2023-11-21 22:06:03

by Ilya Leoshkevich

Subject: [PATCH v2 18/33] lib/string: Add KMSAN support to strlcpy() and strlcat()

Currently KMSAN does not fully propagate metadata in strlcpy() and
strlcat(), because they are built with -ffreestanding and call
memcpy(). In this combination memcpy() calls are not instrumented.

Fix by copying the metadata manually. Add the __STDC_HOSTED__ #ifdef in
case the code is compiled with different flags in the future.

Signed-off-by: Ilya Leoshkevich <[email protected]>
---
lib/string.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/lib/string.c b/lib/string.c
index be26623953d2..e83c6dd77ec6 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -111,6 +111,9 @@ size_t strlcpy(char *dest, const char *src, size_t size)
if (size) {
size_t len = (ret >= size) ? size - 1 : ret;
__builtin_memcpy(dest, src, len);
+#if __STDC_HOSTED__ == 0
+ kmsan_memmove_metadata(dest, src, len);
+#endif
dest[len] = '\0';
}
return ret;
@@ -261,6 +264,9 @@ size_t strlcat(char *dest, const char *src, size_t count)
if (len >= count)
len = count-1;
__builtin_memcpy(dest, src, len);
+#if __STDC_HOSTED__ == 0
+ kmsan_memmove_metadata(dest, src, len);
+#endif
dest[len] = 0;
return res;
}
--
2.41.0

2023-12-08 16:52:10

by Alexander Potapenko

Subject: Re: [PATCH v2 18/33] lib/string: Add KMSAN support to strlcpy() and strlcat()

On Tue, Nov 21, 2023 at 11:02 PM Ilya Leoshkevich <[email protected]> wrote:
>
> Currently KMSAN does not fully propagate metadata in strlcpy() and
> strlcat(), because they are built with -ffreestanding and call
> memcpy(). In this combination memcpy() calls are not instrumented.

Is this something specific to s390?

> Fix by copying the metadata manually. Add the __STDC_HOSTED__ #ifdef in
> case the code is compiled with different flags in the future.
>
> Signed-off-by: Ilya Leoshkevich <[email protected]>
> ---
> lib/string.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/lib/string.c b/lib/string.c
> index be26623953d2..e83c6dd77ec6 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -111,6 +111,9 @@ size_t strlcpy(char *dest, const char *src, size_t size)
> if (size) {
> size_t len = (ret >= size) ? size - 1 : ret;
> __builtin_memcpy(dest, src, len);

On x86, I clearly see this __builtin_memcpy() being replaced with
__msan_memcpy().

2023-12-13 00:54:30

by Ilya Leoshkevich

Subject: Re: [PATCH v2 18/33] lib/string: Add KMSAN support to strlcpy() and strlcat()

On Fri, 2023-12-08 at 17:50 +0100, Alexander Potapenko wrote:
> On Tue, Nov 21, 2023 at 11:02 PM Ilya Leoshkevich <[email protected]>
> wrote:
> >
> > Currently KMSAN does not fully propagate metadata in strlcpy() and
> > strlcat(), because they are built with -ffreestanding and call
> > memcpy(). In this combination memcpy() calls are not instrumented.
>
> Is this something specific to s390?

Nice catch - I can't reproduce this behavior anymore. Even if I go
back to the clang version that first introduced KMSAN on s390x, the
memset() instrumentation with -ffreestanding is still there. I should
have written down more detailed notes after investigating this, but
here we are. I will drop this patch as well as 10/33.

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