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

[Juergen Gross <jgross@xxxxxxxx>]

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.


Juergen

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