Re: [Xen-devel] [PATCH for-4.8] x86/svm: Fix svm_nextrip_insn_length() when crossing the virtual boundary to 0

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 11/21/2016 08:53 AM, Andrew Cooper wrote:
> On 21/11/16 13:38, Boris Ostrovsky wrote:
>> On 11/21/2016 05:40 AM, Andrew Cooper wrote:
>>> On 16/11/16 10:51, Andrew Cooper wrote:
>>>> vmcb->nextrip can legitimately be less than vmcb->rip when execution wraps
>>>> back around to 0.  Instead, complain if the reported length is greater 
>>>> than 15
>>>> and use x86_decode_insn() as a fallback.
>> Why do we need to complain? In the case that you are addressing by this
>> patch wouldn't that be the expected result (length>15)?
> No.  An instruction crossing the boundary looks like:
>
> e.g. nextrip = 0x3, rip = 0xfffffffffffffffe
>
> As this is all evaluated in unsigned long arithmetic, nextrip - rip
> evaluates to 5, which is correct.

Oh, right.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

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