Re: [Xen-devel] [PATCH] x86/svm: Adjust ModRM Mode check in is_invlpg()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.01.17 at 18:33, <andrew.cooper3@xxxxxxxxxx> wrote:
> Coverity points out that x86_insn_modrm() returns -EINVAL for instructions not
> encoded with a ModRM byte.  A consequence is that checking != 3 is
> insufficient to confirm that &ext was actually written to.
> 
> In practice, this check is only used after decode has been successful, and
> 0f01 will have a ModRM byte.

I think there may be one or two more such instances elsewhere.

> Use an unsigned < comparison to exclude the -EINVAL case, guaranteeing that
> ext is only read if it was filled in by x86_insn_modrm(), which should placate
> Coverity.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> 
> RFC.  I haven't actually checked that this fixes the issue.

Provided it does,
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

I'd also be fine with putting it in without double checking, going
the revert or amend route if it doesn't help.

Jan


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