linux-kernel - Re: KASAN: use-after-free Read in sha512_ctx_mgr

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Date:   Tue, 28 Aug 2018 01:01:00 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Megha Dey <megha.dey@...ux.intel.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        syzbot <syzbot+d5455bac3ba1ee9114e5@...kaller.appspotmail.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: KASAN: use-after-free Read in sha512_ctx_mgr_resubmit

On 28 August 2018 at 01:08, Megha Dey <megha.dey@...ux.intel.com> wrote:
> On Wed, 2018-08-22 at 14:20 +0800, Herbert Xu wrote:
>> On Tue, Aug 21, 2018 at 02:43:56PM +0200, Ard Biesheuvel wrote:
>> >
>> > I agree. The code is obviously broken in a way that would have been
>> > noticed if it were in wide use, and it is too complicated for mere
>> > mortals to fix or maintain. I suggest we simply remove it for now, and
>> > if anyone wants to reintroduce it, we can review the code *and* the
>> > justification for the approach from scratch (in which case we should
>> > consider factoring out the algo agnostics plumbing in a way that
>> > allows it to be reused by other architectures as well)
>>
>> I agree too.  Could one of you guys send me a patch to remove
>> them?
>>
>
> Hi,
>
> We are working on a fix to solve these corner cases.
>

Great. thanks.

But it would also be helpful if you could try and answer the questions
raised by Eric:
- in which cases does this driver result in a speedup?
- how should we tune the flush delay to prevent pathological
performance regressions?
- is it still safe in the post-Spectre era of computing to aggregate
hash input from different sources (which may be different users
altogether) and process them as a single source of input?