Re: [PATCH v12 02/15] kasan: arm64: x86: Make special tags arch specific

[Catalin Marinas <catalin.marinas@arm.com>]

On Mon, Mar 30, 2026 at 02:33:16PM +0000, Maciej Wieczor-Retman wrote:
> From: Samuel Holland <samuel.holland@sifive.com>
> 
> KASAN's tag-based mode defines multiple special tag values. They're
> reserved for:
> - Native kernel value. On arm64 it's 0xFF and it causes an early return
>   in the tag checking function.
> - Invalid value. 0xFE marks an area as freed / unallocated. It's also
>   the value that is used to initialize regions of shadow memory.
> - Min and max values. 0xFD is the highest value that can be randomly
>   generated for a new tag. 0 is the minimal value with the exception of
>   arm64's hardware mode where it is equal to 0xF0.
> 
> Metadata macro is also defined:
> - Tag width equal to 8.
> 
> Tag-based mode on x86 is going to use 4 bit wide tags so all the above
> values need to be changed accordingly.
> 
> Make tag width and native kernel tag arch specific for x86 and arm64.
> 
> Base the invalid tag value and the max value on the native kernel tag
> since they follow the same pattern on both mentioned architectures.
> 
> Also generalize KASAN_SHADOW_INIT and 0xff used in various
> page_kasan_tag* helpers.
> 
> Give KASAN_TAG_MIN the default value of zero, and move the special value
> for hw_tags arm64 to its arch specific kasan-tags.h.
> 
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> Co-developed-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
> Acked-by: Will Deacon <will@kernel.org> (for the arm part)
> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
> Reviewed-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>