linux-kernel - Re: [PATCH v2 38/48] objtool: kmsan: list KMSAN API functions as uaccess-safe

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Date:   Thu, 14 Apr 2022 17:38:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Potapenko <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>,
        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>,
        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>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 38/48] objtool: kmsan: list KMSAN API functions as
 uaccess-safe

On Thu, Apr 14, 2022 at 05:30:34PM +0200, Alexander Potapenko wrote:
> On Wed, Mar 30, 2022 at 10:46 AM Peter Zijlstra <peterz@...radead.org>
> wrote:
> 
> > On Tue, Mar 29, 2022 at 02:40:07PM +0200, Alexander Potapenko wrote:
> > > KMSAN inserts API function calls in a lot of places (function entries
> > > and exits, local variables, memory accesses), so they may get called
> > > from the uaccess regions as well.
> >
> > That's insufficient. Explain how you did the right thing and made these
> > functions actually safe to be called in this context.
> >

> As a result, none of KMSAN API functions perform userspace accesses, but
> since they might be called from UACCESS regions they
> use user_access_save/restore().

^ That.. very good.

Thanks!