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Date: Fri, 16 Oct 2015 12:44:53 +0300
From: Andrey Ryabinin <aryabinin@...tuozzo.com>
To: <linux-kernel@...r.kernel.org>
CC: Andrey Ryabinin <aryabinin@...tuozzo.com>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...capital.net>,
Andrey Konovalov <andreyknvl@...gle.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
kasan-dev <kasan-dev@...glegroups.com>,
Borislav Petkov <bp@...en8.de>,
Denys Vlasenko <dvlasenk@...hat.com>,
Andi Kleen <ak@...ux.intel.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
Wolfram Gloger <wmglo@...t.med.uni-muenchen.de>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v4 1/2] compiler, atomics: Provide READ_ONCE_NOKSAN()
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.
This patch creates __read_once_size_noksan() a clone of
__read_once_size(). The only difference between them is
'no_sanitized_address' attribute appended to '*_nokasan' 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_NOKSAN() is just a clone of READ_ONCE().
Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.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..dfa172f7 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_noksan(const volatile void *p, void *res, int size)
+{
+ __READ_ONCE_SIZE;
+}
+#else
+static __always_inline
+void __read_once_size_noksan(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, noksan) \
+({ \
+ union { typeof(x) __val; char __c[1]; } __u; \
+ if (noksan) \
+ __read_once_size_noksan(&(x), __u.__c, sizeof(x)); \
+ else \
+ __read_once_size(&(x), __u.__c, sizeof(x)); \
+ __u.__val; \
+})
+#define READ_ONCE(x) __READ_ONCE(x, 0)
+
+/*
+ * Use READ_ONCE_NOKSAN() instead of READ_ONCE() if you need
+ * to hide memory access from KASAN.
+ */
+#define READ_ONCE_NOKSAN(x) __READ_ONCE(x, 1)
#define WRITE_ONCE(x, val) \
({ \
--
2.4.9
--
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