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Date: Mon, 6 Mar 2017 13:58:51 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Ingo Molnar <mingo@redhat.com>, kasan-dev <kasan-dev@googlegroups.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86, kasan: add KASAN checks to atomic operations
Message-ID: <20170306125851.GL6500@twins.programming.kicks-ass.net>
References: <20170306124254.77615-1-dvyukov@google.com>
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On Mon, Mar 06, 2017 at 01:50:47PM +0100, Dmitry Vyukov wrote:
> On Mon, Mar 6, 2017 at 1:42 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> > KASAN uses compiler instrumentation to intercept all memory accesses.
> > But it does not see memory accesses done in assembly code.
> > One notable user of assembly code is atomic operations. Frequently,
> > for example, an atomic reference decrement is the last access to an
> > object and a good candidate for a racy use-after-free.
> >
> > Add manual KASAN checks to atomic operations.
> > Note: we need checks only before asm blocks and don't need them
> > in atomic functions composed of other atomic functions
> > (e.g. load-cmpxchg loops).
> 
> Peter, also pointed me at arch/x86/include/asm/bitops.h. Will add them in v2.
> 

> >  static __always_inline void atomic_add(int i, atomic_t *v)
> >  {
> > +       kasan_check_write(v, sizeof(*v));
> >         asm volatile(LOCK_PREFIX "addl %1,%0"
> >                      : "+m" (v->counter)
> >                      : "ir" (i));


So the problem is doing load/stores from asm bits, and GCC
(traditionally) doesn't try and interpret APP asm bits.

However, could we not write a GCC plugin that does exactly that?
Something that interprets the APP asm bits and generates these KASAN
bits that go with it?