When a memory region is allocated with vmalloc() and later expanded with vrealloc() — while still within the originally allocated size — KASAN may report a false positive because it does not update the tags for the newly expanded portion of the memory.

A typical example of this pattern occurs in the BPF verifier, and the following is a related false positive report:

[ 2206.486476] ================================================================== [ 2206.486509] BUG: KASAN: invalid-access in __memcpy+0xc/0x30 [ 2206.486607] Write at addr f5ff800083765270 by task test_progs/205 [ 2206.486664] Pointer tag: [f5], memory tag: [fe] [ 2206.486703] [ 2206.486745] CPU: 4 UID: 0 PID: 205 Comm: test_progs Tainted: G OE 6.18.0-rc7+ #145 PREEMPT(full) [ 2206.486861] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE [ 2206.486897] Hardware name: , BIOS [ 2206.486932] Call trace: [ 2206.486961] show_stack+0x24/0x40 (C) [ 2206.487071] __dump_stack+0x28/0x48 [ 2206.487182] dump_stack_lvl+0x7c/0xb0 [ 2206.487293] print_address_description+0x80/0x270 [ 2206.487403] print_report+0x94/0x100 [ 2206.487505] kasan_report+0xd8/0x150 [ 2206.487606] __do_kernel_fault+0x64/0x268 [ 2206.487717] do_bad_area+0x38/0x110 [ 2206.487820] do_tag_check_fault+0x38/0x60 [ 2206.487936] do_mem_abort+0x48/0xc8 [ 2206.488042] el1_abort+0x40/0x70 [ 2206.488127] el1h_64_sync_handler+0x50/0x118 [ 2206.488217] el1h_64_sync+0xa4/0xa8 [ 2206.488303] __memcpy+0xc/0x30 (P) [ 2206.488412] do_misc_fixups+0x4f8/0x1950 [ 2206.488528] bpf_check+0x31c/0x840 [ 2206.488638] bpf_prog_load+0x58c/0x658 [ 2206.488737] __sys_bpf+0x364/0x488 [ 2206.488833] __arm64_sys_bpf+0x30/0x58 [ 2206.488920] invoke_syscall+0x68/0xe8 [ 2206.489033] el0_svc_common+0xb0/0xf8 [ 2206.489143] do_el0_svc+0x28/0x48 [ 2206.489249] el0_svc+0x40/0xe8 [ 2206.489337] el0t_64_sync_handler+0x84/0x140 [ 2206.489427] el0t_64_sync+0x1bc/0x1c0

Here, 0xf5ff800083765000 is vmalloc()ed address for env->insn_aux_data with the size of 0x268. While this region is expanded size by 0x478 and initialise increased region to apply patched instructions, a false positive is triggered at the address 0xf5ff800083765270 because __kasan_unpoison_vmalloc() with KASAN_VMALLOC_PROT_NORMAL flag only doesn't update the tag on increaed region.

To address this, introduces KASAN_VMALLOC_EXPAND flag which is used to expand vmalloc()ed memory in range of real allocated size to update tag for increased region.

Fixes: 23689e91fb22 ("kasan, vmalloc: add vmalloc tagging for HW_TAGS”) Cc: stable@vger.kernel.org Signed-off-by: Yeoreum Yun yeoreum.yun@arm.com --- include/linux/kasan.h | 1 + mm/kasan/hw_tags.c | 11 +++++++++-- mm/vmalloc.c | 1 + 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h index d12e1a5f5a9a..0608c5d4e6cf 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -28,6 +28,7 @@ typedef unsigned int __bitwise kasan_vmalloc_flags_t; #define KASAN_VMALLOC_INIT ((__force kasan_vmalloc_flags_t)0x01u) #define KASAN_VMALLOC_VM_ALLOC ((__force kasan_vmalloc_flags_t)0x02u) #define KASAN_VMALLOC_PROT_NORMAL ((__force kasan_vmalloc_flags_t)0x04u) +#define KASAN_VMALLOC_EXPAND ((__force kasan_vmalloc_flags_t)0x08u)

#define KASAN_VMALLOC_PAGE_RANGE 0x1 /* Apply exsiting page range */ #define KASAN_VMALLOC_TLB_FLUSH 0x2 /* TLB flush */ diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c index 1c373cc4b3fa..d768c7360093 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c @@ -347,7 +347,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, * * For non-VM_ALLOC allocations, page_alloc memory is tagged as usual. */ - if (!(flags & KASAN_VMALLOC_VM_ALLOC)) { + if (!(flags & (KASAN_VMALLOC_VM_ALLOC | KASAN_VMALLOC_EXPAND))) { WARN_ON(flags & KASAN_VMALLOC_INIT); return (void *)start; } @@ -361,7 +361,14 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, return (void *)start; }

- tag = kasan_random_tag(); + if (flags & KASAN_VMALLOC_EXPAND) { + size = round_up(size + ((unsigned long)start & KASAN_GRANULE_MASK), + KASAN_GRANULE_SIZE); + start = PTR_ALIGN_DOWN(start, KASAN_GRANULE_SIZE); + tag = get_tag(start); + } else + tag = kasan_random_tag(); + start = set_tag(start, tag);

/* Unpoison and initialize memory up to size. */ diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 798b2ed21e46..6bfbf26fea3b 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4176,6 +4176,7 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align */ if (size <= alloced_size) { kasan_unpoison_vmalloc(p + old_size, size - old_size, + KASAN_VMALLOC_EXPAND | KASAN_VMALLOC_PROT_NORMAL); /* * No need to zero memory here, as unused memory will have -- LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}