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>
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
@@ -198,20 +198,46 @@
#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)
{
switch (size) {
@@ -248,8 +274,22 @@
* 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) \
({ \