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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.01.17 at 12:31, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 12/01/17 10:09, Jan Beulich wrote:
>>>>> 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.
> 
> I did audit the other callsites, and thought I found them to be safe.
> 
> However, thinking again, I think the gate_op case isn't
> 
>     case 0xff:
>         if ( x86_insn_modrm(state, NULL, &modrm_345) >= 3 )
>             break;
>         switch ( modrm_345 & 7 )
> 
> This also needs to be an unsigned comparison to catch the -EINVAL case.

Right. However, how about using 3U instead of a cast to achieve this?

Jan


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