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

Andrey Ryabinin
2025-08-07T16:35:39Z

On 8/5/25 8:23 AM, Baoquan He wrote:
> 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.
>

Ideally this problem should be solved by having kdump kernel with different
config. Because if we want only reliably collect crash dumps, than we probably
don't want other debug features, e.g. like VM_BUG_ON() crashing our 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(-)
>