vppinfra: fix memcpy undefined behaviour

Calling mem{cpy,move} with NULL pointers results in undefined behaviour.
This in turns is exploited by GCC. For example, the sequence:
    memcpy (dst, src, n);
    if (!src)
      return;
    src[0] = 0xcafe;
will be optimized as
    memcpy (dst, src, n);
    src[0] = 0xcafe;
IOW the test for NULL is gone.

vec_*() functions sometime call memcpy with NULL pointers and 0 length,
triggering this optimization. For example, the sequence:
    vec_append(v1, v2);
    len = vec_len(v2);
will crash if v2 is NULL, because the test for NULL pointer in vec_len()
has been optimized out.

This commit fixes occurrences of such undefined behaviour, and also
introduces a memcpy wrapper to catch those in debug mode.

Type: fix

Change-Id: I175e2dd726a883f97cf7de3b15f66d4b237ddefd
Signed-off-by: Benoît Ganne <bganne@cisco.com>

1 files changed, 21 insertions, 6 deletions

diff --git a/src/vppinfra/string.h b/src/vppinfra/string.h
index 4f96450ce9e..fb46a0c6a0d 100644
--- a/src/vppinfra/string.h
+++ b/src/vppinfra/string.h
@@ -46,6 +46,7 @@
 
 #include <vppinfra/clib.h>	/* for CLIB_LINUX_KERNEL */
 #include <vppinfra/vector.h>
+#include <vppinfra/error_bootstrap.h>
 
 #ifdef CLIB_LINUX_KERNEL
 #include <linux/string.h>
@@ -73,16 +74,30 @@ void clib_memswap (void *_a, void *_b, uword bytes);
 #ifndef __COVERITY__
 #if __AVX512BITALG__
 #include <vppinfra/memcpy_avx512.h>
+#define clib_memcpy_fast_arch(a, b, c) clib_memcpy_fast_avx512 (a, b, c)
 #elif __AVX2__
 #include <vppinfra/memcpy_avx2.h>
+#define clib_memcpy_fast_arch(a, b, c) clib_memcpy_fast_avx2 (a, b, c)
 #elif __SSSE3__
 #include <vppinfra/memcpy_sse3.h>
-#else
-#define clib_memcpy_fast(a,b,c) memcpy(a,b,c)
-#endif
-#else /* __COVERITY__ */
-#define clib_memcpy_fast(a,b,c) memcpy(a,b,c)
-#endif
+#define clib_memcpy_fast_arch(a, b, c) clib_memcpy_fast_sse3 (a, b, c)
+#endif /* __AVX512BITALG__ */
+#endif /* __COVERITY__ */
+
+#ifndef clib_memcpy_fast_arch
+#define clib_memcpy_fast_arch(a, b, c) memcpy (a, b, c)
+#endif /* clib_memcpy_fast_arch */
+
+static_always_inline void *
+clib_memcpy_fast (void *restrict dst, const void *restrict src, size_t n)
+{
+  ASSERT (dst && src &&
+	  "memcpy(src, dst, n) with src == NULL or dst == NULL is undefined "
+	  "behaviour");
+  return clib_memcpy_fast_arch (dst, src, n);
+}
+
+#undef clib_memcpy_fast_arch
 
 /* c-11 string manipulation variants */