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Date:   Thu, 14 Apr 2022 17:38:01 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.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>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Linux-Arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 38/48] objtool: kmsan: list KMSAN API functions as
 uaccess-safe
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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@infradead.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!