Messages in this thread | | | Date | Tue, 24 Jan 2023 13:11:22 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH mm] kasan: reset page tags properly with sampling |
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On Tue, 24 Jan 2023 21:46:51 +0100 Andrey Konovalov <andreyknvl@gmail.com> wrote:
> On Tue, Jan 24, 2023 at 9:45 PM Andrew Morton <akpm@linux-foundation.org> wrote: > > > > On Tue, 24 Jan 2023 21:35:26 +0100 andrey.konovalov@linux.dev wrote: > > > > > The implementation of page_alloc poisoning sampling assumed that > > > tag_clear_highpage resets page tags for __GFP_ZEROTAGS allocations. > > > However, this is no longer the case since commit 70c248aca9e7 > > > ("mm: kasan: Skip unpoisoning of user pages"). > > > > > > This leads to kernel crashes when MTE-enabled userspace mappings are > > > used with Hardware Tag-Based KASAN enabled. > > > > > > Reset page tags for __GFP_ZEROTAGS allocations in post_alloc_hook(). > > > > > > Also clarify and fix related comments. > > > > I assume this is a fix against 44383cef54c0 ("kasan: allow sampling > > page_alloc allocations for HW_TAGS") which is presently in mm-stable, > > yes? > > Correct. I assumed I shouldn't include a Fixes tag, as the patch is > not in the mainline.
I think it's best to add the Fixes: if it's known. If the patch was in mm-unstable then I'd just fold the fix into the base patch, but a Fixes: is still helpful because it tells people (especially me) which patch needs the fix.
If the patch is in mm-stable then the SHA is stable and the Fixes: is desirable for people who are backporting the base patch into earlier kernels - hopefully when doing this they know to search the tree for other patches which fix the patch which they are backporting.
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