Re: [Xen-devel] [PATCH v6 05/10] Clear AC bit in RFLAGS to protect Xen itself by SMAP

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 07/05/14 12:40, Jan Beulich wrote:
>>>> On 07.05.14 at 11:44, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 07/05/14 09:19, Feng Wu wrote:
>>> @@ -673,6 +675,7 @@ ENTRY(nmi_crash)
>>>          ud2
>>>  
>>>  ENTRY(machine_check)
>>> +        ASM_CLAC
>> This is not needed.  the start of handle_ist_exception has a SAVE_ALL,
>> which also covers the nmi entry point.
>>
>> On the subject of IST exceptions, perhaps the double fault explicitly
>> wants a STAC to reduce the likelihood of taking a further fault while
>> trying to dump state. ?
> I agree. And perhaps along with do_double_fault(), fatal_trap()
> should then also get a stac() added?
>
> Jan
>

With doubt_fault: being sole caller of do_double_fault(), editing the
entry point in entry.S to "ASM_STAC; SAVE_ALL 0" is sufficient to avoid
stac() in do_doube_fault() itself.

I would agree that fatal_trap() wants an stac() in it.

~Andrew

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