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From:   Alexander Potapenko <glider@google.com>
Date:   Fri, 9 Sep 2022 10:57:09 +0200
Message-ID: <CAG_fn=Wz1b5nKTACGa_oPBuxXcn4Hb7hDT-3Fcx5P3ODY+ivpA@mail.gmail.com>
Subject: Re: [PATCH v6 40/44] x86: kmsan: don't instrument stack walking functions
To:     Andrew Morton <akpm@linux-foundation.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Marco Elver <elver@google.com>,
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        Matthew Wilcox <willy@infradead.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>,
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On Mon, Sep 5, 2022 at 2:26 PM Alexander Potapenko <glider@google.com> wrote:
>
> Upon function exit, KMSAN marks local variables as uninitialized.
> Further function calls may result in the compiler creating the stack
> frame where these local variables resided. This results in frame
> pointers being marked as uninitialized data, which is normally correct,
> because they are not stack-allocated.
>
> However stack unwinding functions are supposed to read and dereference
> the frame pointers, in which case KMSAN might be reporting uses of
> uninitialized values.
>
> To work around that, we mark update_stack_state(), unwind_next_frame()
> and show_trace_log_lvl() with __no_kmsan_checks, preventing all KMSAN
> reports inside those functions and making them return initialized
> values.
>
> Signed-off-by: Alexander Potapenko <glider@google.com>

Hi Andrew, Stephen,

I've noticed this particular patch is missing in -mm (and, as a
result, in linux-next), which results in tons of false positives at
boot time.
Could you please add it as well?