[PATCH 0/4] mm/kasan: make kasan=on|off work for all three modes

Baoquan He
2025-08-05T06:23:48Z

Currently only hw_tags mode of kasan can be enabled or disabled with
kernel parameter kasan=on|off for built kernel. For kasan generic and
sw_tags mode, there's no way to disable them once kernel is built.
This is not convenient sometime, e.g in system kdump is configured.
When the 1st kernel has KASAN enabled and crash triggered to switch to
kdump kernel, the generic or sw_tags mode will cost much extra memory
for kasan shadow while in fact it's meaningless to have kasan in kdump
kernel.

So this patchset moves the kasan=on|off out of hw_tags scope and into
common code to make it visible in generic and sw_tags mode too. Then we
can add kasan=off in kdump kernel to reduce the unneeded meomry cost for
kasan.

Test:
=====
I only took test on x86_64 for generic mode, and on arm64 for
generic, sw_tags and hw_tags mode. All of them works well.

However when I tested sw_tags on a HPE apollo arm64 machine, it always
breaks kernel with a KASAN bug. Even w/o this patchset applied, the bug
can always be seen too.

"BUG: KASAN: invalid-access in pcpu_alloc_noprof+0x42c/0x9a8"

I haven't got root cause of the bug, will report the bug later in
another thread.
====

Baoquan He (4):
mm/kasan: add conditional checks in functions to return directly if
kasan is disabled
mm/kasan: move kasan= code to common place
mm/kasan: don't initialize kasan if it's disabled
mm/kasan: make kasan=on|off take effect for all three modes

arch/arm/mm/kasan_init.c | 6 +++++
arch/arm64/mm/kasan_init.c | 7 ++++++
arch/loongarch/mm/kasan_init.c | 5 ++++
arch/powerpc/mm/kasan/init_32.c | 8 +++++-
arch/powerpc/mm/kasan/init_book3e_64.c | 6 +++++
arch/powerpc/mm/kasan/init_book3s_64.c | 6 +++++
arch/riscv/mm/kasan_init.c | 6 +++++
arch/um/kernel/mem.c | 6 +++++
arch/x86/mm/kasan_init_64.c | 6 +++++
arch/xtensa/mm/kasan_init.c | 6 +++++
include/linux/kasan-enabled.h | 11 ++------
mm/kasan/common.c | 27 ++++++++++++++++++++
mm/kasan/generic.c | 20 +++++++++++++--
mm/kasan/hw_tags.c | 35 ++------------------------
mm/kasan/init.c | 6 +++++
mm/kasan/quarantine.c | 3 +++
mm/kasan/shadow.c | 23 ++++++++++++++++-
mm/kasan/sw_tags.c | 9 +++++++
18 files changed, 150 insertions(+), 46 deletions(-)

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2.41.0