Re: [Xen-devel] [PATCH v2 2/2] x86/xpti: don't map stack guard pages

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.03.18 at 17:41, <jgross@xxxxxxxx> wrote:
> On 02/03/18 17:10, Jan Beulich wrote:
>>>>> On 02.03.18 at 16:43, <jgross@xxxxxxxx> wrote:
>>> On 02/03/18 15:35, Jan Beulich wrote:
>>>> --- a/xen/arch/x86/mm.c
>>>> +++ b/xen/arch/x86/mm.c
>>>> @@ -5576,6 +5576,14 @@ void memguard_unguard_stack(void *p)
>>>>                             STACK_SIZE - PRIMARY_STACK_SIZE - IST_MAX * 
>>>> PAGE_SIZE);
>>>>  }
>>>>  
>>>> +bool memguard_is_stack_guard_page(unsigned long addr)
>>>> +{
>>>> +    addr &= STACK_SIZE - 1;
>>>> +
>>>> +    return addr >= IST_MAX * PAGE_SIZE &&
>>>> +           addr < STACK_SIZE - PRIMARY_STACK_SIZE;
>>>> +}
>>>> +
>>>
>>> What about making use of memguard_is_stack_guard_page() in
>>> memguard_[un]guard_stack() ?
>> 
>> I was considering this as a follow-up step.
>> 
>>> This would at once ensure the other unused
>>> pages won't be accessed accidentally somewhere.
>> 
>> I don't understand this part, though.
> 
> Today memguard_guard_stack() touches only one of the unused pages, not
> all of them.

That was earlier today, but not anymore at the time I sent this
patch.

Jan


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