[PATCH] powerpc/fault: kernel can extend a user process's stack

[Daniel Axtens]

Michael Ellerman <mpe at ellerman.id.au> writes:

> Michal Suchánek <msuchanek at suse.de> writes:
>> Hello,
>>
>> On Wed, Dec 11, 2019 at 08:37:21PM +1100, Daniel Axtens wrote:
>>> > Fixes: 14cf11af6cf6 ("powerpc: Merge enough to start building in
>>> > arch/powerpc.")
>>> 
>>> Wow, that's pretty ancient! I'm also not sure it's right - in that same
>>> patch, arch/ppc64/mm/fault.c contains:
>>> 
>>> ^1da177e4c3f4 (Linus Torvalds         2005-04-16 15:20:36 -0700 213)            if (address + 2048 < uregs->gpr[1]
>>> ^1da177e4c3f4 (Linus Torvalds         2005-04-16 15:20:36 -0700 214)                && (!user_mode(regs) || !store_updates_sp(regs)))
>>> ^1da177e4c3f4 (Linus Torvalds         2005-04-16 15:20:36 -0700 215)                    goto bad_area;
>>> 
>>> Which is the same as the new arch/powerpc/mm/fault.c code:
>>> 
>>> 14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 234)            if (address + 2048 < uregs->gpr[1]
>>> 14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 235)                && (!user_mode(regs) || !store_updates_sp(regs)))
>>> 14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 236)                    goto bad_area;
>>> 
>>> So either they're both right or they're both wrong, either way I'm not
>>> sure how this patch is to blame.
>>
>> Is there any progress on resolving this?
>>
>> I did not notice any followup patch nor this one being merged/refuted.
>
> It ended up with this:
>
> https://lore.kernel.org/linuxppc-dev/20200703141327.1732550-2-mpe@ellerman.id.au/
>
>
> Which I was hoping would get some reviews :)

Ah, I missed this. I'll give it a look as soon as I can.

Kind regards,
Daniel

>
> I'll probably merge the whole series into next this week.
>
> cheers