From: Paolo Bonzini <pbonzini@redhat.com>
To: Richard Henderson <rth@twiddle.net>,
Pranith Kumar <bobby.prani+qemu@gmail.com>,
Peter Maydell <peter.maydell@linaro.org>
Cc: Qemu Developers <qemu-devel@nongnu.org>, Jann Horn <jannh@google.com>
Subject: Re: [Qemu-devel] [BUG] user-to-root privesc inside VM via bad translation caching
Date: Thu, 23 Mar 2017 11:27:38 +0100 [thread overview]
Message-ID: <df57bde4-a33c-54b0-3f5a-3d0e28cdbca7@redhat.com> (raw)
In-Reply-To: <9f45e912-5fc8-bb99-506e-221f2cb6ac7e@twiddle.net>
On 22/03/2017 21:01, Richard Henderson wrote:
>>
>> Ah, OK. Thanks for the explanation. May be we should check the size of
>> the instruction while decoding the prefixes and error out once we
>> exceed the limit. We would not generate any IR code.
>
> Yes.
>
> It would not enforce a true limit of 15 bytes, since you can't know that
> until you've done the rest of the decode. But you'd be able to say that
> no more than 14 prefix + 1 opc + 6 modrm+sib+ofs + 4 immediate = 25
> bytes is used.
>
> Which does fix the bug.
Yeah, that would work for 2.9 if somebody wants to put together a patch.
Ensuring that all instruction fetching happens before translation side
effects is a little harder, but perhaps it's also the opportunity to get
rid of s->rip_offset which is a little ugly.
Paolo
next prev parent reply other threads:[~2017-03-23 10:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-20 14:36 [Qemu-devel] [BUG] user-to-root privesc inside VM via bad translation caching Jann Horn
2017-03-20 14:46 ` Peter Maydell
2017-03-22 14:55 ` Pranith Kumar
2017-03-22 15:04 ` Peter Maydell
2017-03-22 15:14 ` Pranith Kumar
2017-03-22 15:21 ` Peter Maydell
2017-03-22 16:29 ` Pranith Kumar
2017-03-22 20:01 ` Richard Henderson
2017-03-23 10:27 ` Paolo Bonzini [this message]
2017-03-23 16:50 ` Pranith Kumar
2017-03-23 17:37 ` Paolo Bonzini
2017-03-23 17:43 ` Pranith Kumar
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