From: Aleksei Nikiforov Date: Tue, 30 Sep 2025 11:56:01 +0000 (+0200) Subject: mm/kmsan: fix kmsan kmalloc hook when no stack depots are allocated yet X-Git-Tag: v6.18-rc6~40^2~20 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=7e76b75e5ab3339bebab3a4738226cd9b27d8c42;p=thirdparty%2Fkernel%2Flinux.git mm/kmsan: fix kmsan kmalloc hook when no stack depots are allocated yet 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/20250930115600.709776-2-aleksei.nikiforov@linux.ibm.com Link: https://lkml.kernel.org/r/20251022030213.GA35717@sol Fixes: 97769a53f117 ("mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation") Signed-off-by: Aleksei Nikiforov Reviewed-by: Alexander Potapenko Tested-by: Eric Biggers Cc: Alexei Starovoitov Cc: Dmitriy Vyukov Cc: Ilya Leoshkevich Cc: Marco Elver Cc: Signed-off-by: Andrew Morton --- diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c index 8bca7fece47f0..35ceaa8adb41e 100644 --- a/mm/kmsan/core.c +++ b/mm/kmsan/core.c @@ -72,9 +72,6 @@ depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags, nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0); - /* Don't sleep. */ - flags &= ~(__GFP_DIRECT_RECLAIM | __GFP_KSWAPD_RECLAIM); - handle = stack_depot_save(entries, nr_entries, flags); return stack_depot_set_extra_bits(handle, extra); } diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c index 2cee59d89c808..8f22d1f229813 100644 --- a/mm/kmsan/hooks.c +++ b/mm/kmsan/hooks.c @@ -84,7 +84,8 @@ void kmsan_slab_free(struct kmem_cache *s, void *object) if (s->ctor) return; kmsan_enter_runtime(); - kmsan_internal_poison_memory(object, s->object_size, GFP_KERNEL, + kmsan_internal_poison_memory(object, s->object_size, + GFP_KERNEL & ~(__GFP_RECLAIM), KMSAN_POISON_CHECK | KMSAN_POISON_FREE); kmsan_leave_runtime(); } @@ -114,7 +115,8 @@ void kmsan_kfree_large(const void *ptr) kmsan_enter_runtime(); page = virt_to_head_page((void *)ptr); KMSAN_WARN_ON(ptr != page_address(page)); - kmsan_internal_poison_memory((void *)ptr, page_size(page), GFP_KERNEL, + kmsan_internal_poison_memory((void *)ptr, page_size(page), + GFP_KERNEL & ~(__GFP_RECLAIM), KMSAN_POISON_CHECK | KMSAN_POISON_FREE); kmsan_leave_runtime(); } diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c index 54f3c3c962f07..55fdea199aaf0 100644 --- a/mm/kmsan/shadow.c +++ b/mm/kmsan/shadow.c @@ -208,7 +208,7 @@ void kmsan_free_page(struct page *page, unsigned int order) return; kmsan_enter_runtime(); kmsan_internal_poison_memory(page_address(page), page_size(page), - GFP_KERNEL, + GFP_KERNEL & ~(__GFP_RECLAIM), KMSAN_POISON_CHECK | KMSAN_POISON_FREE); kmsan_leave_runtime(); }