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

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Date:   Fri, 8 Dec 2023 17:50:30 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Marco Elver <elver@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Sven Schnelle <svens@...ux.ibm.com>
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 <iii@...ux.ibm.com> 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 <iii@...ux.ibm.com>
> ---
>  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().