From d155aab90fffa00f93cea1f107aef0a3d548b2ff Mon Sep 17 00:00:00 2001 From: Alexander Potapenko Date: Fri, 20 Feb 2026 15:49:40 +0100 Subject: [PATCH] mm/kfence: fix KASAN hardware tag faults during late enablement When KASAN hardware tags are enabled, re-enabling KFENCE late (via /sys/module/kfence/parameters/sample_interval) causes KASAN faults. This happens because the KFENCE pool and metadata are allocated via the page allocator, which tags the memory, while KFENCE continues to access it using untagged pointers during initialization. Use __GFP_SKIP_KASAN for late KFENCE pool and metadata allocations to ensure the memory remains untagged, consistent with early allocations from memblock. To support this, add __GFP_SKIP_KASAN to the allowlist in __alloc_contig_verify_gfp_mask(). Link: https://lkml.kernel.org/r/20260220144940.2779209-1-glider@google.com Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure") Signed-off-by: Alexander Potapenko Suggested-by: Ernesto Martinez Garcia Cc: Andrey Konovalov Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Greg KH Cc: Kees Cook Cc: Marco Elver Cc: Signed-off-by: Andrew Morton --- mm/kfence/core.c | 14 ++++++++------ mm/page_alloc.c | 3 ++- 2 files changed, 10 insertions(+), 7 deletions(-) diff --git a/mm/kfence/core.c b/mm/kfence/core.c index b5aedf505cec..7393957f9a20 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -1004,14 +1004,14 @@ static int kfence_init_late(void) #ifdef CONFIG_CONTIG_ALLOC struct page *pages; - pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL, first_online_node, - NULL); + pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL | __GFP_SKIP_KASAN, + first_online_node, NULL); if (!pages) return -ENOMEM; __kfence_pool = page_to_virt(pages); - pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL, first_online_node, - NULL); + pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL | __GFP_SKIP_KASAN, + first_online_node, NULL); if (pages) kfence_metadata_init = page_to_virt(pages); #else @@ -1021,11 +1021,13 @@ static int kfence_init_late(void) return -EINVAL; } - __kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, GFP_KERNEL); + __kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, + GFP_KERNEL | __GFP_SKIP_KASAN); if (!__kfence_pool) return -ENOMEM; - kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, GFP_KERNEL); + kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, + GFP_KERNEL | __GFP_SKIP_KASAN); #endif if (!kfence_metadata_init) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index fcc32737f451..2d4b6f1a554e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6928,7 +6928,8 @@ static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask) { const gfp_t reclaim_mask = __GFP_IO | __GFP_FS | __GFP_RECLAIM; const gfp_t action_mask = __GFP_COMP | __GFP_RETRY_MAYFAIL | __GFP_NOWARN | - __GFP_ZERO | __GFP_ZEROTAGS | __GFP_SKIP_ZERO; + __GFP_ZERO | __GFP_ZEROTAGS | __GFP_SKIP_ZERO | + __GFP_SKIP_KASAN; const gfp_t cc_action_mask = __GFP_RETRY_MAYFAIL | __GFP_NOWARN; /*