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

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Message-ID: <CA+fCnZcGyTECP15VMSPh+duLmxNe=ApHfOnbAY3NqtFHZvceZw@mail.gmail.com>
Date: Sun, 29 Jun 2025 22:05:22 +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 Sat, Jun 28, 2025 at 3:25 PM Sabyrzhan Tasbolatov
<snovitoll@...il.com> wrote:
>
> On Sat, Jun 28, 2025 at 3:57 PM Andrey Konovalov <andreyknvl@...il.com> wrote:
> >
> > 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]:
>
> Hello,
> I've removed kasan_arch_is_ready() at all in this series:
> [PATCH v2 11/11] kasan: replace kasan_arch_is_ready with kasan_enabled
>
> Is it not what's expected by unification?

I guess the issue description diverged a bit from what needs to be
done, sorry about that.

The core 2 things I wanted to address with the unification are:

1. Avoid spraying kasan_arch_is_ready() throughout the KASAN
implementation and move these checks into include/linux/kasan.h (and
add __wrappers when required).

2. Avoid architectures redefining the same kasan_enabled global
variable/static key.

Initially, I thought that s/kasan_arch_is_ready/kasan_enabled + simply
moving the calls into affected include/linux/kasan.h functions would
be enough. But then, based on [1], turns out it's not that simple.

So now, I think we likely still need two separate checks/flags:
kasan_enabled() that controls whether KASAN is enabled at all and
kasan_arch_is_ready() that gets turned on by kasan_init() when shadow
is initialized (should we rename it to kasan_shadow_initialized()?).
But then we can still move kasan_arch_is_ready() into
include/linux/kasan.h and use the proper combination of checks for
each affected function before calling __wrappers. And we can still
remove the duplicated flags/keys code from the arch code.

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