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

[Marco Elver <elver@google.com>]

On Tue, 5 Aug 2025 at 08:23, 'Baoquan He' via kasan-dev
<kasan-dev@googlegroups.com> 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.

Are you using KASAN generic or SW-tags is production?
If in a test environment, is the overhead of the kdump kernel really
unacceptable?

> 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.

Does it also work for CONFIG_KASAN_INLINE?

> 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(-)
>
> --
> 2.41.0
>
> --
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