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Re: [Qemu-devel] [BUG] user-to-root privesc inside VM via bad translatio

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [BUG] user-to-root privesc inside VM via bad translation caching
Date: Thu, 23 Mar 2017 11:27:38 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

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.


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