[Baoquan He <bhe@redhat.com>]

alexghiti@rivosinc.com, agordeev@linux.ibm.com, linux@armlinux.org.uk,
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Cc: ryabinin.a.a@gmail.com, glider@google.com, andreyknvl@gmail.com,
	dvyukov@google.com, vincenzo.frascino@arm.com,
	akpm@linux-foundation.org, kasan-dev@googlegroups.com,
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Bcc: bhe@redhat.com
Subject: Re: [PATCH v2 00/12] mm/kasan: make kasan=on|off work for all three
 modes
Reply-To: 
In-Reply-To: <20250812124941.69508-1-bhe@redhat.com>

Forgot adding related ARCH mailing list or people to CC, add them.

On 08/12/25 at 08:49pm, 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.
> 
> 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.
> 
> Changelog:
> ====
> v1->v2:
> - Add __ro_after_init for __ro_after_init, and remove redundant blank
>   lines in mm/kasan/common.c. Thanks to Marco.
> - Fix a code bug in <linux/kasan-enabled.h> when CONFIG_KASAN is unset,
>   this is found out by SeongJae and Lorenzo, and also reported by LKP
>   report, thanks to them.
> - Add a missing kasan_enabled() checking in kasan_report(). This will
>   cause below KASAN report info even though kasan=off is set:
>      ==================================================================
>      BUG: KASAN: stack-out-of-bounds in tick_program_event+0x130/0x150
>      Read of size 4 at addr ffff00005f747778 by task swapper/0/1
>      
>      CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.16.0+ #8 PREEMPT(voluntary) 
>      Hardware name: GIGABYTE R272-P30-JG/MP32-AR0-JG, BIOS F31n (SCP: 2.10.20220810) 09/30/2022
>      Call trace:
>       show_stack+0x30/0x90 (C)
>       dump_stack_lvl+0x7c/0xa0
>       print_address_description.constprop.0+0x90/0x310
>       print_report+0x104/0x1f0
>       kasan_report+0xc8/0x110
>       __asan_report_load4_noabort+0x20/0x30
>       tick_program_event+0x130/0x150
>       ......snip...
>      ==================================================================
> 
> - Add jump_label_init() calling before kasan_init() in setup_arch() in these
>   architectures: xtensa, arm. Because they currenly rely on
>   jump_label_init() in main() which is a little late. Then the early static
>   key kasan_flag_enabled in kasan_init() won't work.
> 
> - In UML architecture, change to enable kasan_flag_enabled in arch_mm_preinit()
>   because kasan_init() is enabled before main(), there's no chance to operate
>   on static key in kasan_init().
> 
> Test:
> =====
> In v1, I took test on x86_64 for generic mode, and on arm64 for
> generic, sw_tags and hw_tags mode. All of them works well.
> 
> In v2, I only tested on arm64 for generic, sw_tags and hw_tags mode, it
> works. For powerpc, I got a BOOK3S/64 machine, while it says
> 'KASAN not enabled as it requires radix' and KASAN is disabled. Will
> look for other POWER machine to test this.
> ====
> 
> Baoquan He (12):
>   mm/kasan: add conditional checks in functions to return directly if
>     kasan is disabled
>   mm/kasan: move kasan= code to common place
>   mm/kasan/sw_tags: don't initialize kasan if it's disabled
>   arch/arm: don't initialize kasan if it's disabled
>   arch/arm64: don't initialize kasan if it's disabled
>   arch/loongarch: don't initialize kasan if it's disabled
>   arch/powerpc: don't initialize kasan if it's disabled
>   arch/riscv: don't initialize kasan if it's disabled
>   arch/x86: don't initialize kasan if it's disabled
>   arch/xtensa: don't initialize kasan if it's disabled
>   arch/um: don't initialize kasan if it's disabled
>   mm/kasan: make kasan=on|off take effect for all three modes
> 
>  arch/arm/kernel/setup.c                |  6 +++++
>  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/kernel/setup.c             |  1 +
>  arch/xtensa/mm/kasan_init.c            |  6 +++++
>  include/linux/kasan-enabled.h          | 18 ++++++-------
>  mm/kasan/common.c                      | 25 ++++++++++++++++++
>  mm/kasan/generic.c                     | 20 +++++++++++++--
>  mm/kasan/hw_tags.c                     | 35 ++------------------------
>  mm/kasan/init.c                        |  6 +++++
>  mm/kasan/quarantine.c                  |  3 +++
>  mm/kasan/report.c                      |  4 ++-
>  mm/kasan/shadow.c                      | 23 ++++++++++++++++-
>  mm/kasan/sw_tags.c                     |  9 +++++++
>  21 files changed, 165 insertions(+), 47 deletions(-)
> 
> -- 
> 2.41.0
>