compiler.h: Add read_word_at_a_time() function.

[ Upstream commit 7f1e541 ] Sometimes we know that it's safe to do potentially out-of-bounds access because we know it won't cross a page boundary. Still, KASAN will report this as a bug. Add read_word_at_a_time() function which is supposed to be used in such cases. In read_word_at_a_time() KASAN performs relaxed check - only the first byte of access is validated. Signed-off-by: Andrey Ryabinin <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
platipus25 · Jul 31, 2019 · 8ac9e06 · 8ac9e06
1 parent 21b1e01
commit 8ac9e06
Showing 1 changed file with 8 additions and 0 deletions.
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
@@ -238,6 +238,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  * required ordering.
  */
 #include <asm/barrier.h>
+#include <linux/kasan-checks.h>
 
 #define __READ_ONCE(x, check)						\
 ({									\
@@ -257,6 +258,13 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  */
 #define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
 
+static __no_kasan_or_inline
+unsigned long read_word_at_a_time(const void *addr)
+{
+	kasan_check_read(addr, 1);
+	return *(unsigned long *)addr;
+}
+
 #define WRITE_ONCE(x, val) \
 ({							\
 	union { typeof(x) __val; char __c[1]; } __u =	\