From 9b47d4eea3f7c1f620e95bda1d6221660bde7d7b Mon Sep 17 00:00:00 2001 From: Andrey Ryabinin Date: Tue, 13 Jan 2026 20:15:15 +0100 Subject: [PATCH] mm/kasan: fix KASAN poisoning in vrealloc() MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit A KASAN warning can be triggered when vrealloc() changes the requested size to a value that is not aligned to KASAN_GRANULE_SIZE. ------------[ cut here ]------------ WARNING: CPU: 2 PID: 1 at mm/kasan/shadow.c:174 kasan_unpoison+0x40/0x48 ... pc : kasan_unpoison+0x40/0x48 lr : __kasan_unpoison_vmalloc+0x40/0x68 Call trace: kasan_unpoison+0x40/0x48 (P) vrealloc_node_align_noprof+0x200/0x320 bpf_patch_insn_data+0x90/0x2f0 convert_ctx_accesses+0x8c0/0x1158 bpf_check+0x1488/0x1900 bpf_prog_load+0xd20/0x1258 __sys_bpf+0x96c/0xdf0 __arm64_sys_bpf+0x50/0xa0 invoke_syscall+0x90/0x160 Introduce a dedicated kasan_vrealloc() helper that centralizes KASAN handling for vmalloc reallocations. The helper accounts for KASAN granule alignment when growing or shrinking an allocation and ensures that partial granules are handled correctly. Use this helper from vrealloc_node_align_noprof() to fix poisoning logic. [ryabinin.a.a@gmail.com: move kasan_enabled() check, fix build] Link: https://lkml.kernel.org/r/20260119144509.32767-1-ryabinin.a.a@gmail.com Link: https://lkml.kernel.org/r/20260113191516.31015-1-ryabinin.a.a@gmail.com Fixes: d699440f58ce ("mm: fix vrealloc()'s KASAN poisoning logic") Signed-off-by: Andrey Ryabinin Reported-by: Maciej Żenczykowski Reported-by: Closes: https://lkml.kernel.org/r/CANP3RGeuRW53vukDy7WDO3FiVgu34-xVJYkfpm08oLO3odYFrA@mail.gmail.com Reviewed-by: Andrey Konovalov Tested-by: Maciej Wieczor-Retman Cc: Alexander Potapenko Cc: Dmitriy Vyukov Cc: Dmitry Vyukov Cc: Uladzislau Rezki Cc: Vincenzo Frascino Cc: Signed-off-by: Andrew Morton --- include/linux/kasan.h | 14 ++++++++++++++ mm/kasan/common.c | 21 +++++++++++++++++++++ mm/vmalloc.c | 7 ++----- 3 files changed, 37 insertions(+), 5 deletions(-) diff --git a/include/linux/kasan.h b/include/linux/kasan.h index 9c6ac4b62eb9..338a1921a50a 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -641,6 +641,17 @@ kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms, __kasan_unpoison_vmap_areas(vms, nr_vms, flags); } +void __kasan_vrealloc(const void *start, unsigned long old_size, + unsigned long new_size); + +static __always_inline void kasan_vrealloc(const void *start, + unsigned long old_size, + unsigned long new_size) +{ + if (kasan_enabled()) + __kasan_vrealloc(start, old_size, new_size); +} + #else /* CONFIG_KASAN_VMALLOC */ static inline void kasan_populate_early_vm_area_shadow(void *start, @@ -670,6 +681,9 @@ kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms, kasan_vmalloc_flags_t flags) { } +static inline void kasan_vrealloc(const void *start, unsigned long old_size, + unsigned long new_size) { } + #endif /* CONFIG_KASAN_VMALLOC */ #if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \ diff --git a/mm/kasan/common.c b/mm/kasan/common.c index ed489a14dddf..b7d05c2a6d93 100644 --- a/mm/kasan/common.c +++ b/mm/kasan/common.c @@ -606,4 +606,25 @@ void __kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms, __kasan_unpoison_vmalloc(addr, size, flags | KASAN_VMALLOC_KEEP_TAG); } } + +void __kasan_vrealloc(const void *addr, unsigned long old_size, + unsigned long new_size) +{ + if (new_size < old_size) { + kasan_poison_last_granule(addr, new_size); + + new_size = round_up(new_size, KASAN_GRANULE_SIZE); + old_size = round_up(old_size, KASAN_GRANULE_SIZE); + if (new_size < old_size) + __kasan_poison_vmalloc(addr + new_size, + old_size - new_size); + } else if (new_size > old_size) { + old_size = round_down(old_size, KASAN_GRANULE_SIZE); + __kasan_unpoison_vmalloc(addr + old_size, + new_size - old_size, + KASAN_VMALLOC_PROT_NORMAL | + KASAN_VMALLOC_VM_ALLOC | + KASAN_VMALLOC_KEEP_TAG); + } +} #endif diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 628f96e83b11..e286c2d2068c 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4322,7 +4322,7 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align if (want_init_on_free() || want_init_on_alloc(flags)) memset((void *)p + size, 0, old_size - size); vm->requested_size = size; - kasan_poison_vmalloc(p + size, old_size - size); + kasan_vrealloc(p, old_size, size); return (void *)p; } @@ -4330,16 +4330,13 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align * We already have the bytes available in the allocation; use them. */ if (size <= alloced_size) { - kasan_unpoison_vmalloc(p + old_size, size - old_size, - KASAN_VMALLOC_PROT_NORMAL | - KASAN_VMALLOC_VM_ALLOC | - KASAN_VMALLOC_KEEP_TAG); /* * No need to zero memory here, as unused memory will have * already been zeroed at initial allocation time or during * realloc shrink time. */ vm->requested_size = size; + kasan_vrealloc(p, old_size, size); return (void *)p; } -- 2.47.3