[PATCH 0/3] KASAN: HW_TAGS: Disable tagging for stack and page-tables

Muhammad Usama Anjum
2026-03-19T11:50:08Z

Stacks and page tables are always accessed with the match‑all tag,
so assigning a new random tag every time at allocation and setting
invalid tag at deallocation time, just adds overhead without improving
the detection.

With __GFP_SKIP_KASAN the page keeps its poison tag and KASAN_TAG_KERNEL
(match-all tag) is stored in the page flags while keeping the poison tag
in the hardware. The benefit of it is that 256 tag setting instruction
per 4 kB page aren't needed at allocation and deallocation time.

Thus match‑all pointers still work, while non‑match tags (other than
poison tag) still fault.

__GFP_SKIP_KASAN only skips for KASAN_HW_TAGS mode, so coverage is
unchanged.

Benchmark:
The benchmark has two modes. In thread mode, the child process forks
and creates N threads. In pgtable mode, the parent maps and faults a
specified memory size and then forks repeatedly with children exiting
immediately.

Thread benchmark:
2000 iterations, 2000 threads: 2.575 s → 2.229 s (~13.4% faster)

The pgtable samples:
- 2048 MB, 2000 iters 19.08 s → 17.62 s (~7.6% faster)

Muhammad Usama Anjum (3):
vmalloc: add __GFP_SKIP_KASAN support
fork: skip MTE tagging for kernel stacks
mm: SKIP KASAN for page table allocations

include/asm-generic/pgalloc.h | 2 +-
kernel/fork.c | 8 +++++---
mm/vmalloc.c | 8 ++++++--
3 files changed, 12 insertions(+), 6 deletions(-)

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2.47.3