linux-kernel - Re: [PATCH v6 40/44] x86: kmsan: don't instrument stack walking functions

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Message-ID: <CAG_fn=Wz1b5nKTACGa_oPBuxXcn4Hb7hDT-3Fcx5P3ODY+ivpA@mail.gmail.com>
Date:   Fri, 9 Sep 2022 10:57:09 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 40/44] x86: kmsan: don't instrument stack walking functions

On Mon, Sep 5, 2022 at 2:26 PM Alexander Potapenko <glider@...gle.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@...gle.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?