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Aleksei Nikiforov
7e76b75e5a
If no stack depot is allocated yet, due to masking out __GFP_RECLAIM flags
kmsan called from kmalloc cannot allocate stack depot. kmsan fails to
record origin and report issues. This may result in KMSAN failing to
report issues.
Reusing flags from kmalloc without modifying them should be safe for kmsan.
For example, such chain of calls is possible:
test_uninit_kmalloc -> kmalloc -> __kmalloc_cache_noprof ->
slab_alloc_node -> slab_post_alloc_hook ->
kmsan_slab_alloc -> kmsan_internal_poison_memory.
Only when it is called in a context without flags present should
__GFP_RECLAIM flags be masked.
With this change all kmsan tests start working reliably.
Eric reported:
: Yes, KMSAN seems to be at least partially broken currently. Besides the
: fact that the kmsan KUnit test is currently failing (which I reported at
: https://lore.kernel.org/r/20250911175145.GA1376@sol), I've confirmed that
: the poly1305 KUnit test causes a KMSAN warning with Aleksei's patch
: applied but does not cause a warning without it. The warning did get
: reached via syzbot somehow
: (https://lore.kernel.org/r/751b3d80293a6f599bb07770afcef24f623c7da0.1761026343.git.xiaopei01@kylinos.cn/),
: so KMSAN must still work in some cases. But it didn't work for me.
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/20251022030213.GA35717@sol
Fixes: 97769a53f1 ("mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation")
Signed-off-by: Aleksei Nikiforov <[email protected]>
Reviewed-by: Alexander Potapenko <[email protected]>
Tested-by: Eric Biggers <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Dmitriy Vyukov <[email protected]>
Cc: Ilya Leoshkevich <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>