diff mbox series

[v2] string: use __builtin_memcpy() in strlcpy/strlcat

Message ID 20230530083911.1104336-1-glider@google.com
State New
Headers
Series [v2] string: use __builtin_memcpy() in strlcpy/strlcat |

Commit Message

Alexander Potapenko May 30, 2023, 8:39 a.m. UTC 
  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@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/all/20230224085942.1791837-1-elver@google.com/
Acked-by: Kees Cook <keescook@chromium.org>
---
 lib/string.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Alexander Potapenko May 30, 2023, 8:40 a.m. UTC | #1 
On Tue, May 30, 2023 at 10:39 AM Alexander Potapenko <glider@google.com> 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@google.com>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> Link: https://lore.kernel.org/all/20230224085942.1791837-1-elver@google.com/

Sorry, missed a "Reviewed-by: Marco Elver <elver@google.com>" from the
previous thread:
https://lore.kernel.org/lkml/CAG_fn=UzQ-jnQrxzvLE6EV37zSVCOGPmsVTxyfp1wXzBir4vAg@mail.gmail.com/T/


> Acked-by: Kees Cook <keescook@chromium.org>
Kees Cook May 30, 2023, 11:10 p.m. UTC | #2 
On Tue, 30 May 2023 10:39:11 +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.
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] string: use __builtin_memcpy() in strlcpy/strlcat
      https://git.kernel.org/kees/c/cfe93c8c9a7a
Alexander Potapenko May 31, 2023, 7:57 a.m. UTC | #3 
On Wed, May 31, 2023 at 1:10 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Tue, 30 May 2023 10:39:11 +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.
> >
> > [...]
>
> Applied to for-next/hardening, thanks!
>
> [1/1] string: use __builtin_memcpy() in strlcpy/strlcat
>       https://git.kernel.org/kees/c/cfe93c8c9a7a

Note that Andrew also picked it to mm-unstable
diff mbox series

Patch

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;
 }