On Mon, Apr 24, 2023 at 01:23:13PM +0200, Alexander Potapenko wrote: > 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. > > Suggested-by: Marco Elver <elver@xxxxxxxxxx> > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> > Link: https://lore.kernel.org/all/20230224085942.1791837-1-elver@xxxxxxxxxx/ > --- > lib/string.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/lib/string.c b/lib/string.c > index 3d55ef8901068..be26623953d2e 100644 > --- a/lib/string.c > +++ b/lib/string.c > @@ -110,7 +110,7 @@ size_t strlcpy(char *dest, const char *src, size_t size) > > if (size) { > size_t len = (ret >= size) ? size - 1 : ret; > - memcpy(dest, src, len); > + __builtin_memcpy(dest, src, len); > dest[len] = '\0'; > } > return ret; > @@ -260,7 +260,7 @@ size_t strlcat(char *dest, const char *src, size_t count) > count -= dsize; > if (len >= count) > len = count-1; > - memcpy(dest, src, len); > + __builtin_memcpy(dest, src, len); > dest[len] = 0; > return res; I *think* this isn't a problem for CONFIG_FORTIFY, since these will be replaced and checked separately -- but it still seems strange that you need to explicitly use __builtin_memcpy. Does this end up changing fortify coverage? -- Kees Cook
