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Groups > linux.kernel > #1245678 > unrolled thread

[PATCH v2 0/2] Silence KASAN warnings in get_wchan()

Started byAndrey Ryabinin <aryabinin@virtuozzo.com>
First post2015-10-13 14:50 +0200
Last post2015-10-20 11:50 +0200
Articles 7 on this page of 47 — 9 participants

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  [PATCH v2 0/2] Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-13 14:50 +0200
    [PATCH v3 0/2] Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-13 17:30 +0200
      [PATCH v3 1/2] Provide READ_ONCE_NOCHECK() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-13 17:40 +0200
        [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK  () tip-bot for Andrey Ryabinin <tipbot@zytor.com> - 2015-10-14 17:40 +0200
          Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-14 17:50 +0200
            Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Dmitry Vyukov <dvyukov@google.com> - 2015-10-14 18:00 +0200
              Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Dmitry Vyukov <dvyukov@google.com> - 2015-10-14 18:10 +0200
                Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () Peter Zijlstra <peterz@infradead.org> - 2015-10-14 18:20 +0200
                  Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Dmitry Vyukov <dvyukov@google.com> - 2015-10-14 18:20 +0200
                    Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Andy Lutomirski <luto@amacapital.net> - 2015-10-14 18:30 +0200
                      Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () Peter Zijlstra <peterz@infradead.org> - 2015-10-14 18:40 +0200
                        Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () Ingo Molnar <mingo@kernel.org> - 2015-10-14 19:50 +0200
                          Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Andy Lutomirski <luto@amacapital.net> - 2015-10-14 20:00 +0200
                    Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () Peter Zijlstra <peterz@infradead.org> - 2015-10-14 18:30 +0200
                      Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Dmitry Vyukov <dvyukov@google.com> - 2015-10-14 18:40 +0200
                        Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () Peter Zijlstra <peterz@infradead.org> - 2015-10-14 19:00 +0200
                Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-14 18:30 +0200
                  Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Dmitry Vyukov <dvyukov@google.com> - 2015-10-14 18:40 +0200
                    Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-14 19:10 +0200
                      Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Dmitry Vyukov <dvyukov@google.com> - 2015-10-14 19:30 +0200
                        Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-14 19:40 +0200
              Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-14 18:10 +0200
              Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK  () Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-14 18:20 +0200
                Re: [tip:locking/urgent] compiler, atomics: Provide READ_ONCE_NOCHECK () Dmitry Vyukov <dvyukov@google.com> - 2015-10-14 18:40 +0200
                  Re: [tip:locking/urgent] compiler, atomics: Provide  READ_ONCE_NOCHECK () "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-14 19:10 +0200
        linux-next: build problems (Was: [PATCH v3 1/2] Provide  READ_ONCE_NOCHECK()) Stephen Rothwell <sfr@canb.auug.org.au> - 2015-10-15 11:20 +0200
          Re: linux-next: build problems (Was: [PATCH v3 1/2] Provide  READ_ONCE_NOCHECK()) Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-15 12:10 +0200
          [PATCH] compiler, READ_ONCE: Fix build failure with some older GCC Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-15 12:30 +0200
            Re: [PATCH] compiler, READ_ONCE: Fix build failure with some older  GCC Ingo Molnar <mingo@kernel.org> - 2015-10-15 13:40 +0200
      [PATCH v3 2/2] x86/process: Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-13 17:40 +0200
        [tip:locking/urgent] x86/mm: Silence KASAN warnings in get_wchan(  ) tip-bot for Andrey Ryabinin <tipbot@zytor.com> - 2015-10-14 17:40 +0200
    [PATCH v4 2/2] x86/mm: Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-16 11:50 +0200
    [PATCH v4 0/2] Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-16 11:50 +0200
      [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-16 11:50 +0200
        Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() Peter Zijlstra <peterz@infradead.org> - 2015-10-16 12:10 +0200
          Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-16 13:00 +0200
            Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() Peter Zijlstra <peterz@infradead.org> - 2015-10-16 13:10 +0200
        Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() Borislav Petkov <bp@alien8.de> - 2015-10-16 12:40 +0200
          Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-16 14:00 +0200
            Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() Ingo Molnar <mingo@kernel.org> - 2015-10-18 09:30 +0200
          Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-16 18:10 +0200
      [PATCH v4 0/2] Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-16 11:50 +0200
    [PATCH v5 2/2] x86/mm: Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-19 10:40 +0200
      [tip:x86/urgent] x86/mm, kasan:   Silence KASAN warnings in get_wchan() tip-bot for Andrey Ryabinin <tipbot@zytor.com> - 2015-10-20 11:50 +0200
    [PATCH v5 0/2] Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-19 10:40 +0200
      [PATCH v5 1/2] compiler, atomics: Provide READ_ONCE_NOCHECK() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-19 10:40 +0200
        [tip:x86/urgent] compiler, atomics, kasan:   Provide READ_ONCE_NOCHECK() tip-bot for Andrey Ryabinin <tipbot@zytor.com> - 2015-10-20 11:50 +0200

Page 3 of 3 — ← Prev page 1 2 [3]

#1248943 — Re: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN()

From"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date2015-10-16 18:10 +0200
SubjectRe: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN()
Message-ID<qkfJV-2V2-27@gated-at.bofh.it>
In reply to#1248570
On Fri, Oct 16, 2015 at 12:33:38PM +0200, Borislav Petkov wrote:
> On Fri, Oct 16, 2015 at 12:44:53PM +0300, Andrey Ryabinin wrote:
> > Some code may perform racy by design memory reads. This could be
> > harmless, yet such code may produce KASAN warnings.
> > 
> > To hide such accesses from KASAN this patch introduces
> > READ_ONCE_NOKSAN() macro. KASAN will not check the memory
> > accessed by READ_ONCE_NOKSAN(). The KernelThreadSanitizer (KTSAN)
> > is going to ignore it as well.
> 
> Frankly, the "NOKSAN" suffix is too specific. I know, I know, I'm
> bikeshedding but what happens if yet another tool wants to be disabled
> from checking there and that tool is not *SAN? We rename again?

Plaid, I say!!!  The color of the bikeshed must be plaid!!!  ;-)

							Thanx, Paul

> So the "NOCHECK" suffix made much more sense, even if it was generic.
> IMNSVHO.
> 
> Thanks.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> ECO tip #101: Trim your mails when you reply.
> 

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#1248533 — [PATCH v4 0/2] Silence KASAN warnings in get_wchan()

FromAndrey Ryabinin <aryabinin@virtuozzo.com>
Date2015-10-16 11:50 +0200
Subject[PATCH v4 0/2] Silence KASAN warnings in get_wchan()
Message-ID<qk9Ob-2oP-21@gated-at.bofh.it>
In reply to#1248527
On 10/16/2015 12:44 PM, Andrey Ryabinin wrote:
> Changes since v3:
>  - Fixed build failure.
>  - Rename: s/READ_ONCE_NOCHECK/READ_ONCE_NOKSAN
>  - Spelling fix.
> 
> Changes since v2:
>  - Added some code comments in the first patch.
> 
> Andrey Ryabinin (2):
>   compiler, atomics: Provide READ_ONCE_NOKSAN()
>   x86/mm: Silence KASAN warnings in get_wchan()
> 
>  arch/x86/kernel/process.c    |  6 ++--
>  include/linux/compiler-gcc.h | 13 +++++++++
>  include/linux/compiler.h     | 66 +++++++++++++++++++++++++++++++++++---------
>  3 files changed, 69 insertions(+), 16 deletions(-)
> 
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#1250452 — [PATCH v5 2/2] x86/mm: Silence KASAN warnings in get_wchan()

FromAndrey Ryabinin <aryabinin@virtuozzo.com>
Date2015-10-19 10:40 +0200
Subject[PATCH v5 2/2] x86/mm: Silence KASAN warnings in get_wchan()
Message-ID<qle93-7rs-11@gated-at.bofh.it>
In reply to#1245678
get_wchan() is racy by design, it may access volatile stack
of running task, thus it may access redzone in a stack frame
and cause KASAN to warn about this.

Use READ_ONCE_NOCHECK() to silence these warnings.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
---
 arch/x86/kernel/process.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 39e585a..e28db18 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -550,14 +550,14 @@ unsigned long get_wchan(struct task_struct *p)
 	if (sp < bottom || sp > top)
 		return 0;
 
-	fp = READ_ONCE(*(unsigned long *)sp);
+	fp = READ_ONCE_NOCHECK(*(unsigned long *)sp);
 	do {
 		if (fp < bottom || fp > top)
 			return 0;
-		ip = READ_ONCE(*(unsigned long *)(fp + sizeof(unsigned long)));
+		ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
 		if (!in_sched_functions(ip))
 			return ip;
-		fp = READ_ONCE(*(unsigned long *)fp);
+		fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
 	} while (count++ < 16 && p->state != TASK_RUNNING);
 	return 0;
 }
-- 
2.4.9

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#1251542 — [tip:x86/urgent] x86/mm, kasan: Silence KASAN warnings in get_wchan()

Fromtip-bot for Andrey Ryabinin <tipbot@zytor.com>
Date2015-10-20 11:50 +0200
Subject[tip:x86/urgent] x86/mm, kasan: Silence KASAN warnings in get_wchan()
Message-ID<qlBIn-8jI-29@gated-at.bofh.it>
In reply to#1250452
Commit-ID:  f7d27c35ddff7c100d7a98db499ac0040149ac05
Gitweb:     http://git.kernel.org/tip/f7d27c35ddff7c100d7a98db499ac0040149ac05
Author:     Andrey Ryabinin <aryabinin@virtuozzo.com>
AuthorDate: Mon, 19 Oct 2015 11:37:18 +0300
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Oct 2015 11:04:19 +0200

x86/mm, kasan: Silence KASAN warnings in get_wchan()

get_wchan() is racy by design, it may access volatile stack
of running task, thus it may access redzone in a stack frame
and cause KASAN to warn about this.

Use READ_ONCE_NOCHECK() to silence these warnings.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
Cc: kasan-dev <kasan-dev@googlegroups.com>
Link: http://lkml.kernel.org/r/1445243838-17763-3-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/process.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 39e585a..e28db18 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -550,14 +550,14 @@ unsigned long get_wchan(struct task_struct *p)
 	if (sp < bottom || sp > top)
 		return 0;
 
-	fp = READ_ONCE(*(unsigned long *)sp);
+	fp = READ_ONCE_NOCHECK(*(unsigned long *)sp);
 	do {
 		if (fp < bottom || fp > top)
 			return 0;
-		ip = READ_ONCE(*(unsigned long *)(fp + sizeof(unsigned long)));
+		ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
 		if (!in_sched_functions(ip))
 			return ip;
-		fp = READ_ONCE(*(unsigned long *)fp);
+		fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
 	} while (count++ < 16 && p->state != TASK_RUNNING);
 	return 0;
 }
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#1250454 — [PATCH v5 0/2] Silence KASAN warnings in get_wchan()

FromAndrey Ryabinin <aryabinin@virtuozzo.com>
Date2015-10-19 10:40 +0200
Subject[PATCH v5 0/2] Silence KASAN warnings in get_wchan()
Message-ID<qle93-7rs-13@gated-at.bofh.it>
In reply to#1245678
Changes since v4:
 - Rename back to READ_ONCE_NOCHECK().

Changes since v3:
 - Fixed build failure.
 - Rename: s/READ_ONCE_NOCHECK/READ_ONCE_NOKSAN
 - Spelling fix.

Changes since v2:
 - Added some code comments in the first patch.

Andrey Ryabinin (2):
  compiler, atomics: Provide READ_ONCE_NOCHECK()
  x86/mm: Silence KASAN warnings in get_wchan()

 arch/x86/kernel/process.c    |  6 ++--
 include/linux/compiler-gcc.h | 13 +++++++++
 include/linux/compiler.h     | 66 +++++++++++++++++++++++++++++++++++---------
 3 files changed, 69 insertions(+), 16 deletions(-)

-- 
2.4.9

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#1250455 — [PATCH v5 1/2] compiler, atomics: Provide READ_ONCE_NOCHECK()

FromAndrey Ryabinin <aryabinin@virtuozzo.com>
Date2015-10-19 10:40 +0200
Subject[PATCH v5 1/2] compiler, atomics: Provide READ_ONCE_NOCHECK()
Message-ID<qle94-7rs-19@gated-at.bofh.it>
In reply to#1250454
Some code may perform racy by design memory reads. This could be
harmless, yet such code may produce KASAN warnings.

To hide such accesses from KASAN this patch introduces
READ_ONCE_NOCHECK() macro. KASAN will not check the memory
accessed by READ_ONCE_NOCHECK(). The KernelThreadSanitizer (KTSAN)
is going to ignore it as well.

This patch creates __read_once_size_nocheck() a clone of
__read_once_size(). The only difference between them is
'no_sanitized_address' attribute appended to '*_nocheck' function.
This attribute tells the compiler that instrumentation of memory
accesses should not be applied to that function. We declare it as
static '__maybe_unsed' because GCC is not capable to inline such
function: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368

With KASAN=n READ_ONCE_NOCHECK() is just a clone of READ_ONCE().

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 include/linux/compiler-gcc.h | 13 +++++++++
 include/linux/compiler.h     | 66 +++++++++++++++++++++++++++++++++++---------
 2 files changed, 66 insertions(+), 13 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index dfaa7b3..8efb40e 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -237,12 +237,25 @@
 #define KASAN_ABI_VERSION 3
 #endif
 
+#if GCC_VERSION >= 40902
+/*
+ * Tell the compiler that address safety instrumentation (KASAN)
+ * should not be applied to that function.
+ * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ */
+#define __no_sanitize_address __attribute__((no_sanitize_address))
+#endif
+
 #endif	/* gcc version >= 40000 specific checks */
 
 #if !defined(__noclone)
 #define __noclone	/* not needed */
 #endif
 
+#if !defined(__no_sanitize_address)
+#define __no_sanitize_address
+#endif
+
 /*
  * A trick to suppress uninitialized variable warning without generating any
  * code
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index c836eb2..3d78103 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -198,19 +198,45 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
 
 #include <uapi/linux/types.h>
 
-static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
+#define __READ_ONCE_SIZE						\
+({									\
+	switch (size) {							\
+	case 1: *(__u8 *)res = *(volatile __u8 *)p; break;		\
+	case 2: *(__u16 *)res = *(volatile __u16 *)p; break;		\
+	case 4: *(__u32 *)res = *(volatile __u32 *)p; break;		\
+	case 8: *(__u64 *)res = *(volatile __u64 *)p; break;		\
+	default:							\
+		barrier();						\
+		__builtin_memcpy((void *)res, (const void *)p, size);	\
+		barrier();						\
+	}								\
+})
+
+static __always_inline
+void __read_once_size(const volatile void *p, void *res, int size)
 {
-	switch (size) {
-	case 1: *(__u8 *)res = *(volatile __u8 *)p; break;
-	case 2: *(__u16 *)res = *(volatile __u16 *)p; break;
-	case 4: *(__u32 *)res = *(volatile __u32 *)p; break;
-	case 8: *(__u64 *)res = *(volatile __u64 *)p; break;
-	default:
-		barrier();
-		__builtin_memcpy((void *)res, (const void *)p, size);
-		barrier();
-	}
+	__READ_ONCE_SIZE;
+}
+
+#ifdef CONFIG_KASAN
+/*
+ * This function is not 'inline' because __no_sanitize_address confilcts
+ * with inlining. Attempt to inline it may cause a build failure.
+ * 	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
+ */
+static __no_sanitize_address __maybe_unused
+void __read_once_size_nocheck(const volatile void *p, void *res, int size)
+{
+	__READ_ONCE_SIZE;
+}
+#else
+static __always_inline
+void __read_once_size_nocheck(const volatile void *p, void *res, int size)
+{
+	__READ_ONCE_SIZE;
 }
+#endif
 
 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
 {
@@ -248,8 +274,22 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  * required ordering.
  */
 
-#define READ_ONCE(x) \
-	({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
+#define __READ_ONCE(x, check)						\
+({									\
+	union { typeof(x) __val; char __c[1]; } __u;			\
+	if (check)							\
+		__read_once_size(&(x), __u.__c, sizeof(x));		\
+	else								\
+		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
+	__u.__val;							\
+})
+#define READ_ONCE(x) __READ_ONCE(x, 1)
+
+/*
+ * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
+ * to hide memory access from KASAN.
+ */
+#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
 
 #define WRITE_ONCE(x, val) \
 ({							\
-- 
2.4.9

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#1251545 — [tip:x86/urgent] compiler, atomics, kasan: Provide READ_ONCE_NOCHECK()

Fromtip-bot for Andrey Ryabinin <tipbot@zytor.com>
Date2015-10-20 11:50 +0200
Subject[tip:x86/urgent] compiler, atomics, kasan: Provide READ_ONCE_NOCHECK()
Message-ID<qlBIn-8jI-37@gated-at.bofh.it>
In reply to#1250455
Commit-ID:  d976441f44bc5d48635d081d277aa76556ffbf8b
Gitweb:     http://git.kernel.org/tip/d976441f44bc5d48635d081d277aa76556ffbf8b
Author:     Andrey Ryabinin <aryabinin@virtuozzo.com>
AuthorDate: Mon, 19 Oct 2015 11:37:17 +0300
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Oct 2015 11:04:19 +0200

compiler, atomics, kasan: Provide READ_ONCE_NOCHECK()

Some code may perform racy by design memory reads. This could be
harmless, yet such code may produce KASAN warnings.

To hide such accesses from KASAN this patch introduces
READ_ONCE_NOCHECK() macro. KASAN will not check the memory
accessed by READ_ONCE_NOCHECK(). The KernelThreadSanitizer
(KTSAN) is going to ignore it as well.

This patch creates __read_once_size_nocheck() a clone of
__read_once_size(). The only difference between them is
'no_sanitized_address' attribute appended to '*_nocheck'
function. This attribute tells the compiler that instrumentation
of memory accesses should not be applied to that function. We
declare it as static '__maybe_unsed' because GCC is not capable
to inline such function:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368

With KASAN=n READ_ONCE_NOCHECK() is just a clone of READ_ONCE().

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
Cc: kasan-dev <kasan-dev@googlegroups.com>
Link: http://lkml.kernel.org/r/1445243838-17763-2-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/compiler-gcc.h | 13 +++++++++
 include/linux/compiler.h     | 66 +++++++++++++++++++++++++++++++++++---------
 2 files changed, 66 insertions(+), 13 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index dfaa7b3..8efb40e 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -237,12 +237,25 @@
 #define KASAN_ABI_VERSION 3
 #endif
 
+#if GCC_VERSION >= 40902
+/*
+ * Tell the compiler that address safety instrumentation (KASAN)
+ * should not be applied to that function.
+ * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ */
+#define __no_sanitize_address __attribute__((no_sanitize_address))
+#endif
+
 #endif	/* gcc version >= 40000 specific checks */
 
 #if !defined(__noclone)
 #define __noclone	/* not needed */
 #endif
 
+#if !defined(__no_sanitize_address)
+#define __no_sanitize_address
+#endif
+
 /*
  * A trick to suppress uninitialized variable warning without generating any
  * code
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index c836eb2..3d78103 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -198,19 +198,45 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
 
 #include <uapi/linux/types.h>
 
-static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
+#define __READ_ONCE_SIZE						\
+({									\
+	switch (size) {							\
+	case 1: *(__u8 *)res = *(volatile __u8 *)p; break;		\
+	case 2: *(__u16 *)res = *(volatile __u16 *)p; break;		\
+	case 4: *(__u32 *)res = *(volatile __u32 *)p; break;		\
+	case 8: *(__u64 *)res = *(volatile __u64 *)p; break;		\
+	default:							\
+		barrier();						\
+		__builtin_memcpy((void *)res, (const void *)p, size);	\
+		barrier();						\
+	}								\
+})
+
+static __always_inline
+void __read_once_size(const volatile void *p, void *res, int size)
 {
-	switch (size) {
-	case 1: *(__u8 *)res = *(volatile __u8 *)p; break;
-	case 2: *(__u16 *)res = *(volatile __u16 *)p; break;
-	case 4: *(__u32 *)res = *(volatile __u32 *)p; break;
-	case 8: *(__u64 *)res = *(volatile __u64 *)p; break;
-	default:
-		barrier();
-		__builtin_memcpy((void *)res, (const void *)p, size);
-		barrier();
-	}
+	__READ_ONCE_SIZE;
+}
+
+#ifdef CONFIG_KASAN
+/*
+ * This function is not 'inline' because __no_sanitize_address confilcts
+ * with inlining. Attempt to inline it may cause a build failure.
+ * 	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
+ * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
+ */
+static __no_sanitize_address __maybe_unused
+void __read_once_size_nocheck(const volatile void *p, void *res, int size)
+{
+	__READ_ONCE_SIZE;
+}
+#else
+static __always_inline
+void __read_once_size_nocheck(const volatile void *p, void *res, int size)
+{
+	__READ_ONCE_SIZE;
 }
+#endif
 
 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
 {
@@ -248,8 +274,22 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  * required ordering.
  */
 
-#define READ_ONCE(x) \
-	({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
+#define __READ_ONCE(x, check)						\
+({									\
+	union { typeof(x) __val; char __c[1]; } __u;			\
+	if (check)							\
+		__read_once_size(&(x), __u.__c, sizeof(x));		\
+	else								\
+		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
+	__u.__val;							\
+})
+#define READ_ONCE(x) __READ_ONCE(x, 1)
+
+/*
+ * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
+ * to hide memory access from KASAN.
+ */
+#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
 
 #define WRITE_ONCE(x, val) \
 ({							\
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