string: use __builtin_memcpy() in strlcpy/strlcat

lib/string.c is built with -ffreestanding, which prevents the compiler from replacing certain functions with calls to their library versions. On the other hand, this also prevents Clang and GCC from instrumenting calls to memcpy() when building with KASAN, KCSAN or KMSAN: - KASAN normally replaces memcpy() with __asan_memcpy() with the additional cc-param,asan-kernel-mem-intrinsic-prefix=1; - KCSAN and KMSAN replace memcpy() with __tsan_memcpy() and __msan_memcpy() by default. To let the tools catch memory accesses from strlcpy/strlcat, replace the calls to memcpy() with __builtin_memcpy(), which KASAN, KCSAN and KMSAN are able to replace even in -ffreestanding mode. This preserves the behavior in normal builds (__builtin_memcpy() ends up being replaced with memcpy()), and does not introduce new instrumentation in unwanted places, as strlcpy/strlcat are already instrumented.

Alexander Potapenko committed 3 years ago

Commit f9cfb191 parent 2af4aa31 file · +2 −2Browse files

Showing the changes to lib/string.c (1 of 1 file). Show all

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lib/string.c+2−2

@@ -110,7 +110,7 @@ size_t strlcpy(char dest, const char src, size_t size) · 109 unmodified lines
110	110
111	111	if (size) {
112	112	size_t len = (ret >= size) ? size - 1 : ret;
113		− memcpy(dest, src, len);
	113	+ __builtin_memcpy(dest, src, len);
114	114	dest[len] = '\0';
115	115	}
116	116	return ret;
@@ -260,7 +260,7 @@ size_t strlcat(char dest, const char src, size_t count) · 143 unmodified lines
260	260	count -= dsize;
261	261	if (len >= count)
262	262	len = count-1;
263		− memcpy(dest, src, len);
	263	+ __builtin_memcpy(dest, src, len);
264	264	dest[len] = 0;
265	265	return res;
266	266	}