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

[Michael Ellerman]

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 :)

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

cheers