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(). Cc: Andrew Morton Cc: Andrey Konovalov Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Greg KH Cc: Kees Cook Cc: Marco Elver Cc: Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure") Suggested-by: Ernesto Martinez Garcia Signed-off-by: Alexander Potapenko --- This is a follow-up for "mm/kfence: disable KFENCE upon KASAN HW tags enablement" that is currently in mm-hotfixes-unstable --- 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 71f87072baf9b..30959c97b881d 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -999,14 +999,14 @@ 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 @@ -1016,11 +1016,13 @@ 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 cbf758e27aa2c..9d1887e3d4074 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6921,7 +6921,8 @@ 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; /* -- 2.53.0.345.g96ddfc5eaa-goog