linux-kernel - Re: [PATCH 39/43] x86: kmsan: handle register passing from uninstrumented code

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Message-ID: <87bl1ec32a.ffs@tglx>
Date:   Fri, 17 Dec 2021 22:51:57 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexander Potapenko <glider@...gle.com>, glider@...gle.com
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.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>,
        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>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 39/43] x86: kmsan: handle register passing from
 uninstrumented code

Alexander,

On Tue, Dec 14 2021 at 17:20, Alexander Potapenko wrote:
> When calling KMSAN-instrumented functions from non-instrumented
> functions, function parameters may not be initialized properly, leading
> to false positive reports. In particular, this happens all the time when
> calling interrupt handlers from `noinstr` IDT entries.
>
> Fortunately, x86 code has instrumentation_begin() and

It's not only x86 code:
>  kernel/entry/common.c           | 3 +++

> @@ -76,6 +77,7 @@ __visible noinstr void do_syscall_64(struct pt_regs *regs, int nr)
>  	nr = syscall_enter_from_user_mode(regs, nr);
>  
>  	instrumentation_begin();
> +	kmsan_instrumentation_begin(regs);

Can we please make this something like:

       instrumentation_begin_at_entry(regs);

or some other sensible name which hides that kmsan gunk and avoids to
touch all of this again when KFOOSAN comes around?

Thanks,

        tglx