Re: [PATCH 0/2] mm: fix UAF caused by race between ptdump and vmap pgtable freeing

[Will Deacon <will@kernel.org>]

On Sun, Jul 12, 2026 at 09:46:46AM +0100, Lorenzo Stoakes wrote:
> On Sun, Jul 12, 2026 at 12:50:08PM +0530, Dev Jain wrote:
> > Will Deacon had pushed back on a similar approach:
> > https://lore.kernel.org/all/20250530123527.GA30463@willie-the-truck/
> >
> > Although now when I read back that thread, it feels more so like my
> > incompetency to convince :) because:
> 
> No haha not so, I think more like this stuff is fiddly.

Yup, not disputing that this is hard to get right.

Conceptually, adding locking purely to deal with a vanishingly rare,
debug reader does turn my head but I'm _far_ less concerned about it if
it's done in the core code, as is the case here. x86 needs it and we're
recently running into related locking issues with the set_memory_*()
APIs if we want to collapse the page-table on arm64 [1]. If the overhead
is flagged as an issue, we can see if it's worth generalising the static
key trick that the second patch reverts but I definitely wouldn't start
from that position.

Will

[1] https://lore.kernel.org/linux-arm-kernel/799181c3-a1a1-4de7-bc6a-576d3282efb0@arm.com/