[RFC/PATCH RESEND -next 17/21] arm: add kasan hooks fort memcpy/memmove/memset functions

[Andrey Ryabinin]

Since functions memset, memmove, memcpy are written in assembly,
compiler can't instrument memory accesses inside them.

This patch replaces these functions with our own instrumented
functions (kasan_mem*) for CONFIG_KASAN = y

In rare circumstances you may need to use the original functions,
in such case put #undef KASAN_HOOKS before includes.

Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
---
 arch/arm/include/asm/string.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/arm/include/asm/string.h b/arch/arm/include/asm/string.h
index cf4f3aa..3cbe47f 100644
--- a/arch/arm/include/asm/string.h
+++ b/arch/arm/include/asm/string.h
@@ -38,4 +38,34 @@ extern void __memzero(void *ptr, __kernel_size_t n);
 		(__p);							\
 	})
 
+
+#if defined(CONFIG_KASAN) && defined(KASAN_HOOKS)
+
+/*
+ * Since some of the following functions (memset, memmove, memcpy)
+ * are written in assembly, compiler can't instrument memory accesses
+ * inside them.
+ *
+ * To solve this issue we replace these functions with our own instrumented
+ * functions (kasan_mem*)
+ *
+ * In case if any of mem*() fucntions are written in C we use our instrumented
+ * functions for perfomance reasons. It's should be faster to check whole
+ * accessed memory range at once, then do a lot of checks at each memory access.
+ *
+ * In rare circumstances you may need to use the original functions,
+ * in such case #undef KASAN_HOOKS before includes.
+ */
+#undef memset
+
+void *kasan_memset(void *ptr, int val, size_t len);
+void *kasan_memcpy(void *dst, const void *src, size_t len);
+void *kasan_memmove(void *dst, const void *src, size_t len);
+
+#define memcpy(dst, src, len) kasan_memcpy((dst), (src), (len))
+#define memset(ptr, val, len) kasan_memset((ptr), (val), (len))
+#define memmove(dst, src, len) kasan_memmove((dst), (src), (len))
+
+#endif /* CONFIG_KASAN && KASAN_HOOKS */
+
 #endif
-- 
1.8.5.5

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