Re: [PATCH] powerpc/mm: Don't see NULL pointer dereference as a KUAP fault

[Christophe Leroy]

Le 03/12/2020 à 12:55, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> > Sometimes, NULL pointer dereferences are expected. Even when they
> > are accidental they are unlikely an exploit attempt because the
> > first page is never mapped.
>
> The first page can be mapped if mmap_min_addr is 0.
>
> Blocking all faults to the first page would potentially break any
> program that does that.
>
> Also if there is something mapped at 0 it's a good chance it is an
> exploit attempt :)

Ok, I see.

In fact, we hit this warning because we don't provide copy_from_kernel_nofault_allowed()

I'll cook a patch for that.

Christophe