_task()
- add preempt IRQ tracking (TF_PREEMPT_IRQ)
- fix print_context_stack_reliable() bug
- improve print_context_stack_reliable() comments
- klp_ftrace_handler comment fixes
- add "patch_state" proc file to tid_base_stuff
- schedule work even for !RELIABLE_STACKTRACE
- forked child inherits patch state from parent
- add detailed comment to livepatch.h klp_func definition about the
  klp_func patched/transition state transitions
- update exit_to_usermode_loop() comment
- clear all TIF_KLP_NEED_UPDATE flags in klp_complete_transition()
- remove unnecessary function externs
- add livepatch documentation, sysfs documentation, /proc documentation
- /proc/pid/patch_state: -1 means no patch is currently being applied/reverted
- "TIF_KLP_NEED_UPDATE" -> "TIF_PATCH_PENDING"
- support for s390 and powerpc-le
- don't assume stacks with dynamic ftrace trampolines are reliable
- add _TIF_ALLWORK_MASK info to commit log

v1.9:
- revive from the dead and rebased
- reliable stacks!
- add support for immediate consistency model
- add a ton of comments
- fix up memory barriers
- remove "allow patch modules to be removed" patch for now, it still 
  needs more discussion and thought - it can be done with something
- "proc/pid/universe" -> "proc/pid/patch_status"
- remove WARN_ON_ONCE from !func condition in ftrace handler -- can
  happen because of RCU
- keep klp_mutex private by putting the work_fn in core.c
- convert states from int to boolean
- remove obsolete '@state' comments
- several header file and include improvements suggested by Jiri S
- change kallsyms_lookup_size_offset() errors from EINVAL -> ENOENT
- change proc file permissions S_IRUGO -> USR
- use klp_for_each_object/func helpers


Jiri Slaby (1):
  livepatch/s390: reorganize TIF thread flag bits

Josh Poimboeuf (12):
  stacktrace/x86: add function for detecting reliable stack traces
  x86/entry: define _TIF_ALLWORK_MASK flags explicitly
  livepatch: create temporary klp_update_patch_state() stub
  livepatch/x86: add TIF_PATCH_PENDING thread flag
  livepatch/powerpc: add TIF_PATCH_PENDING thread flag
  livepatch: separate enabled and patched states
  livepatch: remove unnecessary object loaded check
  livepatch: move patching functions into patch.c
  livepatch: use kstrtobool() in enabled_store()
  livepatch: store function sizes
  livepatch: change to a per-task consistency model
  livepatch: add /proc/<pid>/patch_state

Miroslav Benes (2):
  livepatch/s390: add TIF_PATCH_PENDING thread flag
  livepatch: allow removal of a disabled patch

 Documentation/ABI/testing/sysfs-kernel-livepatch |   8 +
 Documentation/filesystems/proc.txt               |  18 +
 Documentation/livepatch/livepatch.txt            | 214 +++++++--
 arch/Kconfig                                     |   6 +
 arch/powerpc/include/asm/thread_info.h           |   4 +-
 arch/powerpc/kernel/signal.c                     |   4 +
 arch/s390/include/asm/thread_info.h              |  24 +-
 arch/s390/kernel/entry.S                         |  31 +-
 arch/x86/Kconfig                                 |   1 +
 arch/x86/entry/common.c                          |   9 +-
 arch/x86/include/asm/thread_info.h               |  13 +-
 arch/x86/include/asm/unwind.h                    |   6 +
 arch/x86/kernel/stacktrace.c                     |  96 +++-
 arch/x86/kernel/unwind_frame.c                   |   2 +
 fs/proc/base.c                                   |  15 +
 include/linux/init_task.h                        |   9 +
 include/linux/livepatch.h                        |  68 ++-
 include/linux/sched.h                            |   3 +
 include/linux/stacktrace.h                       |   9 +-
 kernel/fork.c                                    |   3 +
 kernel/livepatch/Makefile                        |   2 +-
 kernel/livepatch/core.c                          | 436 +++++++-----------
 kernel/livepatch/patch.c                         | 272 +++++++++++
 kernel/livepatch/patch.h                         |  33 ++
 kernel/livepatch/transition.c                    | 551 +++++++++++++++++++++++
 kernel/livepatch/transition.h                    |  14 +
 kernel/sched/idle.c                              |   4 +
 kernel/stacktrace.c                              |  12 +-
 samples/livepatch/livepatch-sample.c             |  18 +-
 29 files changed, 1531 insertions(+), 354 deletions(-)
 create mode 100644 kernel/livepatch/patch.c
 create mode 100644 kernel/livepatch/patch.h
 create mode 100644 kernel/livepatch/transition.c
 create mode 100644 kernel/livepatch/transition.h

-- 
2.7.4

[PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces

[Josh Poimboeuf]

For live patching and possibly other use cases, a stack trace is only
useful if it can be assured that it's completely reliable.  Add a new
save_stack_trace_tsk_reliable() function to achieve that.

Note that if the target task isn't the current task, and the target task
is allowed to run, then it could be writing the stack while the unwinder
is reading it, resulting in possible corruption.  So the caller of
save_stack_trace_tsk_reliable() must ensure that the task is either
'current' or inactive.

save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
of pt_regs on the stack.  If the pt_regs are not user-mode registers
from a syscall, then they indicate an in-kernel interrupt or exception
(e.g. preemption or a page fault), in which case the stack is considered
unreliable due to the nature of frame pointers.

It also relies on the x86 unwinder's detection of other issues, such as:

- corrupted stack data
- stack grows the wrong way
- stack walk doesn't reach the bottom
- user didn't provide a large enough entries array

Such issues are reported by checking unwind_error() and !unwind_done().

Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
determine at build time whether the function is implemented.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/Kconfig                   |  6 +++
 arch/x86/Kconfig               |  1 +
 arch/x86/include/asm/unwind.h  |  6 +++
 arch/x86/kernel/stacktrace.c   | 96 +++++++++++++++++++++++++++++++++++++++++-
 arch/x86/kernel/unwind_frame.c |  2 +
 include/linux/stacktrace.h     |  9 ++--
 kernel/stacktrace.c            | 12 +++++-
 7 files changed, 126 insertions(+), 6 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 80f3e5e..478b939 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -749,6 +749,12 @@ config HAVE_STACK_VALIDATION
 	  Architecture supports the 'objtool check' host tool command, which
 	  performs compile-time stack metadata validation.
 
+config HAVE_RELIABLE_STACKTRACE
+	bool
+	help
+	  Architecture has a save_stack_trace_tsk_reliable() function which
+	  only returns a stack trace if it can guarantee the trace is reliable.
+
 config HAVE_ARCH_HASH
 	bool
 	default n
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ea82a7b..e79fbf8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -160,6 +160,7 @@ config X86
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_RELIABLE_STACKTRACE		if X86_64 && FRAME_POINTER && STACK_VALIDATION
 	select HAVE_STACK_VALIDATION		if X86_64
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UNSTABLE_SCHED_CLOCK
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index 6fa75b1..137e9cce 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -11,6 +11,7 @@ struct unwind_state {
 	unsigned long stack_mask;
 	struct task_struct *task;
 	int graph_idx;
+	bool error;
 #ifdef CONFIG_FRAME_POINTER
 	unsigned long *bp, *orig_sp;
 	struct pt_regs *regs;
@@ -40,6 +41,11 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
 	__unwind_start(state, task, regs, first_frame);
 }
 
+static inline bool unwind_error(struct unwind_state *state)
+{
+	return state->error;
+}
+
 #ifdef CONFIG_FRAME_POINTER
 
 static inline
diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 0653788..c5490d9 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -74,6 +74,101 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
+#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
+
+#define STACKTRACE_DUMP_ONCE(task) ({				\
+	static bool __section(.data.unlikely) __dumped;		\
+								\
+	if (!__dumped) {					\
+		__dumped = true;				\
+		WARN_ON(1);					\
+		show_stack(task, NULL);				\
+	}							\
+})
+
+static int __save_stack_trace_reliable(struct stack_trace *trace,
+				       struct task_struct *task)
+{
+	struct unwind_state state;
+	struct pt_regs *regs;
+	unsigned long addr;
+
+	for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state);
+	     unwind_next_frame(&state)) {
+
+		regs = unwind_get_entry_regs(&state);
+		if (regs) {
+			/*
+			 * Kernel mode registers on the stack indicate an
+			 * in-kernel interrupt or exception (e.g., preemption
+			 * or a page fault), which can make frame pointers
+			 * unreliable.
+			 */
+			if (!user_mode(regs))
+				return -EINVAL;
+
+			/*
+			 * The last frame contains the user mode syscall
+			 * pt_regs.  Skip it and finish the unwind.
+			 */
+			unwind_next_frame(&state);
+			if (!unwind_done(&state)) {
+				STACKTRACE_DUMP_ONCE(task);
+				return -EINVAL;
+			}
+			break;
+		}
+
+		addr = unwind_get_return_address(&state);
+
+		/*
+		 * A NULL or invalid return address probably means there's some
+		 * generated code which __kernel_text_address() doesn't know
+		 * about.
+		 */
+		if (!addr) {
+			STACKTRACE_DUMP_ONCE(task);
+			return -EINVAL;
+		}
+
+		if (save_stack_address(trace, addr, false))
+			return -EINVAL;
+	}
+
+	/* Check for stack corruption */
+	if (unwind_error(&state)) {
+		STACKTRACE_DUMP_ONCE(task);
+		return -EINVAL;
+	}
+
+	if (trace->nr_entries < trace->max_entries)
+		trace->entries[trace->nr_entries++] = ULONG_MAX;
+
+	return 0;
+}
+
+/*
+ * This function returns an error if it detects any unreliable features of the
+ * stack.  Otherwise it guarantees that the stack trace is reliable.
+ *
+ * If the task is not 'current', the caller *must* ensure the task is inactive.
+ */
+int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+				  struct stack_trace *trace)
+{
+	int ret;
+
+	if (!try_get_task_stack(tsk))
+		return -EINVAL;
+
+	ret = __save_stack_trace_reliable(trace, tsk);
+
+	put_task_stack(tsk);
+
+	return ret;
+}
+#endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */
+
 /* Userspace stacktrace - based on kernel/trace/trace_sysprof.c */
 
 struct stack_frame_user {
@@ -136,4 +231,3 @@ void save_stack_trace_user(struct stack_trace *trace)
 	if (trace->nr_entries < trace->max_entries)
 		trace->entries[trace->nr_entries++] = ULONG_MAX;
 }
-
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 23d1556..b15563d 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -223,6 +223,8 @@ bool unwind_next_frame(struct unwind_state *state)
 	return true;
 
 bad_address:
+	state->error = true;
+
 	/*
 	 * When unwinding a non-current task, the task might actually be
 	 * running on another CPU, in which case it could be modifying its
diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
index 0a34489..4205f71 100644
--- a/include/linux/stacktrace.h
+++ b/include/linux/stacktrace.h
@@ -18,6 +18,8 @@ extern void save_stack_trace_regs(struct pt_regs *regs,
 				  struct stack_trace *trace);
 extern void save_stack_trace_tsk(struct task_struct *tsk,
 				struct stack_trace *trace);
+extern int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+					 struct stack_trace *trace);
 
 extern void print_stack_trace(struct stack_trace *trace, int spaces);
 extern int snprint_stack_trace(char *buf, size_t size,
@@ -29,12 +31,13 @@ extern void save_stack_trace_user(struct stack_trace *trace);
 # define save_stack_trace_user(trace)              do { } while (0)
 #endif
 
-#else
+#else /* !CONFIG_STACKTRACE */
 # define save_stack_trace(trace)			do { } while (0)
 # define save_stack_trace_tsk(tsk, trace)		do { } while (0)
 # define save_stack_trace_user(trace)			do { } while (0)
 # define print_stack_trace(trace, spaces)		do { } while (0)
 # define snprint_stack_trace(buf, size, trace, spaces)	do { } while (0)
-#endif
+# define save_stack_trace_tsk_reliable(tsk, trace)	({ -ENOSYS; })
+#endif /* CONFIG_STACKTRACE */
 
-#endif
+#endif /* __LINUX_STACKTRACE_H */
diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 9c15a91..f8edee9 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -54,8 +54,8 @@ int snprint_stack_trace(char *buf, size_t size,
 EXPORT_SYMBOL_GPL(snprint_stack_trace);
 
 /*
- * Architectures that do not implement save_stack_trace_tsk or
- * save_stack_trace_regs get this weak alias and a once-per-bootup warning
+ * Architectures that do not implement save_stack_trace_*()
+ * get these weak aliases and once-per-bootup warnings
  * (whenever this facility is utilized - for example by procfs):
  */
 __weak void
@@ -69,3 +69,11 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 {
 	WARN_ONCE(1, KERN_INFO "save_stack_trace_regs() not implemented yet.\n");
 }
+
+__weak int
+save_stack_trace_tsk_reliable(struct task_struct *tsk,
+			      struct stack_trace *trace)
+{
+	WARN_ONCE(1, KERN_INFO "save_stack_tsk_reliable() not implemented yet.\n");
+	return -ENOSYS;
+}
-- 
2.7.4

[PATCH v5 02/15] x86/entry: define _TIF_ALLWORK_MASK flags explicitly

[Josh Poimboeuf]

The _TIF_ALLWORK_MASK macro automatically includes the least-significant
16 bits of the thread_info flags, which is less than obvious and tends
to create confusion and surprises when reading or modifying the code.

Define the flags explicitly.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
 arch/x86/include/asm/thread_info.h | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index ad6f5eb0..207d0d9 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -73,9 +73,6 @@ struct thread_info {
  * thread information flags
  * - these are process state flags that various assembly files
  *   may need to access
- * - pending work-to-be-done flags are in LSW
- * - other flags in MSW
- * Warning: layout of LSW is hardcoded in entry.S
  */
 #define TIF_SYSCALL_TRACE	0	/* syscall trace active */
 #define TIF_NOTIFY_RESUME	1	/* callback before returning to user */
@@ -103,8 +100,8 @@ struct thread_info {
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
-#define _TIF_SINGLESTEP		(1 << TIF_SINGLESTEP)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_SINGLESTEP		(1 << TIF_SINGLESTEP)
 #define _TIF_SYSCALL_EMU	(1 << TIF_SYSCALL_EMU)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
@@ -133,8 +130,10 @@ struct thread_info {
 
 /* work to do on any return to user space */
 #define _TIF_ALLWORK_MASK						\
-	((0x0000FFFF & ~_TIF_SECCOMP) | _TIF_SYSCALL_TRACEPOINT |	\
-	_TIF_NOHZ)
+	(_TIF_SYSCALL_TRACE | _TIF_NOTIFY_RESUME | _TIF_SIGPENDING |	\
+	 _TIF_NEED_RESCHED | _TIF_SINGLESTEP | _TIF_SYSCALL_EMU |	\
+	 _TIF_SYSCALL_AUDIT | _TIF_USER_RETURN_NOTIFY | _TIF_UPROBE |	\
+	 _TIF_NOHZ | _TIF_SYSCALL_TRACEPOINT)
 
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW							\
-- 
2.7.4

[PATCH v5 03/15] livepatch: create temporary klp_update_patch_state() stub

[Josh Poimboeuf]

Create temporary stubs for klp_update_patch_state() so we can add
TIF_PATCH_PENDING to different architectures in separate patches without
breaking build bisectability.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/livepatch.h | 5 ++++-
 kernel/livepatch/core.c   | 3 +++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 9072f04..5cc20e5 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -123,10 +123,13 @@ void arch_klp_init_object_loaded(struct klp_patch *patch,
 int klp_module_coming(struct module *mod);
 void klp_module_going(struct module *mod);
 
+void klp_update_patch_state(struct task_struct *task);
+
 #else /* !CONFIG_LIVEPATCH */
 
 static inline int klp_module_coming(struct module *mod) { return 0; }
-static inline void klp_module_going(struct module *mod) { }
+static inline void klp_module_going(struct module *mod) {}
+static inline void klp_update_patch_state(struct task_struct *task) {}
 
 #endif /* CONFIG_LIVEPATCH */
 
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index af46438..217b39d 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -64,6 +64,9 @@ static LIST_HEAD(klp_ops);
 
 static struct kobject *klp_root_kobj;
 
+/* TODO: temporary stub */
+void klp_update_patch_state(struct task_struct *task) {}
+
 static struct klp_ops *klp_find_ops(unsigned long old_addr)
 {
 	struct klp_ops *ops;
-- 
2.7.4

[PATCH v5 04/15] livepatch/x86: add TIF_PATCH_PENDING thread flag

[Josh Poimboeuf]

Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
per-task consistency model for x86_64.  The bit getting set indicates
the thread has a pending patch which needs to be applied when the thread
exits the kernel.

The bit is placed in the _TIF_ALLWORK_MASK macro, which results in
exit_to_usermode_loop() calling klp_update_patch_state() when it's set.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
 arch/x86/entry/common.c            | 9 ++++++---
 arch/x86/include/asm/thread_info.h | 4 +++-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index b83c61c..6a9d564 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -21,6 +21,7 @@
 #include <linux/context_tracking.h>
 #include <linux/user-return-notifier.h>
 #include <linux/uprobes.h>
+#include <linux/livepatch.h>
 
 #include <asm/desc.h>
 #include <asm/traps.h>
@@ -129,14 +130,13 @@ static long syscall_trace_enter(struct pt_regs *regs)
 
 #define EXIT_TO_USERMODE_LOOP_FLAGS				\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
-	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
+	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
 
 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 {
 	/*
 	 * In order to return to user mode, we need to have IRQs off with
-	 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
-	 * _TIF_UPROBE, or _TIF_NEED_RESCHED set.  Several of these flags
+	 * none of EXIT_TO_USERMODE_LOOP_FLAGS set.  Several of these flags
 	 * can be set at any time on preemptable kernels if we have IRQs on,
 	 * so we need to loop.  Disabling preemption wouldn't help: doing the
 	 * work to clear some of the flags can sleep.
@@ -163,6 +163,9 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 			fire_user_return_notifiers();
 
+		if (cached_flags & _TIF_PATCH_PENDING)
+			klp_update_patch_state(current);
+
 		/* Disable IRQs and retry */
 		local_irq_disable();
 
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 207d0d9..83372dc 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -84,6 +84,7 @@ struct thread_info {
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_USER_RETURN_NOTIFY	11	/* notify kernel of userspace return */
 #define TIF_UPROBE		12	/* breakpointed or singlestepping */
+#define TIF_PATCH_PENDING	13	/* pending live patching update */
 #define TIF_NOTSC		16	/* TSC is not accessible in userland */
 #define TIF_IA32		17	/* IA32 compatibility process */
 #define TIF_NOHZ		19	/* in adaptive nohz mode */
@@ -107,6 +108,7 @@ struct thread_info {
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_USER_RETURN_NOTIFY	(1 << TIF_USER_RETURN_NOTIFY)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
+#define _TIF_PATCH_PENDING	(1 << TIF_PATCH_PENDING)
 #define _TIF_NOTSC		(1 << TIF_NOTSC)
 #define _TIF_IA32		(1 << TIF_IA32)
 #define _TIF_NOHZ		(1 << TIF_NOHZ)
@@ -133,7 +135,7 @@ struct thread_info {
 	(_TIF_SYSCALL_TRACE | _TIF_NOTIFY_RESUME | _TIF_SIGPENDING |	\
 	 _TIF_NEED_RESCHED | _TIF_SINGLESTEP | _TIF_SYSCALL_EMU |	\
 	 _TIF_SYSCALL_AUDIT | _TIF_USER_RETURN_NOTIFY | _TIF_UPROBE |	\
-	 _TIF_NOHZ | _TIF_SYSCALL_TRACEPOINT)
+	 _TIF_PATCH_PENDING | _TIF_NOHZ | _TIF_SYSCALL_TRACEPOINT)
 
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW							\
-- 
2.7.4

[PATCH v5 05/15] livepatch/powerpc: add TIF_PATCH_PENDING thread flag

[Josh Poimboeuf]

Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
per-task consistency model for powerpc.  The bit getting set indicates
the thread has a pending patch which needs to be applied when the thread
exits the kernel.

The bit is included in the _TIF_USER_WORK_MASK macro so that
do_notify_resume() and klp_update_patch_state() get called when the bit
is set.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/thread_info.h | 4 +++-
 arch/powerpc/kernel/signal.c           | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 87e4b2d..6fc6464 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -92,6 +92,7 @@ static inline struct thread_info *current_thread_info(void)
 					   TIF_NEED_RESCHED */
 #define TIF_32BIT		4	/* 32 bit binary */
 #define TIF_RESTORE_TM		5	/* need to restore TM FP/VEC/VSX */
+#define TIF_PATCH_PENDING	6	/* pending live patching update */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 #define TIF_SINGLESTEP		8	/* singlestepping active */
 #define TIF_NOHZ		9	/* in adaptive nohz mode */
@@ -115,6 +116,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_32BIT		(1<<TIF_32BIT)
 #define _TIF_RESTORE_TM		(1<<TIF_RESTORE_TM)
+#define _TIF_PATCH_PENDING	(1<<TIF_PATCH_PENDING)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
@@ -131,7 +133,7 @@ static inline struct thread_info *current_thread_info(void)
 
 #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
 				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
-				 _TIF_RESTORE_TM)
+				 _TIF_RESTORE_TM | _TIF_PATCH_PENDING)
 #define _TIF_PERSYSCALL_MASK	(_TIF_RESTOREALL|_TIF_NOERROR)
 
 /* Bits in local_flags */
diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index 3a36711..e9436c5 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -14,6 +14,7 @@
 #include <linux/uprobes.h>
 #include <linux/key.h>
 #include <linux/context_tracking.h>
+#include <linux/livepatch.h>
 #include <asm/hw_breakpoint.h>
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -162,6 +163,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 		tracehook_notify_resume(regs);
 	}
 
+	if (thread_info_flags & _TIF_PATCH_PENDING)
+		klp_update_patch_state(current);
+
 	user_enter();
 }
 
-- 
2.7.4

[PATCH v5 06/15] livepatch/s390: reorganize TIF thread flag bits

[Josh Poimboeuf]

From: Jiri Slaby <jslaby@suse.cz>

Group the TIF thread flag bits by their inclusion in the _TIF_WORK and
_TIF_TRACE macros.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
---
 arch/s390/include/asm/thread_info.h | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index a5b54a4..4977668 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -51,14 +51,12 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 /*
  * thread information flags bit numbers
  */
+/* _TIF_WORK bits */
 #define TIF_NOTIFY_RESUME	0	/* callback before returning to user */
 #define TIF_SIGPENDING		1	/* signal pending */
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
-#define TIF_SYSCALL_TRACE	3	/* syscall trace active */
-#define TIF_SYSCALL_AUDIT	4	/* syscall auditing active */
-#define TIF_SECCOMP		5	/* secure computing */
-#define TIF_SYSCALL_TRACEPOINT	6	/* syscall tracepoint instrumentation */
-#define TIF_UPROBE		7	/* breakpointed or single-stepping */
+#define TIF_UPROBE		3	/* breakpointed or single-stepping */
+
 #define TIF_31BIT		16	/* 32bit process */
 #define TIF_MEMDIE		17	/* is terminating due to OOM killer */
 #define TIF_RESTORE_SIGMASK	18	/* restore signal mask in do_signal() */
@@ -66,15 +64,23 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define TIF_BLOCK_STEP		20	/* This task is block stepped */
 #define TIF_UPROBE_SINGLESTEP	21	/* This task is uprobe single stepped */
 
+/* _TIF_TRACE bits */
+#define TIF_SYSCALL_TRACE	24	/* syscall trace active */
+#define TIF_SYSCALL_AUDIT	25	/* syscall auditing active */
+#define TIF_SECCOMP		26	/* secure computing */
+#define TIF_SYSCALL_TRACEPOINT	27	/* syscall tracepoint instrumentation */
+
 #define _TIF_NOTIFY_RESUME	_BITUL(TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		_BITUL(TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	_BITUL(TIF_NEED_RESCHED)
+#define _TIF_UPROBE		_BITUL(TIF_UPROBE)
+
+#define _TIF_31BIT		_BITUL(TIF_31BIT)
+#define _TIF_SINGLE_STEP	_BITUL(TIF_SINGLE_STEP)
+
 #define _TIF_SYSCALL_TRACE	_BITUL(TIF_SYSCALL_TRACE)
 #define _TIF_SYSCALL_AUDIT	_BITUL(TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		_BITUL(TIF_SECCOMP)
 #define _TIF_SYSCALL_TRACEPOINT	_BITUL(TIF_SYSCALL_TRACEPOINT)
-#define _TIF_UPROBE		_BITUL(TIF_UPROBE)
-#define _TIF_31BIT		_BITUL(TIF_31BIT)
-#define _TIF_SINGLE_STEP	_BITUL(TIF_SINGLE_STEP)
 
 #endif /* _ASM_THREAD_INFO_H */
-- 
2.7.4

[PATCH v5 07/15] livepatch/s390: add TIF_PATCH_PENDING thread flag

[Josh Poimboeuf]

From: Miroslav Benes <mbenes@suse.cz>

Update a task's patch state when returning from a system call or user
space interrupt, or after handling a signal.

This greatly increases the chances of a patch operation succeeding.  If
a task is I/O bound, it can be patched when returning from a system
call.  If a task is CPU bound, it can be patched when returning from an
interrupt.  If a task is sleeping on a to-be-patched function, the user
can send SIGSTOP and SIGCONT to force it to switch.

Since there are two ways the syscall can be restarted on return from a
signal handling process, it is important to clear the flag before
do_signal() is called. Otherwise we could miss the migration if we used
SIGSTOP/SIGCONT procedure or fake signal to migrate patching blocking
tasks. If we place our hook to sysc_work label in entry before
TIF_SIGPENDING is evaluated we kill two birds with one stone. The task
is correctly migrated in all return paths from a syscall.

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/s390/include/asm/thread_info.h |  2 ++
 arch/s390/kernel/entry.S            | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index 4977668..646845e 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -56,6 +56,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define TIF_SIGPENDING		1	/* signal pending */
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_UPROBE		3	/* breakpointed or single-stepping */
+#define TIF_PATCH_PENDING	4	/* pending live patching update */
 
 #define TIF_31BIT		16	/* 32bit process */
 #define TIF_MEMDIE		17	/* is terminating due to OOM killer */
@@ -74,6 +75,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define _TIF_SIGPENDING		_BITUL(TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	_BITUL(TIF_NEED_RESCHED)
 #define _TIF_UPROBE		_BITUL(TIF_UPROBE)
+#define _TIF_PATCH_PENDING	_BITUL(TIF_PATCH_PENDING)
 
 #define _TIF_31BIT		_BITUL(TIF_31BIT)
 #define _TIF_SINGLE_STEP	_BITUL(TIF_SINGLE_STEP)
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 34ab7e8..9a15eac 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -47,7 +47,7 @@ STACK_SIZE  = 1 << STACK_SHIFT
 STACK_INIT = STACK_SIZE - STACK_FRAME_OVERHEAD - __PT_SIZE
 
 _TIF_WORK	= (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED | \
-		   _TIF_UPROBE)
+		   _TIF_UPROBE | _TIF_PATCH_PENDING)
 _TIF_TRACE	= (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | \
 		   _TIF_SYSCALL_TRACEPOINT)
 _CIF_WORK	= (_CIF_MCCK_PENDING | _CIF_ASCE | _CIF_FPU)
@@ -333,6 +333,11 @@ ENTRY(system_call)
 #endif
 	TSTMSK	__PT_FLAGS(%r11),_PIF_PER_TRAP
 	jo	.Lsysc_singlestep
+#ifdef CONFIG_LIVEPATCH
+	TSTMSK	__TI_flags(%r12),_TIF_PATCH_PENDING
+	jo	.Lsysc_patch_pending	# handle live patching just before
+					# signals and possible syscall restart
+#endif
 	TSTMSK	__TI_flags(%r12),_TIF_SIGPENDING
 	jo	.Lsysc_sigpending
 	TSTMSK	__TI_flags(%r12),_TIF_NOTIFY_RESUME
@@ -405,6 +410,16 @@ ENTRY(system_call)
 #endif
 
 #
+# _TIF_PATCH_PENDING is set, call klp_update_patch_state
+#
+#ifdef CONFIG_LIVEPATCH
+.Lsysc_patch_pending:
+	lg	%r2,__LC_CURRENT	# pass pointer to task struct
+	larl	%r14,.Lsysc_return
+	jg	klp_update_patch_state
+#endif
+
+#
 # _PIF_PER_TRAP is set, call do_per_trap
 #
 .Lsysc_singlestep:
@@ -654,6 +669,10 @@ ENTRY(io_int_handler)
 	jo	.Lio_mcck_pending
 	TSTMSK	__TI_flags(%r12),_TIF_NEED_RESCHED
 	jo	.Lio_reschedule
+#ifdef CONFIG_LIVEPATCH
+	TSTMSK	__TI_flags(%r12),_TIF_PATCH_PENDING
+	jo	.Lio_patch_pending
+#endif
 	TSTMSK	__TI_flags(%r12),_TIF_SIGPENDING
 	jo	.Lio_sigpending
 	TSTMSK	__TI_flags(%r12),_TIF_NOTIFY_RESUME
@@ -700,6 +719,16 @@ ENTRY(io_int_handler)
 	j	.Lio_return
 
 #
+# _TIF_PATCH_PENDING is set, call klp_update_patch_state
+#
+#ifdef CONFIG_LIVEPATCH
+.Lio_patch_pending:
+	lg	%r2,__LC_CURRENT	# pass pointer to task struct
+	larl	%r14,.Lio_return
+	jg	klp_update_patch_state
+#endif
+
+#
 # _TIF_SIGPENDING or is set, call do_signal
 #
 .Lio_sigpending:
-- 
2.7.4

[PATCH v5 08/15] livepatch: separate enabled and patched states

[Josh Poimboeuf]

Once we have a consistency model, patches and their objects will be
enabled and disabled at different times.  For example, when a patch is
disabled, its loaded objects' funcs can remain registered with ftrace
indefinitely until the unpatching operation is complete and they're no
longer in use.

It's less confusing if we give them different names: patches can be
enabled or disabled; objects (and their funcs) can be patched or
unpatched:

- Enabled means that a patch is logically enabled (but not necessarily
  fully applied).

- Patched means that an object's funcs are registered with ftrace and
  added to the klp_ops func stack.

Also, since these states are binary, represent them with booleans
instead of ints.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
 include/linux/livepatch.h | 17 ++++-------
 kernel/livepatch/core.c   | 72 +++++++++++++++++++++++------------------------
 2 files changed, 42 insertions(+), 47 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 5cc20e5..9787a63 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -28,11 +28,6 @@
 
 #include <asm/livepatch.h>
 
-enum klp_state {
-	KLP_DISABLED,
-	KLP_ENABLED
-};
-
 /**
  * struct klp_func - function structure for live patching
  * @old_name:	name of the function to be patched
@@ -41,8 +36,8 @@ enum klp_state {
  *		can be found (optional)
  * @old_addr:	the address of the function being patched
  * @kobj:	kobject for sysfs resources
- * @state:	tracks function-level patch application state
  * @stack_node:	list node for klp_ops func_stack list
+ * @patched:	the func has been added to the klp_ops list
  */
 struct klp_func {
 	/* external */
@@ -60,8 +55,8 @@ struct klp_func {
 	/* internal */
 	unsigned long old_addr;
 	struct kobject kobj;
-	enum klp_state state;
 	struct list_head stack_node;
+	bool patched;
 };
 
 /**
@@ -71,7 +66,7 @@ struct klp_func {
  * @kobj:	kobject for sysfs resources
  * @mod:	kernel module associated with the patched object
  * 		(NULL for vmlinux)
- * @state:	tracks object-level patch application state
+ * @patched:	the object's funcs have been added to the klp_ops list
  */
 struct klp_object {
 	/* external */
@@ -81,7 +76,7 @@ struct klp_object {
 	/* internal */
 	struct kobject kobj;
 	struct module *mod;
-	enum klp_state state;
+	bool patched;
 };
 
 /**
@@ -90,7 +85,7 @@ struct klp_object {
  * @objs:	object entries for kernel objects to be patched
  * @list:	list node for global list of registered patches
  * @kobj:	kobject for sysfs resources
- * @state:	tracks patch-level application state
+ * @enabled:	the patch is enabled (but operation may be incomplete)
  */
 struct klp_patch {
 	/* external */
@@ -100,7 +95,7 @@ struct klp_patch {
 	/* internal */
 	struct list_head list;
 	struct kobject kobj;
-	enum klp_state state;
+	bool enabled;
 };
 
 #define klp_for_each_object(patch, obj) \
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 217b39d..2dbd355 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -348,11 +348,11 @@ static unsigned long klp_get_ftrace_location(unsigned long faddr)
 }
 #endif
 
-static void klp_disable_func(struct klp_func *func)
+static void klp_unpatch_func(struct klp_func *func)
 {
 	struct klp_ops *ops;
 
-	if (WARN_ON(func->state != KLP_ENABLED))
+	if (WARN_ON(!func->patched))
 		return;
 	if (WARN_ON(!func->old_addr))
 		return;
@@ -378,10 +378,10 @@ static void klp_disable_func(struct klp_func *func)
 		list_del_rcu(&func->stack_node);
 	}
 
-	func->state = KLP_DISABLED;
+	func->patched = false;
 }
 
-static int klp_enable_func(struct klp_func *func)
+static int klp_patch_func(struct klp_func *func)
 {
 	struct klp_ops *ops;
 	int ret;
@@ -389,7 +389,7 @@ static int klp_enable_func(struct klp_func *func)
 	if (WARN_ON(!func->old_addr))
 		return -EINVAL;
 
-	if (WARN_ON(func->state != KLP_DISABLED))
+	if (WARN_ON(func->patched))
 		return -EINVAL;
 
 	ops = klp_find_ops(func->old_addr);
@@ -437,7 +437,7 @@ static int klp_enable_func(struct klp_func *func)
 		list_add_rcu(&func->stack_node, &ops->func_stack);
 	}
 
-	func->state = KLP_ENABLED;
+	func->patched = true;
 
 	return 0;
 
@@ -448,36 +448,36 @@ static int klp_enable_func(struct klp_func *func)
 	return ret;
 }
 
-static void klp_disable_object(struct klp_object *obj)
+static void klp_unpatch_object(struct klp_object *obj)
 {
 	struct klp_func *func;
 
 	klp_for_each_func(obj, func)
-		if (func->state == KLP_ENABLED)
-			klp_disable_func(func);
+		if (func->patched)
+			klp_unpatch_func(func);
 
-	obj->state = KLP_DISABLED;
+	obj->patched = false;
 }
 
-static int klp_enable_object(struct klp_object *obj)
+static int klp_patch_object(struct klp_object *obj)
 {
 	struct klp_func *func;
 	int ret;
 
-	if (WARN_ON(obj->state != KLP_DISABLED))
+	if (WARN_ON(obj->patched))
 		return -EINVAL;
 
 	if (WARN_ON(!klp_is_object_loaded(obj)))
 		return -EINVAL;
 
 	klp_for_each_func(obj, func) {
-		ret = klp_enable_func(func);
+		ret = klp_patch_func(func);
 		if (ret) {
-			klp_disable_object(obj);
+			klp_unpatch_object(obj);
 			return ret;
 		}
 	}
-	obj->state = KLP_ENABLED;
+	obj->patched = true;
 
 	return 0;
 }
@@ -488,17 +488,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
 
 	/* enforce stacking: only the last enabled patch can be disabled */
 	if (!list_is_last(&patch->list, &klp_patches) &&
-	    list_next_entry(patch, list)->state == KLP_ENABLED)
+	    list_next_entry(patch, list)->enabled)
 		return -EBUSY;
 
 	pr_notice("disabling patch '%s'\n", patch->mod->name);
 
 	klp_for_each_object(patch, obj) {
-		if (obj->state == KLP_ENABLED)
-			klp_disable_object(obj);
+		if (obj->patched)
+			klp_unpatch_object(obj);
 	}
 
-	patch->state = KLP_DISABLED;
+	patch->enabled = false;
 
 	return 0;
 }
@@ -522,7 +522,7 @@ int klp_disable_patch(struct klp_patch *patch)
 		goto err;
 	}
 
-	if (patch->state == KLP_DISABLED) {
+	if (!patch->enabled) {
 		ret = -EINVAL;
 		goto err;
 	}
@@ -540,12 +540,12 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	struct klp_object *obj;
 	int ret;
 
-	if (WARN_ON(patch->state != KLP_DISABLED))
+	if (WARN_ON(patch->enabled))
 		return -EINVAL;
 
 	/* enforce stacking: only the first disabled patch can be enabled */
 	if (patch->list.prev != &klp_patches &&
-	    list_prev_entry(patch, list)->state == KLP_DISABLED)
+	    !list_prev_entry(patch, list)->enabled)
 		return -EBUSY;
 
 	pr_notice("enabling patch '%s'\n", patch->mod->name);
@@ -554,12 +554,12 @@ static int __klp_enable_patch(struct klp_patch *patch)
 		if (!klp_is_object_loaded(obj))
 			continue;
 
-		ret = klp_enable_object(obj);
+		ret = klp_patch_object(obj);
 		if (ret)
 			goto unregister;
 	}
 
-	patch->state = KLP_ENABLED;
+	patch->enabled = true;
 
 	return 0;
 
@@ -617,20 +617,20 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 	if (ret)
 		return -EINVAL;
 
-	if (val != KLP_DISABLED && val != KLP_ENABLED)
+	if (val > 1)
 		return -EINVAL;
 
 	patch = container_of(kobj, struct klp_patch, kobj);
 
 	mutex_lock(&klp_mutex);
 
-	if (val == patch->state) {
+	if (patch->enabled == val) {
 		/* already in requested state */
 		ret = -EINVAL;
 		goto err;
 	}
 
-	if (val == KLP_ENABLED) {
+	if (val) {
 		ret = __klp_enable_patch(patch);
 		if (ret)
 			goto err;
@@ -655,7 +655,7 @@ static ssize_t enabled_show(struct kobject *kobj,
 	struct klp_patch *patch;
 
 	patch = container_of(kobj, struct klp_patch, kobj);
-	return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->state);
+	return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
 }
 
 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
@@ -749,7 +749,7 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 		return -EINVAL;
 
 	INIT_LIST_HEAD(&func->stack_node);
-	func->state = KLP_DISABLED;
+	func->patched = false;
 
 	/* The format for the sysfs directory is <function,sympos> where sympos
 	 * is the nth occurrence of this symbol in kallsyms for the patched
@@ -804,7 +804,7 @@ static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
 	if (!obj->funcs)
 		return -EINVAL;
 
-	obj->state = KLP_DISABLED;
+	obj->patched = false;
 	obj->mod = NULL;
 
 	klp_find_object_module(obj);
@@ -845,7 +845,7 @@ static int klp_init_patch(struct klp_patch *patch)
 
 	mutex_lock(&klp_mutex);
 
-	patch->state = KLP_DISABLED;
+	patch->enabled = false;
 
 	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
 				   klp_root_kobj, "%s", patch->mod->name);
@@ -891,7 +891,7 @@ int klp_unregister_patch(struct klp_patch *patch)
 		goto out;
 	}
 
-	if (patch->state == KLP_ENABLED) {
+	if (patch->enabled) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -978,13 +978,13 @@ int klp_module_coming(struct module *mod)
 				goto err;
 			}
 
-			if (patch->state == KLP_DISABLED)
+			if (!patch->enabled)
 				break;
 
 			pr_notice("applying patch '%s' to loading module '%s'\n",
 				  patch->mod->name, obj->mod->name);
 
-			ret = klp_enable_object(obj);
+			ret = klp_patch_object(obj);
 			if (ret) {
 				pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
 					patch->mod->name, obj->mod->name, ret);
@@ -1035,10 +1035,10 @@ void klp_module_going(struct module *mod)
 			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
 				continue;
 
-			if (patch->state != KLP_DISABLED) {
+			if (patch->enabled) {
 				pr_notice("reverting patch '%s' on unloading module '%s'\n",
 					  patch->mod->name, obj->mod->name);
-				klp_disable_object(obj);
+				klp_unpatch_object(obj);
 			}
 
 			klp_free_object_loaded(obj);
-- 
2.7.4

[PATCH v5 09/15] livepatch: remove unnecessary object loaded check

[Josh Poimboeuf]

klp_patch_object()'s callers already ensure that the object is loaded,
so its call to klp_is_object_loaded() is unnecessary.

This will also make it possible to move the patching code into a
separate file.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
 kernel/livepatch/core.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 2dbd355..47ed643 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -467,9 +467,6 @@ static int klp_patch_object(struct klp_object *obj)
 	if (WARN_ON(obj->patched))
 		return -EINVAL;
 
-	if (WARN_ON(!klp_is_object_loaded(obj)))
-		return -EINVAL;
-
 	klp_for_each_func(obj, func) {
 		ret = klp_patch_func(func);
 		if (ret) {
-- 
2.7.4

[PATCH v5 10/15] livepatch: move patching functions into patch.c

[Josh Poimboeuf]

Move functions related to the actual patching of functions and objects
into a new patch.c file.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
 kernel/livepatch/Makefile |   2 +-
 kernel/livepatch/core.c   | 202 +------------------------------------------
 kernel/livepatch/patch.c  | 213 ++++++++++++++++++++++++++++++++++++++++++++++
 kernel/livepatch/patch.h  |  32 +++++++
 4 files changed, 247 insertions(+), 202 deletions(-)
 create mode 100644 kernel/livepatch/patch.c
 create mode 100644 kernel/livepatch/patch.h

diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
index e8780c0..e136dad 100644
--- a/kernel/livepatch/Makefile
+++ b/kernel/livepatch/Makefile
@@ -1,3 +1,3 @@
 obj-$(CONFIG_LIVEPATCH) += livepatch.o
 
-livepatch-objs := core.o
+livepatch-objs := core.o patch.o
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 47ed643..6a137e1 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -24,32 +24,13 @@
 #include <linux/kernel.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
-#include <linux/ftrace.h>
 #include <linux/list.h>
 #include <linux/kallsyms.h>
 #include <linux/livepatch.h>
 #include <linux/elf.h>
 #include <linux/moduleloader.h>
 #include <asm/cacheflush.h>
-
-/**
- * struct klp_ops - structure for tracking registered ftrace ops structs
- *
- * A single ftrace_ops is shared between all enabled replacement functions
- * (klp_func structs) which have the same old_addr.  This allows the switch
- * between function versions to happen instantaneously by updating the klp_ops
- * struct's func_stack list.  The winner is the klp_func at the top of the
- * func_stack (front of the list).
- *
- * @node:	node for the global klp_ops list
- * @func_stack:	list head for the stack of klp_func's (active func is on top)
- * @fops:	registered ftrace ops struct
- */
-struct klp_ops {
-	struct list_head node;
-	struct list_head func_stack;
-	struct ftrace_ops fops;
-};
+#include "patch.h"
 
 /*
  * The klp_mutex protects the global lists and state transitions of any
@@ -60,28 +41,12 @@ struct klp_ops {
 static DEFINE_MUTEX(klp_mutex);
 
 static LIST_HEAD(klp_patches);
-static LIST_HEAD(klp_ops);
 
 static struct kobject *klp_root_kobj;
 
 /* TODO: temporary stub */
 void klp_update_patch_state(struct task_struct *task) {}
 
-static struct klp_ops *klp_find_ops(unsigned long old_addr)
-{
-	struct klp_ops *ops;
-	struct klp_func *func;
-
-	list_for_each_entry(ops, &klp_ops, node) {
-		func = list_first_entry(&ops->func_stack, struct klp_func,
-					stack_node);
-		if (func->old_addr == old_addr)
-			return ops;
-	}
-
-	return NULL;
-}
-
 static bool klp_is_module(struct klp_object *obj)
 {
 	return obj->name;
@@ -314,171 +279,6 @@ static int klp_write_object_relocations(struct module *pmod,
 	return ret;
 }
 
-static void notrace klp_ftrace_handler(unsigned long ip,
-				       unsigned long parent_ip,
-				       struct ftrace_ops *fops,
-				       struct pt_regs *regs)
-{
-	struct klp_ops *ops;
-	struct klp_func *func;
-
-	ops = container_of(fops, struct klp_ops, fops);
-
-	rcu_read_lock();
-	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
-				      stack_node);
-	if (WARN_ON_ONCE(!func))
-		goto unlock;
-
-	klp_arch_set_pc(regs, (unsigned long)func->new_func);
-unlock:
-	rcu_read_unlock();
-}
-
-/*
- * Convert a function address into the appropriate ftrace location.
- *
- * Usually this is just the address of the function, but on some architectures
- * it's more complicated so allow them to provide a custom behaviour.
- */
-#ifndef klp_get_ftrace_location
-static unsigned long klp_get_ftrace_location(unsigned long faddr)
-{
-	return faddr;
-}
-#endif
-
-static void klp_unpatch_func(struct klp_func *func)
-{
-	struct klp_ops *ops;
-
-	if (WARN_ON(!func->patched))
-		return;
-	if (WARN_ON(!func->old_addr))
-		return;
-
-	ops = klp_find_ops(func->old_addr);
-	if (WARN_ON(!ops))
-		return;
-
-	if (list_is_singular(&ops->func_stack)) {
-		unsigned long ftrace_loc;
-
-		ftrace_loc = klp_get_ftrace_location(func->old_addr);
-		if (WARN_ON(!ftrace_loc))
-			return;
-
-		WARN_ON(unregister_ftrace_function(&ops->fops));
-		WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
-
-		list_del_rcu(&func->stack_node);
-		list_del(&ops->node);
-		kfree(ops);
-	} else {
-		list_del_rcu(&func->stack_node);
-	}
-
-	func->patched = false;
-}
-
-static int klp_patch_func(struct klp_func *func)
-{
-	struct klp_ops *ops;
-	int ret;
-
-	if (WARN_ON(!func->old_addr))
-		return -EINVAL;
-
-	if (WARN_ON(func->patched))
-		return -EINVAL;
-
-	ops = klp_find_ops(func->old_addr);
-	if (!ops) {
-		unsigned long ftrace_loc;
-
-		ftrace_loc = klp_get_ftrace_location(func->old_addr);
-		if (!ftrace_loc) {
-			pr_err("failed to find location for function '%s'\n",
-				func->old_name);
-			return -EINVAL;
-		}
-
-		ops = kzalloc(sizeof(*ops), GFP_KERNEL);
-		if (!ops)
-			return -ENOMEM;
-
-		ops->fops.func = klp_ftrace_handler;
-		ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
-				  FTRACE_OPS_FL_DYNAMIC |
-				  FTRACE_OPS_FL_IPMODIFY;
-
-		list_add(&ops->node, &klp_ops);
-
-		INIT_LIST_HEAD(&ops->func_stack);
-		list_add_rcu(&func->stack_node, &ops->func_stack);
-
-		ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
-		if (ret) {
-			pr_err("failed to set ftrace filter for function '%s' (%d)\n",
-			       func->old_name, ret);
-			goto err;
-		}
-
-		ret = register_ftrace_function(&ops->fops);
-		if (ret) {
-			pr_err("failed to register ftrace handler for function '%s' (%d)\n",
-			       func->old_name, ret);
-			ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
-			goto err;
-		}
-
-
-	} else {
-		list_add_rcu(&func->stack_node, &ops->func_stack);
-	}
-
-	func->patched = true;
-
-	return 0;
-
-err:
-	list_del_rcu(&func->stack_node);
-	list_del(&ops->node);
-	kfree(ops);
-	return ret;
-}
-
-static void klp_unpatch_object(struct klp_object *obj)
-{
-	struct klp_func *func;
-
-	klp_for_each_func(obj, func)
-		if (func->patched)
-			klp_unpatch_func(func);
-
-	obj->patched = false;
-}
-
-static int klp_patch_object(struct klp_object *obj)
-{
-	struct klp_func *func;
-	int ret;
-
-	if (WARN_ON(obj->patched))
-		return -EINVAL;
-
-	klp_for_each_func(obj, func) {
-		ret = klp_patch_func(func);
-		if (ret) {
-			klp_unpatch_object(obj);
-			return ret;
-		}
-	}
-	obj->patched = true;
-
-	return 0;
-}
-
 static int __klp_disable_patch(struct klp_patch *patch)
 {
 	struct klp_object *obj;
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
new file mode 100644
index 0000000..5efa262
--- /dev/null
+++ b/kernel/livepatch/patch.c
@@ -0,0 +1,213 @@
+/*
+ * patch.c - livepatch patching functions
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/livepatch.h>
+#include <linux/list.h>
+#include <linux/ftrace.h>
+#include <linux/rculist.h>
+#include <linux/slab.h>
+#include <linux/bug.h>
+#include <linux/printk.h>
+#include "patch.h"
+
+static LIST_HEAD(klp_ops);
+
+struct klp_ops *klp_find_ops(unsigned long old_addr)
+{
+	struct klp_ops *ops;
+	struct klp_func *func;
+
+	list_for_each_entry(ops, &klp_ops, node) {
+		func = list_first_entry(&ops->func_stack, struct klp_func,
+					stack_node);
+		if (func->old_addr == old_addr)
+			return ops;
+	}
+
+	return NULL;
+}
+
+static void notrace klp_ftrace_handler(unsigned long ip,
+				       unsigned long parent_ip,
+				       struct ftrace_ops *fops,
+				       struct pt_regs *regs)
+{
+	struct klp_ops *ops;
+	struct klp_func *func;
+
+	ops = container_of(fops, struct klp_ops, fops);
+
+	rcu_read_lock();
+	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
+				      stack_node);
+	if (WARN_ON_ONCE(!func))
+		goto unlock;
+
+	klp_arch_set_pc(regs, (unsigned long)func->new_func);
+unlock:
+	rcu_read_unlock();
+}
+
+/*
+ * Convert a function address into the appropriate ftrace location.
+ *
+ * Usually this is just the address of the function, but on some architectures
+ * it's more complicated so allow them to provide a custom behaviour.
+ */
+#ifndef klp_get_ftrace_location
+static unsigned long klp_get_ftrace_location(unsigned long faddr)
+{
+	return faddr;
+}
+#endif
+
+static void klp_unpatch_func(struct klp_func *func)
+{
+	struct klp_ops *ops;
+
+	if (WARN_ON(!func->patched))
+		return;
+	if (WARN_ON(!func->old_addr))
+		return;
+
+	ops = klp_find_ops(func->old_addr);
+	if (WARN_ON(!ops))
+		return;
+
+	if (list_is_singular(&ops->func_stack)) {
+		unsigned long ftrace_loc;
+
+		ftrace_loc = klp_get_ftrace_location(func->old_addr);
+		if (WARN_ON(!ftrace_loc))
+			return;
+
+		WARN_ON(unregister_ftrace_function(&ops->fops));
+		WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
+
+		list_del_rcu(&func->stack_node);
+		list_del(&ops->node);
+		kfree(ops);
+	} else {
+		list_del_rcu(&func->stack_node);
+	}
+
+	func->patched = false;
+}
+
+static int klp_patch_func(struct klp_func *func)
+{
+	struct klp_ops *ops;
+	int ret;
+
+	if (WARN_ON(!func->old_addr))
+		return -EINVAL;
+
+	if (WARN_ON(func->patched))
+		return -EINVAL;
+
+	ops = klp_find_ops(func->old_addr);
+	if (!ops) {
+		unsigned long ftrace_loc;
+
+		ftrace_loc = klp_get_ftrace_location(func->old_addr);
+		if (!ftrace_loc) {
+			pr_err("failed to find location for function '%s'\n",
+				func->old_name);
+			return -EINVAL;
+		}
+
+		ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+		if (!ops)
+			return -ENOMEM;
+
+		ops->fops.func = klp_ftrace_handler;
+		ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
+				  FTRACE_OPS_FL_DYNAMIC |
+				  FTRACE_OPS_FL_IPMODIFY;
+
+		list_add(&ops->node, &klp_ops);
+
+		INIT_LIST_HEAD(&ops->func_stack);
+		list_add_rcu(&func->stack_node, &ops->func_stack);
+
+		ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
+		if (ret) {
+			pr_err("failed to set ftrace filter for function '%s' (%d)\n",
+			       func->old_name, ret);
+			goto err;
+		}
+
+		ret = register_ftrace_function(&ops->fops);
+		if (ret) {
+			pr_err("failed to register ftrace handler for function '%s' (%d)\n",
+			       func->old_name, ret);
+			ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
+			goto err;
+		}
+
+
+	} else {
+		list_add_rcu(&func->stack_node, &ops->func_stack);
+	}
+
+	func->patched = true;
+
+	return 0;
+
+err:
+	list_del_rcu(&func->stack_node);
+	list_del(&ops->node);
+	kfree(ops);
+	return ret;
+}
+
+void klp_unpatch_object(struct klp_object *obj)
+{
+	struct klp_func *func;
+
+	klp_for_each_func(obj, func)
+		if (func->patched)
+			klp_unpatch_func(func);
+
+	obj->patched = false;
+}
+
+int klp_patch_object(struct klp_object *obj)
+{
+	struct klp_func *func;
+	int ret;
+
+	if (WARN_ON(obj->patched))
+		return -EINVAL;
+
+	klp_for_each_func(obj, func) {
+		ret = klp_patch_func(func);
+		if (ret) {
+			klp_unpatch_object(obj);
+			return ret;
+		}
+	}
+	obj->patched = true;
+
+	return 0;
+}
diff --git a/kernel/livepatch/patch.h b/kernel/livepatch/patch.h
new file mode 100644
index 0000000..2d0cce0
--- /dev/null
+++ b/kernel/livepatch/patch.h
@@ -0,0 +1,32 @@
+#ifndef _LIVEPATCH_PATCH_H
+#define _LIVEPATCH_PATCH_H
+
+#include <linux/livepatch.h>
+#include <linux/list.h>
+#include <linux/ftrace.h>
+
+/**
+ * struct klp_ops - structure for tracking registered ftrace ops structs
+ *
+ * A single ftrace_ops is shared between all enabled replacement functions
+ * (klp_func structs) which have the same old_addr.  This allows the switch
+ * between function versions to happen instantaneously by updating the klp_ops
+ * struct's func_stack list.  The winner is the klp_func at the top of the
+ * func_stack (front of the list).
+ *
+ * @node:	node for the global klp_ops list
+ * @func_stack:	list head for the stack of klp_func's (active func is on top)
+ * @fops:	registered ftrace ops struct
+ */
+struct klp_ops {
+	struct list_head node;
+	struct list_head func_stack;
+	struct ftrace_ops fops;
+};
+
+struct klp_ops *klp_find_ops(unsigned long old_addr);
+
+int klp_patch_object(struct klp_object *obj);
+void klp_unpatch_object(struct klp_object *obj);
+
+#endif /* _LIVEPATCH_PATCH_H */
-- 
2.7.4

[PATCH v5 11/15] livepatch: use kstrtobool() in enabled_store()

[Josh Poimboeuf]

The sysfs enabled value is a boolean, so kstrtobool() is a better fit
for parsing the input string since it does the range checking for us.

Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/livepatch/core.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 6a137e1..83c4949 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -408,26 +408,23 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 {
 	struct klp_patch *patch;
 	int ret;
-	unsigned long val;
+	bool enabled;
 
-	ret = kstrtoul(buf, 10, &val);
+	ret = kstrtobool(buf, &enabled);
 	if (ret)
-		return -EINVAL;
-
-	if (val > 1)
-		return -EINVAL;
+		return ret;
 
 	patch = container_of(kobj, struct klp_patch, kobj);
 
 	mutex_lock(&klp_mutex);
 
-	if (patch->enabled == val) {
+	if (patch->enabled == enabled) {
 		/* already in requested state */
 		ret = -EINVAL;
 		goto err;
 	}
 
-	if (val) {
+	if (enabled) {
 		ret = __klp_enable_patch(patch);
 		if (ret)
 			goto err;
-- 
2.7.4

[PATCH v5 12/15] livepatch: store function sizes

[Josh Poimboeuf]

For the consistency model we'll need to know the sizes of the old and
new functions to determine if they're on the stacks of any tasks.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
 include/linux/livepatch.h |  3 +++
 kernel/livepatch/core.c   | 16 ++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 9787a63..6602b34 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -37,6 +37,8 @@
  * @old_addr:	the address of the function being patched
  * @kobj:	kobject for sysfs resources
  * @stack_node:	list node for klp_ops func_stack list
+ * @old_size:	size of the old function
+ * @new_size:	size of the new function
  * @patched:	the func has been added to the klp_ops list
  */
 struct klp_func {
@@ -56,6 +58,7 @@ struct klp_func {
 	unsigned long old_addr;
 	struct kobject kobj;
 	struct list_head stack_node;
+	unsigned long old_size, new_size;
 	bool patched;
 };
 
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 83c4949..10ba3a1 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -584,6 +584,22 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 					     &func->old_addr);
 		if (ret)
 			return ret;
+
+		ret = kallsyms_lookup_size_offset(func->old_addr,
+						  &func->old_size, NULL);
+		if (!ret) {
+			pr_err("kallsyms size lookup failed for '%s'\n",
+			       func->old_name);
+			return -ENOENT;
+		}
+
+		ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
+						  &func->new_size, NULL);
+		if (!ret) {
+			pr_err("kallsyms size lookup failed for '%s' replacement\n",
+			       func->old_name);
+			return -ENOENT;
+		}
 	}
 
 	return 0;
-- 
2.7.4

[PATCH v5 13/15] livepatch: change to a per-task consistency model

[Josh Poimboeuf]

Change livepatch to use a basic per-task consistency model.  This is the
foundation which will eventually enable us to patch those ~10% of
security patches which change function or data semantics.  This is the
biggest remaining piece needed to make livepatch more generally useful.

This code stems from the design proposal made by Vojtech [1] in November
2014.  It's a hybrid of kGraft and kpatch: it uses kGraft's per-task
consistency and syscall barrier switching combined with kpatch's stack
trace switching.  There are also a number of fallback options which make
it quite flexible.

Patches are applied on a per-task basis, when the task is deemed safe to
switch over.  When a patch is enabled, livepatch enters into a
transition state where tasks are converging to the patched state.
Usually this transition state can complete in a few seconds.  The same
sequence occurs when a patch is disabled, except the tasks converge from
the patched state to the unpatched state.

An interrupt handler inherits the patched state of the task it
interrupts.  The same is true for forked tasks: the child inherits the
patched state of the parent.

Livepatch uses several complementary approaches to determine when it's
safe to patch tasks:

1. The first and most effective approach is stack checking of sleeping
   tasks.  If no affected functions are on the stack of a given task,
   the task is patched.  In most cases this will patch most or all of
   the tasks on the first try.  Otherwise it'll keep trying
   periodically.  This option is only available if the architecture has
   reliable stacks (HAVE_RELIABLE_STACKTRACE).

2. The second approach, if needed, is kernel exit switching.  A
   task is switched when it returns to user space from a system call, a
   user space IRQ, or a signal.  It's useful in the following cases:

   a) Patching I/O-bound user tasks which are sleeping on an affected
      function.  In this case you have to send SIGSTOP and SIGCONT to
      force it to exit the kernel and be patched.
   b) Patching CPU-bound user tasks.  If the task is highly CPU-bound
      then it will get patched the next time it gets interrupted by an
      IRQ.
   c) In the future it could be useful for applying patches for
      architectures which don't yet have HAVE_RELIABLE_STACKTRACE.  In
      this case you would have to signal most of the tasks on the
      system.  However this isn't supported yet because there's
      currently no way to patch kthreads without
      HAVE_RELIABLE_STACKTRACE.

3. For idle "swapper" tasks, since they don't ever exit the kernel, they
   instead have a klp_update_patch_state() call in the idle loop which
   allows them to be patched before the CPU enters the idle state.

   (Note there's not yet such an approach for kthreads.)

All the above approaches may be skipped by setting the 'immediate' flag
in the 'klp_patch' struct, which will disable per-task consistency and
patch all tasks immediately.  This can be useful if the patch doesn't
change any function or data semantics.  Note that, even with this flag
set, it's possible that some tasks may still be running with an old
version of the function, until that function returns.

There's also an 'immediate' flag in the 'klp_func' struct which allows
you to specify that certain functions in the patch can be applied
without per-task consistency.  This might be useful if you want to patch
a common function like schedule(), and the function change doesn't need
consistency but the rest of the patch does.

For architectures which don't have HAVE_RELIABLE_STACKTRACE, the user
must set patch->immediate which causes all tasks to be patched
immediately.  This option should be used with care, only when the patch
doesn't change any function or data semantics.

In the future, architectures which don't have HAVE_RELIABLE_STACKTRACE
may be allowed to use per-task consistency if we can come up with
another way to patch kthreads.

The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
is in transition.  Only a single patch (the topmost patch on the stack)
can be in transition at a given time.  A patch can remain in transition
indefinitely, if any of the tasks are stuck in the initial patch state.

A transition can be reversed and effectively canceled by writing the
opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
the transition is in progress.  Then all the tasks will attempt to
converge back to the original patch state.

[1] https://lkml.kernel.org/r/20141107140458.GA21774@suse.cz

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 Documentation/ABI/testing/sysfs-kernel-livepatch |   8 +
 Documentation/livepatch/livepatch.txt            | 186 +++++++-
 include/linux/init_task.h                        |   9 +
 include/linux/livepatch.h                        |  42 +-
 include/linux/sched.h                            |   3 +
 kernel/fork.c                                    |   3 +
 kernel/livepatch/Makefile                        |   2 +-
 kernel/livepatch/core.c                          | 105 ++++-
 kernel/livepatch/patch.c                         |  59 +++
 kernel/livepatch/patch.h                         |   1 +
 kernel/livepatch/transition.c                    | 543 +++++++++++++++++++++++
 kernel/livepatch/transition.h                    |  14 +
 kernel/sched/idle.c                              |   4 +
 samples/livepatch/livepatch-sample.c             |  17 +
 14 files changed, 947 insertions(+), 49 deletions(-)
 create mode 100644 kernel/livepatch/transition.c
 create mode 100644 kernel/livepatch/transition.h

diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
index da87f43..d5d3974 100644
--- a/Documentation/ABI/testing/sysfs-kernel-livepatch
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -25,6 +25,14 @@ Description:
 		code is currently applied.  Writing 0 will disable the patch
 		while writing 1 will re-enable the patch.
 
+What:		/sys/kernel/livepatch/<patch>/transition
+Date:		Feb 2017
+KernelVersion:	4.12.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		An attribute which indicates whether the patch is currently in
+		transition.
+
 What:		/sys/kernel/livepatch/<patch>/<object>
 Date:		Nov 2014
 KernelVersion:	3.19.0
diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index 9d2096c..4f2aec8 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -72,7 +72,8 @@ example, they add a NULL pointer or a boundary check, fix a race by adding
 a missing memory barrier, or add some locking around a critical section.
 Most of these changes are self contained and the function presents itself
 the same way to the rest of the system. In this case, the functions might
-be updated independently one by one.
+be updated independently one by one.  (This can be done by setting the
+'immediate' flag in the klp_patch struct.)
 
 But there are more complex fixes. For example, a patch might change
 ordering of locking in multiple functions at the same time. Or a patch
@@ -86,20 +87,141 @@ or no data are stored in the modified structures at the moment.
 The theory about how to apply functions a safe way is rather complex.
 The aim is to define a so-called consistency model. It attempts to define
 conditions when the new implementation could be used so that the system
-stays consistent. The theory is not yet finished. See the discussion at
-https://lkml.kernel.org/r/20141107140458.GA21774@suse.cz
-
-The current consistency model is very simple. It guarantees that either
-the old or the new function is called. But various functions get redirected
-one by one without any synchronization.
-
-In other words, the current implementation _never_ modifies the behavior
-in the middle of the call. It is because it does _not_ rewrite the entire
-function in the memory. Instead, the function gets redirected at the
-very beginning. But this redirection is used immediately even when
-some other functions from the same patch have not been redirected yet.
-
-See also the section "Limitations" below.
+stays consistent.
+
+Livepatch has a consistency model which is a hybrid of kGraft and
+kpatch:  it uses kGraft's per-task consistency and syscall barrier
+switching combined with kpatch's stack trace switching.  There are also
+a number of fallback options which make it quite flexible.
+
+Patches are applied on a per-task basis, when the task is deemed safe to
+switch over.  When a patch is enabled, livepatch enters into a
+transition state where tasks are converging to the patched state.
+Usually this transition state can complete in a few seconds.  The same
+sequence occurs when a patch is disabled, except the tasks converge from
+the patched state to the unpatched state.
+
+An interrupt handler inherits the patched state of the task it
+interrupts.  The same is true for forked tasks: the child inherits the
+patched state of the parent.
+
+Livepatch uses several complementary approaches to determine when it's
+safe to patch tasks:
+
+1. The first and most effective approach is stack checking of sleeping
+   tasks.  If no affected functions are on the stack of a given task,
+   the task is patched.  In most cases this will patch most or all of
+   the tasks on the first try.  Otherwise it'll keep trying
+   periodically.  This option is only available if the architecture has
+   reliable stacks (HAVE_RELIABLE_STACKTRACE).
+
+2. The second approach, if needed, is kernel exit switching.  A
+   task is switched when it returns to user space from a system call, a
+   user space IRQ, or a signal.  It's useful in the following cases:
+
+   a) Patching I/O-bound user tasks which are sleeping on an affected
+      function.  In this case you have to send SIGSTOP and SIGCONT to
+      force it to exit the kernel and be patched.
+   b) Patching CPU-bound user tasks.  If the task is highly CPU-bound
+      then it will get patched the next time it gets interrupted by an
+      IRQ.
+   c) In the future it could be useful for applying patches for
+      architectures which don't yet have HAVE_RELIABLE_STACKTRACE.  In
+      this case you would have to signal most of the tasks on the
+      system.  However this isn't supported yet because there's
+      currently no way to patch kthreads without
+      HAVE_RELIABLE_STACKTRACE.
+
+3. For idle "swapper" tasks, since they don't ever exit the kernel, they
+   instead have a klp_update_patch_state() call in the idle loop which
+   allows them to be patched before the CPU enters the idle state.
+
+   (Note there's not yet such an approach for kthreads.)
+
+All the above approaches may be skipped by setting the 'immediate' flag
+in the 'klp_patch' struct, which will disable per-task consistency and
+patch all tasks immediately.  This can be useful if the patch doesn't
+change any function or data semantics.  Note that, even with this flag
+set, it's possible that some tasks may still be running with an old
+version of the function, until that function returns.
+
+There's also an 'immediate' flag in the 'klp_func' struct which allows
+you to specify that certain functions in the patch can be applied
+without per-task consistency.  This might be useful if you want to patch
+a common function like schedule(), and the function change doesn't need
+consistency but the rest of the patch does.
+
+For architectures which don't have HAVE_RELIABLE_STACKTRACE, the user
+must set patch->immediate which causes all tasks to be patched
+immediately.  This option should be used with care, only when the patch
+doesn't change any function or data semantics.
+
+In the future, architectures which don't have HAVE_RELIABLE_STACKTRACE
+may be allowed to use per-task consistency if we can come up with
+another way to patch kthreads.
+
+The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
+is in transition.  Only a single patch (the topmost patch on the stack)
+can be in transition at a given time.  A patch can remain in transition
+indefinitely, if any of the tasks are stuck in the initial patch state.
+
+A transition can be reversed and effectively canceled by writing the
+opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
+the transition is in progress.  Then all the tasks will attempt to
+converge back to the original patch state.
+
+There's also a /proc/<pid>/patch_state file which can be used to
+determine which tasks are blocking completion of a patching operation.
+If a patch is in transition, this file shows 0 to indicate the task is
+unpatched and 1 to indicate it's patched.  Otherwise, if no patch is in
+transition, it shows -1.  Any tasks which are blocking the transition
+can be signaled with SIGSTOP and SIGCONT to force them to change their
+patched state.
+
+
+3.1 Adding consistency model support to new architectures
+---------------------------------------------------------
+
+For adding consistency model support to new architectures, there are a
+few options:
+
+1) Add CONFIG_HAVE_RELIABLE_STACKTRACE.  This means porting objtool, and
+   for non-DWARF unwinders, also making sure there's a way for the stack
+   tracing code to detect interrupts on the stack.
+
+2) Alternatively, ensure that every kthread has a call to
+   klp_update_patch_state() in a safe location.  Kthreads are typically
+   in an infinite loop which does some action repeatedly.  The safe
+   location to switch the kthread's patch state would be at a designated
+   point in the loop where there are no locks taken and all data
+   structures are in a well-defined state.
+
+   The location is clear when using workqueues or the kthread worker
+   API.  These kthreads process independent actions in a generic loop.
+
+   It's much more complicated with kthreads which have a custom loop.
+   There the safe location must be carefully selected on a case-by-case
+   basis.
+
+   In that case, arches without HAVE_RELIABLE_STACKTRACE would still be
+   able to use the non-stack-checking parts of the consistency model:
+
+   a) patching user tasks when they cross the kernel/user space
+      boundary; and
+
+   b) patching kthreads and idle tasks at their designated patch points.
+
+   This option isn't as good as option 1 because it requires signaling
+   user tasks and waking kthreads to patch them.  But it could still be
+   a good backup option for those architectures which don't have
+   reliable stack traces yet.
+
+In the meantime, patches for such architectures can bypass the
+consistency model by setting klp_patch.immediate to true.  This option
+is perfectly fine for patches which don't change the semantics of the
+patched functions.  In practice, this is usable for ~90% of security
+fixes.  Use of this option also means the patch can't be unloaded after
+it has been disabled.
 
 
 4. Livepatch module
@@ -134,7 +256,7 @@ Documentation/livepatch/module-elf-format.txt for more details.
 
 
 4.2. Metadata
-------------
+-------------
 
 The patch is described by several structures that split the information
 into three levels:
@@ -156,6 +278,9 @@ into three levels:
     only for a particular object ( vmlinux or a kernel module ). Note that
     kallsyms allows for searching symbols according to the object name.
 
+    There's also an 'immediate' flag which, when set, patches the
+    function immediately, bypassing the consistency model safety checks.
+
   + struct klp_object defines an array of patched functions (struct
     klp_func) in the same object. Where the object is either vmlinux
     (NULL) or a module name.
@@ -172,10 +297,13 @@ into three levels:
     This structure handles all patched functions consistently and eventually,
     synchronously. The whole patch is applied only when all patched
     symbols are found. The only exception are symbols from objects
-    (kernel modules) that have not been loaded yet. Also if a more complex
-    consistency model is supported then a selected unit (thread,
-    kernel as a whole) will see the new code from the entire patch
-    only when it is in a safe state.
+    (kernel modules) that have not been loaded yet.
+
+    Setting the 'immediate' flag applies the patch to all tasks
+    immediately, bypassing the consistency model safety checks.
+
+    For more details on how the patch is applied on a per-task basis,
+    see the "Consistency model" section.
 
 
 4.3. Livepatch module handling
@@ -239,9 +367,15 @@ Registered patches might be enabled either by calling klp_enable_patch() or
 by writing '1' to /sys/kernel/livepatch/<name>/enabled. The system will
 start using the new implementation of the patched functions at this stage.
 
-In particular, if an original function is patched for the first time, a
-function specific struct klp_ops is created and an universal ftrace handler
-is registered.
+When a patch is enabled, livepatch enters into a transition state where
+tasks are converging to the patched state.  This is indicated by a value
+of '1' in /sys/kernel/livepatch/<name>/transition.  Once all tasks have
+been patched, the 'transition' value changes to '0'.  For more
+information about this process, see the "Consistency model" section.
+
+If an original function is patched for the first time, a function
+specific struct klp_ops is created and an universal ftrace handler is
+registered.
 
 Functions might be patched multiple times. The ftrace handler is registered
 only once for the given function. Further patches just add an entry to the
@@ -261,6 +395,12 @@ by writing '0' to /sys/kernel/livepatch/<name>/enabled. At this stage
 either the code from the previously enabled patch or even the original
 code gets used.
 
+When a patch is disabled, livepatch enters into a transition state where
+tasks are converging to the unpatched state.  This is indicated by a
+value of '1' in /sys/kernel/livepatch/<name>/transition.  Once all tasks
+have been unpatched, the 'transition' value changes to '0'.  For more
+information about this process, see the "Consistency model" section.
+
 Here all the functions (struct klp_func) associated with the to-be-disabled
 patch are removed from the corresponding struct klp_ops. The ftrace handler
 is unregistered and the struct klp_ops is freed when the func_stack list
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 3a85d61..e49bf379 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -14,6 +14,7 @@
 #include <linux/rbtree.h>
 #include <net/net_namespace.h>
 #include <linux/sched/rt.h>
+#include <linux/livepatch.h>
 
 #include <asm/thread_info.h>
 
@@ -202,6 +203,13 @@ extern struct task_group root_task_group;
 # define INIT_KASAN(tsk)
 #endif
 
+#ifdef CONFIG_LIVEPATCH
+# define INIT_LIVEPATCH(tsk)						\
+	.patch_state = KLP_UNDEFINED,
+#else
+# define INIT_LIVEPATCH(tsk)
+#endif
+
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 # define INIT_TASK_TI(tsk)			\
 	.thread_info = INIT_THREAD_INFO(tsk),	\
@@ -288,6 +296,7 @@ extern struct task_group root_task_group;
 	INIT_VTIME(tsk)							\
 	INIT_NUMA_BALANCING(tsk)					\
 	INIT_KASAN(tsk)							\
+	INIT_LIVEPATCH(tsk)						\
 }
 
 
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 6602b34..ed90ad1 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -28,18 +28,40 @@
 
 #include <asm/livepatch.h>
 
+/* task patch states */
+#define KLP_UNDEFINED	-1
+#define KLP_UNPATCHED	 0
+#define KLP_PATCHED	 1
+
 /**
  * struct klp_func - function structure for live patching
  * @old_name:	name of the function to be patched
  * @new_func:	pointer to the patched function code
  * @old_sympos: a hint indicating which symbol position the old function
  *		can be found (optional)
+ * @immediate:  patch the func immediately, bypassing safety mechanisms
  * @old_addr:	the address of the function being patched
  * @kobj:	kobject for sysfs resources
  * @stack_node:	list node for klp_ops func_stack list
  * @old_size:	size of the old function
  * @new_size:	size of the new function
  * @patched:	the func has been added to the klp_ops list
+ * @transition:	the func is currently being applied or reverted
+ *
+ * The patched and transition variables define the func's patching state.  When
+ * patching, a func is always in one of the following states:
+ *
+ *   patched=0 transition=0: unpatched
+ *   patched=0 transition=1: unpatched, temporary starting state
+ *   patched=1 transition=1: patched, may be visible to some tasks
+ *   patched=1 transition=0: patched, visible to all tasks
+ *
+ * And when unpatching, it goes in the reverse order:
+ *
+ *   patched=1 transition=0: patched, visible to all tasks
+ *   patched=1 transition=1: patched, may be visible to some tasks
+ *   patched=0 transition=1: unpatched, temporary ending state
+ *   patched=0 transition=0: unpatched
  */
 struct klp_func {
 	/* external */
@@ -53,6 +75,7 @@ struct klp_func {
 	 * in kallsyms for the given object is used.
 	 */
 	unsigned long old_sympos;
+	bool immediate;
 
 	/* internal */
 	unsigned long old_addr;
@@ -60,6 +83,7 @@ struct klp_func {
 	struct list_head stack_node;
 	unsigned long old_size, new_size;
 	bool patched;
+	bool transition;
 };
 
 /**
@@ -68,7 +92,7 @@ struct klp_func {
  * @funcs:	function entries for functions to be patched in the object
  * @kobj:	kobject for sysfs resources
  * @mod:	kernel module associated with the patched object
- * 		(NULL for vmlinux)
+ *		(NULL for vmlinux)
  * @patched:	the object's funcs have been added to the klp_ops list
  */
 struct klp_object {
@@ -86,6 +110,7 @@ struct klp_object {
  * struct klp_patch - patch structure for live patching
  * @mod:	reference to the live patch module
  * @objs:	object entries for kernel objects to be patched
+ * @immediate:  patch all funcs immediately, bypassing safety mechanisms
  * @list:	list node for global list of registered patches
  * @kobj:	kobject for sysfs resources
  * @enabled:	the patch is enabled (but operation may be incomplete)
@@ -94,6 +119,7 @@ struct klp_patch {
 	/* external */
 	struct module *mod;
 	struct klp_object *objs;
+	bool immediate;
 
 	/* internal */
 	struct list_head list;
@@ -121,13 +147,27 @@ void arch_klp_init_object_loaded(struct klp_patch *patch,
 int klp_module_coming(struct module *mod);
 void klp_module_going(struct module *mod);
 
+void klp_copy_process(struct task_struct *child);
 void klp_update_patch_state(struct task_struct *task);
 
+static inline bool klp_patch_pending(struct task_struct *task)
+{
+	return test_tsk_thread_flag(task, TIF_PATCH_PENDING);
+}
+
+static inline bool klp_have_reliable_stack(void)
+{
+	return IS_ENABLED(CONFIG_STACKTRACE) &&
+	       IS_ENABLED(CONFIG_HAVE_RELIABLE_STACKTRACE);
+}
+
 #else /* !CONFIG_LIVEPATCH */
 
 static inline int klp_module_coming(struct module *mod) { return 0; }
 static inline void klp_module_going(struct module *mod) {}
+static inline bool klp_patch_pending(struct task_struct *task) { return false; }
 static inline void klp_update_patch_state(struct task_struct *task) {}
+static inline void klp_copy_process(struct task_struct *child) {}
 
 #endif /* CONFIG_LIVEPATCH */
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5aec804..f653fea 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1980,6 +1980,9 @@ struct task_struct {
 	/* A live task holds one reference. */
 	atomic_t stack_refcount;
 #endif
+#ifdef CONFIG_LIVEPATCH
+	int patch_state;
+#endif
 /* CPU-specific state of this task */
 	struct thread_struct thread;
 /*
diff --git a/kernel/fork.c b/kernel/fork.c
index c6eb727..a1552ab 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -77,6 +77,7 @@
 #include <linux/compiler.h>
 #include <linux/sysctl.h>
 #include <linux/kcov.h>
+#include <linux/livepatch.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -1772,6 +1773,8 @@ static __latent_entropy struct task_struct *copy_process(
 		p->parent_exec_id = current->self_exec_id;
 	}
 
+	klp_copy_process(p);
+
 	spin_lock(&current->sighand->siglock);
 
 	/*
diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
index e136dad..2b8bdb1 100644
--- a/kernel/livepatch/Makefile
+++ b/kernel/livepatch/Makefile
@@ -1,3 +1,3 @@
 obj-$(CONFIG_LIVEPATCH) += livepatch.o
 
-livepatch-objs := core.o patch.o
+livepatch-objs := core.o patch.o transition.o
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 10ba3a1..3dc3c90 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -31,22 +31,22 @@
 #include <linux/moduleloader.h>
 #include <asm/cacheflush.h>
 #include "patch.h"
+#include "transition.h"
 
 /*
- * The klp_mutex protects the global lists and state transitions of any
- * structure reachable from them.  References to any structure must be obtained
- * under mutex protection (except in klp_ftrace_handler(), which uses RCU to
- * ensure it gets consistent data).
+ * klp_mutex is a coarse lock which serializes access to klp data.  All
+ * accesses to klp-related variables and structures must have mutex protection,
+ * except within the following functions which carefully avoid the need for it:
+ *
+ * - klp_ftrace_handler()
+ * - klp_update_patch_state()
  */
-static DEFINE_MUTEX(klp_mutex);
+DEFINE_MUTEX(klp_mutex);
 
 static LIST_HEAD(klp_patches);
 
 static struct kobject *klp_root_kobj;
 
-/* TODO: temporary stub */
-void klp_update_patch_state(struct task_struct *task) {}
-
 static bool klp_is_module(struct klp_object *obj)
 {
 	return obj->name;
@@ -85,7 +85,6 @@ static void klp_find_object_module(struct klp_object *obj)
 	mutex_unlock(&module_mutex);
 }
 
-/* klp_mutex must be held by caller */
 static bool klp_is_patch_registered(struct klp_patch *patch)
 {
 	struct klp_patch *mypatch;
@@ -281,20 +280,27 @@ static int klp_write_object_relocations(struct module *pmod,
 
 static int __klp_disable_patch(struct klp_patch *patch)
 {
-	struct klp_object *obj;
+	if (klp_transition_patch)
+		return -EBUSY;
 
 	/* enforce stacking: only the last enabled patch can be disabled */
 	if (!list_is_last(&patch->list, &klp_patches) &&
 	    list_next_entry(patch, list)->enabled)
 		return -EBUSY;
 
-	pr_notice("disabling patch '%s'\n", patch->mod->name);
+	klp_init_transition(patch, KLP_UNPATCHED);
 
-	klp_for_each_object(patch, obj) {
-		if (obj->patched)
-			klp_unpatch_object(obj);
-	}
+	/*
+	 * Enforce the order of the func->transition writes in
+	 * klp_init_transition() and the TIF_PATCH_PENDING writes in
+	 * klp_start_transition().  In the rare case where klp_ftrace_handler()
+	 * is called shortly after klp_update_patch_state() switches the task,
+	 * this ensures the handler sees that func->transition is set.
+	 */
+	smp_wmb();
 
+	klp_start_transition();
+	klp_try_complete_transition();
 	patch->enabled = false;
 
 	return 0;
@@ -337,6 +343,9 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	struct klp_object *obj;
 	int ret;
 
+	if (klp_transition_patch)
+		return -EBUSY;
+
 	if (WARN_ON(patch->enabled))
 		return -EINVAL;
 
@@ -347,22 +356,36 @@ static int __klp_enable_patch(struct klp_patch *patch)
 
 	pr_notice("enabling patch '%s'\n", patch->mod->name);
 
+	klp_init_transition(patch, KLP_PATCHED);
+
+	/*
+	 * Enforce the order of the func->transition writes in
+	 * klp_init_transition() and the ops->func_stack writes in
+	 * klp_patch_object(), so that klp_ftrace_handler() will see the
+	 * func->transition updates before the handler is registered and the
+	 * new funcs become visible to the handler.
+	 */
+	smp_wmb();
+
 	klp_for_each_object(patch, obj) {
 		if (!klp_is_object_loaded(obj))
 			continue;
 
 		ret = klp_patch_object(obj);
-		if (ret)
-			goto unregister;
+		if (ret) {
+			pr_warn("failed to enable patch '%s'\n",
+				patch->mod->name);
+
+			klp_cancel_transition();
+			return ret;
+		}
 	}
 
+	klp_start_transition();
+	klp_try_complete_transition();
 	patch->enabled = true;
 
 	return 0;
-
-unregister:
-	WARN_ON(__klp_disable_patch(patch));
-	return ret;
 }
 
 /**
@@ -399,6 +422,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
  * /sys/kernel/livepatch
  * /sys/kernel/livepatch/<patch>
  * /sys/kernel/livepatch/<patch>/enabled
+ * /sys/kernel/livepatch/<patch>/transition
  * /sys/kernel/livepatch/<patch>/<object>
  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
  */
@@ -424,7 +448,9 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 		goto err;
 	}
 
-	if (enabled) {
+	if (patch == klp_transition_patch) {
+		klp_reverse_transition();
+	} else if (enabled) {
 		ret = __klp_enable_patch(patch);
 		if (ret)
 			goto err;
@@ -452,9 +478,21 @@ static ssize_t enabled_show(struct kobject *kobj,
 	return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
 }
 
+static ssize_t transition_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	struct klp_patch *patch;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	return snprintf(buf, PAGE_SIZE-1, "%d\n",
+			patch == klp_transition_patch);
+}
+
 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
+static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
 static struct attribute *klp_patch_attrs[] = {
 	&enabled_kobj_attr.attr,
+	&transition_kobj_attr.attr,
 	NULL
 };
 
@@ -544,6 +582,7 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 
 	INIT_LIST_HEAD(&func->stack_node);
 	func->patched = false;
+	func->transition = false;
 
 	/* The format for the sysfs directory is <function,sympos> where sympos
 	 * is the nth occurrence of this symbol in kallsyms for the patched
@@ -740,6 +779,16 @@ int klp_register_patch(struct klp_patch *patch)
 		return -ENODEV;
 
 	/*
+	 * Architectures without reliable stack traces have to set
+	 * patch->immediate because there's currently no way to patch kthreads
+	 * with the consistency model.
+	 */
+	if (!klp_have_reliable_stack() && !patch->immediate) {
+		pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
+		return -ENOSYS;
+	}
+
+	/*
 	 * A reference is taken on the patch module to prevent it from being
 	 * unloaded.  Right now, we don't allow patch modules to unload since
 	 * there is currently no method to determine if a thread is still
@@ -788,7 +837,11 @@ int klp_module_coming(struct module *mod)
 				goto err;
 			}
 
-			if (!patch->enabled)
+			/*
+			 * Only patch the module if the patch is enabled or is
+			 * in transition.
+			 */
+			if (!patch->enabled && patch != klp_transition_patch)
 				break;
 
 			pr_notice("applying patch '%s' to loading module '%s'\n",
@@ -845,7 +898,11 @@ void klp_module_going(struct module *mod)
 			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
 				continue;
 
-			if (patch->enabled) {
+			/*
+			 * Only unpatch the module if the patch is enabled or
+			 * is in transition.
+			 */
+			if (patch->enabled || patch == klp_transition_patch) {
 				pr_notice("reverting patch '%s' on unloading module '%s'\n",
 					  patch->mod->name, obj->mod->name);
 				klp_unpatch_object(obj);
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 5efa262..f826903 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -29,6 +29,7 @@
 #include <linux/bug.h>
 #include <linux/printk.h>
 #include "patch.h"
+#include "transition.h"
 
 static LIST_HEAD(klp_ops);
 
@@ -54,15 +55,64 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 {
 	struct klp_ops *ops;
 	struct klp_func *func;
+	int patch_state;
 
 	ops = container_of(fops, struct klp_ops, fops);
 
 	rcu_read_lock();
+
 	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
 				      stack_node);
+
+	/*
+	 * func should never be NULL because preemption should be disabled here
+	 * and unregister_ftrace_function() does the equivalent of a
+	 * synchronize_sched() before the func_stack removal.
+	 */
 	if (WARN_ON_ONCE(!func))
 		goto unlock;
 
+	/*
+	 * In the enable path, enforce the order of the ops->func_stack and
+	 * func->transition reads.  The corresponding write barrier is in
+	 * __klp_enable_patch().
+	 *
+	 * (Note that this barrier technically isn't needed in the disable
+	 * path.  In the rare case where klp_update_patch_state() runs before
+	 * this handler, its TIF_PATCH_PENDING read and this func->transition
+	 * read need to be ordered.  But klp_update_patch_state() already
+	 * enforces that.)
+	 */
+	smp_rmb();
+
+	if (unlikely(func->transition)) {
+
+		/*
+		 * Enforce the order of the func->transition and
+		 * current->patch_state reads.  Otherwise we could read an
+		 * out-of-date task state and pick the wrong function.  The
+		 * corresponding write barrier is in klp_init_transition().
+		 */
+		smp_rmb();
+
+		patch_state = current->patch_state;
+
+		WARN_ON_ONCE(patch_state == KLP_UNDEFINED);
+
+		if (patch_state == KLP_UNPATCHED) {
+			/*
+			 * Use the previously patched version of the function.
+			 * If no previous patches exist, continue with the
+			 * original function.
+			 */
+			func = list_entry_rcu(func->stack_node.next,
+					      struct klp_func, stack_node);
+
+			if (&func->stack_node == &ops->func_stack)
+				goto unlock;
+		}
+	}
+
 	klp_arch_set_pc(regs, (unsigned long)func->new_func);
 unlock:
 	rcu_read_unlock();
@@ -211,3 +261,12 @@ int klp_patch_object(struct klp_object *obj)
 
 	return 0;
 }
+
+void klp_unpatch_objects(struct klp_patch *patch)
+{
+	struct klp_object *obj;
+
+	klp_for_each_object(patch, obj)
+		if (obj->patched)
+			klp_unpatch_object(obj);
+}
diff --git a/kernel/livepatch/patch.h b/kernel/livepatch/patch.h
index 2d0cce0..0db2271 100644
--- a/kernel/livepatch/patch.h
+++ b/kernel/livepatch/patch.h
@@ -28,5 +28,6 @@ struct klp_ops *klp_find_ops(unsigned long old_addr);
 
 int klp_patch_object(struct klp_object *obj);
 void klp_unpatch_object(struct klp_object *obj);
+void klp_unpatch_objects(struct klp_patch *patch);
 
 #endif /* _LIVEPATCH_PATCH_H */
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
new file mode 100644
index 0000000..428533e
--- /dev/null
+++ b/kernel/livepatch/transition.c
@@ -0,0 +1,543 @@
+/*
+ * transition.c - Kernel Live Patching transition functions
+ *
+ * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/cpu.h>
+#include <linux/stacktrace.h>
+#include "patch.h"
+#include "transition.h"
+#include "../sched/sched.h"
+
+#define MAX_STACK_ENTRIES  100
+#define STACK_ERR_BUF_SIZE 128
+
+extern struct mutex klp_mutex;
+
+struct klp_patch *klp_transition_patch;
+
+static int klp_target_state = KLP_UNDEFINED;
+
+/*
+ * This work can be performed periodically to finish patching or unpatching any
+ * "straggler" tasks which failed to transition in the first attempt.
+ */
+static void klp_transition_work_fn(struct work_struct *work)
+{
+	mutex_lock(&klp_mutex);
+
+	if (klp_transition_patch)
+		klp_try_complete_transition();
+
+	mutex_unlock(&klp_mutex);
+}
+static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
+
+/*
+ * The transition to the target patch state is complete.  Clean up the data
+ * structures.
+ */
+static void klp_complete_transition(void)
+{
+	struct klp_object *obj;
+	struct klp_func *func;
+	struct task_struct *g, *task;
+	unsigned int cpu;
+
+	if (klp_target_state == KLP_UNPATCHED) {
+		/*
+		 * All tasks have transitioned to KLP_UNPATCHED so we can now
+		 * remove the new functions from the func_stack.
+		 */
+		klp_unpatch_objects(klp_transition_patch);
+
+		/*
+		 * Make sure klp_ftrace_handler() can no longer see functions
+		 * from this patch on the ops->func_stack.  Otherwise, after
+		 * func->transition gets cleared, the handler may choose a
+		 * removed function.
+		 */
+		synchronize_rcu();
+	}
+
+	if (klp_transition_patch->immediate)
+		goto done;
+
+	klp_for_each_object(klp_transition_patch, obj)
+		klp_for_each_func(obj, func)
+			func->transition = false;
+
+	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
+	if (klp_target_state == KLP_PATCHED)
+		synchronize_rcu();
+
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task) {
+		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
+		task->patch_state = KLP_UNDEFINED;
+	}
+	read_unlock(&tasklist_lock);
+
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
+		task->patch_state = KLP_UNDEFINED;
+	}
+
+done:
+	klp_target_state = KLP_UNDEFINED;
+	klp_transition_patch = NULL;
+}
+
+/*
+ * This is called in the error path, to cancel a transition before it has
+ * started, i.e. klp_init_transition() has been called but
+ * klp_start_transition() hasn't.  If the transition *has* been started,
+ * klp_reverse_transition() should be used instead.
+ */
+void klp_cancel_transition(void)
+{
+	klp_target_state = !klp_target_state;
+	klp_complete_transition();
+}
+
+/*
+ * Switch the patched state of the task to the set of functions in the target
+ * patch state.
+ *
+ * NOTE: If task is not 'current', the caller must ensure the task is inactive.
+ * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value.
+ */
+void klp_update_patch_state(struct task_struct *task)
+{
+	rcu_read_lock();
+
+	/*
+	 * This test_and_clear_tsk_thread_flag() call also serves as a read
+	 * barrier (smp_rmb) for two cases:
+	 *
+	 * 1) Enforce the order of the TIF_PATCH_PENDING read and the
+	 *    klp_target_state read.  The corresponding write barrier is in
+	 *    klp_init_transition().
+	 *
+	 * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
+	 *    of func->transition, if klp_ftrace_handler() is called later on
+	 *    the same CPU.  See __klp_disable_patch().
+	 */
+	if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
+		task->patch_state = READ_ONCE(klp_target_state);
+
+	rcu_read_unlock();
+}
+
+/*
+ * Determine whether the given stack trace includes any references to a
+ * to-be-patched or to-be-unpatched function.
+ */
+static int klp_check_stack_func(struct klp_func *func,
+				struct stack_trace *trace)
+{
+	unsigned long func_addr, func_size, address;
+	struct klp_ops *ops;
+	int i;
+
+	if (func->immediate)
+		return 0;
+
+	for (i = 0; i < trace->nr_entries; i++) {
+		address = trace->entries[i];
+
+		if (klp_target_state == KLP_UNPATCHED) {
+			 /*
+			  * Check for the to-be-unpatched function
+			  * (the func itself).
+			  */
+			func_addr = (unsigned long)func->new_func;
+			func_size = func->new_size;
+		} else {
+			/*
+			 * Check for the to-be-patched function
+			 * (the previous func).
+			 */
+			ops = klp_find_ops(func->old_addr);
+
+			if (list_is_singular(&ops->func_stack)) {
+				/* original function */
+				func_addr = func->old_addr;
+				func_size = func->old_size;
+			} else {
+				/* previously patched function */
+				struct klp_func *prev;
+
+				prev = list_next_entry(func, stack_node);
+				func_addr = (unsigned long)prev->new_func;
+				func_size = prev->new_size;
+			}
+		}
+
+		if (address >= func_addr && address < func_addr + func_size)
+			return -EAGAIN;
+	}
+
+	return 0;
+}
+
+/*
+ * Determine whether it's safe to transition the task to the target patch state
+ * by looking for any to-be-patched or to-be-unpatched functions on its stack.
+ */
+static int klp_check_stack(struct task_struct *task, char *err_buf)
+{
+	static unsigned long entries[MAX_STACK_ENTRIES];
+	struct stack_trace trace;
+	struct klp_object *obj;
+	struct klp_func *func;
+	int ret;
+
+	trace.skip = 0;
+	trace.nr_entries = 0;
+	trace.max_entries = MAX_STACK_ENTRIES;
+	trace.entries = entries;
+	ret = save_stack_trace_tsk_reliable(task, &trace);
+	WARN_ON_ONCE(ret == -ENOSYS);
+	if (ret) {
+		snprintf(err_buf, STACK_ERR_BUF_SIZE,
+			 "%s: %s:%d has an unreliable stack\n",
+			 __func__, task->comm, task->pid);
+		return ret;
+	}
+
+	klp_for_each_object(klp_transition_patch, obj) {
+		if (!obj->patched)
+			continue;
+		klp_for_each_func(obj, func) {
+			ret = klp_check_stack_func(func, &trace);
+			if (ret) {
+				snprintf(err_buf, STACK_ERR_BUF_SIZE,
+					 "%s: %s:%d is sleeping on function %s\n",
+					 __func__, task->comm, task->pid,
+					 func->old_name);
+				return ret;
+			}
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Try to safely switch a task to the target patch state.  If it's currently
+ * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
+ * if the stack is unreliable, return false.
+ */
+static bool klp_try_switch_task(struct task_struct *task)
+{
+	struct rq *rq;
+	struct rq_flags flags;
+	int ret;
+	bool success = false;
+	char err_buf[STACK_ERR_BUF_SIZE];
+
+	err_buf[0] = '\0';
+
+	/* check if this task has already switched over */
+	if (task->patch_state == klp_target_state)
+		return true;
+
+	/*
+	 * For arches which don't have reliable stack traces, we have to rely
+	 * on other methods (e.g., switching tasks at kernel exit).
+	 */
+	if (!klp_have_reliable_stack())
+		return false;
+
+	/*
+	 * Now try to check the stack for any to-be-patched or to-be-unpatched
+	 * functions.  If all goes well, switch the task to the target patch
+	 * state.
+	 */
+	rq = task_rq_lock(task, &flags);
+
+	if (task_running(rq, task) && task != current) {
+		snprintf(err_buf, STACK_ERR_BUF_SIZE,
+			 "%s: %s:%d is running\n", __func__, task->comm,
+			 task->pid);
+		goto done;
+	}
+
+	ret = klp_check_stack(task, err_buf);
+	if (ret)
+		goto done;
+
+	success = true;
+
+	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	task->patch_state = klp_target_state;
+
+done:
+	task_rq_unlock(rq, task, &flags);
+
+	/*
+	 * Due to console deadlock issues, pr_debug() can't be used while
+	 * holding the task rq lock.  Instead we have to use a temporary buffer
+	 * and print the debug message after releasing the lock.
+	 */
+	if (err_buf[0] != '\0')
+		pr_debug("%s", err_buf);
+
+	return success;
+
+}
+
+/*
+ * Try to switch all remaining tasks to the target patch state by walking the
+ * stacks of sleeping tasks and looking for any to-be-patched or
+ * to-be-unpatched functions.  If such functions are found, the task can't be
+ * switched yet.
+ *
+ * If any tasks are still stuck in the initial patch state, schedule a retry.
+ */
+void klp_try_complete_transition(void)
+{
+	unsigned int cpu;
+	struct task_struct *g, *task;
+	bool complete = true;
+
+	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
+
+	/*
+	 * If the patch can be applied or reverted immediately, skip the
+	 * per-task transitions.
+	 */
+	if (klp_transition_patch->immediate)
+		goto success;
+
+	/*
+	 * Try to switch the tasks to the target patch state by walking their
+	 * stacks and looking for any to-be-patched or to-be-unpatched
+	 * functions.  If such functions are found on a stack, or if the stack
+	 * is deemed unreliable, the task can't be switched yet.
+	 *
+	 * Usually this will transition most (or all) of the tasks on a system
+	 * unless the patch includes changes to a very common function.
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task)
+		if (!klp_try_switch_task(task))
+			complete = false;
+	read_unlock(&tasklist_lock);
+
+	/*
+	 * Ditto for the idle "swapper" tasks.
+	 */
+	get_online_cpus();
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		if (cpu_online(cpu)) {
+			if (!klp_try_switch_task(task))
+				complete = false;
+		} else if (task->patch_state != klp_target_state) {
+			/* offline idle tasks can be switched immediately */
+			clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+			task->patch_state = klp_target_state;
+		}
+	}
+	put_online_cpus();
+
+	if (!complete) {
+		/*
+		 * Some tasks weren't able to be switched over.  Try again
+		 * later and/or wait for other methods like kernel exit
+		 * switching.
+		 */
+		schedule_delayed_work(&klp_transition_work,
+				      round_jiffies_relative(HZ));
+		return;
+	}
+
+success:
+	pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
+		  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+	/* we're done, now cleanup the data structures */
+	klp_complete_transition();
+}
+
+/*
+ * Start the transition to the specified target patch state so tasks can begin
+ * switching to it.
+ */
+void klp_start_transition(void)
+{
+	struct task_struct *g, *task;
+	unsigned int cpu;
+
+	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
+
+	pr_notice("'%s': %s...\n", klp_transition_patch->mod->name,
+		  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+	/*
+	 * If the patch can be applied or reverted immediately, skip the
+	 * per-task transitions.
+	 */
+	if (klp_transition_patch->immediate)
+		return;
+
+	/*
+	 * Mark all normal tasks as needing a patch state update.  They'll
+	 * switch either in klp_try_complete_transition() or as they exit the
+	 * kernel.
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task)
+		if (task->patch_state != klp_target_state)
+			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	read_unlock(&tasklist_lock);
+
+	/*
+	 * Mark all idle tasks as needing a patch state update.  They'll switch
+	 * either in klp_try_complete_transition() or at the idle loop switch
+	 * point.
+	 */
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		if (task->patch_state != klp_target_state)
+			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	}
+}
+
+/*
+ * Initialize the global target patch state and all tasks to the initial patch
+ * state, and initialize all function transition states to true in preparation
+ * for patching or unpatching.
+ */
+void klp_init_transition(struct klp_patch *patch, int state)
+{
+	struct task_struct *g, *task;
+	unsigned int cpu;
+	struct klp_object *obj;
+	struct klp_func *func;
+	int initial_state = !state;
+
+	WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED);
+
+	klp_transition_patch = patch;
+
+	/*
+	 * Set the global target patch state which tasks will switch to.  This
+	 * has no effect until the TIF_PATCH_PENDING flags get set later.
+	 */
+	klp_target_state = state;
+
+	/*
+	 * If the patch can be applied or reverted immediately, skip the
+	 * per-task transitions.
+	 */
+	if (patch->immediate)
+		return;
+
+	/*
+	 * Initialize all tasks to the initial patch state to prepare them for
+	 * switching to the target state.
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task) {
+		WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
+		task->patch_state = initial_state;
+	}
+	read_unlock(&tasklist_lock);
+
+	/*
+	 * Ditto for the idle "swapper" tasks.
+	 */
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
+		task->patch_state = initial_state;
+	}
+
+	/*
+	 * Enforce the order of the task->patch_state initializations and the
+	 * func->transition updates to ensure that klp_ftrace_handler() doesn't
+	 * see a func in transition with a task->patch_state of KLP_UNDEFINED.
+	 *
+	 * Also enforce the order of the klp_target_state write and future
+	 * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
+	 * set a task->patch_state to KLP_UNDEFINED.
+	 */
+	smp_wmb();
+
+	/*
+	 * Set the func transition states so klp_ftrace_handler() will know to
+	 * switch to the transition logic.
+	 *
+	 * When patching, the funcs aren't yet in the func_stack and will be
+	 * made visible to the ftrace handler shortly by the calls to
+	 * klp_patch_object().
+	 *
+	 * When unpatching, the funcs are already in the func_stack and so are
+	 * already visible to the ftrace handler.
+	 */
+	klp_for_each_object(patch, obj)
+		klp_for_each_func(obj, func)
+			func->transition = true;
+}
+
+/*
+ * This function can be called in the middle of an existing transition to
+ * reverse the direction of the target patch state.  This can be done to
+ * effectively cancel an existing enable or disable operation if there are any
+ * tasks which are stuck in the initial patch state.
+ */
+void klp_reverse_transition(void)
+{
+	unsigned int cpu;
+	struct task_struct *g, *task;
+
+	klp_transition_patch->enabled = !klp_transition_patch->enabled;
+
+	klp_target_state = !klp_target_state;
+
+	/*
+	 * Clear all TIF_PATCH_PENDING flags to prevent races caused by
+	 * klp_update_patch_state() running in parallel with
+	 * klp_start_transition().
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task)
+		clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	read_unlock(&tasklist_lock);
+
+	for_each_possible_cpu(cpu)
+		clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
+
+	/* Let any remaining calls to klp_update_patch_state() complete */
+	synchronize_rcu();
+
+	klp_start_transition();
+}
+
+/* Called from copy_process() during fork */
+void klp_copy_process(struct task_struct *child)
+{
+	child->patch_state = current->patch_state;
+
+	/* TIF_PATCH_PENDING gets copied in setup_thread_stack() */
+}
diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
new file mode 100644
index 0000000..ce09b32
--- /dev/null
+++ b/kernel/livepatch/transition.h
@@ -0,0 +1,14 @@
+#ifndef _LIVEPATCH_TRANSITION_H
+#define _LIVEPATCH_TRANSITION_H
+
+#include <linux/livepatch.h>
+
+extern struct klp_patch *klp_transition_patch;
+
+void klp_init_transition(struct klp_patch *patch, int state);
+void klp_cancel_transition(void);
+void klp_start_transition(void);
+void klp_try_complete_transition(void);
+void klp_reverse_transition(void);
+
+#endif /* _LIVEPATCH_TRANSITION_H */
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 6a4bae0..a8b3f1a 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -9,6 +9,7 @@
 #include <linux/mm.h>
 #include <linux/stackprotector.h>
 #include <linux/suspend.h>
+#include <linux/livepatch.h>
 
 #include <asm/tlb.h>
 
@@ -264,6 +265,9 @@ static void do_idle(void)
 
 	sched_ttwu_pending();
 	schedule_preempt_disabled();
+
+	if (unlikely(klp_patch_pending(current)))
+		klp_update_patch_state(current);
 }
 
 bool cpu_in_idle(unsigned long pc)
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
index e34f871..629e0dc 100644
--- a/samples/livepatch/livepatch-sample.c
+++ b/samples/livepatch/livepatch-sample.c
@@ -17,6 +17,8 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/livepatch.h>
@@ -69,6 +71,21 @@ static int livepatch_init(void)
 {
 	int ret;
 
+	if (!klp_have_reliable_stack() && !patch.immediate) {
+		/*
+		 * WARNING: Be very careful when using 'patch.immediate' in
+		 * your patches.  It's ok to use it for simple patches like
+		 * this, but for more complex patches which change function
+		 * semantics, locking semantics, or data structures, it may not
+		 * be safe.  Use of this option will also prevent removal of
+		 * the patch.
+		 *
+		 * See Documentation/livepatch/livepatch.txt for more details.
+		 */
+		patch.immediate = true;
+		pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
+	}
+
 	ret = klp_register_patch(&patch);
 	if (ret)
 		return ret;
-- 
2.7.4

[PATCH v5 14/15] livepatch: add /proc/<pid>/patch_state

[Josh Poimboeuf]

Expose the per-task patch state value so users can determine which tasks
are holding up completion of a patching operation.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
---
 Documentation/filesystems/proc.txt | 18 ++++++++++++++++++
 fs/proc/base.c                     | 15 +++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index c94b467..9036dbf 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -44,6 +44,7 @@ Table of Contents
   3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
   3.9   /proc/<pid>/map_files - Information about memory mapped files
   3.10  /proc/<pid>/timerslack_ns - Task timerslack value
+  3.11	/proc/<pid>/patch_state - Livepatch patch operation state
 
   4	Configuring procfs
   4.1	Mount options
@@ -1887,6 +1888,23 @@ Valid values are from 0 - ULLONG_MAX
 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
 permissions on the task specified to change its timerslack_ns value.
 
+3.11	/proc/<pid>/patch_state - Livepatch patch operation state
+-----------------------------------------------------------------
+When CONFIG_LIVEPATCH is enabled, this file displays the value of the
+patch state for the task.
+
+A value of '-1' indicates that no patch is in transition.
+
+A value of '0' indicates that a patch is in transition and the task is
+unpatched.  If the patch is being enabled, then the task hasn't been
+patched yet.  If the patch is being disabled, then the task has already
+been unpatched.
+
+A value of '1' indicates that a patch is in transition and the task is
+patched.  If the patch is being enabled, then the task has already been
+patched.  If the patch is being disabled, then the task hasn't been
+unpatched yet.
+
 
 ------------------------------------------------------------------------------
 Configuring procfs
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6e86558..5145f40 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2828,6 +2828,15 @@ static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
 	return err;
 }
 
+#ifdef CONFIG_LIVEPATCH
+static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
+				struct pid *pid, struct task_struct *task)
+{
+	seq_printf(m, "%d\n", task->patch_state);
+	return 0;
+}
+#endif /* CONFIG_LIVEPATCH */
+
 /*
  * Thread groups
  */
@@ -2927,6 +2936,9 @@ static const struct pid_entry tgid_base_stuff[] = {
 	REG("timers",	  S_IRUGO, proc_timers_operations),
 #endif
 	REG("timerslack_ns", S_IRUGO|S_IWUGO, proc_pid_set_timerslack_ns_operations),
+#ifdef CONFIG_LIVEPATCH
+	ONE("patch_state",  S_IRUSR, proc_pid_patch_state),
+#endif
 };
 
 static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)
@@ -3309,6 +3321,9 @@ static const struct pid_entry tid_base_stuff[] = {
 	REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations),
 	REG("setgroups",  S_IRUGO|S_IWUSR, proc_setgroups_operations),
 #endif
+#ifdef CONFIG_LIVEPATCH
+	ONE("patch_state",  S_IRUSR, proc_pid_patch_state),
+#endif
 };
 
 static int proc_tid_base_readdir(struct file *file, struct dir_context *ctx)
-- 
2.7.4

[PATCH v5 15/15] livepatch: allow removal of a disabled patch

[Josh Poimboeuf]

From: Miroslav Benes <mbenes@suse.cz>

Currently we do not allow patch module to unload since there is no
method to determine if a task is still running in the patched code.

The consistency model gives us the way because when the unpatching
finishes we know that all tasks were marked as safe to call an original
function. Thus every new call to the function calls the original code
and at the same time no task can be somewhere in the patched code,
because it had to leave that code to be marked as safe.

We can safely let the patch module go after that.

Completion is used for synchronization between module removal and sysfs
infrastructure in a similar way to commit 942e443127e9 ("module: Fix
mod->mkobj.kobj potentially freed too early").

Note that we still do not allow the removal for immediate model, that is
no consistency model. The module refcount may increase in this case if
somebody disables and enables the patch several times. This should not
cause any harm.

With this change a call to try_module_get() is moved to
__klp_enable_patch from klp_register_patch to make module reference
counting symmetric (module_put() is in a patch disable path) and to
allow to take a new reference to a disabled module when being enabled.

Finally, we need to be very careful about possible races between
klp_unregister_patch(), kobject_put() functions and operations
on the related sysfs files.

kobject_put(&patch->kobj) must be called without klp_mutex. Otherwise,
it might be blocked by enabled_store() that needs the mutex as well.
In addition, enabled_store() must check if the patch was not
unregisted in the meantime.

There is no need to do the same for other kobject_put() callsites
at the moment. Their sysfs operations neither take the lock nor
they access any data that might be freed in the meantime.

There was an attempt to use kobjects the right way and prevent these
races by design. But it made the patch definition more complicated
and opened another can of worms. See
https://lkml.kernel.org/r/1464018848-4303-1-git-send-email-pmladek@suse.com

[Thanks to Petr Mladek for improving the commit message.]

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 Documentation/livepatch/livepatch.txt | 28 ++++--------
 include/linux/livepatch.h             |  3 ++
 kernel/livepatch/core.c               | 80 ++++++++++++++++++++++-------------
 kernel/livepatch/transition.c         | 12 +++++-
 samples/livepatch/livepatch-sample.c  |  1 -
 5 files changed, 72 insertions(+), 52 deletions(-)

diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index 4f2aec8..ecdb181 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -316,8 +316,15 @@ section "Livepatch life-cycle" below for more details about these
 two operations.
 
 Module removal is only safe when there are no users of the underlying
-functions.  The immediate consistency model is not able to detect this;
-therefore livepatch modules cannot be removed. See "Limitations" below.
+functions. The immediate consistency model is not able to detect this. The
+code just redirects the functions at the very beginning and it does not
+check if the functions are in use. In other words, it knows when the
+functions get called but it does not know when the functions return.
+Therefore it cannot be decided when the livepatch module can be safely
+removed. This is solved by a hybrid consistency model. When the system is
+transitioned to a new patch state (patched/unpatched) it is guaranteed that
+no task sleeps or runs in the old code.
+
 
 5. Livepatch life-cycle
 =======================
@@ -469,23 +476,6 @@ The current Livepatch implementation has several limitations:
     by "notrace".
 
 
-  + Livepatch modules can not be removed.
-
-    The current implementation just redirects the functions at the very
-    beginning. It does not check if the functions are in use. In other
-    words, it knows when the functions get called but it does not
-    know when the functions return. Therefore it can not decide when
-    the livepatch module can be safely removed.
-
-    This will get most likely solved once a more complex consistency model
-    is supported. The idea is that a safe state for patching should also
-    mean a safe state for removing the patch.
-
-    Note that the patch itself might get disabled by writing zero
-    to /sys/kernel/livepatch/<patch>/enabled. It causes that the new
-    code will not longer get called. But it does not guarantee
-    that anyone is not sleeping anywhere in the new code.
-
 
   + Livepatch works reliably only when the dynamic ftrace is located at
     the very beginning of the function.
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index ed90ad1..194991e 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -23,6 +23,7 @@
 
 #include <linux/module.h>
 #include <linux/ftrace.h>
+#include <linux/completion.h>
 
 #if IS_ENABLED(CONFIG_LIVEPATCH)
 
@@ -114,6 +115,7 @@ struct klp_object {
  * @list:	list node for global list of registered patches
  * @kobj:	kobject for sysfs resources
  * @enabled:	the patch is enabled (but operation may be incomplete)
+ * @finish:	for waiting till it is safe to remove the patch module
  */
 struct klp_patch {
 	/* external */
@@ -125,6 +127,7 @@ struct klp_patch {
 	struct list_head list;
 	struct kobject kobj;
 	bool enabled;
+	struct completion finish;
 };
 
 #define klp_for_each_object(patch, obj) \
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 3dc3c90..6844c12 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -29,6 +29,7 @@
 #include <linux/livepatch.h>
 #include <linux/elf.h>
 #include <linux/moduleloader.h>
+#include <linux/completion.h>
 #include <asm/cacheflush.h>
 #include "patch.h"
 #include "transition.h"
@@ -354,6 +355,18 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	    !list_prev_entry(patch, list)->enabled)
 		return -EBUSY;
 
+	/*
+	 * A reference is taken on the patch module to prevent it from being
+	 * unloaded.
+	 *
+	 * Note: For immediate (no consistency model) patches we don't allow
+	 * patch modules to unload since there is no safe/sane method to
+	 * determine if a thread is still running in the patched code contained
+	 * in the patch module once the ftrace registration is successful.
+	 */
+	if (!try_module_get(patch->mod))
+		return -ENODEV;
+
 	pr_notice("enabling patch '%s'\n", patch->mod->name);
 
 	klp_init_transition(patch, KLP_PATCHED);
@@ -442,6 +455,15 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 
 	mutex_lock(&klp_mutex);
 
+	if (!klp_is_patch_registered(patch)) {
+		/*
+		 * Module with the patch could either disappear meanwhile or is
+		 * not properly initialized yet.
+		 */
+		ret = -EINVAL;
+		goto err;
+	}
+
 	if (patch->enabled == enabled) {
 		/* already in requested state */
 		ret = -EINVAL;
@@ -498,10 +520,10 @@ static struct attribute *klp_patch_attrs[] = {
 
 static void klp_kobj_release_patch(struct kobject *kobj)
 {
-	/*
-	 * Once we have a consistency model we'll need to module_put() the
-	 * patch module here.  See klp_register_patch() for more details.
-	 */
+	struct klp_patch *patch;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	complete(&patch->finish);
 }
 
 static struct kobj_type klp_ktype_patch = {
@@ -572,7 +594,6 @@ static void klp_free_patch(struct klp_patch *patch)
 	klp_free_objects_limited(patch, NULL);
 	if (!list_empty(&patch->list))
 		list_del(&patch->list);
-	kobject_put(&patch->kobj);
 }
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
@@ -695,11 +716,14 @@ static int klp_init_patch(struct klp_patch *patch)
 	mutex_lock(&klp_mutex);
 
 	patch->enabled = false;
+	init_completion(&patch->finish);
 
 	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
 				   klp_root_kobj, "%s", patch->mod->name);
-	if (ret)
-		goto unlock;
+	if (ret) {
+		mutex_unlock(&klp_mutex);
+		return ret;
+	}
 
 	klp_for_each_object(patch, obj) {
 		ret = klp_init_object(patch, obj);
@@ -715,9 +739,12 @@ static int klp_init_patch(struct klp_patch *patch)
 
 free:
 	klp_free_objects_limited(patch, obj);
-	kobject_put(&patch->kobj);
-unlock:
+
 	mutex_unlock(&klp_mutex);
+
+	kobject_put(&patch->kobj);
+	wait_for_completion(&patch->finish);
+
 	return ret;
 }
 
@@ -731,23 +758,29 @@ static int klp_init_patch(struct klp_patch *patch)
  */
 int klp_unregister_patch(struct klp_patch *patch)
 {
-	int ret = 0;
+	int ret;
 
 	mutex_lock(&klp_mutex);
 
 	if (!klp_is_patch_registered(patch)) {
 		ret = -EINVAL;
-		goto out;
+		goto err;
 	}
 
 	if (patch->enabled) {
 		ret = -EBUSY;
-		goto out;
+		goto err;
 	}
 
 	klp_free_patch(patch);
 
-out:
+	mutex_unlock(&klp_mutex);
+
+	kobject_put(&patch->kobj);
+	wait_for_completion(&patch->finish);
+
+	return 0;
+err:
 	mutex_unlock(&klp_mutex);
 	return ret;
 }
@@ -760,12 +793,13 @@ EXPORT_SYMBOL_GPL(klp_unregister_patch);
  * Initializes the data structure associated with the patch and
  * creates the sysfs interface.
  *
+ * There is no need to take the reference on the patch module here. It is done
+ * later when the patch is enabled.
+ *
  * Return: 0 on success, otherwise error
  */
 int klp_register_patch(struct klp_patch *patch)
 {
-	int ret;
-
 	if (!patch || !patch->mod)
 		return -EINVAL;
 
@@ -788,21 +822,7 @@ int klp_register_patch(struct klp_patch *patch)
 		return -ENOSYS;
 	}
 
-	/*
-	 * A reference is taken on the patch module to prevent it from being
-	 * unloaded.  Right now, we don't allow patch modules to unload since
-	 * there is currently no method to determine if a thread is still
-	 * running in the patched code contained in the patch module once
-	 * the ftrace registration is successful.
-	 */
-	if (!try_module_get(patch->mod))
-		return -ENODEV;
-
-	ret = klp_init_patch(patch);
-	if (ret)
-		module_put(patch->mod);
-
-	return ret;
+	return klp_init_patch(patch);
 }
 EXPORT_SYMBOL_GPL(klp_register_patch);
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 428533e..e96346e 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -59,6 +59,7 @@ static void klp_complete_transition(void)
 	struct klp_func *func;
 	struct task_struct *g, *task;
 	unsigned int cpu;
+	bool is_immediate = false;
 
 	if (klp_target_state == KLP_UNPATCHED) {
 		/*
@@ -79,9 +80,16 @@ static void klp_complete_transition(void)
 	if (klp_transition_patch->immediate)
 		goto done;
 
-	klp_for_each_object(klp_transition_patch, obj)
-		klp_for_each_func(obj, func)
+	klp_for_each_object(klp_transition_patch, obj) {
+		klp_for_each_func(obj, func) {
 			func->transition = false;
+			if (func->immediate)
+				is_immediate = true;
+		}
+	}
+
+	if (klp_target_state == KLP_UNPATCHED && !is_immediate)
+		module_put(klp_transition_patch->mod);
 
 	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
 	if (klp_target_state == KLP_PATCHED)
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
index 629e0dc..84795223f 100644
--- a/samples/livepatch/livepatch-sample.c
+++ b/samples/livepatch/livepatch-sample.c
@@ -99,7 +99,6 @@ static int livepatch_init(void)
 
 static void livepatch_exit(void)
 {
-	WARN_ON(klp_disable_patch(&patch));
 	WARN_ON(klp_unregister_patch(&patch));
 }
 
-- 
2.7.4

Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces

[Miroslav Benes]

On Mon, 13 Feb 2017, Josh Poimboeuf wrote:

> For live patching and possibly other use cases, a stack trace is only
> useful if it can be assured that it's completely reliable.  Add a new
> save_stack_trace_tsk_reliable() function to achieve that.
> 
> Note that if the target task isn't the current task, and the target task
> is allowed to run, then it could be writing the stack while the unwinder
> is reading it, resulting in possible corruption.  So the caller of
> save_stack_trace_tsk_reliable() must ensure that the task is either
> 'current' or inactive.
> 
> save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
> of pt_regs on the stack.  If the pt_regs are not user-mode registers
> from a syscall, then they indicate an in-kernel interrupt or exception
> (e.g. preemption or a page fault), in which case the stack is considered
> unreliable due to the nature of frame pointers.
> 
> It also relies on the x86 unwinder's detection of other issues, such as:
> 
> - corrupted stack data
> - stack grows the wrong way
> - stack walk doesn't reach the bottom
> - user didn't provide a large enough entries array
> 
> Such issues are reported by checking unwind_error() and !unwind_done().
> 
> Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
> determine at build time whether the function is implemented.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

I do not see any difference from 4.1 version, so my

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

stays.

Regards,
Miroslav

Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces

[Josh Poimboeuf]

On Wed, Feb 15, 2017 at 01:18:40PM +0100, Miroslav Benes wrote:
> On Mon, 13 Feb 2017, Josh Poimboeuf wrote:
> 
> > For live patching and possibly other use cases, a stack trace is only
> > useful if it can be assured that it's completely reliable.  Add a new
> > save_stack_trace_tsk_reliable() function to achieve that.
> > 
> > Note that if the target task isn't the current task, and the target task
> > is allowed to run, then it could be writing the stack while the unwinder
> > is reading it, resulting in possible corruption.  So the caller of
> > save_stack_trace_tsk_reliable() must ensure that the task is either
> > 'current' or inactive.
> > 
> > save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
> > of pt_regs on the stack.  If the pt_regs are not user-mode registers
> > from a syscall, then they indicate an in-kernel interrupt or exception
> > (e.g. preemption or a page fault), in which case the stack is considered
> > unreliable due to the nature of frame pointers.
> > 
> > It also relies on the x86 unwinder's detection of other issues, such as:
> > 
> > - corrupted stack data
> > - stack grows the wrong way
> > - stack walk doesn't reach the bottom
> > - user didn't provide a large enough entries array
> > 
> > Such issues are reported by checking unwind_error() and !unwind_done().
> > 
> > Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
> > determine at build time whether the function is implemented.
> > 
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> 
> I do not see any difference from 4.1 version, so my
> 
> Reviewed-by: Miroslav Benes <mbenes@suse.cz>

Sorry, forgot to add your Reviewed-by from last time.  The patch is
indeed the same.  Thanks!

-- 
Josh

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Miroslav Benes]

> @@ -347,22 +356,36 @@ static int __klp_enable_patch(struct klp_patch *patch)
>  
>  	pr_notice("enabling patch '%s'\n", patch->mod->name);
>  
> +	klp_init_transition(patch, KLP_PATCHED);
> +
> +	/*
> +	 * Enforce the order of the func->transition writes in
> +	 * klp_init_transition() and the ops->func_stack writes in
> +	 * klp_patch_object(), so that klp_ftrace_handler() will see the
> +	 * func->transition updates before the handler is registered and the
> +	 * new funcs become visible to the handler.
> +	 */
> +	smp_wmb();
> +
>  	klp_for_each_object(patch, obj) {
>  		if (!klp_is_object_loaded(obj))
>  			continue;
>  
>  		ret = klp_patch_object(obj);
> -		if (ret)
> -			goto unregister;
> +		if (ret) {
> +			pr_warn("failed to enable patch '%s'\n",
> +				patch->mod->name);
> +
> +			klp_cancel_transition();
> +			return ret;
> +		}

[...]

> +static void klp_complete_transition(void)
> +{
> +	struct klp_object *obj;
> +	struct klp_func *func;
> +	struct task_struct *g, *task;
> +	unsigned int cpu;
> +
> +	if (klp_target_state == KLP_UNPATCHED) {
> +		/*
> +		 * All tasks have transitioned to KLP_UNPATCHED so we can now
> +		 * remove the new functions from the func_stack.
> +		 */
> +		klp_unpatch_objects(klp_transition_patch);
> +
> +		/*
> +		 * Make sure klp_ftrace_handler() can no longer see functions
> +		 * from this patch on the ops->func_stack.  Otherwise, after
> +		 * func->transition gets cleared, the handler may choose a
> +		 * removed function.
> +		 */
> +		synchronize_rcu();
> +	}
> +
> +	if (klp_transition_patch->immediate)
> +		goto done;
> +
> +	klp_for_each_object(klp_transition_patch, obj)
> +		klp_for_each_func(obj, func)
> +			func->transition = false;
> +
> +	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
> +	if (klp_target_state == KLP_PATCHED)
> +		synchronize_rcu();
> +
> +	read_lock(&tasklist_lock);
> +	for_each_process_thread(g, task) {
> +		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
> +		task->patch_state = KLP_UNDEFINED;
> +	}
> +	read_unlock(&tasklist_lock);
> +
> +	for_each_possible_cpu(cpu) {
> +		task = idle_task(cpu);
> +		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
> +		task->patch_state = KLP_UNDEFINED;
> +	}
> +
> +done:
> +	klp_target_state = KLP_UNDEFINED;
> +	klp_transition_patch = NULL;
> +}
> +
> +/*
> + * This is called in the error path, to cancel a transition before it has
> + * started, i.e. klp_init_transition() has been called but
> + * klp_start_transition() hasn't.  If the transition *has* been started,
> + * klp_reverse_transition() should be used instead.
> + */
> +void klp_cancel_transition(void)
> +{
> +	klp_target_state = !klp_target_state;
> +	klp_complete_transition();
> +}

If we fail to enable patch in __klp_enable_patch(), we call 
klp_cancel_transition() and get to klp_complete_transition(). If the patch 
has immediate set to true, the module would not be allowed to go (the 
changes are in the last patch unfortunately, but my remark is closely 
related to klp_cancel_transition() and __klp_enable_patch()). This could 
annoy a user if it was due to a trivial reason. So we could call  
module_put() in this case. It should be safe as no task could be in a new 
function thanks to klp_ftrace_handler() logic.

Pity I have not spotted this earlier.

Putting module_put(patch->mod) right after klp_cancel_transition() call in 
__klp_enable_patch() would be the simplest fix (as a part of 15/15 patch). 
Maybe with a comment that it is safe to do it there.

What do you think?

Miroslav

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Josh Poimboeuf]

On Thu, Feb 16, 2017 at 03:33:26PM +0100, Miroslav Benes wrote:
> 
> > @@ -347,22 +356,36 @@ static int __klp_enable_patch(struct klp_patch *patch)
> >  
> >  	pr_notice("enabling patch '%s'\n", patch->mod->name);
> >  
> > +	klp_init_transition(patch, KLP_PATCHED);
> > +
> > +	/*
> > +	 * Enforce the order of the func->transition writes in
> > +	 * klp_init_transition() and the ops->func_stack writes in
> > +	 * klp_patch_object(), so that klp_ftrace_handler() will see the
> > +	 * func->transition updates before the handler is registered and the
> > +	 * new funcs become visible to the handler.
> > +	 */
> > +	smp_wmb();
> > +
> >  	klp_for_each_object(patch, obj) {
> >  		if (!klp_is_object_loaded(obj))
> >  			continue;
> >  
> >  		ret = klp_patch_object(obj);
> > -		if (ret)
> > -			goto unregister;
> > +		if (ret) {
> > +			pr_warn("failed to enable patch '%s'\n",
> > +				patch->mod->name);
> > +
> > +			klp_cancel_transition();
> > +			return ret;
> > +		}
> 
> [...]
> 
> > +static void klp_complete_transition(void)
> > +{
> > +	struct klp_object *obj;
> > +	struct klp_func *func;
> > +	struct task_struct *g, *task;
> > +	unsigned int cpu;
> > +
> > +	if (klp_target_state == KLP_UNPATCHED) {
> > +		/*
> > +		 * All tasks have transitioned to KLP_UNPATCHED so we can now
> > +		 * remove the new functions from the func_stack.
> > +		 */
> > +		klp_unpatch_objects(klp_transition_patch);
> > +
> > +		/*
> > +		 * Make sure klp_ftrace_handler() can no longer see functions
> > +		 * from this patch on the ops->func_stack.  Otherwise, after
> > +		 * func->transition gets cleared, the handler may choose a
> > +		 * removed function.
> > +		 */
> > +		synchronize_rcu();
> > +	}
> > +
> > +	if (klp_transition_patch->immediate)
> > +		goto done;
> > +
> > +	klp_for_each_object(klp_transition_patch, obj)
> > +		klp_for_each_func(obj, func)
> > +			func->transition = false;
> > +
> > +	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
> > +	if (klp_target_state == KLP_PATCHED)
> > +		synchronize_rcu();
> > +
> > +	read_lock(&tasklist_lock);
> > +	for_each_process_thread(g, task) {
> > +		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
> > +		task->patch_state = KLP_UNDEFINED;
> > +	}
> > +	read_unlock(&tasklist_lock);
> > +
> > +	for_each_possible_cpu(cpu) {
> > +		task = idle_task(cpu);
> > +		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
> > +		task->patch_state = KLP_UNDEFINED;
> > +	}
> > +
> > +done:
> > +	klp_target_state = KLP_UNDEFINED;
> > +	klp_transition_patch = NULL;
> > +}
> > +
> > +/*
> > + * This is called in the error path, to cancel a transition before it has
> > + * started, i.e. klp_init_transition() has been called but
> > + * klp_start_transition() hasn't.  If the transition *has* been started,
> > + * klp_reverse_transition() should be used instead.
> > + */
> > +void klp_cancel_transition(void)
> > +{
> > +	klp_target_state = !klp_target_state;
> > +	klp_complete_transition();
> > +}
> 
> If we fail to enable patch in __klp_enable_patch(), we call 
> klp_cancel_transition() and get to klp_complete_transition(). If the patch 
> has immediate set to true, the module would not be allowed to go (the 
> changes are in the last patch unfortunately, but my remark is closely 
> related to klp_cancel_transition() and __klp_enable_patch()). This could 
> annoy a user if it was due to a trivial reason. So we could call  
> module_put() in this case. It should be safe as no task could be in a new 
> function thanks to klp_ftrace_handler() logic.
> 
> Pity I have not spotted this earlier.
> 
> Putting module_put(patch->mod) right after klp_cancel_transition() call in 
> __klp_enable_patch() would be the simplest fix (as a part of 15/15 patch). 
> Maybe with a comment that it is safe to do it there.
> 
> What do you think?

Good catch.  I agree that 15/15 should have something like that.

Also, the module_put() will be needed for non-immediate patches which
have a func->immediate set.

What do you think about the following?  I tried to put the logic in
klp_complete_transition(), so the module_put()'s would be in one place.
But it was too messy, so I put it in klp_cancel_transition() instead.


diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index e96346e..bd1c1fd 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -121,8 +121,28 @@ static void klp_complete_transition(void)
  */
 void klp_cancel_transition(void)
 {
+	bool immediate_func = false;
+
 	klp_target_state = !klp_target_state;
 	klp_complete_transition();
+
+	if (klp_target_state == KLP_PATCHED)
+		return;
+
+	/*
+	 * In the enable error path, even immediate patches can be safely
+	 * removed because the transition hasn't been started yet.
+	 *
+	 * klp_complete_transition() doesn't have a module_put() for immediate
+	 * patches, so do it here.
+	 */
+	klp_for_each_object(klp_transition_patch, obj)
+		klp_for_each_func(obj, func)
+			if (func->immediate)
+				immediate_func = true;
+
+	if (klp_transition_patch->immediate || immediate_func)
+		module_put(klp_transition_patch->mod);
 }
 
 /*

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Miroslav Benes]

On Thu, 16 Feb 2017, Josh Poimboeuf wrote:

> On Thu, Feb 16, 2017 at 03:33:26PM +0100, Miroslav Benes wrote:
> > 
> > > @@ -347,22 +356,36 @@ static int __klp_enable_patch(struct klp_patch *patch)
> > >  
> > >  	pr_notice("enabling patch '%s'\n", patch->mod->name);
> > >  
> > > +	klp_init_transition(patch, KLP_PATCHED);
> > > +
> > > +	/*
> > > +	 * Enforce the order of the func->transition writes in
> > > +	 * klp_init_transition() and the ops->func_stack writes in
> > > +	 * klp_patch_object(), so that klp_ftrace_handler() will see the
> > > +	 * func->transition updates before the handler is registered and the
> > > +	 * new funcs become visible to the handler.
> > > +	 */
> > > +	smp_wmb();
> > > +
> > >  	klp_for_each_object(patch, obj) {
> > >  		if (!klp_is_object_loaded(obj))
> > >  			continue;
> > >  
> > >  		ret = klp_patch_object(obj);
> > > -		if (ret)
> > > -			goto unregister;
> > > +		if (ret) {
> > > +			pr_warn("failed to enable patch '%s'\n",
> > > +				patch->mod->name);
> > > +
> > > +			klp_cancel_transition();
> > > +			return ret;
> > > +		}
> > 
> > [...]
> > 
> > > +static void klp_complete_transition(void)
> > > +{
> > > +	struct klp_object *obj;
> > > +	struct klp_func *func;
> > > +	struct task_struct *g, *task;
> > > +	unsigned int cpu;
> > > +
> > > +	if (klp_target_state == KLP_UNPATCHED) {
> > > +		/*
> > > +		 * All tasks have transitioned to KLP_UNPATCHED so we can now
> > > +		 * remove the new functions from the func_stack.
> > > +		 */
> > > +		klp_unpatch_objects(klp_transition_patch);
> > > +
> > > +		/*
> > > +		 * Make sure klp_ftrace_handler() can no longer see functions
> > > +		 * from this patch on the ops->func_stack.  Otherwise, after
> > > +		 * func->transition gets cleared, the handler may choose a
> > > +		 * removed function.
> > > +		 */
> > > +		synchronize_rcu();
> > > +	}
> > > +
> > > +	if (klp_transition_patch->immediate)
> > > +		goto done;
> > > +
> > > +	klp_for_each_object(klp_transition_patch, obj)
> > > +		klp_for_each_func(obj, func)
> > > +			func->transition = false;
> > > +
> > > +	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
> > > +	if (klp_target_state == KLP_PATCHED)
> > > +		synchronize_rcu();
> > > +
> > > +	read_lock(&tasklist_lock);
> > > +	for_each_process_thread(g, task) {
> > > +		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
> > > +		task->patch_state = KLP_UNDEFINED;
> > > +	}
> > > +	read_unlock(&tasklist_lock);
> > > +
> > > +	for_each_possible_cpu(cpu) {
> > > +		task = idle_task(cpu);
> > > +		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
> > > +		task->patch_state = KLP_UNDEFINED;
> > > +	}
> > > +
> > > +done:
> > > +	klp_target_state = KLP_UNDEFINED;
> > > +	klp_transition_patch = NULL;
> > > +}
> > > +
> > > +/*
> > > + * This is called in the error path, to cancel a transition before it has
> > > + * started, i.e. klp_init_transition() has been called but
> > > + * klp_start_transition() hasn't.  If the transition *has* been started,
> > > + * klp_reverse_transition() should be used instead.
> > > + */
> > > +void klp_cancel_transition(void)
> > > +{
> > > +	klp_target_state = !klp_target_state;
> > > +	klp_complete_transition();
> > > +}
> > 
> > If we fail to enable patch in __klp_enable_patch(), we call 
> > klp_cancel_transition() and get to klp_complete_transition(). If the patch 
> > has immediate set to true, the module would not be allowed to go (the 
> > changes are in the last patch unfortunately, but my remark is closely 
> > related to klp_cancel_transition() and __klp_enable_patch()). This could 
> > annoy a user if it was due to a trivial reason. So we could call  
> > module_put() in this case. It should be safe as no task could be in a new 
> > function thanks to klp_ftrace_handler() logic.
> > 
> > Pity I have not spotted this earlier.
> > 
> > Putting module_put(patch->mod) right after klp_cancel_transition() call in 
> > __klp_enable_patch() would be the simplest fix (as a part of 15/15 patch). 
> > Maybe with a comment that it is safe to do it there.
> > 
> > What do you think?
> 
> Good catch.  I agree that 15/15 should have something like that.
> 
> Also, the module_put() will be needed for non-immediate patches which
> have a func->immediate set.

Right. This further complicates it.
 
> What do you think about the following?  I tried to put the logic in
> klp_complete_transition(), so the module_put()'s would be in one place.
> But it was too messy, so I put it in klp_cancel_transition() instead.
>
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index e96346e..bd1c1fd 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -121,8 +121,28 @@ static void klp_complete_transition(void)
>   */
>  void klp_cancel_transition(void)
>  {
> +	bool immediate_func = false;
> +
>  	klp_target_state = !klp_target_state;
>  	klp_complete_transition();
> +
> +	if (klp_target_state == KLP_PATCHED)
> +		return;

This is not needed, I think. We call klp_cancel_transition() in 
__klp_enable_patch() only. klp_target_state is set to KLP_PATCHED there 
(through klp_init_transition()) and negated here. We know it must be 
KLP_UNPATCHED.

Moreover, due to klp_complete_transition() klp_target_state is always 
KLP_UNDEFINED after it.

> +
> +	/*
> +	 * In the enable error path, even immediate patches can be safely
> +	 * removed because the transition hasn't been started yet.
> +	 *
> +	 * klp_complete_transition() doesn't have a module_put() for immediate
> +	 * patches, so do it here.
> +	 */
> +	klp_for_each_object(klp_transition_patch, obj)
> +		klp_for_each_func(obj, func)
> +			if (func->immediate)
> +				immediate_func = true;
> +
> +	if (klp_transition_patch->immediate || immediate_func)
> +		module_put(klp_transition_patch->mod);

Almost correct. The only problem is that klp_transition_patch is NULL at 
this point. klp_complete_transition() does that and it should stay there 
in my opinion to keep it simple.

So we could either move all this to __klp_enable_patch(), where patch 
variable is defined, or we could store klp_transition_patch to a local 
variable here in klp_cancel_transition() before klp_complete_transition() 
is called. That should be safe. I like the latter more, because it keeps 
the code in klp_cancel_transition() where it belongs.

Miroslav

Re: [PATCH v5 00/15] livepatch: hybrid consistency model

[Miroslav Benes]

On Mon, 13 Feb 2017, Josh Poimboeuf wrote:

> Here's v5 of the consistency model, targeted for 4.12.  Only a few minor
> changes this time.
> 
> v5:
> - return -EINVAL in __save_stack_trace_reliable()
> - only call show_stack() once
> - add save_stack_trace_tsk_reliable() define for !CONFIG_STACKTRACE
> - update kernel version and date in ABI doc
> - make suggested improvements to livepatch.txt
> - update barrier comments
> - remove klp_try_complete_transition() call from klp_start_transition()
> - move end of klp_try_complete_transition() into klp_complete_transition()
> - fix __klp_enable_patch() error path
> - check for transition in klp_module_going()

All the changes since v4 look good to me (except for module_put() in 
__klp_enable_patch() mentioned elsewhere).

Thanks,
Miroslav

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Josh Poimboeuf]

On Fri, Feb 17, 2017 at 09:51:29AM +0100, Miroslav Benes wrote:
> On Thu, 16 Feb 2017, Josh Poimboeuf wrote:
> > What do you think about the following?  I tried to put the logic in
> > klp_complete_transition(), so the module_put()'s would be in one place.
> > But it was too messy, so I put it in klp_cancel_transition() instead.
> >
> > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> > index e96346e..bd1c1fd 100644
> > --- a/kernel/livepatch/transition.c
> > +++ b/kernel/livepatch/transition.c
> > @@ -121,8 +121,28 @@ static void klp_complete_transition(void)
> >   */
> >  void klp_cancel_transition(void)
> >  {
> > +	bool immediate_func = false;
> > +
> >  	klp_target_state = !klp_target_state;
> >  	klp_complete_transition();
> > +
> > +	if (klp_target_state == KLP_PATCHED)
> > +		return;
> 
> This is not needed, I think. We call klp_cancel_transition() in 
> __klp_enable_patch() only. klp_target_state is set to KLP_PATCHED there 
> (through klp_init_transition()) and negated here. We know it must be 
> KLP_UNPATCHED.

Yeah, I was trying to hedge against the possibility of future code
calling this function in the disable path.  But that probably won't
happen and it would probably be cleaner to just add a warning if
klp_target_state isn't KLP_PATCHED.

> Moreover, due to klp_complete_transition() klp_target_state is always 
> KLP_UNDEFINED after it.
> 
> > +
> > +	/*
> > +	 * In the enable error path, even immediate patches can be safely
> > +	 * removed because the transition hasn't been started yet.
> > +	 *
> > +	 * klp_complete_transition() doesn't have a module_put() for immediate
> > +	 * patches, so do it here.
> > +	 */
> > +	klp_for_each_object(klp_transition_patch, obj)
> > +		klp_for_each_func(obj, func)
> > +			if (func->immediate)
> > +				immediate_func = true;
> > +
> > +	if (klp_transition_patch->immediate || immediate_func)
> > +		module_put(klp_transition_patch->mod);
> 
> Almost correct. The only problem is that klp_transition_patch is NULL at 
> this point. klp_complete_transition() does that and it should stay there 
> in my opinion to keep it simple.
> 
> So we could either move all this to __klp_enable_patch(), where patch 
> variable is defined, or we could store klp_transition_patch to a local 
> variable here in klp_cancel_transition() before klp_complete_transition() 
> is called. That should be safe. I like the latter more, because it keeps 
> the code in klp_cancel_transition() where it belongs.

Good points.  Here's another try:

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index e96346e..a23c63c 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -121,8 +121,31 @@ static void klp_complete_transition(void)
  */
 void klp_cancel_transition(void)
 {
-	klp_target_state = !klp_target_state;
+	struct klp_patch *patch = klp_transition_patch;
+	struct klp_object *obj;
+	struct klp_func *func;
+	bool immediate_func = false;
+
+	if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
+		return;
+
+	klp_target_state = KLP_UNPATCHED;
 	klp_complete_transition();
+
+	/*
+	 * In the enable error path, even immediate patches can be safely
+	 * removed because the transition hasn't been started yet.
+	 *
+	 * klp_complete_transition() doesn't have a module_put() for immediate
+	 * patches, so do it here.
+	 */
+	klp_for_each_object(patch, obj)
+		klp_for_each_func(obj, func)
+			if (func->immediate)
+				immediate_func = true;
+
+	if (patch->immediate || immediate_func)
+		module_put(patch->mod);
 }
 
 /*

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Miroslav Benes]

On Tue, 21 Feb 2017, Josh Poimboeuf wrote:

> On Fri, Feb 17, 2017 at 09:51:29AM +0100, Miroslav Benes wrote:
> > On Thu, 16 Feb 2017, Josh Poimboeuf wrote:
> > > What do you think about the following?  I tried to put the logic in
> > > klp_complete_transition(), so the module_put()'s would be in one place.
> > > But it was too messy, so I put it in klp_cancel_transition() instead.
> > >
> > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> > > index e96346e..bd1c1fd 100644
> > > --- a/kernel/livepatch/transition.c
> > > +++ b/kernel/livepatch/transition.c
> > > @@ -121,8 +121,28 @@ static void klp_complete_transition(void)
> > >   */
> > >  void klp_cancel_transition(void)
> > >  {
> > > +	bool immediate_func = false;
> > > +
> > >  	klp_target_state = !klp_target_state;
> > >  	klp_complete_transition();
> > > +
> > > +	if (klp_target_state == KLP_PATCHED)
> > > +		return;
> > 
> > This is not needed, I think. We call klp_cancel_transition() in 
> > __klp_enable_patch() only. klp_target_state is set to KLP_PATCHED there 
> > (through klp_init_transition()) and negated here. We know it must be 
> > KLP_UNPATCHED.
> 
> Yeah, I was trying to hedge against the possibility of future code
> calling this function in the disable path.  But that probably won't
> happen and it would probably be cleaner to just add a warning if
> klp_target_state isn't KLP_PATCHED.
> 
> > Moreover, due to klp_complete_transition() klp_target_state is always 
> > KLP_UNDEFINED after it.
> > 
> > > +
> > > +	/*
> > > +	 * In the enable error path, even immediate patches can be safely
> > > +	 * removed because the transition hasn't been started yet.
> > > +	 *
> > > +	 * klp_complete_transition() doesn't have a module_put() for immediate
> > > +	 * patches, so do it here.
> > > +	 */
> > > +	klp_for_each_object(klp_transition_patch, obj)
> > > +		klp_for_each_func(obj, func)
> > > +			if (func->immediate)
> > > +				immediate_func = true;
> > > +
> > > +	if (klp_transition_patch->immediate || immediate_func)
> > > +		module_put(klp_transition_patch->mod);
> > 
> > Almost correct. The only problem is that klp_transition_patch is NULL at 
> > this point. klp_complete_transition() does that and it should stay there 
> > in my opinion to keep it simple.
> > 
> > So we could either move all this to __klp_enable_patch(), where patch 
> > variable is defined, or we could store klp_transition_patch to a local 
> > variable here in klp_cancel_transition() before klp_complete_transition() 
> > is called. That should be safe. I like the latter more, because it keeps 
> > the code in klp_cancel_transition() where it belongs.
> 
> Good points.  Here's another try:
> 
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index e96346e..a23c63c 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -121,8 +121,31 @@ static void klp_complete_transition(void)
>   */
>  void klp_cancel_transition(void)
>  {
> -	klp_target_state = !klp_target_state;
> +	struct klp_patch *patch = klp_transition_patch;
> +	struct klp_object *obj;
> +	struct klp_func *func;
> +	bool immediate_func = false;
> +
> +	if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
> +		return;
> +
> +	klp_target_state = KLP_UNPATCHED;
>  	klp_complete_transition();
> +
> +	/*
> +	 * In the enable error path, even immediate patches can be safely
> +	 * removed because the transition hasn't been started yet.
> +	 *
> +	 * klp_complete_transition() doesn't have a module_put() for immediate
> +	 * patches, so do it here.
> +	 */
> +	klp_for_each_object(patch, obj)
> +		klp_for_each_func(obj, func)
> +			if (func->immediate)
> +				immediate_func = true;
> +
> +	if (patch->immediate || immediate_func)
> +		module_put(patch->mod);
>  }

Looks ok.

Thanks,
Miroslav

[PATCH v5.1 15/15] livepatch: allow removal of a disabled patch

[Josh Poimboeuf]

Currently we do not allow patch module to unload since there is no
method to determine if a task is still running in the patched code.

The consistency model gives us the way because when the unpatching
finishes we know that all tasks were marked as safe to call an original
function. Thus every new call to the function calls the original code
and at the same time no task can be somewhere in the patched code,
because it had to leave that code to be marked as safe.

We can safely let the patch module go after that.

Completion is used for synchronization between module removal and sysfs
infrastructure in a similar way to commit 942e443127e9 ("module: Fix
mod->mkobj.kobj potentially freed too early").

Note that we still do not allow the removal for immediate model, that is
no consistency model. The module refcount may increase in this case if
somebody disables and enables the patch several times. This should not
cause any harm.

With this change a call to try_module_get() is moved to
__klp_enable_patch from klp_register_patch to make module reference
counting symmetric (module_put() is in a patch disable path) and to
allow to take a new reference to a disabled module when being enabled.

Finally, we need to be very careful about possible races between
klp_unregister_patch(), kobject_put() functions and operations
on the related sysfs files.

kobject_put(&patch->kobj) must be called without klp_mutex. Otherwise,
it might be blocked by enabled_store() that needs the mutex as well.
In addition, enabled_store() must check if the patch was not
unregisted in the meantime.

There is no need to do the same for other kobject_put() callsites
at the moment. Their sysfs operations neither take the lock nor
they access any data that might be freed in the meantime.

There was an attempt to use kobjects the right way and prevent these
races by design. But it made the patch definition more complicated
and opened another can of worms. See
https://lkml.kernel.org/r/1464018848-4303-1-git-send-email-pmladek@suse.com

[Thanks to Petr Mladek for improving the commit message.]

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
v5.1: improve error handling in enable path -- call module_put() in
      klp_cancel_transition()

 Documentation/livepatch/livepatch.txt | 28 ++++--------
 include/linux/livepatch.h             |  3 ++
 kernel/livepatch/core.c               | 80 ++++++++++++++++++++++-------------
 kernel/livepatch/transition.c         | 37 ++++++++++++++--
 samples/livepatch/livepatch-sample.c  |  1 -
 5 files changed, 96 insertions(+), 53 deletions(-)

diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index 4f2aec8..ecdb181 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -316,8 +316,15 @@ section "Livepatch life-cycle" below for more details about these
 two operations.
 
 Module removal is only safe when there are no users of the underlying
-functions.  The immediate consistency model is not able to detect this;
-therefore livepatch modules cannot be removed. See "Limitations" below.
+functions. The immediate consistency model is not able to detect this. The
+code just redirects the functions at the very beginning and it does not
+check if the functions are in use. In other words, it knows when the
+functions get called but it does not know when the functions return.
+Therefore it cannot be decided when the livepatch module can be safely
+removed. This is solved by a hybrid consistency model. When the system is
+transitioned to a new patch state (patched/unpatched) it is guaranteed that
+no task sleeps or runs in the old code.
+
 
 5. Livepatch life-cycle
 =======================
@@ -469,23 +476,6 @@ The current Livepatch implementation has several limitations:
     by "notrace".
 
 
-  + Livepatch modules can not be removed.
-
-    The current implementation just redirects the functions at the very
-    beginning. It does not check if the functions are in use. In other
-    words, it knows when the functions get called but it does not
-    know when the functions return. Therefore it can not decide when
-    the livepatch module can be safely removed.
-
-    This will get most likely solved once a more complex consistency model
-    is supported. The idea is that a safe state for patching should also
-    mean a safe state for removing the patch.
-
-    Note that the patch itself might get disabled by writing zero
-    to /sys/kernel/livepatch/<patch>/enabled. It causes that the new
-    code will not longer get called. But it does not guarantee
-    that anyone is not sleeping anywhere in the new code.
-
 
   + Livepatch works reliably only when the dynamic ftrace is located at
     the very beginning of the function.
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index ed90ad1..194991e 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -23,6 +23,7 @@
 
 #include <linux/module.h>
 #include <linux/ftrace.h>
+#include <linux/completion.h>
 
 #if IS_ENABLED(CONFIG_LIVEPATCH)
 
@@ -114,6 +115,7 @@ struct klp_object {
  * @list:	list node for global list of registered patches
  * @kobj:	kobject for sysfs resources
  * @enabled:	the patch is enabled (but operation may be incomplete)
+ * @finish:	for waiting till it is safe to remove the patch module
  */
 struct klp_patch {
 	/* external */
@@ -125,6 +127,7 @@ struct klp_patch {
 	struct list_head list;
 	struct kobject kobj;
 	bool enabled;
+	struct completion finish;
 };
 
 #define klp_for_each_object(patch, obj) \
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 3dc3c90..6844c12 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -29,6 +29,7 @@
 #include <linux/livepatch.h>
 #include <linux/elf.h>
 #include <linux/moduleloader.h>
+#include <linux/completion.h>
 #include <asm/cacheflush.h>
 #include "patch.h"
 #include "transition.h"
@@ -354,6 +355,18 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	    !list_prev_entry(patch, list)->enabled)
 		return -EBUSY;
 
+	/*
+	 * A reference is taken on the patch module to prevent it from being
+	 * unloaded.
+	 *
+	 * Note: For immediate (no consistency model) patches we don't allow
+	 * patch modules to unload since there is no safe/sane method to
+	 * determine if a thread is still running in the patched code contained
+	 * in the patch module once the ftrace registration is successful.
+	 */
+	if (!try_module_get(patch->mod))
+		return -ENODEV;
+
 	pr_notice("enabling patch '%s'\n", patch->mod->name);
 
 	klp_init_transition(patch, KLP_PATCHED);
@@ -442,6 +455,15 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 
 	mutex_lock(&klp_mutex);
 
+	if (!klp_is_patch_registered(patch)) {
+		/*
+		 * Module with the patch could either disappear meanwhile or is
+		 * not properly initialized yet.
+		 */
+		ret = -EINVAL;
+		goto err;
+	}
+
 	if (patch->enabled == enabled) {
 		/* already in requested state */
 		ret = -EINVAL;
@@ -498,10 +520,10 @@ static struct attribute *klp_patch_attrs[] = {
 
 static void klp_kobj_release_patch(struct kobject *kobj)
 {
-	/*
-	 * Once we have a consistency model we'll need to module_put() the
-	 * patch module here.  See klp_register_patch() for more details.
-	 */
+	struct klp_patch *patch;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	complete(&patch->finish);
 }
 
 static struct kobj_type klp_ktype_patch = {
@@ -572,7 +594,6 @@ static void klp_free_patch(struct klp_patch *patch)
 	klp_free_objects_limited(patch, NULL);
 	if (!list_empty(&patch->list))
 		list_del(&patch->list);
-	kobject_put(&patch->kobj);
 }
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
@@ -695,11 +716,14 @@ static int klp_init_patch(struct klp_patch *patch)
 	mutex_lock(&klp_mutex);
 
 	patch->enabled = false;
+	init_completion(&patch->finish);
 
 	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
 				   klp_root_kobj, "%s", patch->mod->name);
-	if (ret)
-		goto unlock;
+	if (ret) {
+		mutex_unlock(&klp_mutex);
+		return ret;
+	}
 
 	klp_for_each_object(patch, obj) {
 		ret = klp_init_object(patch, obj);
@@ -715,9 +739,12 @@ static int klp_init_patch(struct klp_patch *patch)
 
 free:
 	klp_free_objects_limited(patch, obj);
-	kobject_put(&patch->kobj);
-unlock:
+
 	mutex_unlock(&klp_mutex);
+
+	kobject_put(&patch->kobj);
+	wait_for_completion(&patch->finish);
+
 	return ret;
 }
 
@@ -731,23 +758,29 @@ static int klp_init_patch(struct klp_patch *patch)
  */
 int klp_unregister_patch(struct klp_patch *patch)
 {
-	int ret = 0;
+	int ret;
 
 	mutex_lock(&klp_mutex);
 
 	if (!klp_is_patch_registered(patch)) {
 		ret = -EINVAL;
-		goto out;
+		goto err;
 	}
 
 	if (patch->enabled) {
 		ret = -EBUSY;
-		goto out;
+		goto err;
 	}
 
 	klp_free_patch(patch);
 
-out:
+	mutex_unlock(&klp_mutex);
+
+	kobject_put(&patch->kobj);
+	wait_for_completion(&patch->finish);
+
+	return 0;
+err:
 	mutex_unlock(&klp_mutex);
 	return ret;
 }
@@ -760,12 +793,13 @@ EXPORT_SYMBOL_GPL(klp_unregister_patch);
  * Initializes the data structure associated with the patch and
  * creates the sysfs interface.
  *
+ * There is no need to take the reference on the patch module here. It is done
+ * later when the patch is enabled.
+ *
  * Return: 0 on success, otherwise error
  */
 int klp_register_patch(struct klp_patch *patch)
 {
-	int ret;
-
 	if (!patch || !patch->mod)
 		return -EINVAL;
 
@@ -788,21 +822,7 @@ int klp_register_patch(struct klp_patch *patch)
 		return -ENOSYS;
 	}
 
-	/*
-	 * A reference is taken on the patch module to prevent it from being
-	 * unloaded.  Right now, we don't allow patch modules to unload since
-	 * there is currently no method to determine if a thread is still
-	 * running in the patched code contained in the patch module once
-	 * the ftrace registration is successful.
-	 */
-	if (!try_module_get(patch->mod))
-		return -ENODEV;
-
-	ret = klp_init_patch(patch);
-	if (ret)
-		module_put(patch->mod);
-
-	return ret;
+	return klp_init_patch(patch);
 }
 EXPORT_SYMBOL_GPL(klp_register_patch);
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 428533e..0ab7abd 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -59,6 +59,7 @@ static void klp_complete_transition(void)
 	struct klp_func *func;
 	struct task_struct *g, *task;
 	unsigned int cpu;
+	bool immediate_func = false;
 
 	if (klp_target_state == KLP_UNPATCHED) {
 		/*
@@ -79,9 +80,16 @@ static void klp_complete_transition(void)
 	if (klp_transition_patch->immediate)
 		goto done;
 
-	klp_for_each_object(klp_transition_patch, obj)
-		klp_for_each_func(obj, func)
+	klp_for_each_object(klp_transition_patch, obj) {
+		klp_for_each_func(obj, func) {
 			func->transition = false;
+			if (func->immediate)
+				immediate_func = true;
+		}
+	}
+
+	if (klp_target_state == KLP_UNPATCHED && !immediate_func)
+		module_put(klp_transition_patch->mod);
 
 	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
 	if (klp_target_state == KLP_PATCHED)
@@ -113,8 +121,31 @@ static void klp_complete_transition(void)
  */
 void klp_cancel_transition(void)
 {
-	klp_target_state = !klp_target_state;
+	struct klp_patch *patch = klp_transition_patch;
+	struct klp_object *obj;
+	struct klp_func *func;
+	bool immediate_func = false;
+
+	if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
+		return;
+
+	klp_target_state = KLP_UNPATCHED;
 	klp_complete_transition();
+
+	/*
+	 * In the enable error path, even immediate patches can be safely
+	 * removed because the transition hasn't been started yet.
+	 *
+	 * klp_complete_transition() doesn't have a module_put() for immediate
+	 * patches, so do it here.
+	 */
+	klp_for_each_object(patch, obj)
+		klp_for_each_func(obj, func)
+			if (func->immediate)
+				immediate_func = true;
+
+	if (patch->immediate || immediate_func)
+		module_put(patch->mod);
 }
 
 /*
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
index 629e0dc..84795223f 100644
--- a/samples/livepatch/livepatch-sample.c
+++ b/samples/livepatch/livepatch-sample.c
@@ -99,7 +99,6 @@ static int livepatch_init(void)
 
 static void livepatch_exit(void)
 {
-	WARN_ON(klp_disable_patch(&patch));
 	WARN_ON(klp_unregister_patch(&patch));
 }
 
-- 
2.7.4

Re: [PATCH v5 05/15] livepatch/powerpc: add TIF_PATCH_PENDING thread flag

[Balbir Singh]

On Mon, 2017-02-13 at 19:42 -0600, Josh Poimboeuf wrote:
> Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
> per-task consistency model for powerpc.  The bit getting set indicates
> the thread has a pending patch which needs to be applied when the thread
> exits the kernel.
> 
> The bit is included in the _TIF_USER_WORK_MASK macro so that
> do_notify_resume() and klp_update_patch_state() get called when the bit
> is set.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> Reviewed-by: Miroslav Benes <mbenes@suse.cz>
> Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> ---

Reviewed-by: Balbir Singh <bsingharora@gmail.com>

Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces

[Balbir Singh]

On Mon, 2017-02-13 at 19:42 -0600, Josh Poimboeuf wrote:
> For live patching and possibly other use cases, a stack trace is only
> useful if it can be assured that it's completely reliable.  Add a new
> save_stack_trace_tsk_reliable() function to achieve that.
> 
> Note that if the target task isn't the current task, and the target task
> is allowed to run, then it could be writing the stack while the unwinder
> is reading it, resulting in possible corruption.  So the caller of
> save_stack_trace_tsk_reliable() must ensure that the task is either
> 'current' or inactive.
> 
> save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
> of pt_regs on the stack.  If the pt_regs are not user-mode registers
> from a syscall, then they indicate an in-kernel interrupt or exception
> (e.g. preemption or a page fault), in which case the stack is considered
> unreliable due to the nature of frame pointers.
> 
> It also relies on the x86 unwinder's detection of other issues, such as:
> 
> - corrupted stack data
> - stack grows the wrong way
> - stack walk doesn't reach the bottom
> - user didn't provide a large enough entries array
> 
> Such issues are reported by checking unwind_error() and !unwind_done().
> 
> Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
> determine at build time whether the function is implemented.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---

Could you comment on why we need a reliable trace for live-patching? Are
we in any way reliant on the stack trace to patch something broken?

Thanks,
Balbir Singh.

Re: [PATCH v5 00/15] livepatch: hybrid consistency model

[Ingo Molnar]

* Josh Poimboeuf <jpoimboe@redhat.com> wrote:

>  arch/Kconfig                                     |   6 +
>  arch/powerpc/include/asm/thread_info.h           |   4 +-
>  arch/powerpc/kernel/signal.c                     |   4 +
>  arch/s390/include/asm/thread_info.h              |  24 +-
>  arch/s390/kernel/entry.S                         |  31 +-
>  arch/x86/Kconfig                                 |   1 +
>  arch/x86/entry/common.c                          |   9 +-
>  arch/x86/include/asm/thread_info.h               |  13 +-
>  arch/x86/include/asm/unwind.h                    |   6 +
>  arch/x86/kernel/stacktrace.c                     |  96 +++-
>  arch/x86/kernel/unwind_frame.c                   |   2 +

for the x86 and scheduler changes:

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Miroslav Benes]

On Mon, 13 Feb 2017, Josh Poimboeuf wrote:

> Change livepatch to use a basic per-task consistency model.  This is the
> foundation which will eventually enable us to patch those ~10% of
> security patches which change function or data semantics.  This is the
> biggest remaining piece needed to make livepatch more generally useful.
> 
> This code stems from the design proposal made by Vojtech [1] in November
> 2014.  It's a hybrid of kGraft and kpatch: it uses kGraft's per-task
> consistency and syscall barrier switching combined with kpatch's stack
> trace switching.  There are also a number of fallback options which make
> it quite flexible.
> 
> Patches are applied on a per-task basis, when the task is deemed safe to
> switch over.  When a patch is enabled, livepatch enters into a
> transition state where tasks are converging to the patched state.
> Usually this transition state can complete in a few seconds.  The same
> sequence occurs when a patch is disabled, except the tasks converge from
> the patched state to the unpatched state.
> 
> An interrupt handler inherits the patched state of the task it
> interrupts.  The same is true for forked tasks: the child inherits the
> patched state of the parent.
> 
> Livepatch uses several complementary approaches to determine when it's
> safe to patch tasks:
> 
> 1. The first and most effective approach is stack checking of sleeping
>    tasks.  If no affected functions are on the stack of a given task,
>    the task is patched.  In most cases this will patch most or all of
>    the tasks on the first try.  Otherwise it'll keep trying
>    periodically.  This option is only available if the architecture has
>    reliable stacks (HAVE_RELIABLE_STACKTRACE).
> 
> 2. The second approach, if needed, is kernel exit switching.  A
>    task is switched when it returns to user space from a system call, a
>    user space IRQ, or a signal.  It's useful in the following cases:
> 
>    a) Patching I/O-bound user tasks which are sleeping on an affected
>       function.  In this case you have to send SIGSTOP and SIGCONT to
>       force it to exit the kernel and be patched.
>    b) Patching CPU-bound user tasks.  If the task is highly CPU-bound
>       then it will get patched the next time it gets interrupted by an
>       IRQ.
>    c) In the future it could be useful for applying patches for
>       architectures which don't yet have HAVE_RELIABLE_STACKTRACE.  In
>       this case you would have to signal most of the tasks on the
>       system.  However this isn't supported yet because there's
>       currently no way to patch kthreads without
>       HAVE_RELIABLE_STACKTRACE.
> 
> 3. For idle "swapper" tasks, since they don't ever exit the kernel, they
>    instead have a klp_update_patch_state() call in the idle loop which
>    allows them to be patched before the CPU enters the idle state.
> 
>    (Note there's not yet such an approach for kthreads.)
> 
> All the above approaches may be skipped by setting the 'immediate' flag
> in the 'klp_patch' struct, which will disable per-task consistency and
> patch all tasks immediately.  This can be useful if the patch doesn't
> change any function or data semantics.  Note that, even with this flag
> set, it's possible that some tasks may still be running with an old
> version of the function, until that function returns.
> 
> There's also an 'immediate' flag in the 'klp_func' struct which allows
> you to specify that certain functions in the patch can be applied
> without per-task consistency.  This might be useful if you want to patch
> a common function like schedule(), and the function change doesn't need
> consistency but the rest of the patch does.
> 
> For architectures which don't have HAVE_RELIABLE_STACKTRACE, the user
> must set patch->immediate which causes all tasks to be patched
> immediately.  This option should be used with care, only when the patch
> doesn't change any function or data semantics.
> 
> In the future, architectures which don't have HAVE_RELIABLE_STACKTRACE
> may be allowed to use per-task consistency if we can come up with
> another way to patch kthreads.
> 
> The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
> is in transition.  Only a single patch (the topmost patch on the stack)
> can be in transition at a given time.  A patch can remain in transition
> indefinitely, if any of the tasks are stuck in the initial patch state.
> 
> A transition can be reversed and effectively canceled by writing the
> opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
> the transition is in progress.  Then all the tasks will attempt to
> converge back to the original patch state.
> 
> [1] https://lkml.kernel.org/r/20141107140458.GA21774@suse.cz
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

I looked at the patch again and could not see any problem with it. I 
tested it with a couple of live patches too and it worked as expected. 
Good job.

Acked-by: Miroslav Benes <mbenes@suse.cz>

Thanks,
Miroslav

Re: [PATCH v5.1 15/15] livepatch: allow removal of a disabled patch

[Miroslav Benes]

On Mon, 6 Mar 2017, Josh Poimboeuf wrote:

> 
> Currently we do not allow patch module to unload since there is no
> method to determine if a task is still running in the patched code.
> 
> The consistency model gives us the way because when the unpatching
> finishes we know that all tasks were marked as safe to call an original
> function. Thus every new call to the function calls the original code
> and at the same time no task can be somewhere in the patched code,
> because it had to leave that code to be marked as safe.
> 
> We can safely let the patch module go after that.
> 
> Completion is used for synchronization between module removal and sysfs
> infrastructure in a similar way to commit 942e443127e9 ("module: Fix
> mod->mkobj.kobj potentially freed too early").
> 
> Note that we still do not allow the removal for immediate model, that is
> no consistency model. The module refcount may increase in this case if
> somebody disables and enables the patch several times. This should not
> cause any harm.
> 
> With this change a call to try_module_get() is moved to
> __klp_enable_patch from klp_register_patch to make module reference
> counting symmetric (module_put() is in a patch disable path) and to
> allow to take a new reference to a disabled module when being enabled.
> 
> Finally, we need to be very careful about possible races between
> klp_unregister_patch(), kobject_put() functions and operations
> on the related sysfs files.
> 
> kobject_put(&patch->kobj) must be called without klp_mutex. Otherwise,
> it might be blocked by enabled_store() that needs the mutex as well.
> In addition, enabled_store() must check if the patch was not
> unregisted in the meantime.
> 
> There is no need to do the same for other kobject_put() callsites
> at the moment. Their sysfs operations neither take the lock nor
> they access any data that might be freed in the meantime.
> 
> There was an attempt to use kobjects the right way and prevent these
> races by design. But it made the patch definition more complicated
> and opened another can of worms. See
> https://lkml.kernel.org/r/1464018848-4303-1-git-send-email-pmladek@suse.com
> 
> [Thanks to Petr Mladek for improving the commit message.]
> 
> Signed-off-by: Miroslav Benes <mbenes@suse.cz>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> ---
> v5.1: improve error handling in enable path -- call module_put() in
>       klp_cancel_transition()

Looks good.

Acked-by: Miroslav Benes <mbenes@suse.cz>

if it is needed for Josh's code.

Regards,
Miroslav

Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces

[Josh Poimboeuf]

On Tue, Mar 07, 2017 at 05:50:55PM +1100, Balbir Singh wrote:
> On Mon, 2017-02-13 at 19:42 -0600, Josh Poimboeuf wrote:
> > For live patching and possibly other use cases, a stack trace is only
> > useful if it can be assured that it's completely reliable.  Add a new
> > save_stack_trace_tsk_reliable() function to achieve that.
> > 
> > Note that if the target task isn't the current task, and the target task
> > is allowed to run, then it could be writing the stack while the unwinder
> > is reading it, resulting in possible corruption.  So the caller of
> > save_stack_trace_tsk_reliable() must ensure that the task is either
> > 'current' or inactive.
> > 
> > save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
> > of pt_regs on the stack.  If the pt_regs are not user-mode registers
> > from a syscall, then they indicate an in-kernel interrupt or exception
> > (e.g. preemption or a page fault), in which case the stack is considered
> > unreliable due to the nature of frame pointers.
> > 
> > It also relies on the x86 unwinder's detection of other issues, such as:
> > 
> > - corrupted stack data
> > - stack grows the wrong way
> > - stack walk doesn't reach the bottom
> > - user didn't provide a large enough entries array
> > 
> > Such issues are reported by checking unwind_error() and !unwind_done().
> > 
> > Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
> > determine at build time whether the function is implemented.
> > 
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> 
> Could you comment on why we need a reliable trace for live-patching? Are
> we in any way reliant on the stack trace to patch something broken?

I tried to cover this comprehensively in patch 13/15 in
Documentation/livepatch/livepatch.txt.  Does that answer your questions?

-- 
Josh

Re: [PATCH v5 05/15] livepatch/powerpc: add TIF_PATCH_PENDING thread flag

[Michael Ellerman]

Josh Poimboeuf <jpoimboe@redhat.com> writes:

> Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
> per-task consistency model for powerpc.  The bit getting set indicates
> the thread has a pending patch which needs to be applied when the thread
> exits the kernel.
>
> The bit is included in the _TIF_USER_WORK_MASK macro so that
> do_notify_resume() and klp_update_patch_state() get called when the bit
> is set.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> Reviewed-by: Miroslav Benes <mbenes@suse.cz>
> Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/thread_info.h | 4 +++-
>  arch/powerpc/kernel/signal.c           | 4 ++++
>  2 files changed, 7 insertions(+), 1 deletion(-)

The arch changes here seem fine. I haven't tested the whole series
though.

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers

Re: [PATCH v5 00/15] livepatch: hybrid consistency model

[Jiri Kosina]

On Mon, 13 Feb 2017, Josh Poimboeuf wrote:

> Here's v5 of the consistency model

I have ammended the patches with all the received ACKs and applied to 
'for-4.12/klp-hybrid-consistency-model' branch of livepatching.git.

Thanks,

-- 
Jiri Kosina
SUSE Labs

Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces

[Balbir Singh]

On Tue, 2017-03-07 at 10:12 -0600, Josh Poimboeuf wrote:
> On Tue, Mar 07, 2017 at 05:50:55PM +1100, Balbir Singh wrote:
> > On Mon, 2017-02-13 at 19:42 -0600, Josh Poimboeuf wrote:
> > > For live patching and possibly other use cases, a stack trace is only
> > > useful if it can be assured that it's completely reliable.  Add a new
> > > save_stack_trace_tsk_reliable() function to achieve that.
> > > 
> > > Note that if the target task isn't the current task, and the target task
> > > is allowed to run, then it could be writing the stack while the unwinder
> > > is reading it, resulting in possible corruption.  So the caller of
> > > save_stack_trace_tsk_reliable() must ensure that the task is either
> > > 'current' or inactive.
> > > 
> > > save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
> > > of pt_regs on the stack.  If the pt_regs are not user-mode registers
> > > from a syscall, then they indicate an in-kernel interrupt or exception
> > > (e.g. preemption or a page fault), in which case the stack is considered
> > > unreliable due to the nature of frame pointers.
> > > 
> > > It also relies on the x86 unwinder's detection of other issues, such as:
> > > 
> > > - corrupted stack data
> > > - stack grows the wrong way
> > > - stack walk doesn't reach the bottom
> > > - user didn't provide a large enough entries array
> > > 
> > > Such issues are reported by checking unwind_error() and !unwind_done().
> > > 
> > > Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
> > > determine at build time whether the function is implemented.
> > > 
> > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > > ---
> > 
> > Could you comment on why we need a reliable trace for live-patching? Are
> > we in any way reliant on the stack trace to patch something broken?
> 
> I tried to cover this comprehensively in patch 13/15 in
> Documentation/livepatch/livepatch.txt.  Does that answer your questions?
>

Yes, it answers my questions

Thanks,
Balbir Singh.

Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces

[Petr Mladek]

On Mon 2017-02-13 19:42:28, Josh Poimboeuf wrote:
> For live patching and possibly other use cases, a stack trace is only
> useful if it can be assured that it's completely reliable.  Add a new
> save_stack_trace_tsk_reliable() function to achieve that.
> 
> Note that if the target task isn't the current task, and the target task
> is allowed to run, then it could be writing the stack while the unwinder
> is reading it, resulting in possible corruption.  So the caller of
> save_stack_trace_tsk_reliable() must ensure that the task is either
> 'current' or inactive.
> 
> save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
> of pt_regs on the stack.  If the pt_regs are not user-mode registers
> from a syscall, then they indicate an in-kernel interrupt or exception
> (e.g. preemption or a page fault), in which case the stack is considered
> unreliable due to the nature of frame pointers.
> 
> It also relies on the x86 unwinder's detection of other issues, such as:
> 
> - corrupted stack data
> - stack grows the wrong way
> - stack walk doesn't reach the bottom
> - user didn't provide a large enough entries array
> 
> Such issues are reported by checking unwind_error() and !unwind_done().
> 
> Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
> determine at build time whether the function is implemented.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

Just for record, this version looks fine to me:

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

PS: I was on the sick leave longer then expected. The patch set
has been pushed into the for-4.12 branch in jikos/livepatching.git
in the meantime. I check it there just for completeness. You do not
need to add my Reviewed-by tags.

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Petr Mladek]

On Mon 2017-02-13 19:42:40, Josh Poimboeuf wrote:
> Change livepatch to use a basic per-task consistency model.  This is the
> foundation which will eventually enable us to patch those ~10% of
> security patches which change function or data semantics.  This is the
> biggest remaining piece needed to make livepatch more generally useful.
> 
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

Just for record, this last version looks fine to me. I do not see
problems any longer. Everything looks consistent now ;-)
It is a great work. Feel free to use:

Reviewed-by: Petr Mladek <pmladek@suse.com>

Thanks a lot for patience.

Best Regards,
Petr

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Peter Zijlstra]

On Mon, Feb 13, 2017 at 07:42:40PM -0600, Josh Poimboeuf wrote:
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 6a4bae0..a8b3f1a 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -9,6 +9,7 @@
>  #include <linux/mm.h>
>  #include <linux/stackprotector.h>
>  #include <linux/suspend.h>
> +#include <linux/livepatch.h>
>  
>  #include <asm/tlb.h>
>  
> @@ -264,6 +265,9 @@ static void do_idle(void)
>  
>  	sched_ttwu_pending();
>  	schedule_preempt_disabled();
> +
> +	if (unlikely(klp_patch_pending(current)))
> +		klp_update_patch_state(current);
>  }

Can someone explain this one? This is a very weird place to add things.
What was the expectation?

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Petr Mladek]

On Thu 2018-01-25 10:04:44, Peter Zijlstra wrote:
> On Mon, Feb 13, 2017 at 07:42:40PM -0600, Josh Poimboeuf wrote:
> > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> > index 6a4bae0..a8b3f1a 100644
> > --- a/kernel/sched/idle.c
> > +++ b/kernel/sched/idle.c
> > @@ -9,6 +9,7 @@
> >  #include <linux/mm.h>
> >  #include <linux/stackprotector.h>
> >  #include <linux/suspend.h>
> > +#include <linux/livepatch.h>
> >  
> >  #include <asm/tlb.h>
> >  
> > @@ -264,6 +265,9 @@ static void do_idle(void)
> >  
> >  	sched_ttwu_pending();
> >  	schedule_preempt_disabled();
> > +
> > +	if (unlikely(klp_patch_pending(current)))
> > +		klp_update_patch_state(current);
> >  }
> 
> Can someone explain this one? This is a very weird place to add things.
> What was the expectation?

AFAIK, it was the least ugly and minimalist solution that we came with.

The tasks are migrated to the new patch when neither of the patched
functions is on the stack. The stack can be checked safely only when
the task is not running. It might be very hard to catch the idle
task on a such a place if we patch something that is used there.

If the idle task is scheduled, you would need to create some fake
load on the system, try to migrate the idle task, stop the fake load
on the CPU.

The above code makes the idle task to migrate itself on a sane place.
You just need to schedule some minimalist job on the CPU. The idle
task will do one loop, gets migrated, and might be scheduled again
immediately.

Best Regards,
Petr

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Peter Zijlstra]

On Thu, Jan 25, 2018 at 11:24:14AM +0100, Petr Mladek wrote:
> On Thu 2018-01-25 10:04:44, Peter Zijlstra wrote:
> > On Mon, Feb 13, 2017 at 07:42:40PM -0600, Josh Poimboeuf wrote:
> > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> > > index 6a4bae0..a8b3f1a 100644
> > > --- a/kernel/sched/idle.c
> > > +++ b/kernel/sched/idle.c
> > > @@ -9,6 +9,7 @@
> > >  #include <linux/mm.h>
> > >  #include <linux/stackprotector.h>
> > >  #include <linux/suspend.h>
> > > +#include <linux/livepatch.h>
> > >  
> > >  #include <asm/tlb.h>
> > >  
> > > @@ -264,6 +265,9 @@ static void do_idle(void)
> > >  
> > >  	sched_ttwu_pending();
> > >  	schedule_preempt_disabled();
> > > +
> > > +	if (unlikely(klp_patch_pending(current)))
> > > +		klp_update_patch_state(current);
> > >  }
> > 
> > Can someone explain this one? This is a very weird place to add things.
> > What was the expectation?
> 
> AFAIK, it was the least ugly and minimalist solution that we came with.
> 
> The tasks are migrated to the new patch when neither of the patched
> functions is on the stack. The stack can be checked safely only when
> the task is not running. It might be very hard to catch the idle
> task on a such a place if we patch something that is used there.
> 
> If the idle task is scheduled, you would need to create some fake
> load on the system, try to migrate the idle task, stop the fake load
> on the CPU.
> 
> The above code makes the idle task to migrate itself on a sane place.
> You just need to schedule some minimalist job on the CPU. The idle
> task will do one loop, gets migrated, and might be scheduled again
> immediately.

What I was getting at, the klp stuff is the very first thing we run when
we schedule the idle task, but its placed at the very end of the
function. This is confusing.

The above still doesn't help with solving that. Do you want to run
something before we go idle, or before we leave idle, in neither cases
would I place it where it is.

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Petr Mladek]

On Thu 2018-01-25 11:38:55, Peter Zijlstra wrote:
> On Thu, Jan 25, 2018 at 11:24:14AM +0100, Petr Mladek wrote:
> > On Thu 2018-01-25 10:04:44, Peter Zijlstra wrote:
> > > On Mon, Feb 13, 2017 at 07:42:40PM -0600, Josh Poimboeuf wrote:
> > > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> > > > index 6a4bae0..a8b3f1a 100644
> > > > --- a/kernel/sched/idle.c
> > > > +++ b/kernel/sched/idle.c
> > > > @@ -9,6 +9,7 @@
> > > >  #include <linux/mm.h>
> > > >  #include <linux/stackprotector.h>
> > > >  #include <linux/suspend.h>
> > > > +#include <linux/livepatch.h>
> > > >  
> > > >  #include <asm/tlb.h>
> > > >  
> > > > @@ -264,6 +265,9 @@ static void do_idle(void)
> > > >  
> > > >  	sched_ttwu_pending();
> > > >  	schedule_preempt_disabled();
> > > > +
> > > > +	if (unlikely(klp_patch_pending(current)))
> > > > +		klp_update_patch_state(current);
> > > >  }
> > > 
> > > Can someone explain this one? This is a very weird place to add things.
> > > What was the expectation?
> > 
> > AFAIK, it was the least ugly and minimalist solution that we came with.
> > 
> > The tasks are migrated to the new patch when neither of the patched
> > functions is on the stack. The stack can be checked safely only when
> > the task is not running. It might be very hard to catch the idle
> > task on a such a place if we patch something that is used there.
> > 
> > If the idle task is scheduled, you would need to create some fake
> > load on the system, try to migrate the idle task, stop the fake load
> > on the CPU.
> > 
> > The above code makes the idle task to migrate itself on a sane place.
> > You just need to schedule some minimalist job on the CPU. The idle
> > task will do one loop, gets migrated, and might be scheduled again
> > immediately.
> 
> What I was getting at, the klp stuff is the very first thing we run when
> we schedule the idle task, but its placed at the very end of the
> function. This is confusing.

I see.


> The above still doesn't help with solving that. Do you want to run
> something before we go idle, or before we leave idle, in neither cases
> would I place it where it is.

In fact, both ways are fine. We require going the idle task
through the entire cycle anyway. It is because both situations,
too long idling or non-idling, would block finishing the patch
transition.

Feel free to move it right before schedule_idle() or
__current_set_polling().

Or should I send a patch?

Best Regards,
Petr

Re: [PATCH v5 13/15] livepatch: change to a per-task consistency model

[Peter Zijlstra]

On Thu, Jan 25, 2018 at 01:13:21PM +0100, Petr Mladek wrote:
> > What I was getting at, the klp stuff is the very first thing we run when
> > we schedule the idle task, but its placed at the very end of the
> > function. This is confusing.
> 
> I see.
> 
> 
> > The above still doesn't help with solving that. Do you want to run
> > something before we go idle, or before we leave idle, in neither cases
> > would I place it where it is.
> 
> In fact, both ways are fine. We require going the idle task
> through the entire cycle anyway. It is because both situations,
> too long idling or non-idling, would block finishing the patch
> transition.
> 
> Feel free to move it right before schedule_idle() or
> __current_set_polling().

OK, I'll move it. Thanks!