Re: [PATCH v2 0/5] implement lightweight guard pages

[David Hildenbrand <david@redhat.com>]

On 23.10.24 11:06, Vlastimil Babka wrote:
> On 10/23/24 10:56, Dmitry Vyukov wrote:
>>>
>>> Overall while I sympathise with this, it feels dangerous and a pretty major
>>> change, because there'll be something somewhere that will break because it
>>> expects faults to be swallowed that we no longer do swallow.
>>>
>>> So I'd say it'd be something we should defer, but of course it's a highly
>>> user-facing change so how easy that would be I don't know.
>>>
>>> But I definitely don't think a 'introduce the ability to do cheap PROT_NONE
>>> guards' series is the place to also fundmentally change how user access
>>> page faults are handled within the kernel :)
>>
>> Will delivering signals on kernel access be a backwards compatible
>> change? Or will we need a different API? MADV_GUARD_POISON_KERNEL?
>> It's just somewhat painful to detect/update all userspace if we add
>> this feature in future. Can we say signal delivery on kernel accesses
>> is unspecified?
> 
> Would adding signal delivery to guard PTEs only help enough the ASAN etc
> usecase? Wouldn't it be instead possible to add some prctl to opt-in the
> whole ASANized process to deliver all existing segfaults as signals instead
> of -EFAULT ?

Not sure if it is an "instead", you might have to deliver the signal in 
addition to letting the syscall fail (not that I would be an expert on 
signal delivery :D ).

prctl sounds better, or some way to configure the behavior on VMA 
ranges; otherwise we would need yet another marker, which is not the end 
of the world but would make it slightly more confusing.

-- 
Cheers,

David / dhildenb