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

[Paolo Bonzini]

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