linux-kernel - Re: [PATCH] powerpc/mm: fix mmap

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Date:   Mon, 6 Mar 2023 15:09:04 +0100
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, Sachin Sant <sachinp@...ux.ibm.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH] powerpc/mm: fix mmap_lock bad unlock

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@...ux.ibm.com>
>> Link:
>> https://lore.kernel.org/linux-mm/842502FB-F99C-417C-9648-A37D0ECDC9CE@linux.ibm.com
>> Cc: Suren Baghdasaryan <surenb@...gle.com>
>> Signed-off-by: Laurent Dufour <ldufour@...ux.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.