From: David Miller <davem@davemloft.net>
To: alexei.starovoitov@gmail.com
Cc: dvyukov@google.com, ast@kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, syzkaller@googlegroups.com,
kcc@google.com, glider@google.com, sasha.levin@oracle.com,
edumazet@google.com, ryabinin.a.a@gmail.com
Subject: Re: bpf: undefined shift in __bpf_prog_run
Date: Fri, 04 Dec 2015 16:37:53 -0500 (EST) [thread overview]
Message-ID: <20151204.163753.594151588498690658.davem@davemloft.net> (raw)
In-Reply-To: <20151204203522.GB64517@ast-mbp.thefacebook.com>
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Fri, 4 Dec 2015 12:35:23 -0800
> On Fri, Dec 04, 2015 at 08:48:57PM +0100, Dmitry Vyukov wrote:
>>
>> For example, a compiler can assume that result of left shift is larger
>> or equal to first operand, which in turn can allow it to elide some
>> bounds check in code, which in turn can lead to an exploit. I am not
>> saying that this particular pattern is present in the code, what I
>> want to say is that such undefined behaviors can lead to very
>> unpredictable and unexpected consequences.
>
> Within bpf it cannot.
> shift is not used in any memory or bounds operations.
> so reg <<= 1234 cannot be exploited.
+1
next prev parent reply other threads:[~2015-12-04 21:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-04 11:17 Dmitry Vyukov
2015-12-04 18:43 ` Alexei Starovoitov
2015-12-04 19:03 ` Dmitry Vyukov
2015-12-04 19:10 ` Alexei Starovoitov
2015-12-04 19:26 ` David Miller
2015-12-04 19:48 ` Dmitry Vyukov
2015-12-04 20:35 ` Alexei Starovoitov
[not found] ` <CAN=P9ph-_w-ekSabGGKq-pu50enZXfGWp3k=x9zTb=Xy+ccjwA@mail.gmail.com>
2015-12-04 20:50 ` Alexei Starovoitov
2015-12-04 21:37 ` David Miller [this message]
2015-12-04 21:21 ` Hannes Frederic Sowa
2015-12-07 11:14 ` David Laight
2015-12-09 18:04 ` Daniel Borkmann
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