linux-kernel - Re: [PATCH v2 00/11] kasan: unify kasan_arch_is_ready with kasan

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Message-ID: <CA+fCnZfAtKWx=+to=XQBREhou=Snb0Yms4D8GNGaxE+BQUYm4A@mail.gmail.com>
Date: Sat, 28 Jun 2025 12:56:46 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Sabyrzhan Tasbolatov <snovitoll@...il.com>
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Subject: Re: [PATCH v2 00/11] kasan: unify kasan_arch_is_ready with kasan_enabled

On Thu, Jun 26, 2025 at 5:32 PM Sabyrzhan Tasbolatov
<snovitoll@...il.com> wrote:
>
> This patch series unifies the kasan_arch_is_ready() and kasan_enabled()
> interfaces by extending the existing kasan_enabled() infrastructure to
> work consistently across all KASAN modes (Generic, SW_TAGS, HW_TAGS).
>
> Currently, kasan_enabled() only works for HW_TAGS mode using a static key,
> while other modes either return IS_ENABLED(CONFIG_KASAN) (compile-time
> constant) or rely on architecture-specific kasan_arch_is_ready()
> implementations with custom static keys and global variables.
>
> This leads to:
> - Code duplication across architectures
> - Inconsistent runtime behavior between KASAN modes
> - Architecture-specific readiness tracking
>
> After this series:
> - All KASAN modes use the same kasan_flag_enabled static key
> - Consistent runtime enable/disable behavior across modes
> - Simplified architecture code with unified kasan_init_generic() calls
> - Elimination of arch specific kasan_arch_is_ready() implementations
> - Unified vmalloc integration using kasan_enabled() checks
>
> This addresses the bugzilla issue [1] about making
> kasan_flag_enabled and kasan_enabled() work for Generic mode,
> and extends it to provide true unification across all modes.
>
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=217049

Hi Sabyrzhan,

Thank you for working on this!

One aspect that is missing from the patches is moving the
kasan_arch_is_ready() calls into the include/linux/kasan.h (this is
not explicitly mentioned in the issue, but this is what the "adding
__wrappers" part is about).

Another thing that needs careful consideration is whether it's
possible to combine kasan_arch_is_ready() and kasan_enabled() into the
same check logically at all. There's one issue mentioned in [1]:

> In kasan_cache_create() we unconditionally allocate a metadata buffer,
> but the kasan_init_slab_obj() call to initialise it is guarded by
> kasan_enabled(). But later parts of the code only check the presence of
> the buffer before using it, so bad things happen if kasan_enabled()
> later turns on (I was getting some error about invalid lock state).

And there might be other callbacks that should be executed even before
kasan_init_...() completes. But then for the HW_TAGS mode, if
kasan_enabled() is off, then we don't want to execute any callbacks.

So maybe we do actually need a separate static key for
kasan_arch_is_ready(). But even if so, it still makes sense to move
kasan_arch_is_ready() into the __wrappers for the affected callbacks.

Thanks!

[1] https://lore.kernel.org/linux-mm/CA+fCnZf7JqTH46C7oG2Wk9NnLU7hgiVDEK0EA8RAtyr-KgkHdg@mail.gmail.com/