Re: [PATCH] powerpc/mm: fix mmap_lock bad unlock

[Suren Baghdasaryan <surenb@google.com>]

On Mon, Mar 6, 2023 at 6:09 AM Laurent Dufour <ldufour@linux.ibm.com> wrote:
>
> On 06/03/2023 15:07:26, David Hildenbrand wrote:
> > On 06.03.23 14:55, Laurent Dufour wrote:
> >> When page fault is tried holding the per VMA lock, bad_access_pkey() and
> >> bad_access() should not be called because it is assuming the mmap_lock is
> >> held.
> >> In the case a bad access is detected, fall back to the default path,
> >> grabbing the mmap_lock to handle the fault and report the error.
> >>
> >> Fixes: 169db3bb4609 ("powerc/mm: try VMA lock-based page fault handling
> >> first")
> >> Reported-by: Sachin Sant <sachinp@linux.ibm.com>
> >> Link:
> >> https://lore.kernel.org/linux-mm/842502FB-F99C-417C-9648-A37D0ECDC9CE@linux.ibm.com
> >> Cc: Suren Baghdasaryan <surenb@google.com>
> >> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> >> ---
> >>   arch/powerpc/mm/fault.c | 8 ++------
> >>   1 file changed, 2 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> >> index c7ae86b04b8a..e191b3ebd8d6 100644
> >> --- a/arch/powerpc/mm/fault.c
> >> +++ b/arch/powerpc/mm/fault.c
> >> @@ -479,17 +479,13 @@ static int ___do_page_fault(struct pt_regs *regs,
> >> unsigned long address,
> >>         if (unlikely(access_pkey_error(is_write, is_exec,
> >>                          (error_code & DSISR_KEYFAULT), vma))) {
> >> -        int rc = bad_access_pkey(regs, address, vma);
> >> -
> >>           vma_end_read(vma);
> >> -        return rc;
> >> +        goto lock_mmap;
> >>       }
> >>         if (unlikely(access_error(is_write, is_exec, vma))) {
> >> -        int rc = bad_access(regs, address);
> >> -
> >>           vma_end_read(vma);
> >> -        return rc;
> >> +        goto lock_mmap;
> >>       }
> >>         fault = handle_mm_fault(vma, address, flags |
> >> FAULT_FLAG_VMA_LOCK, regs);
> >
> > IIUC, that commit is neither upstream not in mm-stable -- it's unstable.
> > Maybe raise that as a review comment in reply to the original patch, so we
> > can easily connect the dots and squash it into the original, problematic
> > patch that is still under review.
> >
> Oh yes, I missed that. I'll reply to the Suren's thread.

Thanks Laurent! Seems simple enough to patch the original change.

>
> Thanks,
> Laurent.