Re: [PATCH v5 1/2] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 08/08/2025 à 17:33, Sabyrzhan Tasbolatov a écrit :
> On Fri, Aug 8, 2025 at 10:03 AM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>>
>>
>>
>> Le 07/08/2025 à 21:40, Sabyrzhan Tasbolatov a écrit :
>>> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures [1] that need
>>> to defer KASAN initialization until shadow memory is properly set up,
>>> and unify the static key infrastructure across all KASAN modes.
>>
>> That probably desserves more details, maybe copy in informations from
>> the top of cover letter.
>>
>> I think there should also be some exeplanations about
>> kasan_arch_is_ready() becoming kasan_enabled(), and also why
>> kasan_arch_is_ready() completely disappear from mm/kasan/common.c
>> without being replaced by kasan_enabled().
>>
>>>
>>> [1] PowerPC, UML, LoongArch selects ARCH_DEFER_KASAN.
>>>
>>> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D217049&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cfe4f5a759ad6452b047408ddd691024a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638902640503259176%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=UM4uvQihJdeWwcC6DIiJXbn4wGsrijjRcHc55uCMErI%3D&reserved=0
>>> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
>>> ---
>>> Changes in v5:
>>> - Unified patches where arch (powerpc, UML, loongarch) selects
>>>     ARCH_DEFER_KASAN in the first patch not to break
>>>     bisectability
>>> - Removed kasan_arch_is_ready completely as there is no user
>>> - Removed __wrappers in v4, left only those where it's necessary
>>>     due to different implementations
>>>
>>> Changes in v4:
>>> - Fixed HW_TAGS static key functionality (was broken in v3)
>>> - Merged configuration and implementation for atomicity
>>> ---
>>>    arch/loongarch/Kconfig                 |  1 +
>>>    arch/loongarch/include/asm/kasan.h     |  7 ------
>>>    arch/loongarch/mm/kasan_init.c         |  8 +++----
>>>    arch/powerpc/Kconfig                   |  1 +
>>>    arch/powerpc/include/asm/kasan.h       | 12 ----------
>>>    arch/powerpc/mm/kasan/init_32.c        |  2 +-
>>>    arch/powerpc/mm/kasan/init_book3e_64.c |  2 +-
>>>    arch/powerpc/mm/kasan/init_book3s_64.c |  6 +----
>>>    arch/um/Kconfig                        |  1 +
>>>    arch/um/include/asm/kasan.h            |  5 ++--
>>>    arch/um/kernel/mem.c                   | 10 ++++++--
>>>    include/linux/kasan-enabled.h          | 32 ++++++++++++++++++--------
>>>    include/linux/kasan.h                  |  6 +++++
>>>    lib/Kconfig.kasan                      |  8 +++++++
>>>    mm/kasan/common.c                      | 17 ++++++++++----
>>>    mm/kasan/generic.c                     | 19 +++++++++++----
>>>    mm/kasan/hw_tags.c                     |  9 +-------
>>>    mm/kasan/kasan.h                       |  8 ++++++-
>>>    mm/kasan/shadow.c                      | 12 +++++-----
>>>    mm/kasan/sw_tags.c                     |  1 +
>>>    mm/kasan/tags.c                        |  2 +-
>>>    21 files changed, 100 insertions(+), 69 deletions(-)
>>>
>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>> index f0abc38c40a..cd64b2bc12d 100644
>>> --- a/arch/loongarch/Kconfig
>>> +++ b/arch/loongarch/Kconfig
>>> @@ -9,6 +9,7 @@ config LOONGARCH
>>>        select ACPI_PPTT if ACPI
>>>        select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
>>>        select ARCH_BINFMT_ELF_STATE
>>> +     select ARCH_DEFER_KASAN if KASAN
>>
>> Instead of adding 'if KASAN' in all users, you could do in two steps:
>>
>> Add a symbol ARCH_NEEDS_DEFER_KASAN.
>>
>> +config ARCH_NEEDS_DEFER_KASAN
>> +       bool
>>
>> And then:
>>
>> +config ARCH_DEFER_KASAN
>> +       def_bool
>> +       depends on KASAN
>> +       depends on ARCH_DEFER_KASAN
>> +       help
>> +         Architectures should select this if they need to defer KASAN
>> +         initialization until shadow memory is properly set up. This
>> +         enables runtime control via static keys. Otherwise, KASAN uses
>> +         compile-time constants for better performance.
>>
> 
> Actually, I don't see the benefits from this option. Sorry, have just
> revisited this again.
> With the new symbol, arch (PowerPC, UML, LoongArch) still needs select
> 2 options:
> 
> select ARCH_NEEDS_DEFER_KASAN
> select ARCH_DEFER_KASAN

Sorry, my mistake, ARCH_DEFER_KASAN has to be 'def_bool y'. Missing the 
'y'. That way it is automatically set to 'y' as long as KASAN and 
ARCH_NEEDS_DEFER_KASAN are selected. Should be:

config ARCH_DEFER_KASAN
	def_bool y
	depends on KASAN
	depends on ARCH_NEEDS_DEFER_KASAN


> 
> and the oneline with `if` condition is cleaner.
> select ARCH_DEFER_KASAN if KASAN
> 

I don't think so because it requires all architectures to add 'if KASAN' 
which is not convenient.

Christophe