[v1] powerpc/mm: fix mmap_lock bad unlock

[PATCH] powerpc/mm: fix mmap_lock bad unlock

Posted by Laurent Dufour 3 years, 1 month ago

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);
-- 
2.39.2

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

Posted by David Hildenbrand 3 years, 1 month ago

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.

-- 
Thanks,

David / dhildenb

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

Posted by Laurent Dufour 3 years, 1 month ago

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.

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

Posted by Suren Baghdasaryan 3 years, 1 month ago

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.