linux-kernel - Re: [PATCH v2 23/33] s390/boot: Add the KMSAN runtime stub

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Date:   Fri, 8 Dec 2023 17:56:29 +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 23/33] s390/boot: Add the KMSAN runtime stub

On Tue, Nov 21, 2023 at 11:02 PM Ilya Leoshkevich <iii@...ux.ibm.com> wrote:
>
> It should be possible to have inline functions in the s390 header
> files, which call kmsan_unpoison_memory(). The problem is that these
> header files might be included by the decompressor, which does not
> contain KMSAN runtime, causing linker errors.
>
> Not compiling these calls if __SANITIZE_MEMORY__ is not defined -
> either by changing kmsan-checks.h or at the call sites - may cause
> unintended side effects, since calling these functions from an
> uninstrumented code that is linked into the kernel is valid use case.
>
> One might want to explicitly distinguish between the kernel and the
> decompressor. Checking for a decompressor-specific #define is quite
> heavy-handed, and will have to be done at all call sites.
>
> A more generic approach is to provide a dummy kmsan_unpoison_memory()
> definition. This produces some runtime overhead, but only when building
> with CONFIG_KMSAN. The benefit is that it does not disturb the existing
> KMSAN build logic and call sites don't need to be changed.
>
> Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@...gle.com>