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Fri, Oct 24, 2025 at 03:19:57AM +0200, Andrey Konovalov wrote: > On Fri, Oct 24, 2025 at 2:41 AM Harry Yoo wrote: > > > > Adding more details on how I discovered this and why I care: > > > > I was developing a feature that uses unused bytes in s->size as the > > slabobj_ext metadata. Unlike other metadata where slab disables KASAN > > when accessing it, this should be unpoisoned to avoid adding complexity > > and overhead when accessing it. > > Generally, unpoisoining parts of slabs that should not be accessed by > non-slab code is undesirable - this would prevent KASAN from detecting > OOB accesses into that memory. > > An alternative to unpoisoning or disabling KASAN could be to add > helper functions annotated with __no_sanitize_address that do the > required accesses. And make them inlined when KASAN is disabled to > avoid the performance hit. This sounds reasonable, let me try this instead of unpoisoning metadata. Thanks. > On a side note, you might also need to check whether SW_TAGS KASAN and > KMSAN would be unhappy with your changes: > > - When we do kasan_disable_current() or metadata_access_enable(), we > also do kasan_reset_tag(); > - In metadata_access_enable(), we disable KMSAN as well. Thanks for pointing this out! Just to clarify, by calling kasan_reset_tag() we clear tag from the address so that SW or HW tag based KASAN won't report access violation? (because there is no valid tag in the address?) -- Cheers, Harry / Hyeonggon