[patch V4 00/15] entry, x86, kvm: Generic entry/exit functionality for host and guest

[patch V4 00/15] entry, x86, kvm: Generic entry/exit functionality for host and guest

[Thomas Gleixner]

This is the 4rd version of generic entry/exit functionality for host and
guest.

The 3rd version is available here:

    https://lore.kernel.org/r/20200716182208.180916541@linutronix.de

Changes vs. V3:

  - Drop the architecture wrappers for seccomp and audit (Kees)
  - Move the user return notifier out of the loop
  - Bring I/O bitmap handling back
  - Use the existing helpers to get syscall number and return value
  - Drop dummy defines for SYSCALL_TRACE and NOTIFY_RESUME as all
    architectures define them
  - Fix TIF_SYSCALL_AUDIT dummy define
  - Adjust comments

The patches depend on:

    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/entry

The lot is also available from git:

    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git x86/entry

Thanks,

	tglx
---
 arch/Kconfig                        |    3 
 arch/x86/Kconfig                    |    1 
 arch/x86/entry/common.c             |  632 ++----------------------------------
 arch/x86/entry/entry_32.S           |    2 
 arch/x86/entry/entry_64.S           |    2 
 arch/x86/include/asm/entry-common.h |   76 ++++
 arch/x86/include/asm/idtentry.h     |   39 --
 arch/x86/include/asm/ptrace.h       |    5 
 arch/x86/include/asm/signal.h       |    1 
 arch/x86/include/asm/thread_info.h  |    5 
 arch/x86/kernel/cpu/mce/core.c      |    4 
 arch/x86/kernel/kvm.c               |    6 
 arch/x86/kernel/signal.c            |    3 
 arch/x86/kernel/traps.c             |   24 -
 arch/x86/kvm/Kconfig                |    1 
 arch/x86/kvm/vmx/vmx.c              |   11 
 arch/x86/kvm/x86.c                  |   15 
 arch/x86/mm/fault.c                 |    6 
 include/linux/entry-common.h        |  372 +++++++++++++++++++++
 include/linux/entry-kvm.h           |   80 ++++
 include/linux/kvm_host.h            |    8 
 include/linux/seccomp.h             |    1 
 kernel/Makefile                     |    1 
 kernel/entry/Makefile               |    4 
 kernel/entry/common.c               |  374 +++++++++++++++++++++
 kernel/entry/kvm.c                  |   51 ++
 virt/kvm/Kconfig                    |    3 
 27 files changed, 1067 insertions(+), 663 deletions(-)

[patch V4 01/15] seccomp: Provide stub for __secure_computing()

[Thomas Gleixner]

To avoid #ifdeffery in the upcoming generic syscall entry work code provide
a stub for __secure_computing() as this is preferred over
secure_computing() because the TIF flag is already evaluated.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V4: New patch
---
 include/linux/seccomp.h |    1 +
 1 file changed, 1 insertion(+)

--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -61,6 +61,7 @@ struct seccomp_filter { };
 
 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
 static inline int secure_computing(void) { return 0; }
+static inline int __secure_computing(void) { return 0; }
 #else
 static inline void secure_computing_strict(int this_syscall) { return; }
 #endif

Re: [patch V4 01/15] seccomp: Provide stub for __secure_computing()

[Kees Cook]

On Tue, Jul 21, 2020 at 12:57:07PM +0200, Thomas Gleixner wrote:
> To avoid #ifdeffery in the upcoming generic syscall entry work code provide
> a stub for __secure_computing() as this is preferred over
> secure_computing() because the TIF flag is already evaluated.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[patch V4 02/15] entry: Provide generic syscall entry functionality

[Thomas Gleixner]

On syscall entry certain work needs to be done:

   - Establish state (lockdep, context tracking, tracing)
   - Conditional work (ptrace, seccomp, audit...)

This code is needlessly duplicated and  different in all
architectures.

Provide a generic version based on the x86 implementation which has all the
RCU and instrumentation bits right.

As interrupt/exception entry from user space needs parts of the same
functionality, provide a function for this as well.

syscall_enter_from_user_mode() and irqentry_enter_from_user_mode() must be
called right after the low level ASM entry. The calling code must be
non-instrumentable. After the functions returns state is correct and the
subsequent functions can be instrumented.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V4: Remove the architecture wrappers for seccomp and audit and use
    the generic code (Kees)

    Fix TIF_SYSCALL_AUDIT dummy define and remove TIF_SYSCALL_TRACE as it's
    defined in all architectures.

V3: Adapt to noinstr changes. Add interrupt/exception entry function.

V2: Fix function documentation (Mike)
    Add comment about return value (Andy)
---
 arch/Kconfig                 |    3 +
 include/linux/entry-common.h |  121 +++++++++++++++++++++++++++++++++++++++++++
 kernel/Makefile              |    1 
 kernel/entry/Makefile        |    3 +
 kernel/entry/common.c        |   88 +++++++++++++++++++++++++++++++
 5 files changed, 216 insertions(+)

--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -27,6 +27,9 @@ config HAVE_IMA_KEXEC
 config HOTPLUG_SMT
 	bool
 
+config GENERIC_ENTRY
+       bool
+
 config OPROFILE
 	tristate "OProfile system profiling"
 	depends on PROFILING
--- /dev/null
+++ b/include/linux/entry-common.h
@@ -0,0 +1,121 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_ENTRYCOMMON_H
+#define __LINUX_ENTRYCOMMON_H
+
+#include <linux/tracehook.h>
+#include <linux/syscalls.h>
+#include <linux/seccomp.h>
+#include <linux/sched.h>
+
+#include <asm/entry-common.h>
+
+/*
+ * Define dummy _TIF work flags if not defined by the architecture or for
+ * disabled functionality.
+ */
+#ifndef _TIF_SYSCALL_EMU
+# define _TIF_SYSCALL_EMU		(0)
+#endif
+
+#ifndef _TIF_SYSCALL_TRACEPOINT
+# define _TIF_SYSCALL_TRACEPOINT	(0)
+#endif
+
+#ifndef _TIF_SECCOMP
+# define _TIF_SECCOMP			(0)
+#endif
+
+#ifndef _TIF_SYSCALL_AUDIT
+# define _TIF_SYSCALL_AUDIT		(0)
+#endif
+
+/*
+ * TIF flags handled in syscall_enter_from_usermode()
+ */
+#ifndef ARCH_SYSCALL_ENTER_WORK
+# define ARCH_SYSCALL_ENTER_WORK	(0)
+#endif
+
+#define SYSCALL_ENTER_WORK						\
+	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | TIF_SECCOMP |	\
+	 _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_EMU |			\
+	 ARCH_SYSCALL_ENTER_WORK)
+
+/**
+ * arch_check_user_regs - Architecture specific sanity check for user mode regs
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Defaults to an empty implementation. Can be replaced by architecture
+ * specific code.
+ *
+ * Invoked from syscall_enter_from_user_mode() in the non-instrumentable
+ * section. Use __always_inline so the compiler cannot push it out of line
+ * and make it instrumentable.
+ */
+static __always_inline void arch_check_user_regs(struct pt_regs *regs);
+
+#ifndef arch_check_user_regs
+static __always_inline void arch_check_user_regs(struct pt_regs *regs) {}
+#endif
+
+/**
+ * arch_syscall_enter_tracehook - Wrapper around tracehook_report_syscall_entry()
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Returns: 0 on success or an error code to skip the syscall.
+ *
+ * Defaults to tracehook_report_syscall_entry(). Can be replaced by
+ * architecture specific code.
+ *
+ * Invoked from syscall_enter_from_user_mode()
+ */
+static inline __must_check int arch_syscall_enter_tracehook(struct pt_regs *regs);
+
+#ifndef arch_syscall_enter_tracehook
+static inline __must_check int arch_syscall_enter_tracehook(struct pt_regs *regs)
+{
+	return tracehook_report_syscall_entry(regs);
+}
+#endif
+
+/**
+ * syscall_enter_from_user_mode - Check and handle work before invoking
+ *				 a syscall
+ * @regs:	Pointer to currents pt_regs
+ * @syscall:	The syscall number
+ *
+ * Invoked from architecture specific syscall entry code with interrupts
+ * disabled. The calling code has to be non-instrumentable. When the
+ * function returns all state is correct and the subsequent functions can be
+ * instrumented.
+ *
+ * Returns: The original or a modified syscall number
+ *
+ * If the returned syscall number is -1 then the syscall should be
+ * skipped. In this case the caller may invoke syscall_set_error() or
+ * syscall_set_return_value() first.  If neither of those are called and -1
+ * is returned, then the syscall will fail with ENOSYS.
+ *
+ * The following functionality is handled here:
+ *
+ *  1) Establish state (lockdep, RCU (context tracking), tracing)
+ *  2) TIF flag dependent invocations of arch_syscall_enter_tracehook(),
+ *     __secure_computing(), trace_sys_enter()
+ *  3) Invocation of audit_syscall_entry()
+ */
+long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall);
+
+/**
+ * irqentry_enter_from_user_mode - Establish state before invoking the irq handler
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Invoked from architecture specific entry code with interrupts disabled.
+ * Can only be called when the interrupt entry came from user mode. The
+ * calling code must be non-instrumentable.  When the function returns all
+ * state is correct and the subsequent functions can be instrumented.
+ *
+ * The function establishes state (lockdep, RCU (context tracking), tracing)
+ */
+void irqentry_enter_from_user_mode(struct pt_regs *regs);
+
+#endif
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -48,6 +48,7 @@ obj-y += irq/
 obj-y += rcu/
 obj-y += livepatch/
 obj-y += dma/
+obj-y += entry/
 
 obj-$(CONFIG_CHECKPOINT_RESTORE) += kcmp.o
 obj-$(CONFIG_FREEZER) += freezer.o
--- /dev/null
+++ b/kernel/entry/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_GENERIC_ENTRY) += common.o
--- /dev/null
+++ b/kernel/entry/common.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/context_tracking.h>
+#include <linux/entry-common.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/syscalls.h>
+
+/**
+ * enter_from_user_mode - Establish state when coming from user mode
+ *
+ * Syscall/interrupt entry disables interrupts, but user mode is traced as
+ * interrupts enabled. Also with NO_HZ_FULL RCU might be idle.
+ *
+ * 1) Tell lockdep that interrupts are disabled
+ * 2) Invoke context tracking if enabled to reactivate RCU
+ * 3) Trace interrupts off state
+ */
+static __always_inline void enter_from_user_mode(struct pt_regs *regs)
+{
+	arch_check_user_regs(regs);
+	lockdep_hardirqs_off(CALLER_ADDR0);
+
+	CT_WARN_ON(ct_state() != CONTEXT_USER);
+	user_exit_irqoff();
+
+	instrumentation_begin();
+	trace_hardirqs_off_finish();
+	instrumentation_end();
+}
+
+static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
+{
+	if (unlikely(audit_context())) {
+		unsigned long args[6];
+
+		syscall_get_arguments(current, regs, args);
+		audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]);
+	}
+}
+
+static long syscall_trace_enter(struct pt_regs *regs, long syscall,
+				unsigned long ti_work)
+{
+	long ret = 0;
+
+	/* Handle ptrace */
+	if (ti_work & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU)) {
+		ret = arch_syscall_enter_tracehook(regs);
+		if (ret || (ti_work & _TIF_SYSCALL_EMU))
+			return -1L;
+	}
+
+	/* Do seccomp after ptrace, to catch any tracer changes. */
+	if (ti_work & _TIF_SECCOMP) {
+		ret = __secure_computing(NULL);
+		if (ret == -1L)
+			return ret;
+	}
+
+	if (unlikely(ti_work & _TIF_SYSCALL_TRACEPOINT))
+		trace_sys_enter(regs, syscall);
+
+	syscall_enter_audit(regs, syscall);
+
+	return ret ? : syscall;
+}
+
+noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
+{
+	unsigned long ti_work;
+
+	enter_from_user_mode(regs);
+	instrumentation_begin();
+
+	local_irq_enable();
+	ti_work = READ_ONCE(current_thread_info()->flags);
+	if (ti_work & SYSCALL_ENTER_WORK)
+		syscall = syscall_trace_enter(regs, syscall, ti_work);
+	instrumentation_end();
+
+	return syscall;
+}
+
+noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
+{
+	enter_from_user_mode(regs);
+}

Re: [patch V4 02/15] entry: Provide generic syscall entry functionality

[Kees Cook]

On Tue, Jul 21, 2020 at 12:57:08PM +0200, Thomas Gleixner wrote:
> On syscall entry certain work needs to be done:
> 
>    - Establish state (lockdep, context tracking, tracing)
>    - Conditional work (ptrace, seccomp, audit...)
> 
> This code is needlessly duplicated and  different in all
> architectures.
> 
> Provide a generic version based on the x86 implementation which has all the
> RCU and instrumentation bits right.
> 
> As interrupt/exception entry from user space needs parts of the same
> functionality, provide a function for this as well.
> 
> syscall_enter_from_user_mode() and irqentry_enter_from_user_mode() must be
> called right after the low level ASM entry. The calling code must be
> non-instrumentable. After the functions returns state is correct and the
> subsequent functions can be instrumented.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Kees Cook <keescook@chromium.org>

With one suggestion...

> [...]
> --- /dev/null
> +++ b/kernel/entry/common.c
> @@ -0,0 +1,88 @@
> [...]
> +static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
> +{
> +	if (unlikely(audit_context())) {
> +		unsigned long args[6];
> +
> +		syscall_get_arguments(current, regs, args);
> +		audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]);
> +	}
> +}

One thing I noticed while doing syscall entry timings for the kernel
stack base offset randomization was that the stack protector was being
needlessly enabled in certain paths (seccomp, audit) due to seeing a
register array being declared on the stack. As part of that series I
suggested down-grading the stack protector. Since then, Peter's changes
entirely disabled the stack protector on the entry code, which I
grudgingly accept (I'd rather have a way to mark a variable as "ignore
this for stack protector detection", but ... there isn't, so fine.)

> [...]
> --- /dev/null
> +++ b/kernel/entry/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_GENERIC_ENTRY) += common.o

But, my point is, let's avoid tripping over this again, and retain the
disabling here:

CFLAGS_common.o += -fno-stack-protector

I can add this again later, but it'd be nice if it was done here to
avoid gaining back the TIF_WORK stack protector overhead penalty (which
we're free of in v5.8 for the first time). ;)

-- 
Kees Cook

Re: [patch V4 02/15] entry: Provide generic syscall entry functionality

[Thomas Gleixner]

Kees Cook <keescook@chromium.org> writes:
> On Tue, Jul 21, 2020 at 12:57:08PM +0200, Thomas Gleixner wrote:
>> --- /dev/null
>> +++ b/kernel/entry/Makefile
>> @@ -0,0 +1,3 @@
>> +# SPDX-License-Identifier: GPL-2.0
>> +
>> +obj-$(CONFIG_GENERIC_ENTRY) += common.o
>
> But, my point is, let's avoid tripping over this again, and retain the
> disabling here:
>
> CFLAGS_common.o += -fno-stack-protector
>
> I can add this again later, but it'd be nice if it was done here to
> avoid gaining back the TIF_WORK stack protector overhead penalty (which
> we're free of in v5.8 for the first time). ;)

Duh, yes. I completely forgot about that.

Thanks for spotting it!

       tglx

Re: [patch V4 02/15] entry: Provide generic syscall entry functionality

[peterz]

On Tue, Jul 21, 2020 at 02:38:16PM -0700, Kees Cook wrote:
> One thing I noticed while doing syscall entry timings for the kernel
> stack base offset randomization was that the stack protector was being
> needlessly enabled in certain paths (seccomp, audit) due to seeing a
> register array being declared on the stack. As part of that series I
> suggested down-grading the stack protector. Since then, Peter's changes
> entirely disabled the stack protector on the entry code, which I
> grudgingly accept (I'd rather have a way to mark a variable as "ignore
> this for stack protector detection", but ... there isn't, so fine.)

I don't think I'd like to have that per variable, but a function
attribute to disable stack protector would be awesome, except our
GCC-besties forgot to create that function attribute :-(

If/when we get such a function attribute, we can add it to noinstr.

Also see this here:

  https://lkml.kernel.org/r/20200314164451.346497-1-slyfox@gentoo.org

[patch V4 03/15] entry: Provide generic syscall exit function

[Thomas Gleixner]

Like syscall entry all architectures have similar and pointlessly different
code to handle pending work before returning from a syscall to user space.

  1) One-time syscall exit work:
      - rseq syscall exit
      - audit
      - syscall tracing
      - tracehook (single stepping)

  2) Preparatory work
      - Exit to user mode loop (common TIF handling).
      - Architecture specific one time work arch_exit_to_user_mode_prepare()
      - Address limit and lockdep checks
     
  3) Final transition (lockdep, tracing, context tracking, RCU). Invokes
     arch_exit_to_user_mode() to handle e.g. speculation mitigations

Provide a generic version based on the x86 code which has all the RCU and
instrumentation protections right.

Provide a variant for interrupt return to user mode as well which shares
the above #2 and #3 work items.

After syscall_exit_to_user_mode() and irqentry_exit_to_user_mode() the
architecture code just has to return to user space. The code after
returning from these functions must not be instrumented.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
V4: Remove _TIF_NOTIFY_RESUME dummy define as it is defined by all architectures
    Remove the return value helper and use the existing regs_return_value()
---
 include/linux/entry-common.h |  189 +++++++++++++++++++++++++++++++++++++++++++
 kernel/entry/common.c        |  169 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 358 insertions(+)

--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -29,6 +29,14 @@
 # define _TIF_SYSCALL_AUDIT		(0)
 #endif
 
+#ifndef _TIF_PATCH_PENDING
+# define _TIF_PATCH_PENDING		(0)
+#endif
+
+#ifndef _TIF_UPROBE
+# define _TIF_UPROBE			(0)
+#endif
+
 /*
  * TIF flags handled in syscall_enter_from_usermode()
  */
@@ -41,6 +49,29 @@
 	 _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_EMU |			\
 	 ARCH_SYSCALL_ENTER_WORK)
 
+/*
+ * TIF flags handled in syscall_exit_to_user_mode()
+ */
+#ifndef ARCH_SYSCALL_EXIT_WORK
+# define ARCH_SYSCALL_EXIT_WORK		(0)
+#endif
+
+#define SYSCALL_EXIT_WORK						\
+	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |			\
+	 _TIF_SYSCALL_TRACEPOINT | ARCH_SYSCALL_EXIT_WORK)
+
+/*
+ * TIF flags handled in exit_to_user_mode_loop()
+ */
+#ifndef ARCH_EXIT_TO_USER_MODE_WORK
+# define ARCH_EXIT_TO_USER_MODE_WORK		(0)
+#endif
+
+#define EXIT_TO_USER_MODE_WORK						\
+	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |		\
+	 _TIF_NEED_RESCHED | _TIF_PATCH_PENDING |			\
+	 ARCH_EXIT_TO_USER_MODE_WORK)
+
 /**
  * arch_check_user_regs - Architecture specific sanity check for user mode regs
  * @regs:	Pointer to currents pt_regs
@@ -106,6 +137,149 @@ static inline __must_check int arch_sysc
 long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall);
 
 /**
+ * local_irq_enable_exit_to_user - Exit to user variant of local_irq_enable()
+ * @ti_work:	Cached TIF flags gathered with interrupts disabled
+ *
+ * Defaults to local_irq_enable(). Can be supplied by architecture specific
+ * code.
+ */
+static inline void local_irq_enable_exit_to_user(unsigned long ti_work);
+
+#ifndef local_irq_enable_exit_to_user
+static inline void local_irq_enable_exit_to_user(unsigned long ti_work)
+{
+	local_irq_enable();
+}
+#endif
+
+/**
+ * local_irq_disable_exit_to_user - Exit to user variant of local_irq_disable()
+ *
+ * Defaults to local_irq_disable(). Can be supplied by architecture specific
+ * code.
+ */
+static inline void local_irq_disable_exit_to_user(void);
+
+#ifndef local_irq_disable_exit_to_user
+static inline void local_irq_disable_exit_to_user(void)
+{
+	local_irq_disable();
+}
+#endif
+
+/**
+ * arch_exit_to_user_mode_work - Architecture specific TIF work for exit
+ *				 to user mode.
+ * @regs:	Pointer to currents pt_regs
+ * @ti_work:	Cached TIF flags gathered with interrupts disabled
+ *
+ * Invoked from exit_to_user_mode_loop() with interrupt enabled
+ *
+ * Defaults to NOOP. Can be supplied by architecture specific code.
+ */
+static inline void arch_exit_to_user_mode_work(struct pt_regs *regs,
+					       unsigned long ti_work);
+
+#ifndef arch_exit_to_user_mode_work
+static inline void arch_exit_to_user_mode_work(struct pt_regs *regs,
+					       unsigned long ti_work)
+{
+}
+#endif
+
+/**
+ * arch_exit_to_user_mode_prepare - Architecture specific preparation for
+ *				    exit to user mode.
+ * @regs:	Pointer to currents pt_regs
+ * @ti_work:	Cached TIF flags gathered with interrupts disabled
+ *
+ * Invoked from exit_to_user_mode_prepare() with interrupt disabled as the last
+ * function before return. Defaults to NOOP.
+ */
+static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
+						  unsigned long ti_work);
+
+#ifndef arch_exit_to_user_mode_prepare
+static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
+						  unsigned long ti_work)
+{
+}
+#endif
+
+/**
+ * arch_exit_to_user_mode - Architecture specific final work before
+ *			    exit to user mode.
+ *
+ * Invoked from exit_to_user_mode() with interrupt disabled as the last
+ * function before return. Defaults to NOOP.
+ *
+ * This needs to be __always_inline because it is non-instrumentable code
+ * invoked after context tracking switched to user mode.
+ *
+ * An architecture implementation must not do anything complex, no locking
+ * etc. The main purpose is for speculation mitigations.
+ */
+static __always_inline void arch_exit_to_user_mode(void);
+
+#ifndef arch_exit_to_user_mode
+static __always_inline void arch_exit_to_user_mode(void) { }
+#endif
+
+/**
+ * arch_do_signal -  Architecture specific signal delivery function
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Invoked from exit_to_user_mode_loop().
+ */
+void arch_do_signal(struct pt_regs *regs);
+
+/**
+ * arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()
+ * @regs:	Pointer to currents pt_regs
+ * @step:	Indicator for single step
+ *
+ * Defaults to tracehook_report_syscall_exit(). Can be replaced by
+ * architecture specific code.
+ *
+ * Invoked from syscall_exit_to_user_mode()
+ */
+static inline void arch_syscall_exit_tracehook(struct pt_regs *regs, bool step);
+
+#ifndef arch_syscall_exit_tracehook
+static inline void arch_syscall_exit_tracehook(struct pt_regs *regs, bool step)
+{
+	tracehook_report_syscall_exit(regs, step);
+}
+#endif
+
+/**
+ * syscall_exit_to_user_mode - Handle work before returning to user mode
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Invoked with interrupts enabled and fully valid regs. Returns with all
+ * work handled, interrupts disabled such that the caller can immediately
+ * switch to user mode. Called from architecture specific syscall and ret
+ * from fork code.
+ *
+ * The call order is:
+ *  1) One-time syscall exit work:
+ *	- rseq syscall exit
+ *      - audit
+ *	- syscall tracing
+ *	- tracehook (single stepping)
+ *
+ *  2) Preparatory work
+ *	- Exit to user mode loop (common TIF handling). Invokes
+ *	  arch_exit_to_user_mode_work() for architecture specific TIF work
+ *	- Architecture specific one time work arch_exit_to_user_mode_prepare()
+ *	- Address limit and lockdep checks
+ *
+ *  3) Final transition (lockdep, tracing, context tracking, RCU). Invokes
+ *     arch_exit_to_user_mode() to handle e.g. speculation mitigations
+ */
+void syscall_exit_to_user_mode(struct pt_regs *regs);
+
+/**
  * irqentry_enter_from_user_mode - Establish state before invoking the irq handler
  * @regs:	Pointer to currents pt_regs
  *
@@ -118,4 +292,19 @@ long syscall_enter_from_user_mode(struct
  */
 void irqentry_enter_from_user_mode(struct pt_regs *regs);
 
+/**
+ * irqentry_exit_to_user_mode - Interrupt exit work
+ * @regs:	Pointer to current's pt_regs
+ *
+ * Invoked with interrupts disbled and fully valid regs. Returns with all
+ * work handled, interrupts disabled such that the caller can immediately
+ * switch to user mode. Called from architecture specific interrupt
+ * handling code.
+ *
+ * The call order is #2 and #3 as described in syscall_exit_to_user_mode().
+ * Interrupt exit is not invoking #1 which is the syscall specific one time
+ * work.
+ */
+void irqentry_exit_to_user_mode(struct pt_regs *regs);
+
 #endif
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -2,6 +2,8 @@
 
 #include <linux/context_tracking.h>
 #include <linux/entry-common.h>
+#include <linux/livepatch.h>
+#include <linux/audit.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
@@ -82,7 +84,174 @@ noinstr long syscall_enter_from_user_mod
 	return syscall;
 }
 
+/**
+ * exit_to_user_mode - Fixup state when exiting to user mode
+ *
+ * Syscall/interupt exit enables interrupts, but the kernel state is
+ * interrupts disabled when this is invoked. Also tell RCU about it.
+ *
+ * 1) Trace interrupts on state
+ * 2) Invoke context tracking if enabled to adjust RCU state
+ * 3) Invoke architecture specific last minute exit code, e.g. speculation
+ *    mitigations, etc.
+ * 4) Tell lockdep that interrupts are enabled
+ */
+static __always_inline void exit_to_user_mode(void)
+{
+	instrumentation_begin();
+	trace_hardirqs_on_prepare();
+	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
+	instrumentation_end();
+
+	user_enter_irqoff();
+	arch_exit_to_user_mode();
+	lockdep_hardirqs_on(CALLER_ADDR0);
+}
+
+/* Workaround to allow gradual conversion of architecture code */
+void __weak arch_do_signal(struct pt_regs *regs) { }
+
+static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
+					    unsigned long ti_work)
+{
+	/*
+	 * Before returning to user space ensure that all pending work
+	 * items have been completed.
+	 */
+	while (ti_work & EXIT_TO_USER_MODE_WORK) {
+
+		local_irq_enable_exit_to_user(ti_work);
+
+		if (ti_work & _TIF_NEED_RESCHED)
+			schedule();
+
+		if (ti_work & _TIF_UPROBE)
+			uprobe_notify_resume(regs);
+
+		if (ti_work & _TIF_PATCH_PENDING)
+			klp_update_patch_state(current);
+
+		if (ti_work & _TIF_SIGPENDING)
+			arch_do_signal(regs);
+
+		if (ti_work & _TIF_NOTIFY_RESUME) {
+			clear_thread_flag(TIF_NOTIFY_RESUME);
+			tracehook_notify_resume(regs);
+			rseq_handle_notify_resume(NULL, regs);
+		}
+
+		/* Architecture specific TIF work */
+		arch_exit_to_user_mode_work(regs, ti_work);
+
+		/*
+		 * Disable interrupts and reevaluate the work flags as they
+		 * might have changed while interrupts and preemption was
+		 * enabled above.
+		 */
+		local_irq_disable_exit_to_user();
+		ti_work = READ_ONCE(current_thread_info()->flags);
+	}
+
+	/* Return the latest work state for arch_exit_to_user_mode() */
+	return ti_work;
+}
+
+static void exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+	unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
+
+	lockdep_assert_irqs_disabled();
+
+	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
+		ti_work = exit_to_user_mode_loop(regs, ti_work);
+
+	arch_exit_to_user_mode_prepare(regs, ti_work);
+
+	/* Ensure that the address limit is intact and no locks are held */
+	addr_limit_user_check();
+	lockdep_assert_irqs_disabled();
+	lockdep_sys_exit();
+}
+
+#ifndef _TIF_SINGLESTEP
+static inline bool report_single_step(unsigned long ti_work)
+{
+	return false;
+}
+#else
+/*
+ * If TIF_SYSCALL_EMU is set, then the only reason to report is when
+ * TIF_SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP).  This syscall
+ * instruction has been already reported in syscall_enter_from_usermode().
+ */
+#define SYSEMU_STEP	(_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)
+
+static inline bool report_single_step(unsigned long ti_work)
+{
+	return (ti_work & SYSEMU_STEP) == _TIF_SINGLESTEP;
+}
+#endif
+
+static void syscall_exit_work(struct pt_regs *regs, unsigned long ti_work)
+{
+	bool step;
+
+	audit_syscall_exit(regs);
+
+	if (ti_work & _TIF_SYSCALL_TRACEPOINT)
+		trace_sys_exit(regs, syscall_get_return_value(current, regs));
+
+	step = report_single_step(ti_work);
+	if (step || ti_work & _TIF_SYSCALL_TRACE)
+		arch_syscall_exit_tracehook(regs, step);
+}
+
+/*
+ * Syscall specific exit to user mode preparation. Runs with interrupts
+ * enabled.
+ */
+static void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+	u32 cached_flags = READ_ONCE(current_thread_info()->flags);
+	unsigned long nr = syscall_get_nr(current, regs);
+
+	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+
+	if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
+		if (WARN(irqs_disabled(), "syscall %lu left IRQs disabled", nr))
+			local_irq_enable();
+	}
+
+	rseq_syscall(regs);
+
+	/*
+	 * Do one-time syscall specific work. If these work items are
+	 * enabled, we want to run them exactly once per syscall exit with
+	 * interrupts enabled.
+	 */
+	if (unlikely(cached_flags & SYSCALL_EXIT_WORK))
+		syscall_exit_work(regs, cached_flags);
+}
+
+__visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
+{
+	instrumentation_begin();
+	syscall_exit_to_user_mode_prepare(regs);
+	local_irq_disable_exit_to_user();
+	exit_to_user_mode_prepare(regs);
+	instrumentation_end();
+	exit_to_user_mode();
+}
+
 noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
 {
 	enter_from_user_mode(regs);
 }
+
+noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
+{
+	instrumentation_begin();
+	exit_to_user_mode_prepare(regs);
+	instrumentation_end();
+	exit_to_user_mode();
+}

Re: [patch V4 03/15] entry: Provide generic syscall exit function

[Andy Lutomirski]

On Tue, Jul 21, 2020 at 4:08 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> Like syscall entry all architectures have similar and pointlessly different
> code to handle pending work before returning from a syscall to user space.
>
>   1) One-time syscall exit work:
>       - rseq syscall exit
>       - audit
>       - syscall tracing
>       - tracehook (single stepping)
>
>   2) Preparatory work
>       - Exit to user mode loop (common TIF handling).
>       - Architecture specific one time work arch_exit_to_user_mode_prepare()
>       - Address limit and lockdep checks
>
>   3) Final transition (lockdep, tracing, context tracking, RCU). Invokes
>      arch_exit_to_user_mode() to handle e.g. speculation mitigations
>
> Provide a generic version based on the x86 code which has all the RCU and
> instrumentation protections right.
>
> Provide a variant for interrupt return to user mode as well which shares
> the above #2 and #3 work items.

I still don't love making the syscall exit path also do the
non-syscall stuff.  Do you like my suggestion of instead having a
generic function to do the syscall complete with all the entry and
exit stuff?

The singlestep handling is a mess.  I'm not convinced that x86 does
this sensibly.  Right now, I *think* we are quite likely to not send
SIGTRAP on the way out of syscalls if TF is set, and we'll actually
execute one more user instruction before sending the signal.  One
might reasonably debate whether this is a bug, but we should probably
figure it out at some point.

That latter bit is relevant to your patch because the fix might end up
being something like this:

void do_syscall_64(...)
{
  unsigned long orig_flags;
  idtentry_enter();
  instrumentation_begin();
  generic_do_syscall(regs, regs->orig_ax, AUDIT_ARCH_X86_64);
  if (unlikely(orig_flags & regs->flags & X86_EFLAGS_TF))
    raise SIGTRAP -- pretend we got #DB.
  instrumentation_end();
  idtentry_exit(); <-- signal is delivered here
}

That logic is probably all kinds of buggy, but the point is that the
special handling probably wants to be done between the generic syscall
code and the exit code.

[patch V4 04/15] entry: Provide generic interrupt entry/exit code

[Thomas Gleixner]

From: Thomas Gleixner <tglx@linutronix.de>

Like the syscall entry/exit code interrupt/exception entry after the real
low level ASM bits should not be different accross architectures.

Provide a generic version based on the x86 code.

irqentry_enter() is called after the low level entry code and
irqentry_exit() must be invoked right before returning to the low level
code which just contains the actual return logic. The code before
irqentry_enter() and irqentry_exit() must not be instrumented. Code after
irqentry_enter() and before irqentry_exit() can be instrumented.

irqentry_enter() invokes irqentry_enter_from_user_mode() if the
interrupt/exception came from user mode. If if entered from kernel mode it
handles the kernel mode variant of establishing state for lockdep, RCU and
tracing depending on the kernel context it interrupted (idle, non-idle).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/entry-common.h |   62 ++++++++++++++++++++++
 kernel/entry/common.c        |  117 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 179 insertions(+)

--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -307,4 +307,66 @@ void irqentry_enter_from_user_mode(struc
  */
 void irqentry_exit_to_user_mode(struct pt_regs *regs);
 
+#ifndef irqentry_state
+typedef struct irqentry_state {
+	bool	exit_rcu;
+} irqentry_state_t;
+#endif
+
+/**
+ * irqentry_enter - Handle state tracking on ordinary interrupt entries
+ * @regs:	Pointer to pt_regs of interrupted context
+ *
+ * Invokes:
+ *  - lockdep irqflag state tracking as low level ASM entry disabled
+ *    interrupts.
+ *
+ *  - Context tracking if the exception hit user mode.
+ *
+ *  - The hardirq tracer to keep the state consistent as low level ASM
+ *    entry disabled interrupts.
+ *
+ * As a precondition, this requires that the entry came from user mode,
+ * idle, or a kernel context in which RCU is watching.
+ *
+ * For kernel mode entries RCU handling is done conditional. If RCU is
+ * watching then the only RCU requirement is to check whether the tick has
+ * to be restarted. If RCU is not watching then rcu_irq_enter() has to be
+ * invoked on entry and rcu_irq_exit() on exit.
+ *
+ * Avoiding the rcu_irq_enter/exit() calls is an optimization but also
+ * solves the problem of kernel mode pagefaults which can schedule, which
+ * is not possible after invoking rcu_irq_enter() without undoing it.
+ *
+ * For user mode entries irqentry_enter_from_user_mode() is invoked to
+ * establish the proper context for NOHZ_FULL. Otherwise scheduling on exit
+ * would not be possible.
+ *
+ * Returns: An opaque object that must be passed to idtentry_exit()
+ */
+irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
+
+/**
+ * irqentry_exit_cond_resched - Conditionally reschedule on return from interrupt
+ *
+ * Conditional reschedule with additional sanity checks.
+ */
+void irqentry_exit_cond_resched(void);
+
+/**
+ * irqentry_exit - Handle return from exception that used irqentry_enter()
+ * @regs:	Pointer to pt_regs (exception entry regs)
+ * @state:	Return value from matching call to irqentry_enter()
+ *
+ * Depending on the return target (kernel/user) this runs the necessary
+ * preemption and work checks if possible and reguired and returns to
+ * the caller with interrupts disabled and no further work pending.
+ *
+ * This is the last action before returning to the low level ASM code which
+ * just needs to return to the appropriate context.
+ *
+ * Counterpart to irqentry_enter().
+ */
+void noinstr irqentry_exit(struct pt_regs *regs, irqentry_state_t state);
+
 #endif
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -255,3 +255,120 @@ noinstr void irqentry_exit_to_user_mode(
 	instrumentation_end();
 	exit_to_user_mode();
 }
+
+irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs)
+{
+	irqentry_state_t ret = {
+		.exit_rcu = false,
+	};
+
+	if (user_mode(regs)) {
+		irqentry_enter_from_user_mode(regs);
+		return ret;
+	}
+
+	/*
+	 * If this entry hit the idle task invoke rcu_irq_enter() whether
+	 * RCU is watching or not.
+	 *
+	 * Interupts can nest when the first interrupt invokes softirq
+	 * processing on return which enables interrupts.
+	 *
+	 * Scheduler ticks in the idle task can mark quiescent state and
+	 * terminate a grace period, if and only if the timer interrupt is
+	 * not nested into another interrupt.
+	 *
+	 * Checking for __rcu_is_watching() here would prevent the nesting
+	 * interrupt to invoke rcu_irq_enter(). If that nested interrupt is
+	 * the tick then rcu_flavor_sched_clock_irq() would wrongfully
+	 * assume that it is the first interupt and eventually claim
+	 * quiescient state and end grace periods prematurely.
+	 *
+	 * Unconditionally invoke rcu_irq_enter() so RCU state stays
+	 * consistent.
+	 *
+	 * TINY_RCU does not support EQS, so let the compiler eliminate
+	 * this part when enabled.
+	 */
+	if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) {
+		/*
+		 * If RCU is not watching then the same careful
+		 * sequence vs. lockdep and tracing is required
+		 * as in irq_enter_from_user_mode().
+		 */
+		lockdep_hardirqs_off(CALLER_ADDR0);
+		rcu_irq_enter();
+		instrumentation_begin();
+		trace_hardirqs_off_finish();
+		instrumentation_end();
+
+		ret.exit_rcu = true;
+		return ret;
+	}
+
+	/*
+	 * If RCU is watching then RCU only wants to check whether it needs
+	 * to restart the tick in NOHZ mode. rcu_irq_enter_check_tick()
+	 * already contains a warning when RCU is not watching, so no point
+	 * in having another one here.
+	 */
+	instrumentation_begin();
+	rcu_irq_enter_check_tick();
+	/* Use the combo lockdep/tracing function */
+	trace_hardirqs_off();
+	instrumentation_end();
+
+	return ret;
+}
+
+void irqentry_exit_cond_resched(void)
+{
+	if (!preempt_count()) {
+		/* Sanity check RCU and thread stack */
+		rcu_irq_exit_check_preempt();
+		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
+			WARN_ON_ONCE(!on_thread_stack());
+		if (need_resched())
+			preempt_schedule_irq();
+	}
+}
+
+void noinstr irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
+{
+	lockdep_assert_irqs_disabled();
+
+	/* Check whether this returns to user mode */
+	if (user_mode(regs)) {
+		irqentry_exit_to_user_mode(regs);
+	} else if (!regs_irqs_disabled(regs)) {
+		/*
+		 * If RCU was not watching on entry this needs to be done
+		 * carefully and needs the same ordering of lockdep/tracing
+		 * and RCU as the return to user mode path.
+		 */
+		if (state.exit_rcu) {
+			instrumentation_begin();
+			/* Tell the tracer that IRET will enable interrupts */
+			trace_hardirqs_on_prepare();
+			lockdep_hardirqs_on_prepare(CALLER_ADDR0);
+			instrumentation_end();
+			rcu_irq_exit();
+			lockdep_hardirqs_on(CALLER_ADDR0);
+			return;
+		}
+
+		instrumentation_begin();
+		if (IS_ENABLED(CONFIG_PREEMPTION))
+			irqentry_exit_cond_resched();
+		/* Covers both tracing and lockdep */
+		trace_hardirqs_on();
+		instrumentation_end();
+	} else {
+		/*
+		 * IRQ flags state is correct already. Just tell RCU if it
+		 * was not watching on entry.
+		 */
+		if (state.exit_rcu)
+			rcu_irq_exit();
+	}
+}

Re: [patch V4 04/15] entry: Provide generic interrupt entry/exit code

[Andy Lutomirski]

On Tue, Jul 21, 2020 at 4:08 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> From: Thomas Gleixner <tglx@linutronix.de>
>
> Like the syscall entry/exit code interrupt/exception entry after the real
> low level ASM bits should not be different accross architectures.
>
> Provide a generic version based on the x86 code.

I don't like the name.  Sure, idtentry is ugly and x86-specific, but
irq gives the wrong impression.  This is an entry path suitable for
any entry that is guaranteed not to hit during entry/exit handling.
Syscalls, page faults, etc are not "irqs".

Re: [patch V4 04/15] entry: Provide generic interrupt entry/exit code

[Thomas Gleixner]

Andy Lutomirski <luto@kernel.org> writes:
> On Tue, Jul 21, 2020 at 4:08 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>>
>> From: Thomas Gleixner <tglx@linutronix.de>
>>
>> Like the syscall entry/exit code interrupt/exception entry after the real
>> low level ASM bits should not be different accross architectures.
>>
>> Provide a generic version based on the x86 code.
>
> I don't like the name.  Sure, idtentry is ugly and x86-specific, but
> irq gives the wrong impression.  This is an entry path suitable for
> any entry that is guaranteed not to hit during entry/exit handling.
> Syscalls, page faults, etc are not "irqs".

Yeah, it's exceptions and interrupts, but I did not come up with a
better name so far.

Thanks,

        tglx

[patch V4 05/15] entry: Provide infrastructure for work before exiting to guest mode

[Thomas Gleixner]

From: Thomas Gleixner <tglx@linutronix.de>

Entering a guest is similar to exiting to user space. Pending work like
handling signals, rescheduling, task work etc. needs to be handled before
that.

Provide generic infrastructure to avoid duplication of the same handling
code all over the place.

The exit to guest mode handling is different from the exit to usermode
handling, e.g. vs. rseq and live patching, so a separate function is used.

The initial list of work items handled is:

    TIF_SIGPENDING, TIF_NEED_RESCHED, TIF_NOTIFY_RESUME

Architecture specific TIF flags can be added via defines in the
architecture specific include files.

The calling convention is also different from the syscall/interrupt entry
functions as KVM invokes this from the outer vcpu_run() loop with
interrupts and preemption disabled. To prevent missing a pending work item
it invokes a check for pending TIF work from interrupt disabled code right
before exiting to guest mode. The lockdep, RCU and tracing state handling
is also done directly around the switch to and from guest mode.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V3: Reworked and simplified version adopted to recent X86 and KVM changes
    
V2: Moved KVM specific functions to kvm (Paolo)
    Added lockdep assert (Andy)
    Dropped live patching from enter guest mode work (Miroslav)
---
 include/linux/entry-kvm.h |   80 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/kvm_host.h  |    8 ++++
 kernel/entry/Makefile     |    3 +
 kernel/entry/kvm.c        |   51 +++++++++++++++++++++++++++++
 virt/kvm/Kconfig          |    3 +
 5 files changed, 144 insertions(+), 1 deletion(-)

--- /dev/null
+++ b/include/linux/entry-kvm.h
@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_ENTRYKVM_H
+#define __LINUX_ENTRYKVM_H
+
+#include <linux/entry-common.h>
+
+/* Exit to guest mode work */
+#ifdef CONFIG_KVM_EXIT_TO_GUEST_WORK
+
+#ifndef ARCH_EXIT_TO_GUEST_MODE_WORK
+# define ARCH_EXIT_TO_GUEST_MODE_WORK	(0)
+#endif
+
+#define EXIT_TO_GUEST_MODE_WORK					\
+	(_TIF_NEED_RESCHED | _TIF_SIGPENDING |			\
+	 _TIF_NOTIFY_RESUME | ARCH_EXIT_TO_GUEST_MODE_WORK)
+
+struct kvm_vcpu;
+
+/**
+ * arch_exit_to_guest_mode_work - Architecture specific exit to guest mode
+ *				  work function.
+ * @vcpu:	Pointer to current's VCPU data
+ * @ti_work:	Cached TIF flags gathered in exit_to_guest_mode()
+ *
+ * Invoked from exit_to_guest_mode_work(). Defaults to NOOP. Can be
+ * replaced by architecture specific code.
+ */
+static inline int arch_exit_to_guest_mode_work(struct kvm_vcpu *vcpu,
+					      unsigned long ti_work);
+
+#ifndef arch_exit_to_guest_mode_work
+static inline int arch_exit_to_guest_mode_work(struct kvm_vcpu *vcpu,
+					       unsigned long ti_work)
+{
+	return 0;
+}
+#endif
+
+/**
+ * exit_to_guest_mode - Check and handle pending work which needs to be
+ *			handled before returning to guest mode
+ * @vcpu:	Pointer to current's VCPU data
+ *
+ * Returns: 0 or an error code
+ */
+int exit_to_guest_mode(struct kvm_vcpu *vcpu);
+
+/**
+ * __exit_to_guest_mode_work_pending - Check if work is pending
+ *
+ * Returns: True if work pending, False otherwise.
+ *
+ * Bare variant of exit_to_guest_mode_work_pending(). Can be called from
+ * interrupt enabled code for racy quick checks with care.
+ */
+static inline bool __exit_to_guest_mode_work_pending(void)
+{
+	unsigned long ti_work = READ_ONCE(current_thread_info()->flags);
+
+	return !!(ti_work & EXIT_TO_GUEST_MODE_WORK);
+}
+
+/**
+ * exit_to_guest_mode_work_pending - Check if work is pending which needs to be
+ *				     handled before returning to guest mode
+ *
+ * Returns: True if work pending, False otherwise.
+ *
+ * Has to be invoked with interrupts disabled before the transition to
+ * guest mode.
+ */
+static inline bool exit_to_guest_mode_work_pending(void)
+{
+	lockdep_assert_irqs_disabled();
+	return __exit_to_guest_mode_work_pending();
+}
+#endif /* CONFIG_KVM_EXIT_TO_GUEST_WORK */
+
+#endif

--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1439,4 +1439,12 @@ int kvm_vm_create_worker_thread(struct k
 				uintptr_t data, const char *name,
 				struct task_struct **thread_ptr);
 
+#ifdef CONFIG_KVM_EXIT_TO_GUEST_WORK
+static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
+{
+	vcpu->run->exit_reason = KVM_EXIT_INTR;
+	vcpu->stat.signal_exits++;
+}
+#endif /* CONFIG_KVM_EXIT_TO_GUEST_WORK */
+
 #endif
--- a/kernel/entry/Makefile
+++ b/kernel/entry/Makefile
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 
-obj-$(CONFIG_GENERIC_ENTRY) += common.o
+obj-$(CONFIG_GENERIC_ENTRY) 		+= common.o
+obj-$(CONFIG_KVM_EXIT_TO_GUEST_WORK)	+= kvm.o
--- /dev/null
+++ b/kernel/entry/kvm.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/entry-kvm.h>
+#include <linux/kvm_host.h>
+
+static int exit_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
+{
+	do {
+		int ret;
+
+		if (ti_work & _TIF_SIGPENDING) {
+			kvm_handle_signal_exit(vcpu);
+			return -EINTR;
+		}
+
+		if (ti_work & _TIF_NEED_RESCHED)
+			schedule();
+
+		if (ti_work & _TIF_NOTIFY_RESUME) {
+			clear_thread_flag(TIF_NOTIFY_RESUME);
+			tracehook_notify_resume(NULL);
+		}
+
+		ret = arch_exit_to_guest_mode_work(vcpu, ti_work);
+		if (ret)
+			return ret;
+
+		ti_work = READ_ONCE(current_thread_info()->flags);
+	} while (ti_work & EXIT_TO_GUEST_MODE_WORK || need_resched());
+	return 0;
+}
+
+int exit_to_guest_mode(struct kvm_vcpu *vcpu)
+{
+	unsigned long ti_work;
+
+	/*
+	 * This is invoked from the outer guest loop with interrupts and
+	 * preemption enabled.
+	 *
+	 * KVM invokes exit_to_guest_mode_work_pending() with interrupts
+	 * disabled in the inner loop before going into guest mode. No need
+	 * to disable interrupts here.
+	 */
+	ti_work = READ_ONCE(current_thread_info()->flags);
+	if (!(ti_work & EXIT_TO_GUEST_MODE_WORK))
+		return 0;
+
+	return exit_to_guest_mode_work(vcpu, ti_work);
+}
+EXPORT_SYMBOL_GPL(exit_to_guest_mode);
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -60,3 +60,6 @@ config HAVE_KVM_VCPU_RUN_PID_CHANGE
 
 config HAVE_KVM_NO_POLL
        bool
+
+config KVM_EXIT_TO_GUEST_WORK
+       bool

[patch V4 06/15] x86/entry: Consolidate check_user_regs()

[Thomas Gleixner]

From: Thomas Gleixner <tglx@linutronix.de>

The user register sanity check is sprinkled all over the place. Move it
into enter_from_user_mode().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/entry/common.c |   24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -82,10 +82,11 @@ static noinstr void check_user_regs(stru
  * 2) Invoke context tracking if enabled to reactivate RCU
  * 3) Trace interrupts off state
  */
-static noinstr void enter_from_user_mode(void)
+static noinstr void enter_from_user_mode(struct pt_regs *regs)
 {
 	enum ctx_state state = ct_state();
 
+	check_user_regs(regs);
 	lockdep_hardirqs_off(CALLER_ADDR0);
 	user_exit_irqoff();
 
@@ -95,8 +96,9 @@ static noinstr void enter_from_user_mode
 	instrumentation_end();
 }
 #else
-static __always_inline void enter_from_user_mode(void)
+static __always_inline void enter_from_user_mode(struct pt_regs *regs)
 {
+	check_user_regs(regs);
 	lockdep_hardirqs_off(CALLER_ADDR0);
 	instrumentation_begin();
 	trace_hardirqs_off_finish();
@@ -369,9 +371,7 @@ static void __syscall_return_slowpath(st
 {
 	struct thread_info *ti;
 
-	check_user_regs(regs);
-
-	enter_from_user_mode();
+	enter_from_user_mode(regs);
 	instrumentation_begin();
 
 	local_irq_enable();
@@ -434,9 +434,7 @@ static void do_syscall_32_irqs_on(struct
 /* Handles int $0x80 */
 __visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
 {
-	check_user_regs(regs);
-
-	enter_from_user_mode();
+	enter_from_user_mode(regs);
 	instrumentation_begin();
 
 	local_irq_enable();
@@ -487,8 +485,6 @@ static bool __do_fast_syscall_32(struct
 					vdso_image_32.sym_int80_landing_pad;
 	bool success;
 
-	check_user_regs(regs);
-
 	/*
 	 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
 	 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
@@ -496,7 +492,7 @@ static bool __do_fast_syscall_32(struct
 	 */
 	regs->ip = landing_pad;
 
-	enter_from_user_mode();
+	enter_from_user_mode(regs);
 	instrumentation_begin();
 
 	local_irq_enable();
@@ -599,8 +595,7 @@ idtentry_state_t noinstr idtentry_enter(
 	};
 
 	if (user_mode(regs)) {
-		check_user_regs(regs);
-		enter_from_user_mode();
+		enter_from_user_mode(regs);
 		return ret;
 	}
 
@@ -733,8 +728,7 @@ void noinstr idtentry_exit(struct pt_reg
  */
 void noinstr idtentry_enter_user(struct pt_regs *regs)
 {
-	check_user_regs(regs);
-	enter_from_user_mode();
+	enter_from_user_mode(regs);
 }
 
 /**

Re: [patch V4 06/15] x86/entry: Consolidate check_user_regs()

[Andy Lutomirski]

On Tue, Jul 21, 2020 at 4:08 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> From: Thomas Gleixner <tglx@linutronix.de>
>
> The user register sanity check is sprinkled all over the place. Move it
> into enter_from_user_mode().
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reviewed-by: Kees Cook <keescook@chromium.org>

Acked-by: Andy Lutomirski <luto@kernel.org>

[patch V4 07/15] x86/entry: Consolidate 32/64 bit syscall entry

[Thomas Gleixner]

From: Thomas Gleixner <tglx@linutronix.de>

64bit and 32bit entry code have the same open coded syscall entry handling
after the bitwidth specific bits.

Move it to a helper function and share the code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/entry/common.c |   93 +++++++++++++++++++++---------------------------
 1 file changed, 41 insertions(+), 52 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -366,8 +366,7 @@ static void __syscall_return_slowpath(st
 	exit_to_user_mode();
 }
 
-#ifdef CONFIG_X86_64
-__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
+static noinstr long syscall_enter(struct pt_regs *regs, unsigned long nr)
 {
 	struct thread_info *ti;
 
@@ -379,6 +378,16 @@ static void __syscall_return_slowpath(st
 	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
 		nr = syscall_trace_enter(regs);
 
+	instrumentation_end();
+	return nr;
+}
+
+#ifdef CONFIG_X86_64
+__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
+{
+	nr = syscall_enter(regs, nr);
+
+	instrumentation_begin();
 	if (likely(nr < NR_syscalls)) {
 		nr = array_index_nospec(nr, NR_syscalls);
 		regs->ax = sys_call_table[nr](regs);
@@ -390,64 +399,53 @@ static void __syscall_return_slowpath(st
 		regs->ax = x32_sys_call_table[nr](regs);
 #endif
 	}
-	__syscall_return_slowpath(regs);
-
 	instrumentation_end();
-	exit_to_user_mode();
+	syscall_return_slowpath(regs);
 }
 #endif
 
 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
+static __always_inline unsigned int syscall_32_enter(struct pt_regs *regs)
+{
+	if (IS_ENABLED(CONFIG_IA32_EMULATION))
+		current_thread_info()->status |= TS_COMPAT;
+	/*
+	 * Subtlety here: if ptrace pokes something larger than 2^32-1 into
+	 * orig_ax, the unsigned int return value truncates it.  This may
+	 * or may not be necessary, but it matches the old asm behavior.
+	 */
+	return syscall_enter(regs, (unsigned int)regs->orig_ax);
+}
+
 /*
- * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
- * all entry and exit work and returns with IRQs off.  This function is
- * extremely hot in workloads that use it, and it's usually called from
- * do_fast_syscall_32, so forcibly inline it to improve performance.
+ * Invoke a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.
  */
-static void do_syscall_32_irqs_on(struct pt_regs *regs)
+static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs,
+						  unsigned int nr)
 {
-	struct thread_info *ti = current_thread_info();
-	unsigned int nr = (unsigned int)regs->orig_ax;
-
-#ifdef CONFIG_IA32_EMULATION
-	ti->status |= TS_COMPAT;
-#endif
-
-	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
-		/*
-		 * Subtlety here: if ptrace pokes something larger than
-		 * 2^32-1 into orig_ax, this truncates it.  This may or
-		 * may not be necessary, but it matches the old asm
-		 * behavior.
-		 */
-		nr = syscall_trace_enter(regs);
-	}
-
 	if (likely(nr < IA32_NR_syscalls)) {
+		instrumentation_begin();
 		nr = array_index_nospec(nr, IA32_NR_syscalls);
 		regs->ax = ia32_sys_call_table[nr](regs);
+		instrumentation_end();
 	}
-
-	__syscall_return_slowpath(regs);
 }
 
 /* Handles int $0x80 */
 __visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
 {
-	enter_from_user_mode(regs);
-	instrumentation_begin();
-
-	local_irq_enable();
-	do_syscall_32_irqs_on(regs);
+	unsigned int nr = syscall_32_enter(regs);
 
-	instrumentation_end();
-	exit_to_user_mode();
+	do_syscall_32_irqs_on(regs, nr);
+	syscall_return_slowpath(regs);
 }
 
-static bool __do_fast_syscall_32(struct pt_regs *regs)
+static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
 {
+	unsigned int nr	= syscall_32_enter(regs);
 	int res;
 
+	instrumentation_begin();
 	/* Fetch EBP from where the vDSO stashed it. */
 	if (IS_ENABLED(CONFIG_X86_64)) {
 		/*
@@ -460,17 +458,18 @@ static bool __do_fast_syscall_32(struct
 		res = get_user(*(u32 *)&regs->bp,
 		       (u32 __user __force *)(unsigned long)(u32)regs->sp);
 	}
+	instrumentation_end();
 
 	if (res) {
 		/* User code screwed up. */
 		regs->ax = -EFAULT;
-		local_irq_disable();
-		__prepare_exit_to_usermode(regs);
+		syscall_return_slowpath(regs);
 		return false;
 	}
 
 	/* Now this is just like a normal syscall. */
-	do_syscall_32_irqs_on(regs);
+	do_syscall_32_irqs_on(regs, nr);
+	syscall_return_slowpath(regs);
 	return true;
 }
 
@@ -483,7 +482,6 @@ static bool __do_fast_syscall_32(struct
 	 */
 	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
 					vdso_image_32.sym_int80_landing_pad;
-	bool success;
 
 	/*
 	 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
@@ -492,17 +490,8 @@ static bool __do_fast_syscall_32(struct
 	 */
 	regs->ip = landing_pad;
 
-	enter_from_user_mode(regs);
-	instrumentation_begin();
-
-	local_irq_enable();
-	success = __do_fast_syscall_32(regs);
-
-	instrumentation_end();
-	exit_to_user_mode();
-
-	/* If it failed, keep it simple: use IRET. */
-	if (!success)
+	/* Invoke the syscall. If it failed, keep it simple: use IRET. */
+	if (!__do_fast_syscall_32(regs))
 		return 0;
 
 #ifdef CONFIG_X86_64

[patch V4 08/15] x86/entry: Move user return notifier out of loop

[Thomas Gleixner]

Guests and user space share certain MSRs. KVM sets these MSRs to guest
values once and does not set them back to user space values on every VM
exit to spare the costly MSR operations.

User return notifiers ensure that these MSRs are set back to the correct
values before returning to user space in exit_to_usermode_loop().

There is no reason to evaluate the TIF flag indicating that user return
notifiers need to be invoked in the loop. The important point is that they
are invoked before returning to user space.

Move the invocation out of the loop into the section which does the last
preperatory steps before returning to user space. That section is not
preemptible and runs with interrupts disabled until the actual return.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V4: New patch
---
 arch/x86/entry/common.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -208,7 +208,7 @@ static long syscall_trace_enter(struct p
 
 #define EXIT_TO_USERMODE_LOOP_FLAGS				\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
-	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
+	 _TIF_NEED_RESCHED | _TIF_PATCH_PENDING)
 
 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 {
@@ -242,9 +242,6 @@ static void exit_to_usermode_loop(struct
 			rseq_handle_notify_resume(NULL, regs);
 		}
 
-		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
-			fire_user_return_notifiers();
-
 		/* Disable IRQs and retry */
 		local_irq_disable();
 
@@ -273,6 +270,9 @@ static void __prepare_exit_to_usermode(s
 	/* Reload ti->flags; we may have rescheduled above. */
 	cached_flags = READ_ONCE(ti->flags);
 
+	if (cached_flags & _TIF_USER_RETURN_NOTIFY)
+		fire_user_return_notifiers();
+
 	if (unlikely(cached_flags & _TIF_IO_BITMAP))
 		tss_update_io_bitmap();
 

[patch V4 09/15] x86/ptrace: Provide pt_regs helper for entry/exit

[Thomas Gleixner]

From: Thomas Gleixner <tglx@linutronix.de>

As a preparatory step for moving the syscall and interrupt entry/exit
handling into generic code, provide a pt_regs helper which retrieves the
interrupt state from pt_regs. This is required to check whether interrupts
are reenabled by return from interrupt/exception.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
V4: Remove the syscall nr and return value helpers as they alredy exist
---
 arch/x86/include/asm/ptrace.h |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -209,6 +209,11 @@ static inline void user_stack_pointer_se
 	regs->sp = val;
 }
 
+static __always_inline bool regs_irqs_disabled(struct pt_regs *regs)
+{
+	return !(regs->flags & X86_EFLAGS_IF);
+}
+
 /* Query offset/name of register from its name/offset */
 extern int regs_query_register_offset(const char *name);
 extern const char *regs_query_register_name(unsigned int offset);

[patch V4 10/15] x86/entry: Use generic syscall entry function

[Thomas Gleixner]

Replace the syscall entry work handling with the generic version. Provide
the necessary helper inlines to handle the real architecture specific
parts, e.g. ptrace.

Use a temporary define for idtentry_enter_user which will be cleaned up
seperately.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V4: Drop the seccomp/audit wrappers as they are not longer required (Kees)

V3: Adapt to the noinstr changes
---
 arch/x86/Kconfig                    |    1 
 arch/x86/entry/common.c             |  181 +-----------------------------------
 arch/x86/include/asm/entry-common.h |   32 ++++++
 arch/x86/include/asm/idtentry.h     |    5 
 arch/x86/include/asm/thread_info.h  |    5 
 5 files changed, 45 insertions(+), 179 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -115,6 +115,7 @@ config X86
 	select GENERIC_CPU_AUTOPROBE
 	select GENERIC_CPU_VULNERABILITIES
 	select GENERIC_EARLY_IOREMAP
+	select GENERIC_ENTRY
 	select GENERIC_FIND_FIRST_BIT
 	select GENERIC_IOMAP
 	select GENERIC_IRQ_EFFECTIVE_AFF_MASK	if SMP
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -10,13 +10,13 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
+#include <linux/entry-common.h>
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/errno.h>
 #include <linux/ptrace.h>
 #include <linux/tracehook.h>
 #include <linux/audit.h>
-#include <linux/seccomp.h>
 #include <linux/signal.h>
 #include <linux/export.h>
 #include <linux/context_tracking.h>
@@ -42,70 +42,8 @@
 #include <asm/syscall.h>
 #include <asm/irq_stack.h>
 
-#define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
 
-/* Check that the stack and regs on entry from user mode are sane. */
-static noinstr void check_user_regs(struct pt_regs *regs)
-{
-	if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
-		/*
-		 * Make sure that the entry code gave us a sensible EFLAGS
-		 * register.  Native because we want to check the actual CPU
-		 * state, not the interrupt state as imagined by Xen.
-		 */
-		unsigned long flags = native_save_fl();
-		WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF |
-				      X86_EFLAGS_NT));
-
-		/* We think we came from user mode. Make sure pt_regs agrees. */
-		WARN_ON_ONCE(!user_mode(regs));
-
-		/*
-		 * All entries from user mode (except #DF) should be on the
-		 * normal thread stack and should have user pt_regs in the
-		 * correct location.
-		 */
-		WARN_ON_ONCE(!on_thread_stack());
-		WARN_ON_ONCE(regs != task_pt_regs(current));
-	}
-}
-
-#ifdef CONFIG_CONTEXT_TRACKING
-/**
- * enter_from_user_mode - Establish state when coming from user mode
- *
- * Syscall entry disables interrupts, but user mode is traced as interrupts
- * enabled. Also with NO_HZ_FULL RCU might be idle.
- *
- * 1) Tell lockdep that interrupts are disabled
- * 2) Invoke context tracking if enabled to reactivate RCU
- * 3) Trace interrupts off state
- */
-static noinstr void enter_from_user_mode(struct pt_regs *regs)
-{
-	enum ctx_state state = ct_state();
-
-	check_user_regs(regs);
-	lockdep_hardirqs_off(CALLER_ADDR0);
-	user_exit_irqoff();
-
-	instrumentation_begin();
-	CT_WARN_ON(state != CONTEXT_USER);
-	trace_hardirqs_off_finish();
-	instrumentation_end();
-}
-#else
-static __always_inline void enter_from_user_mode(struct pt_regs *regs)
-{
-	check_user_regs(regs);
-	lockdep_hardirqs_off(CALLER_ADDR0);
-	instrumentation_begin();
-	trace_hardirqs_off_finish();
-	instrumentation_end();
-}
-#endif
-
 /**
  * exit_to_user_mode - Fixup state when exiting to user mode
  *
@@ -129,83 +67,6 @@ static __always_inline void exit_to_user
 	lockdep_hardirqs_on(CALLER_ADDR0);
 }
 
-static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
-{
-#ifdef CONFIG_X86_64
-	if (arch == AUDIT_ARCH_X86_64) {
-		audit_syscall_entry(regs->orig_ax, regs->di,
-				    regs->si, regs->dx, regs->r10);
-	} else
-#endif
-	{
-		audit_syscall_entry(regs->orig_ax, regs->bx,
-				    regs->cx, regs->dx, regs->si);
-	}
-}
-
-/*
- * Returns the syscall nr to run (which should match regs->orig_ax) or -1
- * to skip the syscall.
- */
-static long syscall_trace_enter(struct pt_regs *regs)
-{
-	u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
-
-	struct thread_info *ti = current_thread_info();
-	unsigned long ret = 0;
-	u32 work;
-
-	work = READ_ONCE(ti->flags);
-
-	if (work & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU)) {
-		ret = tracehook_report_syscall_entry(regs);
-		if (ret || (work & _TIF_SYSCALL_EMU))
-			return -1L;
-	}
-
-#ifdef CONFIG_SECCOMP
-	/*
-	 * Do seccomp after ptrace, to catch any tracer changes.
-	 */
-	if (work & _TIF_SECCOMP) {
-		struct seccomp_data sd;
-
-		sd.arch = arch;
-		sd.nr = regs->orig_ax;
-		sd.instruction_pointer = regs->ip;
-#ifdef CONFIG_X86_64
-		if (arch == AUDIT_ARCH_X86_64) {
-			sd.args[0] = regs->di;
-			sd.args[1] = regs->si;
-			sd.args[2] = regs->dx;
-			sd.args[3] = regs->r10;
-			sd.args[4] = regs->r8;
-			sd.args[5] = regs->r9;
-		} else
-#endif
-		{
-			sd.args[0] = regs->bx;
-			sd.args[1] = regs->cx;
-			sd.args[2] = regs->dx;
-			sd.args[3] = regs->si;
-			sd.args[4] = regs->di;
-			sd.args[5] = regs->bp;
-		}
-
-		ret = __secure_computing(&sd);
-		if (ret == -1)
-			return ret;
-	}
-#endif
-
-	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
-		trace_sys_enter(regs, regs->orig_ax);
-
-	do_audit_syscall_entry(regs, arch);
-
-	return ret ?: regs->orig_ax;
-}
-
 #define EXIT_TO_USERMODE_LOOP_FLAGS				\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
 	 _TIF_NEED_RESCHED | _TIF_PATCH_PENDING)
@@ -366,26 +227,10 @@ static void __syscall_return_slowpath(st
 	exit_to_user_mode();
 }
 
-static noinstr long syscall_enter(struct pt_regs *regs, unsigned long nr)
-{
-	struct thread_info *ti;
-
-	enter_from_user_mode(regs);
-	instrumentation_begin();
-
-	local_irq_enable();
-	ti = current_thread_info();
-	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
-		nr = syscall_trace_enter(regs);
-
-	instrumentation_end();
-	return nr;
-}
-
 #ifdef CONFIG_X86_64
 __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
 {
-	nr = syscall_enter(regs, nr);
+	nr = syscall_enter_from_user_mode(regs, nr);
 
 	instrumentation_begin();
 	if (likely(nr < NR_syscalls)) {
@@ -407,6 +252,8 @@ static noinstr long syscall_enter(struct
 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 static __always_inline unsigned int syscall_32_enter(struct pt_regs *regs)
 {
+	unsigned int nr = (unsigned int)regs->orig_ax;
+
 	if (IS_ENABLED(CONFIG_IA32_EMULATION))
 		current_thread_info()->status |= TS_COMPAT;
 	/*
@@ -414,7 +261,7 @@ static __always_inline unsigned int sysc
 	 * orig_ax, the unsigned int return value truncates it.  This may
 	 * or may not be necessary, but it matches the old asm behavior.
 	 */
-	return syscall_enter(regs, (unsigned int)regs->orig_ax);
+	return (unsigned int)syscall_enter_from_user_mode(regs, nr);
 }
 
 /*
@@ -568,7 +415,7 @@ SYSCALL_DEFINE0(ni_syscall)
  * solves the problem of kernel mode pagefaults which can schedule, which
  * is not possible after invoking rcu_irq_enter() without undoing it.
  *
- * For user mode entries enter_from_user_mode() must be invoked to
+ * For user mode entries irqentry_enter_from_user_mode() must be invoked to
  * establish the proper context for NOHZ_FULL. Otherwise scheduling on exit
  * would not be possible.
  *
@@ -584,7 +431,7 @@ idtentry_state_t noinstr idtentry_enter(
 	};
 
 	if (user_mode(regs)) {
-		enter_from_user_mode(regs);
+		irqentry_enter_from_user_mode(regs);
 		return ret;
 	}
 
@@ -615,7 +462,7 @@ idtentry_state_t noinstr idtentry_enter(
 		/*
 		 * If RCU is not watching then the same careful
 		 * sequence vs. lockdep and tracing is required
-		 * as in enter_from_user_mode().
+		 * as in irqentry_enter_from_user_mode().
 		 */
 		lockdep_hardirqs_off(CALLER_ADDR0);
 		rcu_irq_enter();
@@ -709,18 +556,6 @@ void noinstr idtentry_exit(struct pt_reg
 }
 
 /**
- * idtentry_enter_user - Handle state tracking on idtentry from user mode
- * @regs:	Pointer to pt_regs of interrupted context
- *
- * Invokes enter_from_user_mode() to establish the proper context for
- * NOHZ_FULL. Otherwise scheduling on exit would not be possible.
- */
-void noinstr idtentry_enter_user(struct pt_regs *regs)
-{
-	enter_from_user_mode(regs);
-}
-
-/**
  * idtentry_exit_user - Handle return from exception to user mode
  * @regs:	Pointer to pt_regs (exception entry regs)
  *
--- /dev/null
+++ b/arch/x86/include/asm/entry-common.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _ASM_X86_ENTRY_COMMON_H
+#define _ASM_X86_ENTRY_COMMON_H
+
+/* Check that the stack and regs on entry from user mode are sane. */
+static __always_inline void arch_check_user_regs(struct pt_regs *regs)
+{
+	if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
+		/*
+		 * Make sure that the entry code gave us a sensible EFLAGS
+		 * register.  Native because we want to check the actual CPU
+		 * state, not the interrupt state as imagined by Xen.
+		 */
+		unsigned long flags = native_save_fl();
+		WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF |
+				      X86_EFLAGS_NT));
+
+		/* We think we came from user mode. Make sure pt_regs agrees. */
+		WARN_ON_ONCE(!user_mode(regs));
+
+		/*
+		 * All entries from user mode (except #DF) should be on the
+		 * normal thread stack and should have user pt_regs in the
+		 * correct location.
+		 */
+		WARN_ON_ONCE(!on_thread_stack());
+		WARN_ON_ONCE(regs != task_pt_regs(current));
+	}
+}
+#define arch_check_user_regs arch_check_user_regs
+
+#endif
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -6,11 +6,14 @@
 #include <asm/trapnr.h>
 
 #ifndef __ASSEMBLY__
+#include <linux/entry-common.h>
 #include <linux/hardirq.h>
 
 #include <asm/irq_stack.h>
 
-void idtentry_enter_user(struct pt_regs *regs);
+/* Temporary define */
+#define idtentry_enter_user	irqentry_enter_from_user_mode
+
 void idtentry_exit_user(struct pt_regs *regs);
 
 typedef struct idtentry_state {
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -133,11 +133,6 @@ struct thread_info {
 #define _TIF_X32		(1 << TIF_X32)
 #define _TIF_FSCHECK		(1 << TIF_FSCHECK)
 
-/* Work to do before invoking the actual syscall. */
-#define _TIF_WORK_SYSCALL_ENTRY	\
-	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_AUDIT |	\
-	 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT)
-
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW_BASE					\
 	(_TIF_NOCPUID | _TIF_NOTSC | _TIF_BLOCKSTEP |		\

Re: [patch V4 10/15] x86/entry: Use generic syscall entry function

[Kees Cook]

On Tue, Jul 21, 2020 at 12:57:16PM +0200, Thomas Gleixner wrote:
> Replace the syscall entry work handling with the generic version. Provide
> the necessary helper inlines to handle the real architecture specific
> parts, e.g. ptrace.
> 
> Use a temporary define for idtentry_enter_user which will be cleaned up
> seperately.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: Kees Cook <keescook@chromium.org>

Though, notes and a comment below...

> +/* Check that the stack and regs on entry from user mode are sane. */
> +static __always_inline void arch_check_user_regs(struct pt_regs *regs)
> +{
> +	if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
> +		/*
> +		 * Make sure that the entry code gave us a sensible EFLAGS
> +		 * register.  Native because we want to check the actual CPU
> +		 * state, not the interrupt state as imagined by Xen.
> +		 */
> +		unsigned long flags = native_save_fl();
> +		WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF |
> +				      X86_EFLAGS_NT));

push, pop, bit test

> +
> +		/* We think we came from user mode. Make sure pt_regs agrees. */
> +		WARN_ON_ONCE(!user_mode(regs));

memory deref, bit test

> +
> +		/*
> +		 * All entries from user mode (except #DF) should be on the
> +		 * normal thread stack and should have user pt_regs in the
> +		 * correct location.
> +		 */
> +		WARN_ON_ONCE(!on_thread_stack());

per-cpu deref, subtract, test

> +		WARN_ON_ONCE(regs != task_pt_regs(current));

memory deref, test

> +	}
> +}

This doesn't look very expensive, and they certain indicate really bad
conditions. Does this need to be behind a CONFIG? (Whatever the answer,
we can probably make those changes in a later series -- some of these
also look not arch-specific...)

-- 
Kees Cook

Re: [patch V4 10/15] x86/entry: Use generic syscall entry function

[Thomas Gleixner]

Kees,

Kees Cook <keescook@chromium.org> writes:
> On Tue, Jul 21, 2020 at 12:57:16PM +0200, Thomas Gleixner wrote:
>
> This doesn't look very expensive, and they certain indicate really bad
> conditions. Does this need to be behind a CONFIG? (Whatever the answer,
> we can probably make those changes in a later series -- some of these
> also look not arch-specific...)

The most expensive part is native_save_flags(). The extra branches could
be visible in benchmarks, but its a good question whether this should be
just enabled.

I just keep it as is for now as I would need to make the flags and the
on_thread_stack() part x86 specific anyway, but yes we can revisit that
once we agreed on the general direction of this.

Thanks,

        tglx

[patch V4 11/15] x86/entry: Use generic syscall exit functionality

[Thomas Gleixner]

Replace the x86 variant with the generic version. Provide the relevant
architecture specific helper functions and defines.

Use a temporary define for idtentry_exit_user which will be cleaned up
seperately.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V4: Drop a pointless define
    Adjust to moved TIF_USER_RETURN_NOTIFY handling
    Bring back I/O bitmap handling
---
 arch/x86/entry/common.c             |  221 ------------------------------------
 arch/x86/entry/entry_32.S           |    2 
 arch/x86/entry/entry_64.S           |    2 
 arch/x86/include/asm/entry-common.h |   44 +++++++
 arch/x86/include/asm/idtentry.h     |    3 
 arch/x86/include/asm/signal.h       |    1 
 arch/x86/kernel/signal.c            |    3 
 7 files changed, 54 insertions(+), 222 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -15,15 +15,8 @@
 #include <linux/smp.h>
 #include <linux/errno.h>
 #include <linux/ptrace.h>
-#include <linux/tracehook.h>
-#include <linux/audit.h>
-#include <linux/signal.h>
 #include <linux/export.h>
-#include <linux/context_tracking.h>
-#include <linux/user-return-notifier.h>
 #include <linux/nospec.h>
-#include <linux/uprobes.h>
-#include <linux/livepatch.h>
 #include <linux/syscalls.h>
 #include <linux/uaccess.h>
 
@@ -42,191 +35,6 @@
 #include <asm/syscall.h>
 #include <asm/irq_stack.h>
 
-#include <trace/events/syscalls.h>
-
-/**
- * exit_to_user_mode - Fixup state when exiting to user mode
- *
- * Syscall exit enables interrupts, but the kernel state is interrupts
- * disabled when this is invoked. Also tell RCU about it.
- *
- * 1) Trace interrupts on state
- * 2) Invoke context tracking if enabled to adjust RCU state
- * 3) Clear CPU buffers if CPU is affected by MDS and the migitation is on.
- * 4) Tell lockdep that interrupts are enabled
- */
-static __always_inline void exit_to_user_mode(void)
-{
-	instrumentation_begin();
-	trace_hardirqs_on_prepare();
-	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
-	instrumentation_end();
-
-	user_enter_irqoff();
-	mds_user_clear_cpu_buffers();
-	lockdep_hardirqs_on(CALLER_ADDR0);
-}
-
-#define EXIT_TO_USERMODE_LOOP_FLAGS				\
-	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
-	 _TIF_NEED_RESCHED | _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 EXIT_TO_USERMODE_LOOP_FLAGS set.  Several of these flags
-	 * can be set at any time on preemptible 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.
-	 */
-	while (true) {
-		/* We have work to do. */
-		local_irq_enable();
-
-		if (cached_flags & _TIF_NEED_RESCHED)
-			schedule();
-
-		if (cached_flags & _TIF_UPROBE)
-			uprobe_notify_resume(regs);
-
-		if (cached_flags & _TIF_PATCH_PENDING)
-			klp_update_patch_state(current);
-
-		/* deal with pending signal delivery */
-		if (cached_flags & _TIF_SIGPENDING)
-			do_signal(regs);
-
-		if (cached_flags & _TIF_NOTIFY_RESUME) {
-			clear_thread_flag(TIF_NOTIFY_RESUME);
-			tracehook_notify_resume(regs);
-			rseq_handle_notify_resume(NULL, regs);
-		}
-
-		/* Disable IRQs and retry */
-		local_irq_disable();
-
-		cached_flags = READ_ONCE(current_thread_info()->flags);
-
-		if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
-			break;
-	}
-}
-
-static void __prepare_exit_to_usermode(struct pt_regs *regs)
-{
-	struct thread_info *ti = current_thread_info();
-	u32 cached_flags;
-
-	addr_limit_user_check();
-
-	lockdep_assert_irqs_disabled();
-	lockdep_sys_exit();
-
-	cached_flags = READ_ONCE(ti->flags);
-
-	if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
-		exit_to_usermode_loop(regs, cached_flags);
-
-	/* Reload ti->flags; we may have rescheduled above. */
-	cached_flags = READ_ONCE(ti->flags);
-
-	if (cached_flags & _TIF_USER_RETURN_NOTIFY)
-		fire_user_return_notifiers();
-
-	if (unlikely(cached_flags & _TIF_IO_BITMAP))
-		tss_update_io_bitmap();
-
-	fpregs_assert_state_consistent();
-	if (unlikely(cached_flags & _TIF_NEED_FPU_LOAD))
-		switch_fpu_return();
-
-#ifdef CONFIG_COMPAT
-	/*
-	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
-	 * returning to user mode.  We need to clear it *after* signal
-	 * handling, because syscall restart has a fixup for compat
-	 * syscalls.  The fixup is exercised by the ptrace_syscall_32
-	 * selftest.
-	 *
-	 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
-	 * special case only applies after poking regs and before the
-	 * very next return to user mode.
-	 */
-	ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
-#endif
-}
-
-static noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
-{
-	instrumentation_begin();
-	__prepare_exit_to_usermode(regs);
-	instrumentation_end();
-	exit_to_user_mode();
-}
-
-#define SYSCALL_EXIT_WORK_FLAGS				\
-	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |	\
-	 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
-
-static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
-{
-	bool step;
-
-	audit_syscall_exit(regs);
-
-	if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
-		trace_sys_exit(regs, regs->ax);
-
-	/*
-	 * If TIF_SYSCALL_EMU is set, we only get here because of
-	 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
-	 * We already reported this syscall instruction in
-	 * syscall_trace_enter().
-	 */
-	step = unlikely(
-		(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
-		== _TIF_SINGLESTEP);
-	if (step || cached_flags & _TIF_SYSCALL_TRACE)
-		tracehook_report_syscall_exit(regs, step);
-}
-
-static void __syscall_return_slowpath(struct pt_regs *regs)
-{
-	struct thread_info *ti = current_thread_info();
-	u32 cached_flags = READ_ONCE(ti->flags);
-
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
-
-	if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
-	    WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
-		local_irq_enable();
-
-	rseq_syscall(regs);
-
-	/*
-	 * First do one-time work.  If these work items are enabled, we
-	 * want to run them exactly once per syscall exit with IRQs on.
-	 */
-	if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
-		syscall_slow_exit_work(regs, cached_flags);
-
-	local_irq_disable();
-	__prepare_exit_to_usermode(regs);
-}
-
-/*
- * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
- * state such that we can immediately switch to user mode.
- */
-__visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
-{
-	instrumentation_begin();
-	__syscall_return_slowpath(regs);
-	instrumentation_end();
-	exit_to_user_mode();
-}
-
 #ifdef CONFIG_X86_64
 __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
 {
@@ -245,7 +53,7 @@ static void __syscall_return_slowpath(st
 #endif
 	}
 	instrumentation_end();
-	syscall_return_slowpath(regs);
+	syscall_exit_to_user_mode(regs);
 }
 #endif
 
@@ -284,7 +92,7 @@ static __always_inline void do_syscall_3
 	unsigned int nr = syscall_32_enter(regs);
 
 	do_syscall_32_irqs_on(regs, nr);
-	syscall_return_slowpath(regs);
+	syscall_exit_to_user_mode(regs);
 }
 
 static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
@@ -310,13 +118,13 @@ static noinstr bool __do_fast_syscall_32
 	if (res) {
 		/* User code screwed up. */
 		regs->ax = -EFAULT;
-		syscall_return_slowpath(regs);
+		syscall_exit_to_user_mode(regs);
 		return false;
 	}
 
 	/* Now this is just like a normal syscall. */
 	do_syscall_32_irqs_on(regs, nr);
-	syscall_return_slowpath(regs);
+	syscall_exit_to_user_mode(regs);
 	return true;
 }
 
@@ -524,7 +332,7 @@ void noinstr idtentry_exit(struct pt_reg
 
 	/* Check whether this returns to user mode */
 	if (user_mode(regs)) {
-		prepare_exit_to_usermode(regs);
+		irqentry_exit_to_user_mode(regs);
 	} else if (regs->flags & X86_EFLAGS_IF) {
 		/*
 		 * If RCU was not watching on entry this needs to be done
@@ -555,25 +363,6 @@ void noinstr idtentry_exit(struct pt_reg
 	}
 }
 
-/**
- * idtentry_exit_user - Handle return from exception to user mode
- * @regs:	Pointer to pt_regs (exception entry regs)
- *
- * Runs the necessary preemption and work checks and returns to the caller
- * with interrupts disabled and no further work pending.
- *
- * This is the last action before returning to the low level ASM code which
- * just needs to return to the appropriate context.
- *
- * Counterpart to idtentry_enter_user().
- */
-void noinstr idtentry_exit_user(struct pt_regs *regs)
-{
-	lockdep_assert_irqs_disabled();
-
-	prepare_exit_to_usermode(regs);
-}
-
 #ifdef CONFIG_XEN_PV
 #ifndef CONFIG_PREEMPTION
 /*
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -846,7 +846,7 @@ SYM_CODE_START(ret_from_fork)
 2:
 	/* When we fork, we trace the syscall return in the child, too. */
 	movl    %esp, %eax
-	call    syscall_return_slowpath
+	call    syscall_exit_to_user_mode
 	jmp     .Lsyscall_32_done
 
 	/* kernel thread */
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -283,7 +283,7 @@ SYM_CODE_START(ret_from_fork)
 2:
 	UNWIND_HINT_REGS
 	movq	%rsp, %rdi
-	call	syscall_return_slowpath	/* returns with IRQs disabled */
+	call	syscall_exit_to_user_mode	/* returns with IRQs disabled */
 	jmp	swapgs_restore_regs_and_return_to_usermode
 
 1:
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -2,6 +2,12 @@
 #ifndef _ASM_X86_ENTRY_COMMON_H
 #define _ASM_X86_ENTRY_COMMON_H
 
+#include <linux/user-return-notifier.h>
+
+#include <asm/nospec-branch.h>
+#include <asm/io_bitmap.h>
+#include <asm/fpu/api.h>
+
 /* Check that the stack and regs on entry from user mode are sane. */
 static __always_inline void arch_check_user_regs(struct pt_regs *regs)
 {
@@ -29,4 +35,42 @@ static __always_inline void arch_check_u
 }
 #define arch_check_user_regs arch_check_user_regs
 
+#define ARCH_SYSCALL_EXIT_WORK		(_TIF_SINGLESTEP)
+
+static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
+						  unsigned long ti_work)
+{
+	if (ti_work & _TIF_USER_RETURN_NOTIFY)
+		fire_user_return_notifiers();
+
+	if (unlikely(ti_work & _TIF_IO_BITMAP))
+		tss_update_io_bitmap();
+
+	fpregs_assert_state_consistent();
+	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
+		switch_fpu_return();
+
+#ifdef CONFIG_COMPAT
+	/*
+	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
+	 * returning to user mode.  We need to clear it *after* signal
+	 * handling, because syscall restart has a fixup for compat
+	 * syscalls.  The fixup is exercised by the ptrace_syscall_32
+	 * selftest.
+	 *
+	 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
+	 * special case only applies after poking regs and before the
+	 * very next return to user mode.
+	 */
+	current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED);
+#endif
+}
+#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
+
+static __always_inline void arch_exit_to_user_mode(void)
+{
+	mds_user_clear_cpu_buffers();
+}
+#define arch_exit_to_user_mode arch_exit_to_user_mode
+
 #endif
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -13,8 +13,7 @@
 
 /* Temporary define */
 #define idtentry_enter_user	irqentry_enter_from_user_mode
-
-void idtentry_exit_user(struct pt_regs *regs);
+#define idtentry_exit_user	irqentry_exit_to_user_mode
 
 typedef struct idtentry_state {
 	bool exit_rcu;
--- a/arch/x86/include/asm/signal.h
+++ b/arch/x86/include/asm/signal.h
@@ -35,7 +35,6 @@ typedef sigset_t compat_sigset_t;
 #endif /* __ASSEMBLY__ */
 #include <uapi/asm/signal.h>
 #ifndef __ASSEMBLY__
-extern void do_signal(struct pt_regs *regs);
 
 #define __ARCH_HAS_SA_RESTORER
 
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -25,6 +25,7 @@
 #include <linux/user-return-notifier.h>
 #include <linux/uprobes.h>
 #include <linux/context_tracking.h>
+#include <linux/entry-common.h>
 #include <linux/syscalls.h>
 
 #include <asm/processor.h>
@@ -803,7 +804,7 @@ static inline unsigned long get_nr_resta
  * want to handle. Thus you cannot kill init even with a SIGKILL even by
  * mistake.
  */
-void do_signal(struct pt_regs *regs)
+void arch_do_signal(struct pt_regs *regs)
 {
 	struct ksignal ksig;
 

Re: [patch V4 11/15] x86/entry: Use generic syscall exit functionality

[Kees Cook]

On Tue, Jul 21, 2020 at 12:57:17PM +0200, Thomas Gleixner wrote:
> Replace the x86 variant with the generic version. Provide the relevant
> architecture specific helper functions and defines.
> 
> Use a temporary define for idtentry_exit_user which will be cleaned up
> seperately.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[patch V4 12/15] x86/entry: Cleanup idtentry_entry/exit_user

[Thomas Gleixner]

Cleanup the temporary defines and use irqentry_ instead of idtentry_.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/idtentry.h |    4 ----
 arch/x86/kernel/cpu/mce/core.c  |    4 ++--
 arch/x86/kernel/traps.c         |   18 +++++++++---------
 3 files changed, 11 insertions(+), 15 deletions(-)

--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -11,10 +11,6 @@
 
 #include <asm/irq_stack.h>
 
-/* Temporary define */
-#define idtentry_enter_user	irqentry_enter_from_user_mode
-#define idtentry_exit_user	irqentry_exit_to_user_mode
-
 typedef struct idtentry_state {
 	bool exit_rcu;
 } idtentry_state_t;
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1927,11 +1927,11 @@ static __always_inline void exc_machine_
 
 static __always_inline void exc_machine_check_user(struct pt_regs *regs)
 {
-	idtentry_enter_user(regs);
+	irqentry_enter_from_user_mode(regs);
 	instrumentation_begin();
 	machine_check_vector(regs);
 	instrumentation_end();
-	idtentry_exit_user(regs);
+	irqentry_exit_to_user_mode(regs);
 }
 
 #ifdef CONFIG_X86_64
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -638,18 +638,18 @@ DEFINE_IDTENTRY_RAW(exc_int3)
 		return;
 
 	/*
-	 * idtentry_enter_user() uses static_branch_{,un}likely() and therefore
-	 * can trigger INT3, hence poke_int3_handler() must be done
-	 * before. If the entry came from kernel mode, then use nmi_enter()
-	 * because the INT3 could have been hit in any context including
-	 * NMI.
+	 * irqentry_enter_from_user_mode() uses static_branch_{,un}likely()
+	 * and therefore can trigger INT3, hence poke_int3_handler() must
+	 * be done before. If the entry came from kernel mode, then use
+	 * nmi_enter() because the INT3 could have been hit in any context
+	 * including NMI.
 	 */
 	if (user_mode(regs)) {
-		idtentry_enter_user(regs);
+		irqentry_enter_from_user_mode(regs);
 		instrumentation_begin();
 		do_int3_user(regs);
 		instrumentation_end();
-		idtentry_exit_user(regs);
+		irqentry_exit_to_user_mode(regs);
 	} else {
 		nmi_enter();
 		instrumentation_begin();
@@ -901,12 +901,12 @@ static __always_inline void exc_debug_us
 	 */
 	WARN_ON_ONCE(!user_mode(regs));
 
-	idtentry_enter_user(regs);
+	irqentry_enter_from_user_mode(regs);
 	instrumentation_begin();
 
 	handle_debug(regs, dr6, true);
 	instrumentation_end();
-	idtentry_exit_user(regs);
+	irqentry_exit_to_user_mode(regs);
 }
 
 #ifdef CONFIG_X86_64

Re: [patch V4 12/15] x86/entry: Cleanup idtentry_entry/exit_user

[Kees Cook]

On Tue, Jul 21, 2020 at 12:57:18PM +0200, Thomas Gleixner wrote:
> Cleanup the temporary defines and use irqentry_ instead of idtentry_.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[patch V4 13/15] x86/entry: Use generic interrupt entry/exit code

[Thomas Gleixner]

Replace the x86 code with the generic variant. Use temporary defines for
idtentry_* which will be cleaned up in the next step.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/entry/common.c         |  167 ----------------------------------------
 arch/x86/include/asm/idtentry.h |   10 --
 2 files changed, 5 insertions(+), 172 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -198,171 +198,6 @@ SYSCALL_DEFINE0(ni_syscall)
 	return -ENOSYS;
 }
 
-/**
- * idtentry_enter - Handle state tracking on ordinary idtentries
- * @regs:	Pointer to pt_regs of interrupted context
- *
- * Invokes:
- *  - lockdep irqflag state tracking as low level ASM entry disabled
- *    interrupts.
- *
- *  - Context tracking if the exception hit user mode.
- *
- *  - The hardirq tracer to keep the state consistent as low level ASM
- *    entry disabled interrupts.
- *
- * As a precondition, this requires that the entry came from user mode,
- * idle, or a kernel context in which RCU is watching.
- *
- * For kernel mode entries RCU handling is done conditional. If RCU is
- * watching then the only RCU requirement is to check whether the tick has
- * to be restarted. If RCU is not watching then rcu_irq_enter() has to be
- * invoked on entry and rcu_irq_exit() on exit.
- *
- * Avoiding the rcu_irq_enter/exit() calls is an optimization but also
- * solves the problem of kernel mode pagefaults which can schedule, which
- * is not possible after invoking rcu_irq_enter() without undoing it.
- *
- * For user mode entries irqentry_enter_from_user_mode() must be invoked to
- * establish the proper context for NOHZ_FULL. Otherwise scheduling on exit
- * would not be possible.
- *
- * Returns: An opaque object that must be passed to idtentry_exit()
- *
- * The return value must be fed into the state argument of
- * idtentry_exit().
- */
-idtentry_state_t noinstr idtentry_enter(struct pt_regs *regs)
-{
-	idtentry_state_t ret = {
-		.exit_rcu = false,
-	};
-
-	if (user_mode(regs)) {
-		irqentry_enter_from_user_mode(regs);
-		return ret;
-	}
-
-	/*
-	 * If this entry hit the idle task invoke rcu_irq_enter() whether
-	 * RCU is watching or not.
-	 *
-	 * Interupts can nest when the first interrupt invokes softirq
-	 * processing on return which enables interrupts.
-	 *
-	 * Scheduler ticks in the idle task can mark quiescent state and
-	 * terminate a grace period, if and only if the timer interrupt is
-	 * not nested into another interrupt.
-	 *
-	 * Checking for __rcu_is_watching() here would prevent the nesting
-	 * interrupt to invoke rcu_irq_enter(). If that nested interrupt is
-	 * the tick then rcu_flavor_sched_clock_irq() would wrongfully
-	 * assume that it is the first interupt and eventually claim
-	 * quiescient state and end grace periods prematurely.
-	 *
-	 * Unconditionally invoke rcu_irq_enter() so RCU state stays
-	 * consistent.
-	 *
-	 * TINY_RCU does not support EQS, so let the compiler eliminate
-	 * this part when enabled.
-	 */
-	if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) {
-		/*
-		 * If RCU is not watching then the same careful
-		 * sequence vs. lockdep and tracing is required
-		 * as in irqentry_enter_from_user_mode().
-		 */
-		lockdep_hardirqs_off(CALLER_ADDR0);
-		rcu_irq_enter();
-		instrumentation_begin();
-		trace_hardirqs_off_finish();
-		instrumentation_end();
-
-		ret.exit_rcu = true;
-		return ret;
-	}
-
-	/*
-	 * If RCU is watching then RCU only wants to check whether it needs
-	 * to restart the tick in NOHZ mode. rcu_irq_enter_check_tick()
-	 * already contains a warning when RCU is not watching, so no point
-	 * in having another one here.
-	 */
-	instrumentation_begin();
-	rcu_irq_enter_check_tick();
-	/* Use the combo lockdep/tracing function */
-	trace_hardirqs_off();
-	instrumentation_end();
-
-	return ret;
-}
-
-static void idtentry_exit_cond_resched(struct pt_regs *regs, bool may_sched)
-{
-	if (may_sched && !preempt_count()) {
-		/* Sanity check RCU and thread stack */
-		rcu_irq_exit_check_preempt();
-		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
-			WARN_ON_ONCE(!on_thread_stack());
-		if (need_resched())
-			preempt_schedule_irq();
-	}
-	/* Covers both tracing and lockdep */
-	trace_hardirqs_on();
-}
-
-/**
- * idtentry_exit - Handle return from exception that used idtentry_enter()
- * @regs:	Pointer to pt_regs (exception entry regs)
- * @state:	Return value from matching call to idtentry_enter()
- *
- * Depending on the return target (kernel/user) this runs the necessary
- * preemption and work checks if possible and reguired and returns to
- * the caller with interrupts disabled and no further work pending.
- *
- * This is the last action before returning to the low level ASM code which
- * just needs to return to the appropriate context.
- *
- * Counterpart to idtentry_enter(). The return value of the entry
- * function must be fed into the @state argument.
- */
-void noinstr idtentry_exit(struct pt_regs *regs, idtentry_state_t state)
-{
-	lockdep_assert_irqs_disabled();
-
-	/* Check whether this returns to user mode */
-	if (user_mode(regs)) {
-		irqentry_exit_to_user_mode(regs);
-	} else if (regs->flags & X86_EFLAGS_IF) {
-		/*
-		 * If RCU was not watching on entry this needs to be done
-		 * carefully and needs the same ordering of lockdep/tracing
-		 * and RCU as the return to user mode path.
-		 */
-		if (state.exit_rcu) {
-			instrumentation_begin();
-			/* Tell the tracer that IRET will enable interrupts */
-			trace_hardirqs_on_prepare();
-			lockdep_hardirqs_on_prepare(CALLER_ADDR0);
-			instrumentation_end();
-			rcu_irq_exit();
-			lockdep_hardirqs_on(CALLER_ADDR0);
-			return;
-		}
-
-		instrumentation_begin();
-		idtentry_exit_cond_resched(regs, IS_ENABLED(CONFIG_PREEMPTION));
-		instrumentation_end();
-	} else {
-		/*
-		 * IRQ flags state is correct already. Just tell RCU if it
-		 * was not watching on entry.
-		 */
-		if (state.exit_rcu)
-			rcu_irq_exit();
-	}
-}
-
 #ifdef CONFIG_XEN_PV
 #ifndef CONFIG_PREEMPTION
 /*
@@ -427,7 +262,7 @@ static void __xen_pv_evtchn_do_upcall(vo
 	inhcall = get_and_clear_inhcall();
 	if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
 		instrumentation_begin();
-		idtentry_exit_cond_resched(regs, true);
+		irqentry_exit_cond_resched();
 		instrumentation_end();
 		restore_inhcall(inhcall);
 	} else {
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -11,12 +11,10 @@
 
 #include <asm/irq_stack.h>
 
-typedef struct idtentry_state {
-	bool exit_rcu;
-} idtentry_state_t;
-
-idtentry_state_t idtentry_enter(struct pt_regs *regs);
-void idtentry_exit(struct pt_regs *regs, idtentry_state_t state);
+/* Temporary defines */
+typedef irqentry_state_t idtentry_state_t;
+#define idtentry_enter irqentry_enter
+#define idtentry_exit irqentry_exit
 
 /**
  * DECLARE_IDTENTRY - Declare functions for simple IDT entry points

[patch V4 14/15] x86/entry: Cleanup idtentry_enter/exit

[Thomas Gleixner]

Remove the temporary defines and fixup all references.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/entry/common.c         |    6 +++---
 arch/x86/include/asm/idtentry.h |   33 ++++++++++++++-------------------
 arch/x86/kernel/kvm.c           |    6 +++---
 arch/x86/kernel/traps.c         |    6 +++---
 arch/x86/mm/fault.c             |    6 +++---
 5 files changed, 26 insertions(+), 31 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -248,9 +248,9 @@ static void __xen_pv_evtchn_do_upcall(vo
 {
 	struct pt_regs *old_regs;
 	bool inhcall;
-	idtentry_state_t state;
+	irqentry_state_t state;
 
-	state = idtentry_enter(regs);
+	state = irqentry_enter(regs);
 	old_regs = set_irq_regs(regs);
 
 	instrumentation_begin();
@@ -266,7 +266,7 @@ static void __xen_pv_evtchn_do_upcall(vo
 		instrumentation_end();
 		restore_inhcall(inhcall);
 	} else {
-		idtentry_exit(regs, state);
+		irqentry_exit(regs, state);
 	}
 }
 #endif /* CONFIG_XEN_PV */
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -11,11 +11,6 @@
 
 #include <asm/irq_stack.h>
 
-/* Temporary defines */
-typedef irqentry_state_t idtentry_state_t;
-#define idtentry_enter irqentry_enter
-#define idtentry_exit irqentry_exit
-
 /**
  * DECLARE_IDTENTRY - Declare functions for simple IDT entry points
  *		      No error code pushed by hardware
@@ -45,8 +40,8 @@ typedef irqentry_state_t idtentry_state_
  * The macro is written so it acts as function definition. Append the
  * body with a pair of curly brackets.
  *
- * idtentry_enter() contains common code which has to be invoked before
- * arbitrary code in the body. idtentry_exit() contains common code
+ * irqentry_enter() contains common code which has to be invoked before
+ * arbitrary code in the body. irqentry_exit() contains common code
  * which has to run before returning to the low level assembly code.
  */
 #define DEFINE_IDTENTRY(func)						\
@@ -54,12 +49,12 @@ static __always_inline void __##func(str
 									\
 __visible noinstr void func(struct pt_regs *regs)			\
 {									\
-	idtentry_state_t state = idtentry_enter(regs);			\
+	irqentry_state_t state = irqentry_enter(regs);			\
 									\
 	instrumentation_begin();					\
 	__##func (regs);						\
 	instrumentation_end();						\
-	idtentry_exit(regs, state);					\
+	irqentry_exit(regs, state);					\
 }									\
 									\
 static __always_inline void __##func(struct pt_regs *regs)
@@ -101,12 +96,12 @@ static __always_inline void __##func(str
 __visible noinstr void func(struct pt_regs *regs,			\
 			    unsigned long error_code)			\
 {									\
-	idtentry_state_t state = idtentry_enter(regs);			\
+	irqentry_state_t state = irqentry_enter(regs);			\
 									\
 	instrumentation_begin();					\
 	__##func (regs, error_code);					\
 	instrumentation_end();						\
-	idtentry_exit(regs, state);					\
+	irqentry_exit(regs, state);					\
 }									\
 									\
 static __always_inline void __##func(struct pt_regs *regs,		\
@@ -161,7 +156,7 @@ static __always_inline void __##func(str
  * body with a pair of curly brackets.
  *
  * Contrary to DEFINE_IDTENTRY_ERRORCODE() this does not invoke the
- * idtentry_enter/exit() helpers before and after the body invocation. This
+ * irqentry_enter/exit() helpers before and after the body invocation. This
  * needs to be done in the body itself if applicable. Use if extra work
  * is required before the enter/exit() helpers are invoked.
  */
@@ -197,7 +192,7 @@ static __always_inline void __##func(str
 __visible noinstr void func(struct pt_regs *regs,			\
 			    unsigned long error_code)			\
 {									\
-	idtentry_state_t state = idtentry_enter(regs);			\
+	irqentry_state_t state = irqentry_enter(regs);			\
 									\
 	instrumentation_begin();					\
 	irq_enter_rcu();						\
@@ -205,7 +200,7 @@ static __always_inline void __##func(str
 	__##func (regs, (u8)error_code);				\
 	irq_exit_rcu();							\
 	instrumentation_end();						\
-	idtentry_exit(regs, state);					\
+	irqentry_exit(regs, state);					\
 }									\
 									\
 static __always_inline void __##func(struct pt_regs *regs, u8 vector)
@@ -229,7 +224,7 @@ static __always_inline void __##func(str
  * DEFINE_IDTENTRY_SYSVEC - Emit code for system vector IDT entry points
  * @func:	Function name of the entry point
  *
- * idtentry_enter/exit() and irq_enter/exit_rcu() are invoked before the
+ * irqentry_enter/exit() and irq_enter/exit_rcu() are invoked before the
  * function body. KVM L1D flush request is set.
  *
  * Runs the function on the interrupt stack if the entry hit kernel mode
@@ -239,7 +234,7 @@ static void __##func(struct pt_regs *reg
 									\
 __visible noinstr void func(struct pt_regs *regs)			\
 {									\
-	idtentry_state_t state = idtentry_enter(regs);			\
+	irqentry_state_t state = irqentry_enter(regs);			\
 									\
 	instrumentation_begin();					\
 	irq_enter_rcu();						\
@@ -247,7 +242,7 @@ static void __##func(struct pt_regs *reg
 	run_on_irqstack_cond(__##func, regs, regs);			\
 	irq_exit_rcu();							\
 	instrumentation_end();						\
-	idtentry_exit(regs, state);					\
+	irqentry_exit(regs, state);					\
 }									\
 									\
 static noinline void __##func(struct pt_regs *regs)
@@ -268,7 +263,7 @@ static __always_inline void __##func(str
 									\
 __visible noinstr void func(struct pt_regs *regs)			\
 {									\
-	idtentry_state_t state = idtentry_enter(regs);			\
+	irqentry_state_t state = irqentry_enter(regs);			\
 									\
 	instrumentation_begin();					\
 	__irq_enter_raw();						\
@@ -276,7 +271,7 @@ static __always_inline void __##func(str
 	__##func (regs);						\
 	__irq_exit_raw();						\
 	instrumentation_end();						\
-	idtentry_exit(regs, state);					\
+	irqentry_exit(regs, state);					\
 }									\
 									\
 static __always_inline void __##func(struct pt_regs *regs)
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -233,7 +233,7 @@ EXPORT_SYMBOL_GPL(kvm_read_and_reset_apf
 noinstr bool __kvm_handle_async_pf(struct pt_regs *regs, u32 token)
 {
 	u32 reason = kvm_read_and_reset_apf_flags();
-	idtentry_state_t state;
+	irqentry_state_t state;
 
 	switch (reason) {
 	case KVM_PV_REASON_PAGE_NOT_PRESENT:
@@ -243,7 +243,7 @@ noinstr bool __kvm_handle_async_pf(struc
 		return false;
 	}
 
-	state = idtentry_enter(regs);
+	state = irqentry_enter(regs);
 	instrumentation_begin();
 
 	/*
@@ -264,7 +264,7 @@ noinstr bool __kvm_handle_async_pf(struc
 	}
 
 	instrumentation_end();
-	idtentry_exit(regs, state);
+	irqentry_exit(regs, state);
 	return true;
 }
 
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -245,7 +245,7 @@ static noinstr bool handle_bug(struct pt
 
 DEFINE_IDTENTRY_RAW(exc_invalid_op)
 {
-	idtentry_state_t state;
+	irqentry_state_t state;
 
 	/*
 	 * We use UD2 as a short encoding for 'CALL __WARN', as such
@@ -255,11 +255,11 @@ DEFINE_IDTENTRY_RAW(exc_invalid_op)
 	if (!user_mode(regs) && handle_bug(regs))
 		return;
 
-	state = idtentry_enter(regs);
+	state = irqentry_enter(regs);
 	instrumentation_begin();
 	handle_invalid_op(regs);
 	instrumentation_end();
-	idtentry_exit(regs, state);
+	irqentry_exit(regs, state);
 }
 
 DEFINE_IDTENTRY(exc_coproc_segment_overrun)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1377,7 +1377,7 @@ handle_page_fault(struct pt_regs *regs,
 DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
 {
 	unsigned long address = read_cr2();
-	idtentry_state_t state;
+	irqentry_state_t state;
 
 	prefetchw(&current->mm->mmap_lock);
 
@@ -1412,11 +1412,11 @@ DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_f
 	 * code reenabled RCU to avoid subsequent wreckage which helps
 	 * debugability.
 	 */
-	state = idtentry_enter(regs);
+	state = irqentry_enter(regs);
 
 	instrumentation_begin();
 	handle_page_fault(regs, error_code, address);
 	instrumentation_end();
 
-	idtentry_exit(regs, state);
+	irqentry_exit(regs, state);
 }

Re: [patch V4 14/15] x86/entry: Cleanup idtentry_enter/exit

[Kees Cook]

On Tue, Jul 21, 2020 at 12:57:20PM +0200, Thomas Gleixner wrote:
> Remove the temporary defines and fixup all references.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[patch V4 15/15] x86/kvm: Use generic exit to guest work function

[Thomas Gleixner]

Use the generic infrastructure to check for and handle pending work before
entering into guest mode.

This now handles TIF_NOTIFY_RESUME as well which was ignored so
far. Handling it is important as this covers task work and task work will
be used to offload the heavy lifting of POSIX CPU timers to thread context.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kvm/Kconfig   |    1 +
 arch/x86/kvm/vmx/vmx.c |   11 +++++------
 arch/x86/kvm/x86.c     |   15 ++++++---------
 3 files changed, 12 insertions(+), 15 deletions(-)

--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -42,6 +42,7 @@ config KVM
 	select HAVE_KVM_MSI
 	select HAVE_KVM_CPU_RELAX_INTERCEPT
 	select HAVE_KVM_NO_POLL
+	select KVM_EXIT_TO_GUEST_WORK
 	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
 	select KVM_VFIO
 	select SRCU
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -27,6 +27,7 @@
 #include <linux/slab.h>
 #include <linux/tboot.h>
 #include <linux/trace_events.h>
+#include <linux/entry-kvm.h>
 
 #include <asm/apic.h>
 #include <asm/asm.h>
@@ -5376,14 +5377,12 @@ static int handle_invalid_guest_state(st
 		}
 
 		/*
-		 * Note, return 1 and not 0, vcpu_run() is responsible for
-		 * morphing the pending signal into the proper return code.
+		 * Note, return 1 and not 0, vcpu_run() will invoke
+		 * exit_to_guest_mode() which will create a proper return
+		 * code.
 		 */
-		if (signal_pending(current))
+		if (__exit_to_guest_mode_work_pending())
 			return 1;
-
-		if (need_resched())
-			schedule();
 	}
 
 	return 1;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -56,6 +56,7 @@
 #include <linux/sched/stat.h>
 #include <linux/sched/isolation.h>
 #include <linux/mem_encrypt.h>
+#include <linux/entry-kvm.h>
 
 #include <trace/events/kvm.h>
 
@@ -1585,7 +1586,7 @@ EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
 bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu)
 {
 	return vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu) ||
-		need_resched() || signal_pending(current);
+		exit_to_guest_mode_work_pending();
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_exit_request);
 
@@ -8676,15 +8677,11 @@ static int vcpu_run(struct kvm_vcpu *vcp
 			break;
 		}
 
-		if (signal_pending(current)) {
-			r = -EINTR;
-			vcpu->run->exit_reason = KVM_EXIT_INTR;
-			++vcpu->stat.signal_exits;
-			break;
-		}
-		if (need_resched()) {
+		if (exit_to_guest_mode_work_pending()) {
 			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
-			cond_resched();
+			r = exit_to_guest_mode(vcpu);
+			if (r)
+				return r;
 			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
 		}
 	}

Re: [patch V4 15/15] x86/kvm: Use generic exit to guest work function

[Sean Christopherson]

On Tue, Jul 21, 2020 at 12:57:21PM +0200, Thomas Gleixner wrote:
> Use the generic infrastructure to check for and handle pending work before
> entering into guest mode.
> 
> This now handles TIF_NOTIFY_RESUME as well which was ignored so
> far. Handling it is important as this covers task work and task work will
> be used to offload the heavy lifting of POSIX CPU timers to thread context.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/kvm/Kconfig   |    1 +
>  arch/x86/kvm/vmx/vmx.c |   11 +++++------
>  arch/x86/kvm/x86.c     |   15 ++++++---------
>  3 files changed, 12 insertions(+), 15 deletions(-)
> 
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -42,6 +42,7 @@ config KVM
>  	select HAVE_KVM_MSI
>  	select HAVE_KVM_CPU_RELAX_INTERCEPT
>  	select HAVE_KVM_NO_POLL
> +	select KVM_EXIT_TO_GUEST_WORK
>  	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
>  	select KVM_VFIO
>  	select SRCU
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -27,6 +27,7 @@
>  #include <linux/slab.h>
>  #include <linux/tboot.h>
>  #include <linux/trace_events.h>
> +#include <linux/entry-kvm.h>
>  
>  #include <asm/apic.h>
>  #include <asm/asm.h>
> @@ -5376,14 +5377,12 @@ static int handle_invalid_guest_state(st
>  		}
>  
>  		/*
> -		 * Note, return 1 and not 0, vcpu_run() is responsible for
> -		 * morphing the pending signal into the proper return code.
> +		 * Note, return 1 and not 0, vcpu_run() will invoke
> +		 * exit_to_guest_mode() which will create a proper return
> +		 * code.
>  		 */
> -		if (signal_pending(current))
> +		if (__exit_to_guest_mode_work_pending())

I whined about this back in v2[*].  "exit to guest mode" is confusing becuase
virt terminology is "enter to guest" and "exit from guest", whereas the
kernel's terminology here is "exit from kernel to guest".

My past and current self still like XFER_TO_GUEST as the base terminology.

[*] https://lkml.kernel.org/r/20191023144848.GH329@linux.intel.com

>  			return 1;
> -
> -		if (need_resched())
> -			schedule();
>  	}
>  
>  	return 1;
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -56,6 +56,7 @@
>  #include <linux/sched/stat.h>
>  #include <linux/sched/isolation.h>
>  #include <linux/mem_encrypt.h>
> +#include <linux/entry-kvm.h>
>  
>  #include <trace/events/kvm.h>
>  
> @@ -1585,7 +1586,7 @@ EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
>  bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu)
>  {
>  	return vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu) ||
> -		need_resched() || signal_pending(current);
> +		exit_to_guest_mode_work_pending();
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_exit_request);
>  
> @@ -8676,15 +8677,11 @@ static int vcpu_run(struct kvm_vcpu *vcp
>  			break;
>  		}
>  
> -		if (signal_pending(current)) {
> -			r = -EINTR;
> -			vcpu->run->exit_reason = KVM_EXIT_INTR;
> -			++vcpu->stat.signal_exits;
> -			break;
> -		}
> -		if (need_resched()) {
> +		if (exit_to_guest_mode_work_pending()) {
>  			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
> -			cond_resched();
> +			r = exit_to_guest_mode(vcpu);
> +			if (r)

This loses the stat.signal_exits accounting.  Maybe this?

			if (r) {
				if (r == -EINTR)
					++vcpu->stat.signal_exits;
				return r;
			}

> +				return r;
>  			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
>  		}
>  	}
> 

Re: [patch V4 15/15] x86/kvm: Use generic exit to guest work function

[Thomas Gleixner]

Sean Christopherson <sean.j.christopherson@intel.com> writes:
> On Tue, Jul 21, 2020 at 12:57:21PM +0200, Thomas Gleixner wrote:
>> -		if (signal_pending(current))
>> +		if (__exit_to_guest_mode_work_pending())
>
> I whined about this back in v2[*].  "exit to guest mode" is confusing becuase
> virt terminology is "enter to guest" and "exit from guest", whereas the
> kernel's terminology here is "exit from kernel to guest".
>
> My past and current self still like XFER_TO_GUEST as the base terminology.
>
> [*] https://lkml.kernel.org/r/20191023144848.GH329@linux.intel.com

Forgot about that, sorry. Will fix.

>> @@ -8676,15 +8677,11 @@ static int vcpu_run(struct kvm_vcpu *vcp
>>  			break;
>>  		}
>>  
>> -		if (signal_pending(current)) {
>> -			r = -EINTR;
>> -			vcpu->run->exit_reason = KVM_EXIT_INTR;
>> -			++vcpu->stat.signal_exits;
>> -			break;
>> -		}
>> -		if (need_resched()) {
>> +		if (exit_to_guest_mode_work_pending()) {
>>  			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
>> -			cond_resched();
>> +			r = exit_to_guest_mode(vcpu);
>> +			if (r)
>
> This loses the stat.signal_exits accounting.  Maybe this?

No, it does not:

+		if (ti_work & _TIF_SIGPENDING) {
+			kvm_handle_signal_exit(vcpu);
+			return -EINTR;
+		}

and

+#ifdef CONFIG_KVM_EXIT_TO_GUEST_WORK
+static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
+{
+	vcpu->run->exit_reason = KVM_EXIT_INTR;
+	vcpu->stat.signal_exits++;
+}
+#endif /* CONFIG_KVM_EXIT_TO_GUEST_WORK */

in patch 5/15

Thanks,

        tglx