Re: [PATCH 0/3] MIPS executable stack protection

[Leonid Yegoshin]

Linus, it works on CPU with hardware page table walker - MIPS P5600 aka Apache.

I was involved in architecture development of HTW and took care of it.


Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:


On Sat, Oct 4, 2014 at 1:23 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Fri, Oct 03, 2014 at 08:17:14PM -0700, Leonid Yegoshin wrote:
>> The following series implements an executable stack protection in MIPS.
>>
>> It sets up a per-thread 'VDSO' page and appropriate TLB support.
>
> So traditionally we've always avoided per-thread pages like that. What
> makes it worth it on MIPS?

Nothing makes it worth it on MIPS.

It may be easy to implement when you have all software-fill of TLB's,
but it's a mistake even then - because it means that you'll never be
able to do hardware TLB walkers.

And MIPS *does* have hardware TLB walkers, even if they are not
necessarily available everywhere.

So this is a horrible idea. Don't do it. Page tables need to be
per-process, not per thread, so that page tables can be shared.

              Linus
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