Re: [NEEDS-REVIEW] Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

Yu, Yu-cheng
2020-09-15T22:09:43Z

On 9/15/2020 12:24 PM, Dave Hansen wrote:
> On 9/15/20 12:08 PM, Yu-cheng Yu wrote:
>> On Mon, 2020-09-14 at 17:12 -0700, Yu, Yu-cheng wrote:
>>> On 9/14/2020 7:50 AM, Dave Hansen wrote:
>>>> On 9/11/20 3:59 PM, Yu-cheng Yu wrote:
>>>> ...
>>>>> Here are the changes if we take the mprotect(PROT_SHSTK) approach.
>>>>> Any comments/suggestions?
>>>> I still don't like it. :)
>>>>
>>>> I'll also be much happier when there's a proper changelog to accompany
>>>> this which also spells out the alternatives any why they suck so much.
>> [...]
>>
>> I revised it. If this turns out needing more work/discussion, we can split it
>> out from the shadow stack series.
>
> Where does that leave things? You only get shadow stacks for
> single-threaded apps which have the ELF bits set?
>

As long as the system supports shadow stack, any application can
mmap()/mprotect() a shadow stack. A pthread can allocate a shadow stack
too. However, only shadow stack-enabled programs can activate/use the
shadow stack.