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* [PATCH v6 00/10] x86/alternative: text_poke() fixes
@ 2018-11-20 20:35 Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
                   ` (10 more replies)
  0 siblings, 11 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit

This patch-set addresses some issues that might affect the security and
the correctness of code patching.

The main issue that the patches deal with is the fact that the fixmap
PTEs that are used for patching are available for access from other
cores and might be exploited. They are not even flushed from the TLB in
remote cores, so the risk is even higher. This set addresses this issue
by introducing a temporary mm that is only used during patching.

To do so, we need to avoid using text_poke() before the poking-mm is
initialized and instead use text_poke_early().

During v3 of this set, Andy & Thomas suggested that early patching of
modules can be improved by simply writing to the memory. This actually
raises a security concern: there should not be any W+X mappings at any
given moment, and modules loading breaks this protection for no good
reason. So this patch also addresses this issue, while (presumably)
improving patching speed by making module memory initially RW(+NX) and
before execution changing it into RO(+X).

In addition the patch addresses various issues that are related to code
patching, and do some cleanup.

v5->v6:
- Panic if anything goes wrong when poking [peterZ]

v4->v5:
- Fix Xen breakage [Damian Tometzki]
- BUG_ON() when poking_mm initialization fails [peterZ]
- Better comments on "x86/mm: temporary mm struct"
- Cleaner removal of the custom poker

v3->v4:
- Setting modules as RO when loading [andy, tglx]
- Adding text_poke_kgdb() to keep the text_mutex assertion [tglx]
- Simpler logic to decide when to use early-poking [peterZ]
- More cleanup

v2->v3:
- Remove the fallback path in text_poke() [peterZ]
- poking_init() was broken due to the local variable poking_addr
- Preallocate tables for the temporary-mm to avoid sleep-in-atomic
- Prevent KASAN from yelling at text_poke()

v1->v2:
- Partial revert of 9222f606506c added to 1/6 [masami]
- Added Masami's reviewed-by tag

RFC->v1:
- Added handling of error in get_locked_pte()
- Remove lockdep assertion, clarify text_mutex use instead [masami]
- Comment fix [peterz]
- Removed remainders of text_poke return value [masami]
- Use __weak for poking_init instead of macros [masami]
- Simplify error handling in poking_init [masami]

andy Lutomirski (1):
  x86/mm: temporary mm struct

Nadav Amit (9):
  Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
  x86/jump_label: Use text_poke_early() during early init
  fork: provide a function for copying init_mm
  x86/alternative: initializing temporary mm for patching
  x86/alternative: use temporary mm for text poking
  x86/kgdb: avoid redundant comparison of patched code
  x86: avoid W^X being broken during modules loading
  x86/jump-label: remove support for custom poker
  x86/alternative: remove the return value of text_poke_*()

 arch/x86/include/asm/fixmap.h        |   2 -
 arch/x86/include/asm/mmu_context.h   |  32 +++++
 arch/x86/include/asm/pgtable.h       |   3 +
 arch/x86/include/asm/text-patching.h |   7 +-
 arch/x86/kernel/alternative.c        | 197 ++++++++++++++++++++-------
 arch/x86/kernel/jump_label.c         |  19 ++-
 arch/x86/kernel/kgdb.c               |  25 +---
 arch/x86/kernel/module.c             |   2 +-
 arch/x86/mm/init_64.c                |  35 +++++
 arch/x86/xen/mmu_pv.c                |   2 -
 include/linux/filter.h               |   6 +
 include/linux/sched/task.h           |   1 +
 init/main.c                          |   3 +
 kernel/fork.c                        |  24 +++-
 kernel/module.c                      |  10 ++
 15 files changed, 279 insertions(+), 89 deletions(-)

-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 02/10] x86/jump_label: Use text_poke_early() during early init Nadav Amit
                   ` (9 subsequent siblings)
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit,
	Andy Lutomirski, Kees Cook, Dave Hansen, Masami Hiramatsu

text_mutex is currently expected to be held before text_poke() is
called, but we kgdb does not take the mutex, and instead *supposedly*
ensures the lock is not taken and will not be acquired by any other core
while text_poke() is running.

The reason for the "supposedly" comment is that it is not entirely clear
that this would be the case if gdb_do_roundup is zero.

This patch creates two wrapper functions, text_poke() and
text_poke_kgdb() which do or do not run the lockdep assertion
respectively.

While we are at it, change the return code of text_poke() to something
meaningful. One day, callers might actually respect it and the existing
BUG_ON() when patching fails could be removed. For kgdb, the return
value can actually be used.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/include/asm/text-patching.h |  1 +
 arch/x86/kernel/alternative.c        | 52 ++++++++++++++++++++--------
 arch/x86/kernel/kgdb.c               | 11 +++---
 3 files changed, 45 insertions(+), 19 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index e85ff65c43c3..f8fc8e86cf01 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -35,6 +35,7 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len);
  * inconsistent instruction while you patch.
  */
 extern void *text_poke(void *addr, const void *opcode, size_t len);
+extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
 extern int poke_int3_handler(struct pt_regs *regs);
 extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
 extern int after_bootmem;
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index ebeac487a20c..c6a3a10a2fd5 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -678,18 +678,7 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
 	return addr;
 }
 
-/**
- * text_poke - Update instructions on a live kernel
- * @addr: address to modify
- * @opcode: source of the copy
- * @len: length to copy
- *
- * Only atomic text poke/set should be allowed when not doing early patching.
- * It means the size must be writable atomically and the address must be aligned
- * in a way that permits an atomic write. It also makes sure we fit on a single
- * page.
- */
-void *text_poke(void *addr, const void *opcode, size_t len)
+static void *__text_poke(void *addr, const void *opcode, size_t len)
 {
 	unsigned long flags;
 	char *vaddr;
@@ -702,8 +691,6 @@ void *text_poke(void *addr, const void *opcode, size_t len)
 	 */
 	BUG_ON(!after_bootmem);
 
-	lockdep_assert_held(&text_mutex);
-
 	if (!core_kernel_text((unsigned long)addr)) {
 		pages[0] = vmalloc_to_page(addr);
 		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
@@ -732,6 +719,43 @@ void *text_poke(void *addr, const void *opcode, size_t len)
 	return addr;
 }
 
+/**
+ * text_poke - Update instructions on a live kernel
+ * @addr: address to modify
+ * @opcode: source of the copy
+ * @len: length to copy
+ *
+ * Only atomic text poke/set should be allowed when not doing early patching.
+ * It means the size must be writable atomically and the address must be aligned
+ * in a way that permits an atomic write. It also makes sure we fit on a single
+ * page.
+ */
+void *text_poke(void *addr, const void *opcode, size_t len)
+{
+	lockdep_assert_held(&text_mutex);
+
+	return __text_poke(addr, opcode, len);
+}
+
+/**
+ * text_poke_kgdb - Update instructions on a live kernel by kgdb
+ * @addr: address to modify
+ * @opcode: source of the copy
+ * @len: length to copy
+ *
+ * Only atomic text poke/set should be allowed when not doing early patching.
+ * It means the size must be writable atomically and the address must be aligned
+ * in a way that permits an atomic write. It also makes sure we fit on a single
+ * page.
+ *
+ * Context: should only be used by kgdb, which ensures no other core is running,
+ *	    despite the fact it does not hold the text_mutex.
+ */
+void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
+{
+	return __text_poke(addr, opcode, len);
+}
+
 static void do_sync_core(void *info)
 {
 	sync_core();
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 8e36f249646e..2636ca8394bd 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -763,13 +763,13 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 	if (!err)
 		return err;
 	/*
-	 * It is safe to call text_poke() because normal kernel execution
+	 * It is safe to call text_poke_kgdb() because normal kernel execution
 	 * is stopped on all cores, so long as the text_mutex is not locked.
 	 */
 	if (mutex_is_locked(&text_mutex))
 		return -EBUSY;
-	text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
-		  BREAK_INSTR_SIZE);
+	text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
+		       BREAK_INSTR_SIZE);
 	err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
 	if (err)
 		return err;
@@ -788,12 +788,13 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 	if (bpt->type != BP_POKE_BREAKPOINT)
 		goto knl_write;
 	/*
-	 * It is safe to call text_poke() because normal kernel execution
+	 * It is safe to call text_poke_kgdb() because normal kernel execution
 	 * is stopped on all cores, so long as the text_mutex is not locked.
 	 */
 	if (mutex_is_locked(&text_mutex))
 		goto knl_write;
-	text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE);
+	text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr,
+		       BREAK_INSTR_SIZE);
 	err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
 	if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE))
 		goto knl_write;
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 02/10] x86/jump_label: Use text_poke_early() during early init
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 03/10] x86/mm: temporary mm struct Nadav Amit
                   ` (8 subsequent siblings)
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit,
	Andy Lutomirski, Kees Cook, Dave Hansen, Masami Hiramatsu

There is no apparent reason not to use text_poke_early() while we are
during early-init and we do not patch code that might be on the stack
(i.e., we'll return to the middle of the patched code). This appears to
be the case of jump-labels, so do so.

This is required for the next patches that would set a temporary mm for
patching, which is initialized after some static-keys are
enabled/disabled.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Co-Developed-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/kernel/jump_label.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index aac0c1f7e354..ed5fe274a7d8 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -52,7 +52,12 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
 	jmp.offset = jump_entry_target(entry) -
 		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 
-	if (early_boot_irqs_disabled)
+	/*
+	 * As long as we're UP and not yet marked RO, we can use
+	 * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to
+	 * SYSTEM_SCHEDULING before going either.
+	 */
+	if (system_state == SYSTEM_BOOTING)
 		poker = text_poke_early;
 
 	if (type == JUMP_LABEL_JMP) {
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 03/10] x86/mm: temporary mm struct
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 02/10] x86/jump_label: Use text_poke_early() during early init Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 04/10] fork: provide a function for copying init_mm Nadav Amit
                   ` (7 subsequent siblings)
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Andy Lutomirski,
	Kees Cook, Dave Hansen, Nadav Amit

From: Andy Lutomirski <luto@kernel.org>

Sometimes we want to set a temporary page-table entries (PTEs) in one of
the cores, without allowing other cores to use - even speculatively -
these mappings. There are two benefits for doing so:

(1) Security: if sensitive PTEs are set, temporary mm prevents their use
in other cores. This hardens the security as it prevents exploding a
dangling pointer to overwrite sensitive data using the sensitive PTE.

(2) Avoiding TLB shootdowns: the PTEs do not need to be flushed in
remote page-tables.

To do so a temporary mm_struct can be used. Mappings which are private
for this mm can be set in the userspace part of the address-space.
During the whole time in which the temporary mm is loaded, interrupts
must be disabled.

The first use-case for temporary PTEs, which will follow, is for poking
the kernel text.

[ Commit message was written by Nadav ]

Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/include/asm/mmu_context.h | 32 ++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 0ca50611e8ce..0141b7fa6d01 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -338,4 +338,36 @@ static inline unsigned long __get_current_cr3_fast(void)
 	return cr3;
 }
 
+typedef struct {
+	struct mm_struct *prev;
+} temporary_mm_state_t;
+
+/*
+ * Using a temporary mm allows to set temporary mappings that are not accessible
+ * by other cores. Such mappings are needed to perform sensitive memory writes
+ * that override the kernel memory protections (e.g., W^X), without exposing the
+ * temporary page-table mappings that are required for these write operations to
+ * other cores.
+ *
+ * Context: The temporary mm needs to be used exclusively by a single core. To
+ *          harden security IRQs must be disabled while the temporary mm is
+ *          loaded, thereby preventing interrupt handler bugs from override the
+ *          kernel memory protection.
+ */
+static inline temporary_mm_state_t use_temporary_mm(struct mm_struct *mm)
+{
+	temporary_mm_state_t state;
+
+	lockdep_assert_irqs_disabled();
+	state.prev = this_cpu_read(cpu_tlbstate.loaded_mm);
+	switch_mm_irqs_off(NULL, mm, current);
+	return state;
+}
+
+static inline void unuse_temporary_mm(temporary_mm_state_t prev)
+{
+	lockdep_assert_irqs_disabled();
+	switch_mm_irqs_off(NULL, prev.prev, current);
+}
+
 #endif /* _ASM_X86_MMU_CONTEXT_H */
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 04/10] fork: provide a function for copying init_mm
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (2 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 03/10] x86/mm: temporary mm struct Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 05/10] x86/alternative: initializing temporary mm for patching Nadav Amit
                   ` (6 subsequent siblings)
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit,
	Andy Lutomirski, Kees Cook, Dave Hansen

Provide a function for copying init_mm. This function will be later used
for setting a temporary mm.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 include/linux/sched/task.h |  1 +
 kernel/fork.c              | 24 ++++++++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 108ede99e533..ac0a675678f5 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -74,6 +74,7 @@ extern void exit_itimers(struct signal_struct *);
 extern long _do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *, unsigned long);
 extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);
 struct task_struct *fork_idle(int);
+struct mm_struct *copy_init_mm(void);
 extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
 extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 07cddff89c7b..01d3f5b39363 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1297,13 +1297,20 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 		complete_vfork_done(tsk);
 }
 
-/*
- * Allocate a new mm structure and copy contents from the
- * mm structure of the passed in task structure.
+/**
+ * dup_mm() - duplicates an existing mm structure
+ * @tsk: the task_struct with which the new mm will be associated.
+ * @oldmm: the mm to duplicate.
+ *
+ * Allocates a new mm structure and copy contents from the provided
+ * @oldmm structure.
+ *
+ * Return: the duplicated mm or NULL on failure.
  */
-static struct mm_struct *dup_mm(struct task_struct *tsk)
+static struct mm_struct *dup_mm(struct task_struct *tsk,
+				struct mm_struct *oldmm)
 {
-	struct mm_struct *mm, *oldmm = current->mm;
+	struct mm_struct *mm;
 	int err;
 
 	mm = allocate_mm();
@@ -1370,7 +1377,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 	}
 
 	retval = -ENOMEM;
-	mm = dup_mm(tsk);
+	mm = dup_mm(tsk, current->mm);
 	if (!mm)
 		goto fail_nomem;
 
@@ -2176,6 +2183,11 @@ struct task_struct *fork_idle(int cpu)
 	return task;
 }
 
+struct mm_struct *copy_init_mm(void)
+{
+	return dup_mm(NULL, &init_mm);
+}
+
 /*
  *  Ok, this is the main fork-routine.
  *
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 05/10] x86/alternative: initializing temporary mm for patching
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (3 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 04/10] fork: provide a function for copying init_mm Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 06/10] x86/alternative: use temporary mm for text poking Nadav Amit
                   ` (5 subsequent siblings)
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit, Kees Cook,
	Dave Hansen

To prevent improper use of the PTEs that are used for text patching, we
want to use a temporary mm struct. We initailize it by copying the init
mm.

The address that will be used for patching is taken from the lower area
that is usually used for the task memory. Doing so prevents the need to
frequently synchronize the temporary-mm (e.g., when BPF programs are
installed), since different PGDs are used for the task memory.

Finally, we randomize the address of the PTEs to harden against exploits
that use these PTEs.

Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/include/asm/pgtable.h       |  3 +++
 arch/x86/include/asm/text-patching.h |  2 ++
 arch/x86/kernel/alternative.c        |  3 +++
 arch/x86/mm/init_64.c                | 35 ++++++++++++++++++++++++++++
 init/main.c                          |  3 +++
 5 files changed, 46 insertions(+)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 40616e805292..e8f630d9a2ed 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1021,6 +1021,9 @@ static inline void __meminit init_trampoline_default(void)
 	/* Default trampoline pgd value */
 	trampoline_pgd_entry = init_top_pgt[pgd_index(__PAGE_OFFSET)];
 }
+
+void __init poking_init(void);
+
 # ifdef CONFIG_RANDOMIZE_MEMORY
 void __meminit init_trampoline(void);
 # else
diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index f8fc8e86cf01..a75eed841eed 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -39,5 +39,7 @@ extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
 extern int poke_int3_handler(struct pt_regs *regs);
 extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
 extern int after_bootmem;
+extern __ro_after_init struct mm_struct *poking_mm;
+extern __ro_after_init unsigned long poking_addr;
 
 #endif /* _ASM_X86_TEXT_PATCHING_H */
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index c6a3a10a2fd5..57fdde308bb6 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -678,6 +678,9 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
 	return addr;
 }
 
+__ro_after_init struct mm_struct *poking_mm;
+__ro_after_init unsigned long poking_addr;
+
 static void *__text_poke(void *addr, const void *opcode, size_t len)
 {
 	unsigned long flags;
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 5fab264948c2..356a28569a19 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -53,6 +53,7 @@
 #include <asm/init.h>
 #include <asm/uv/uv.h>
 #include <asm/setup.h>
+#include <asm/text-patching.h>
 
 #include "mm_internal.h"
 
@@ -1388,6 +1389,40 @@ unsigned long memory_block_size_bytes(void)
 	return memory_block_size_probed;
 }
 
+/*
+ * Initialize an mm_struct to be used during poking and a pointer to be used
+ * during patching.
+ */
+void __init poking_init(void)
+{
+	spinlock_t *ptl;
+	pte_t *ptep;
+
+	poking_mm = copy_init_mm();
+	BUG_ON(!poking_mm);
+
+	/*
+	 * Randomize the poking address, but make sure that the following page
+	 * will be mapped at the same PMD. We need 2 pages, so find space for 3,
+	 * and adjust the address if the PMD ends after the first one.
+	 */
+	poking_addr = TASK_UNMAPPED_BASE +
+		(kaslr_get_random_long("Poking") & PAGE_MASK) %
+		(TASK_SIZE - TASK_UNMAPPED_BASE - 3 * PAGE_SIZE);
+
+	if (((poking_addr + PAGE_SIZE) & ~PMD_MASK) == 0)
+		poking_addr += PAGE_SIZE;
+
+	/*
+	 * We need to trigger the allocation of the page-tables that will be
+	 * needed for poking now. Later, poking may be performed in an atomic
+	 * section, which might cause allocation to fail.
+	 */
+	ptep = get_locked_pte(poking_mm, poking_addr, &ptl);
+	BUG_ON(!ptep);
+	pte_unmap_unlock(ptep, ptl);
+}
+
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 /*
  * Initialise the sparsemem vmemmap using huge-pages at the PMD level.
diff --git a/init/main.c b/init/main.c
index ee147103ba1b..a461150adfb1 100644
--- a/init/main.c
+++ b/init/main.c
@@ -497,6 +497,8 @@ void __init __weak thread_stack_cache_init(void)
 
 void __init __weak mem_encrypt_init(void) { }
 
+void __init __weak poking_init(void) { }
+
 bool initcall_debug;
 core_param(initcall_debug, initcall_debug, bool, 0644);
 
@@ -731,6 +733,7 @@ asmlinkage __visible void __init start_kernel(void)
 	taskstats_init_early();
 	delayacct_init();
 
+	poking_init();
 	check_bugs();
 
 	acpi_subsystem_init();
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 06/10] x86/alternative: use temporary mm for text poking
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (4 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 05/10] x86/alternative: initializing temporary mm for patching Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 07/10] x86/kgdb: avoid redundant comparison of patched code Nadav Amit
                   ` (4 subsequent siblings)
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit,
	Andy Lutomirski, Kees Cook, Dave Hansen, Masami Hiramatsu

text_poke() can potentially compromise the security as it sets temporary
PTEs in the fixmap. These PTEs might be used to rewrite the kernel code
from other cores accidentally or maliciously, if an attacker gains the
ability to write onto kernel memory.

Moreover, since remote TLBs are not flushed after the temporary PTEs are
removed, the time-window in which the code is writable is not limited if
the fixmap PTEs - maliciously or accidentally - are cached in the TLB.
To address these potential security hazards, we use a temporary mm for
patching the code.

Finally, text_poke() is also not conservative enough when mapping pages,
as it always tries to map 2 pages, even when a single one is sufficient.
So try to be more conservative, and do not map more than needed.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/include/asm/fixmap.h |   2 -
 arch/x86/kernel/alternative.c | 109 +++++++++++++++++++++++++++-------
 arch/x86/xen/mmu_pv.c         |   2 -
 3 files changed, 87 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index 50ba74a34a37..9da8cccdf3fb 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -103,8 +103,6 @@ enum fixed_addresses {
 #ifdef CONFIG_PARAVIRT
 	FIX_PARAVIRT_BOOTMAP,
 #endif
-	FIX_TEXT_POKE1,	/* reserve 2 pages for text_poke() */
-	FIX_TEXT_POKE0, /* first page is last, because allocation is backward */
 #ifdef	CONFIG_X86_INTEL_MID
 	FIX_LNW_VRTC,
 #endif
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 57fdde308bb6..8fc4685f3117 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -11,6 +11,7 @@
 #include <linux/stop_machine.h>
 #include <linux/slab.h>
 #include <linux/kdebug.h>
+#include <linux/mmu_context.h>
 #include <asm/text-patching.h>
 #include <asm/alternative.h>
 #include <asm/sections.h>
@@ -683,41 +684,105 @@ __ro_after_init unsigned long poking_addr;
 
 static void *__text_poke(void *addr, const void *opcode, size_t len)
 {
+	bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE;
+	temporary_mm_state_t prev;
+	struct page *pages[2] = {NULL};
 	unsigned long flags;
-	char *vaddr;
-	struct page *pages[2];
-	int i;
+	pte_t pte, *ptep;
+	spinlock_t *ptl;
 
 	/*
-	 * While boot memory allocator is runnig we cannot use struct
-	 * pages as they are not yet initialized.
+	 * While boot memory allocator is running we cannot use struct pages as
+	 * they are not yet initialized.
 	 */
 	BUG_ON(!after_bootmem);
 
 	if (!core_kernel_text((unsigned long)addr)) {
 		pages[0] = vmalloc_to_page(addr);
-		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
+		if (cross_page_boundary)
+			pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
 	} else {
 		pages[0] = virt_to_page(addr);
 		WARN_ON(!PageReserved(pages[0]));
-		pages[1] = virt_to_page(addr + PAGE_SIZE);
+		if (cross_page_boundary)
+			pages[1] = virt_to_page(addr + PAGE_SIZE);
 	}
-	BUG_ON(!pages[0]);
+	BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));
+
 	local_irq_save(flags);
-	set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
-	if (pages[1])
-		set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
-	vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
-	memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
-	clear_fixmap(FIX_TEXT_POKE0);
-	if (pages[1])
-		clear_fixmap(FIX_TEXT_POKE1);
-	local_flush_tlb();
-	sync_core();
-	/* Could also do a CLFLUSH here to speed up CPU recovery; but
-	   that causes hangs on some VIA CPUs. */
-	for (i = 0; i < len; i++)
-		BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
+
+	/*
+	 * The lock is not really needed, but this allows to avoid open-coding.
+	 */
+	ptep = get_locked_pte(poking_mm, poking_addr, &ptl);
+
+	/*
+	 * This must not fail; preallocated in poking_init().
+	 */
+	VM_BUG_ON(!ptep);
+
+	pte = mk_pte(pages[0], PAGE_KERNEL);
+	set_pte_at(poking_mm, poking_addr, ptep, pte);
+
+	if (cross_page_boundary) {
+		pte = mk_pte(pages[1], PAGE_KERNEL);
+		set_pte_at(poking_mm, poking_addr + PAGE_SIZE, ptep + 1, pte);
+	}
+
+	/*
+	 * Loading the temporary mm behaves as a compiler barrier, which
+	 * guarantees that the PTE will be set at the time memcpy() is done.
+	 */
+	prev = use_temporary_mm(poking_mm);
+
+	kasan_disable_current();
+	memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len);
+	kasan_enable_current();
+
+	/*
+	 * Ensure that the PTE is only cleared after the instructions of memcpy
+	 * were issued by using a compiler barrier.
+	 */
+	barrier();
+
+	pte_clear(poking_mm, poking_addr, ptep);
+
+	/*
+	 * __flush_tlb_one_user() performs a redundant TLB flush when PTI is on,
+	 * as it also flushes the corresponding "user" address spaces, which
+	 * does not exist.
+	 *
+	 * Poking, however, is already very inefficient since it does not try to
+	 * batch updates, so we ignore this problem for the time being.
+	 *
+	 * Since the PTEs do not exist in other kernel address-spaces, we do
+	 * not use __flush_tlb_one_kernel(), which when PTI is on would cause
+	 * more unwarranted TLB flushes.
+	 *
+	 * There is a slight anomaly here: the PTE is a supervisor-only and
+	 * (potentially) global and we use __flush_tlb_one_user() but this
+	 * should be fine.
+	 */
+	__flush_tlb_one_user(poking_addr);
+	if (cross_page_boundary) {
+		pte_clear(poking_mm, poking_addr + PAGE_SIZE, ptep + 1);
+		__flush_tlb_one_user(poking_addr + PAGE_SIZE);
+	}
+
+	/*
+	 * Loading the previous page-table hierarchy requires a serializing
+	 * instruction that already allows the core to see the updated version.
+	 * Xen-PV is assumed to serialize execution in a similar manner.
+	 */
+	unuse_temporary_mm(prev);
+
+	pte_unmap_unlock(ptep, ptl);
+	/*
+	 * If the text doesn't match what we just wrote; something is
+	 * fundamentally screwy, there's nothing we can really do about that.
+	 */
+	BUG_ON(memcmp(addr, opcode, len));
+
 	local_irq_restore(flags);
 	return addr;
 }
diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index a5d7ed125337..e9b474c396d2 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -2318,8 +2318,6 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
 #elif defined(CONFIG_X86_VSYSCALL_EMULATION)
 	case VSYSCALL_PAGE:
 #endif
-	case FIX_TEXT_POKE0:
-	case FIX_TEXT_POKE1:
 		/* All local page mappings */
 		pte = pfn_pte(phys, prot);
 		break;
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 07/10] x86/kgdb: avoid redundant comparison of patched code
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (5 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 06/10] x86/alternative: use temporary mm for text poking Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 08/10] x86: avoid W^X being broken during modules loading Nadav Amit
                   ` (3 subsequent siblings)
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit

text_poke() already ensures that the written value is the correct one
and fails if that is not the case. There is no need for an additional
comparison. Remove it.

Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/kernel/kgdb.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 2636ca8394bd..86484510bf54 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -751,7 +751,6 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 {
 	int err;
-	char opc[BREAK_INSTR_SIZE];
 
 	bpt->type = BP_BREAKPOINT;
 	err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
@@ -770,11 +769,6 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 		return -EBUSY;
 	text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
 		       BREAK_INSTR_SIZE);
-	err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
-	if (err)
-		return err;
-	if (memcmp(opc, arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE))
-		return -EINVAL;
 	bpt->type = BP_POKE_BREAKPOINT;
 
 	return err;
@@ -782,9 +776,6 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 
 int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 {
-	int err;
-	char opc[BREAK_INSTR_SIZE];
-
 	if (bpt->type != BP_POKE_BREAKPOINT)
 		goto knl_write;
 	/*
@@ -795,10 +786,7 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 		goto knl_write;
 	text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr,
 		       BREAK_INSTR_SIZE);
-	err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
-	if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE))
-		goto knl_write;
-	return err;
+	return 0;
 
 knl_write:
 	return probe_kernel_write((char *)bpt->bpt_addr,
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 08/10] x86: avoid W^X being broken during modules loading
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (6 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 07/10] x86/kgdb: avoid redundant comparison of patched code Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-28 18:59   ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 09/10] x86/jump-label: remove support for custom poker Nadav Amit
                   ` (2 subsequent siblings)
  10 siblings, 1 reply; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit,
	Andy Lutomirski, Kees Cook, Dave Hansen, Masami Hiramatsu

When modules and BPF filters are loaded, there is a time window in
which some memory is both writable and executable. An attacker that has
already found another vulnerability (e.g., a dangling pointer) might be
able to exploit this behavior to overwrite kernel code. This patch
prevents having writable executable PTEs in this stage.

In addition, avoiding having R+X mappings can also slightly simplify the
patching of modules code on initialization (e.g., by alternatives and
static-key), as would be done in the next patch.

To avoid having W+X mappings, set them initially as RW (NX) and after
they are set as RO set them as X as well. Setting them as executable is
done as a separate step to avoid one core in which the old PTE is cached
(hence writable), and another which sees the updated PTE (executable),
which would break the W^X protection.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/kernel/alternative.c | 28 +++++++++++++++++++++-------
 arch/x86/kernel/module.c      |  2 +-
 include/linux/filter.h        |  6 ++++++
 kernel/module.c               | 10 ++++++++++
 4 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 8fc4685f3117..18415e3b6000 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -667,15 +667,29 @@ void __init alternative_instructions(void)
  * handlers seeing an inconsistent instruction while you patch.
  */
 void *__init_or_module text_poke_early(void *addr, const void *opcode,
-					      size_t len)
+				       size_t len)
 {
 	unsigned long flags;
-	local_irq_save(flags);
-	memcpy(addr, opcode, len);
-	local_irq_restore(flags);
-	sync_core();
-	/* Could also do a CLFLUSH here to speed up CPU recovery; but
-	   that causes hangs on some VIA CPUs. */
+
+	if (static_cpu_has(X86_FEATURE_NX) &&
+	    is_module_text_address((unsigned long)addr)) {
+		/*
+		 * Modules text is marked initially as non-executable, so the
+		 * code cannot be running and speculative code-fetches are
+		 * prevented. We can just change the code.
+		 */
+		memcpy(addr, opcode, len);
+	} else {
+		local_irq_save(flags);
+		memcpy(addr, opcode, len);
+		local_irq_restore(flags);
+		sync_core();
+
+		/*
+		 * Could also do a CLFLUSH here to speed up CPU recovery; but
+		 * that causes hangs on some VIA CPUs.
+		 */
+	}
 	return addr;
 }
 
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index b052e883dd8c..cfa3106faee4 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -87,7 +87,7 @@ void *module_alloc(unsigned long size)
 	p = __vmalloc_node_range(size, MODULE_ALIGN,
 				    MODULES_VADDR + get_module_load_offset(),
 				    MODULES_END, GFP_KERNEL,
-				    PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
+				    PAGE_KERNEL, 0, NUMA_NO_NODE,
 				    __builtin_return_address(0));
 	if (p && (kasan_module_alloc(p, size) < 0)) {
 		vfree(p);
diff --git a/include/linux/filter.h b/include/linux/filter.h
index de629b706d1d..ee9ae03c5f56 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -704,7 +704,13 @@ static inline void bpf_prog_unlock_ro(struct bpf_prog *fp)
 
 static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)
 {
+	/*
+	 * Perform mapping changes in two stages to avoid opening a time-window
+	 * in which a PTE is cached in any TLB as writable, but marked as
+	 * executable in the memory-resident mappings (e.g., page-tables).
+	 */
 	set_memory_ro((unsigned long)hdr, hdr->pages);
+	set_memory_x((unsigned long)hdr, hdr->pages);
 }
 
 static inline void bpf_jit_binary_unlock_ro(struct bpf_binary_header *hdr)
diff --git a/kernel/module.c b/kernel/module.c
index 49a405891587..7cb207249437 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1946,9 +1946,19 @@ void module_enable_ro(const struct module *mod, bool after_init)
 	if (!rodata_enabled)
 		return;
 
+	/*
+	 * Perform mapping changes in two stages to avoid opening a time-window
+	 * in which a PTE is cached in any TLB as writable, but marked as
+	 * executable in the memory-resident mappings (e.g., page-tables).
+	 */
 	frob_text(&mod->core_layout, set_memory_ro);
+	frob_text(&mod->core_layout, set_memory_x);
+
 	frob_rodata(&mod->core_layout, set_memory_ro);
+
 	frob_text(&mod->init_layout, set_memory_ro);
+	frob_text(&mod->init_layout, set_memory_x);
+
 	frob_rodata(&mod->init_layout, set_memory_ro);
 
 	if (after_init)
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 09/10] x86/jump-label: remove support for custom poker
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (7 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 08/10] x86: avoid W^X being broken during modules loading Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-20 20:35 ` [PATCH v6 10/10] x86/alternative: remove the return value of text_poke_*() Nadav Amit
  2018-11-26 10:32 ` [PATCH v6 00/10] x86/alternative: text_poke() fixes Peter Zijlstra
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit,
	Andy Lutomirski, Kees Cook, Dave Hansen, Masami Hiramatsu

There are only two types of poking: early and breakpoint based. The use
of a function pointer to perform poking complicates the code and is
probably inefficient due to the use of indirect branches.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/kernel/jump_label.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index ed5fe274a7d8..994c13e2867d 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -39,7 +39,6 @@ static void bug_at(unsigned char *ip, int line)
 
 static void __ref __jump_label_transform(struct jump_entry *entry,
 					 enum jump_label_type type,
-					 void *(*poker)(void *, const void *, size_t),
 					 int init)
 {
 	union jump_code_union jmp;
@@ -52,14 +51,6 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
 	jmp.offset = jump_entry_target(entry) -
 		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 
-	/*
-	 * As long as we're UP and not yet marked RO, we can use
-	 * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to
-	 * SYSTEM_SCHEDULING before going either.
-	 */
-	if (system_state == SYSTEM_BOOTING)
-		poker = text_poke_early;
-
 	if (type == JUMP_LABEL_JMP) {
 		if (init) {
 			expect = default_nop; line = __LINE__;
@@ -82,16 +73,17 @@ static void __ref __jump_label_transform(struct jump_entry *entry,
 		bug_at((void *)jump_entry_code(entry), line);
 
 	/*
-	 * Make text_poke_bp() a default fallback poker.
+	 * As long as we're UP and not yet marked RO, we can use
+	 * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to
+	 * SYSTEM_SCHEDULING before going either.
 	 *
 	 * At the time the change is being done, just ignore whether we
 	 * are doing nop -> jump or jump -> nop transition, and assume
 	 * always nop being the 'currently valid' instruction
-	 *
 	 */
-	if (poker) {
-		(*poker)((void *)jump_entry_code(entry), code,
-			 JUMP_LABEL_NOP_SIZE);
+	if (init || system_state == SYSTEM_BOOTING) {
+		text_poke_early((void *)jump_entry_code(entry), code,
+				JUMP_LABEL_NOP_SIZE);
 		return;
 	}
 
@@ -103,7 +95,7 @@ void arch_jump_label_transform(struct jump_entry *entry,
 			       enum jump_label_type type)
 {
 	mutex_lock(&text_mutex);
-	__jump_label_transform(entry, type, NULL, 0);
+	__jump_label_transform(entry, type, 0);
 	mutex_unlock(&text_mutex);
 }
 
@@ -133,7 +125,7 @@ __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 			jlstate = JL_STATE_NO_UPDATE;
 	}
 	if (jlstate == JL_STATE_UPDATE)
-		__jump_label_transform(entry, type, text_poke_early, 1);
+		__jump_label_transform(entry, type, 1);
 }
 
 #endif
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH v6 10/10] x86/alternative: remove the return value of text_poke_*()
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (8 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 09/10] x86/jump-label: remove support for custom poker Nadav Amit
@ 2018-11-20 20:35 ` Nadav Amit
  2018-11-26 10:32 ` [PATCH v6 00/10] x86/alternative: text_poke() fixes Peter Zijlstra
  10 siblings, 0 replies; 16+ messages in thread
From: Nadav Amit @ 2018-11-20 20:35 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, Peter Zijlstra, linux_dti,
	linux-integrity, linux-security-module, Nadav Amit,
	Andy Lutomirski, Kees Cook, Dave Hansen, Masami Hiramatsu

The return value of text_poke_early() and text_poke_bp() is useless.
Remove it.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/include/asm/text-patching.h |  4 ++--
 arch/x86/kernel/alternative.c        | 11 ++++-------
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index a75eed841eed..c90678fd391a 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -18,7 +18,7 @@ static inline void apply_paravirt(struct paravirt_patch_site *start,
 #define __parainstructions_end	NULL
 #endif
 
-extern void *text_poke_early(void *addr, const void *opcode, size_t len);
+extern void text_poke_early(void *addr, const void *opcode, size_t len);
 
 /*
  * Clear and restore the kernel write-protection flag on the local CPU.
@@ -37,7 +37,7 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len);
 extern void *text_poke(void *addr, const void *opcode, size_t len);
 extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
 extern int poke_int3_handler(struct pt_regs *regs);
-extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
+extern void text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
 extern int after_bootmem;
 extern __ro_after_init struct mm_struct *poking_mm;
 extern __ro_after_init unsigned long poking_addr;
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 18415e3b6000..2740ad2c6f21 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -264,7 +264,7 @@ static void __init_or_module add_nops(void *insns, unsigned int len)
 
 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 extern s32 __smp_locks[], __smp_locks_end[];
-void *text_poke_early(void *addr, const void *opcode, size_t len);
+void text_poke_early(void *addr, const void *opcode, size_t len);
 
 /*
  * Are we looking at a near JMP with a 1 or 4-byte displacement.
@@ -666,8 +666,8 @@ void __init alternative_instructions(void)
  * instructions. And on the local CPU you need to be protected again NMI or MCE
  * handlers seeing an inconsistent instruction while you patch.
  */
-void *__init_or_module text_poke_early(void *addr, const void *opcode,
-				       size_t len)
+void __init_or_module text_poke_early(void *addr, const void *opcode,
+				      size_t len)
 {
 	unsigned long flags;
 
@@ -690,7 +690,6 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
 		 * that causes hangs on some VIA CPUs.
 		 */
 	}
-	return addr;
 }
 
 __ro_after_init struct mm_struct *poking_mm;
@@ -893,7 +892,7 @@ int poke_int3_handler(struct pt_regs *regs)
  *	  replacing opcode
  *	- sync cores
  */
-void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
+void text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
 {
 	unsigned char int3 = 0xcc;
 
@@ -935,7 +934,5 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
 	 * the writing of the new instruction.
 	 */
 	bp_patching_in_progress = false;
-
-	return addr;
 }
 
-- 
2.17.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 00/10] x86/alternative: text_poke() fixes
  2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
                   ` (9 preceding siblings ...)
  2018-11-20 20:35 ` [PATCH v6 10/10] x86/alternative: remove the return value of text_poke_*() Nadav Amit
@ 2018-11-26 10:32 ` Peter Zijlstra
  2018-11-26 17:46   ` Nadav Amit
  10 siblings, 1 reply; 16+ messages in thread
From: Peter Zijlstra @ 2018-11-26 10:32 UTC (permalink / raw)
  To: Nadav Amit
  Cc: Ingo Molnar, linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, linux_dti, linux-integrity,
	linux-security-module

On Tue, Nov 20, 2018 at 12:35:35PM -0800, Nadav Amit wrote:

> Nadav Amit (9):
>   Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
>   x86/jump_label: Use text_poke_early() during early init
>   fork: provide a function for copying init_mm
>   x86/alternative: initializing temporary mm for patching
>   x86/alternative: use temporary mm for text poking
>   x86/kgdb: avoid redundant comparison of patched code
>   x86: avoid W^X being broken during modules loading
>   x86/jump-label: remove support for custom poker
>   x86/alternative: remove the return value of text_poke_*()
> 
>  arch/x86/include/asm/fixmap.h        |   2 -
>  arch/x86/include/asm/mmu_context.h   |  32 +++++
>  arch/x86/include/asm/pgtable.h       |   3 +
>  arch/x86/include/asm/text-patching.h |   7 +-
>  arch/x86/kernel/alternative.c        | 197 ++++++++++++++++++++-------
>  arch/x86/kernel/jump_label.c         |  19 ++-
>  arch/x86/kernel/kgdb.c               |  25 +---
>  arch/x86/kernel/module.c             |   2 +-
>  arch/x86/mm/init_64.c                |  35 +++++
>  arch/x86/xen/mmu_pv.c                |   2 -
>  include/linux/filter.h               |   6 +
>  include/linux/sched/task.h           |   1 +
>  init/main.c                          |   3 +
>  kernel/fork.c                        |  24 +++-
>  kernel/module.c                      |  10 ++
>  15 files changed, 279 insertions(+), 89 deletions(-)

Thanks Nadav!

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 00/10] x86/alternative: text_poke() fixes
  2018-11-26 10:32 ` [PATCH v6 00/10] x86/alternative: text_poke() fixes Peter Zijlstra
@ 2018-11-26 17:46   ` Nadav Amit
  2018-11-29 12:58     ` Peter Zijlstra
  0 siblings, 1 reply; 16+ messages in thread
From: Nadav Amit @ 2018-11-26 17:46 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Ingo Molnar, LKML, X86 ML, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, linux_dti, linux-integrity,
	linux-security-module

> On Nov 26, 2018, at 2:32 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> On Tue, Nov 20, 2018 at 12:35:35PM -0800, Nadav Amit wrote:
> 
>> Nadav Amit (9):
>>  Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
>>  x86/jump_label: Use text_poke_early() during early init
>>  fork: provide a function for copying init_mm
>>  x86/alternative: initializing temporary mm for patching
>>  x86/alternative: use temporary mm for text poking
>>  x86/kgdb: avoid redundant comparison of patched code
>>  x86: avoid W^X being broken during modules loading
>>  x86/jump-label: remove support for custom poker
>>  x86/alternative: remove the return value of text_poke_*()
>> 
>> arch/x86/include/asm/fixmap.h        |   2 -
>> arch/x86/include/asm/mmu_context.h   |  32 +++++
>> arch/x86/include/asm/pgtable.h       |   3 +
>> arch/x86/include/asm/text-patching.h |   7 +-
>> arch/x86/kernel/alternative.c        | 197 ++++++++++++++++++++-------
>> arch/x86/kernel/jump_label.c         |  19 ++-
>> arch/x86/kernel/kgdb.c               |  25 +---
>> arch/x86/kernel/module.c             |   2 +-
>> arch/x86/mm/init_64.c                |  35 +++++
>> arch/x86/xen/mmu_pv.c                |   2 -
>> include/linux/filter.h               |   6 +
>> include/linux/sched/task.h           |   1 +
>> init/main.c                          |   3 +
>> kernel/fork.c                        |  24 +++-
>> kernel/module.c                      |  10 ++
>> 15 files changed, 279 insertions(+), 89 deletions(-)
> 
> Thanks Nadav!
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

No problem, Peter.

One small request - on [02/10], since after your review the patch changed to
be the single line that you provided, I set you as a co-developer. IIUC this
requires your signed-off-by.

Thanks again for all the reviews and the help.


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 08/10] x86: avoid W^X being broken during modules loading
  2018-11-20 20:35 ` [PATCH v6 08/10] x86: avoid W^X being broken during modules loading Nadav Amit
@ 2018-11-28 18:59   ` Nadav Amit
  2018-11-30  2:32     ` Masami Hiramatsu
  0 siblings, 1 reply; 16+ messages in thread
From: Nadav Amit @ 2018-11-28 18:59 UTC (permalink / raw)
  To: Ingo Molnar, Edgecombe, Rick P
  Cc: LKML, X86 ML, H. Peter Anvin, Thomas Gleixner, Borislav Petkov,
	Dave Hansen, Peter Zijlstra, Damian Tometzki, linux-integrity,
	LSM List, Andy Lutomirski, Kees Cook, Dave Hansen,
	Masami Hiramatsu

> On Nov 20, 2018, at 12:35 PM, Nadav Amit <namit@vmware.com> wrote:
> 
> When modules and BPF filters are loaded, there is a time window in
> which some memory is both writable and executable. An attacker that has
> already found another vulnerability (e.g., a dangling pointer) might be
> able to exploit this behavior to overwrite kernel code. This patch
> prevents having writable executable PTEs in this stage.
> 
> In addition, avoiding having R+X mappings can also slightly simplify the
> patching of modules code on initialization (e.g., by alternatives and
> static-key), as would be done in the next patch.
> 
> To avoid having W+X mappings, set them initially as RW (NX) and after
> they are set as RO set them as X as well. Setting them as executable is
> done as a separate step to avoid one core in which the old PTE is cached
> (hence writable), and another which sees the updated PTE (executable),
> which would break the W^X protection.
> 
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Suggested-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Nadav Amit <namit@vmware.com>
> ---
> arch/x86/kernel/alternative.c | 28 +++++++++++++++++++++-------
> arch/x86/kernel/module.c      |  2 +-
> include/linux/filter.h        |  6 ++++++
> kernel/module.c               | 10 ++++++++++
> 4 files changed, 38 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 8fc4685f3117..18415e3b6000 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -667,15 +667,29 @@ void __init alternative_instructions(void)
>  * handlers seeing an inconsistent instruction while you patch.
>  */
> void *__init_or_module text_poke_early(void *addr, const void *opcode,
> -					      size_t len)
> +				       size_t len)
> {
> 	unsigned long flags;
> -	local_irq_save(flags);
> -	memcpy(addr, opcode, len);
> -	local_irq_restore(flags);
> -	sync_core();
> -	/* Could also do a CLFLUSH here to speed up CPU recovery; but
> -	   that causes hangs on some VIA CPUs. */
> +
> +	if (static_cpu_has(X86_FEATURE_NX) &&
> +	    is_module_text_address((unsigned long)addr)) {
> +		/*
> +		 * Modules text is marked initially as non-executable, so the
> +		 * code cannot be running and speculative code-fetches are
> +		 * prevented. We can just change the code.
> +		 */
> +		memcpy(addr, opcode, len);
> +	} else {
> +		local_irq_save(flags);
> +		memcpy(addr, opcode, len);
> +		local_irq_restore(flags);
> +		sync_core();
> +
> +		/*
> +		 * Could also do a CLFLUSH here to speed up CPU recovery; but
> +		 * that causes hangs on some VIA CPUs.
> +		 */
> +	}
> 	return addr;
> }
> 
> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> index b052e883dd8c..cfa3106faee4 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -87,7 +87,7 @@ void *module_alloc(unsigned long size)
> 	p = __vmalloc_node_range(size, MODULE_ALIGN,
> 				    MODULES_VADDR + get_module_load_offset(),
> 				    MODULES_END, GFP_KERNEL,
> -				    PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
> +				    PAGE_KERNEL, 0, NUMA_NO_NODE,
> 				    __builtin_return_address(0));
> 	if (p && (kasan_module_alloc(p, size) < 0)) {
> 		vfree(p);
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index de629b706d1d..ee9ae03c5f56 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -704,7 +704,13 @@ static inline void bpf_prog_unlock_ro(struct bpf_prog *fp)
> 
> static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)
> {
> +	/*
> +	 * Perform mapping changes in two stages to avoid opening a time-window
> +	 * in which a PTE is cached in any TLB as writable, but marked as
> +	 * executable in the memory-resident mappings (e.g., page-tables).
> +	 */
> 	set_memory_ro((unsigned long)hdr, hdr->pages);
> +	set_memory_x((unsigned long)hdr, hdr->pages);
> }
> 
> static inline void bpf_jit_binary_unlock_ro(struct bpf_binary_header *hdr)
> diff --git a/kernel/module.c b/kernel/module.c
> index 49a405891587..7cb207249437 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1946,9 +1946,19 @@ void module_enable_ro(const struct module *mod, bool after_init)
> 	if (!rodata_enabled)
> 		return;
> 
> +	/*
> +	 * Perform mapping changes in two stages to avoid opening a time-window
> +	 * in which a PTE is cached in any TLB as writable, but marked as
> +	 * executable in the memory-resident mappings (e.g., page-tables).
> +	 */
> 	frob_text(&mod->core_layout, set_memory_ro);
> +	frob_text(&mod->core_layout, set_memory_x);
> +
> 	frob_rodata(&mod->core_layout, set_memory_ro);
> +
> 	frob_text(&mod->init_layout, set_memory_ro);
> +	frob_text(&mod->init_layout, set_memory_x);
> +
> 	frob_rodata(&mod->init_layout, set_memory_ro);
> 
> 	if (after_init)
> -- 
> 2.17.1

Rick pointed out that I screwed up ftrace and kprobes.

For kprobes, I think I need to add set_memory_x() to alloc_insn_page() and
change arch_ftrace_update_trampoline().

For arch_ftrace_update_trampoline(), I think I should remove not use
set_memory_rw() when patching in __probe_kernel_write() should be done
through text_poke().

I’ll give it another look and send another version later.

Regards,
Nadav



^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 00/10] x86/alternative: text_poke() fixes
  2018-11-26 17:46   ` Nadav Amit
@ 2018-11-29 12:58     ` Peter Zijlstra
  0 siblings, 0 replies; 16+ messages in thread
From: Peter Zijlstra @ 2018-11-29 12:58 UTC (permalink / raw)
  To: Nadav Amit
  Cc: Ingo Molnar, LKML, X86 ML, H. Peter Anvin, Thomas Gleixner,
	Borislav Petkov, Dave Hansen, linux_dti, linux-integrity,
	linux-security-module

On Mon, Nov 26, 2018 at 05:46:09PM +0000, Nadav Amit wrote:

> One small request - on [02/10], since after your review the patch changed to
> be the single line that you provided, I set you as a co-developer. IIUC this
> requires your signed-off-by.

I really wouldn't know. Feel free to do as you with. It's just a few
lines.

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH v6 08/10] x86: avoid W^X being broken during modules loading
  2018-11-28 18:59   ` Nadav Amit
@ 2018-11-30  2:32     ` Masami Hiramatsu
  0 siblings, 0 replies; 16+ messages in thread
From: Masami Hiramatsu @ 2018-11-30  2:32 UTC (permalink / raw)
  To: Nadav Amit
  Cc: Ingo Molnar, Edgecombe, Rick P, LKML, X86 ML, H. Peter Anvin,
	Thomas Gleixner, Borislav Petkov, Dave Hansen, Peter Zijlstra,
	Damian Tometzki, linux-integrity, LSM List, Andy Lutomirski,
	Kees Cook, Dave Hansen, Masami Hiramatsu

On Wed, 28 Nov 2018 18:59:30 +0000
Nadav Amit <namit@vmware.com> wrote:

> > On Nov 20, 2018, at 12:35 PM, Nadav Amit <namit@vmware.com> wrote:
> > 
> > When modules and BPF filters are loaded, there is a time window in
> > which some memory is both writable and executable. An attacker that has
> > already found another vulnerability (e.g., a dangling pointer) might be
> > able to exploit this behavior to overwrite kernel code. This patch
> > prevents having writable executable PTEs in this stage.
> > 
> > In addition, avoiding having R+X mappings can also slightly simplify the
> > patching of modules code on initialization (e.g., by alternatives and
> > static-key), as would be done in the next patch.
> > 
> > To avoid having W+X mappings, set them initially as RW (NX) and after
> > they are set as RO set them as X as well. Setting them as executable is
> > done as a separate step to avoid one core in which the old PTE is cached
> > (hence writable), and another which sees the updated PTE (executable),
> > which would break the W^X protection.
> > 
> > Cc: Andy Lutomirski <luto@kernel.org>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Dave Hansen <dave.hansen@intel.com>
> > Cc: Masami Hiramatsu <mhiramat@kernel.org>
> > Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> > Suggested-by: Andy Lutomirski <luto@amacapital.net>
> > Signed-off-by: Nadav Amit <namit@vmware.com>
> > ---
> > arch/x86/kernel/alternative.c | 28 +++++++++++++++++++++-------
> > arch/x86/kernel/module.c      |  2 +-
> > include/linux/filter.h        |  6 ++++++
> > kernel/module.c               | 10 ++++++++++
> > 4 files changed, 38 insertions(+), 8 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> > index 8fc4685f3117..18415e3b6000 100644
> > --- a/arch/x86/kernel/alternative.c
> > +++ b/arch/x86/kernel/alternative.c
> > @@ -667,15 +667,29 @@ void __init alternative_instructions(void)
> >  * handlers seeing an inconsistent instruction while you patch.
> >  */
> > void *__init_or_module text_poke_early(void *addr, const void *opcode,
> > -					      size_t len)
> > +				       size_t len)
> > {
> > 	unsigned long flags;
> > -	local_irq_save(flags);
> > -	memcpy(addr, opcode, len);
> > -	local_irq_restore(flags);
> > -	sync_core();
> > -	/* Could also do a CLFLUSH here to speed up CPU recovery; but
> > -	   that causes hangs on some VIA CPUs. */
> > +
> > +	if (static_cpu_has(X86_FEATURE_NX) &&
> > +	    is_module_text_address((unsigned long)addr)) {
> > +		/*
> > +		 * Modules text is marked initially as non-executable, so the
> > +		 * code cannot be running and speculative code-fetches are
> > +		 * prevented. We can just change the code.
> > +		 */
> > +		memcpy(addr, opcode, len);
> > +	} else {
> > +		local_irq_save(flags);
> > +		memcpy(addr, opcode, len);
> > +		local_irq_restore(flags);
> > +		sync_core();
> > +
> > +		/*
> > +		 * Could also do a CLFLUSH here to speed up CPU recovery; but
> > +		 * that causes hangs on some VIA CPUs.
> > +		 */
> > +	}
> > 	return addr;
> > }
> > 
> > diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> > index b052e883dd8c..cfa3106faee4 100644
> > --- a/arch/x86/kernel/module.c
> > +++ b/arch/x86/kernel/module.c
> > @@ -87,7 +87,7 @@ void *module_alloc(unsigned long size)
> > 	p = __vmalloc_node_range(size, MODULE_ALIGN,
> > 				    MODULES_VADDR + get_module_load_offset(),
> > 				    MODULES_END, GFP_KERNEL,
> > -				    PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
> > +				    PAGE_KERNEL, 0, NUMA_NO_NODE,
> > 				    __builtin_return_address(0));
> > 	if (p && (kasan_module_alloc(p, size) < 0)) {
> > 		vfree(p);
> > diff --git a/include/linux/filter.h b/include/linux/filter.h
> > index de629b706d1d..ee9ae03c5f56 100644
> > --- a/include/linux/filter.h
> > +++ b/include/linux/filter.h
> > @@ -704,7 +704,13 @@ static inline void bpf_prog_unlock_ro(struct bpf_prog *fp)
> > 
> > static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)
> > {
> > +	/*
> > +	 * Perform mapping changes in two stages to avoid opening a time-window
> > +	 * in which a PTE is cached in any TLB as writable, but marked as
> > +	 * executable in the memory-resident mappings (e.g., page-tables).
> > +	 */
> > 	set_memory_ro((unsigned long)hdr, hdr->pages);
> > +	set_memory_x((unsigned long)hdr, hdr->pages);
> > }
> > 
> > static inline void bpf_jit_binary_unlock_ro(struct bpf_binary_header *hdr)
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 49a405891587..7cb207249437 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -1946,9 +1946,19 @@ void module_enable_ro(const struct module *mod, bool after_init)
> > 	if (!rodata_enabled)
> > 		return;
> > 
> > +	/*
> > +	 * Perform mapping changes in two stages to avoid opening a time-window
> > +	 * in which a PTE is cached in any TLB as writable, but marked as
> > +	 * executable in the memory-resident mappings (e.g., page-tables).
> > +	 */
> > 	frob_text(&mod->core_layout, set_memory_ro);
> > +	frob_text(&mod->core_layout, set_memory_x);
> > +
> > 	frob_rodata(&mod->core_layout, set_memory_ro);
> > +
> > 	frob_text(&mod->init_layout, set_memory_ro);
> > +	frob_text(&mod->init_layout, set_memory_x);
> > +
> > 	frob_rodata(&mod->init_layout, set_memory_ro);
> > 
> > 	if (after_init)
> > -- 
> > 2.17.1
> 
> Rick pointed out that I screwed up ftrace and kprobes.
> 
> For kprobes, I think I need to add set_memory_x() to alloc_insn_page() and
> change arch_ftrace_update_trampoline().

Oops, right. It should be easy to fix for kprobe :) what you need is below.

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index c33b06f..51818f3 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -431,8 +431,10 @@ void *alloc_insn_page(void)
        void *page;
 
        page = module_alloc(PAGE_SIZE);
-       if (page)
+       if (page) {
                set_memory_ro((unsigned long)page & PAGE_MASK, 1);
+               set_memory_x((unsigned long)page & PAGE_MASK, 1);
+       }
 
        return page;
 }


> 
> For arch_ftrace_update_trampoline(), I think I should remove not use
> set_memory_rw() when patching in __probe_kernel_write() should be done
> through text_poke().

right.

> 
> I’ll give it another look and send another version later.

Thank you,

> 
> Regards,
> Nadav
> 
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>

^ permalink raw reply	[flat|nested] 16+ messages in thread

end of thread, back to index

Thread overview: 16+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
2018-11-20 20:35 ` [PATCH v6 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-11-20 20:35 ` [PATCH v6 02/10] x86/jump_label: Use text_poke_early() during early init Nadav Amit
2018-11-20 20:35 ` [PATCH v6 03/10] x86/mm: temporary mm struct Nadav Amit
2018-11-20 20:35 ` [PATCH v6 04/10] fork: provide a function for copying init_mm Nadav Amit
2018-11-20 20:35 ` [PATCH v6 05/10] x86/alternative: initializing temporary mm for patching Nadav Amit
2018-11-20 20:35 ` [PATCH v6 06/10] x86/alternative: use temporary mm for text poking Nadav Amit
2018-11-20 20:35 ` [PATCH v6 07/10] x86/kgdb: avoid redundant comparison of patched code Nadav Amit
2018-11-20 20:35 ` [PATCH v6 08/10] x86: avoid W^X being broken during modules loading Nadav Amit
2018-11-28 18:59   ` Nadav Amit
2018-11-30  2:32     ` Masami Hiramatsu
2018-11-20 20:35 ` [PATCH v6 09/10] x86/jump-label: remove support for custom poker Nadav Amit
2018-11-20 20:35 ` [PATCH v6 10/10] x86/alternative: remove the return value of text_poke_*() Nadav Amit
2018-11-26 10:32 ` [PATCH v6 00/10] x86/alternative: text_poke() fixes Peter Zijlstra
2018-11-26 17:46   ` Nadav Amit
2018-11-29 12:58     ` Peter Zijlstra

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