Re: [RFC v3 PATCH 5/5] x86: check VM_DEAD flag in page fault

[Laurent Dufour]

On 02/07/2018 14:15, Michal Hocko wrote:
> On Mon 02-07-18 10:45:03, Laurent Dufour wrote:
>> On 30/06/2018 00:39, Yang Shi wrote:
>>> Check VM_DEAD flag of vma in page fault handler, if it is set, trigger
>>> SIGSEGV.
>>>
>>> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>>> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
>>> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
>>> ---
>>>  arch/x86/mm/fault.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
>>> index 9a84a0d..3fd2da5 100644
>>> --- a/arch/x86/mm/fault.c
>>> +++ b/arch/x86/mm/fault.c
>>> @@ -1357,6 +1357,10 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs)
>>>  		bad_area(regs, error_code, address);
>>>  		return;
>>>  	}
>>> +	if (unlikely(vma->vm_flags & VM_DEAD)) {
>>> +		bad_area(regs, error_code, address);
>>> +		return;
>>> +	}
>>
>> This will have to be done for all the supported architectures, what about doing
>> this check in handle_mm_fault() and return VM_FAULT_SIGSEGV ?
> 
> We already do have a model for that. Have a look at MMF_UNSTABLE.

MMF_UNSTABLE is a mm's flag, here this is a VMA's flag which is checked.