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In-Reply-To: <1452516679-32040-2-git-send-email-aryabinin@virtuozzo.com>
References: <20160110185916.GD22896@pd.tnic> <1452516679-32040-1-git-send-email-aryabinin@virtuozzo.com>
 <1452516679-32040-2-git-send-email-aryabinin@virtuozzo.com>
From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 18 Jan 2016 14:24:06 -0800
Message-ID: <CALCETrUJfc10=gGPYruw8MLvAGm+5VKP2bj8ex1Y=oXaMUA6Jg@mail.gmail.com>
Subject: Re: [PATCH 1/2] x86/kasan: clear kasan_zero_page after TLB flush
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To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Brian Gerst <brgerst@gmail.com>, Dave Hansen <dave.hansen@linux.intel.com>, Linus Torvalds <torvalds@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>

On Mon, Jan 11, 2016 at 4:51 AM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
> Currently we clear kasan_zero_page before __flush_tlb_all(). This
> works with current implementation of native_flush_tlb[_global]()
> because it doesn't cause do any writes to kasan shadow memory.
> But any subtle change made in native_flush_tlb*() could break this.
> Also current code seems doesn't work for paravirt guests (lguest).
>
> Only after the TLB flush we can be sure that kasan_zero_page is not
> used as early shadow anymore (instrumented code will not write to it).
> So it should cleared it only after the TLB flush.

This seems to fix the issue with my patch set.  Thanks.

Tested-by: Andy Lutomirski <luto@kernel.org>

--Andy

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