[RFC PATCH 3/7] kasan: sw_tags: Support tag widths less than 8 bits

[Andrey Konovalov]

On Wed, Aug 14, 2024 at 10:56 AM Samuel Holland
<samuel.holland at sifive.com> wrote:
>
> Allow architectures to override KASAN_TAG_KERNEL in asm/kasan.h. This
> is needed on RISC-V, which supports 57-bit virtual addresses and 7-bit
> pointer tags. For consistency, move the arm64 MTE definition of
> KASAN_TAG_MIN to asm/kasan.h, since it is also architecture-dependent;
> RISC-V's equivalent extension is expected to support 7-bit hardware
> memory tags.
>
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
> ---
>
>  arch/arm64/include/asm/kasan.h   |  6 ++++--
>  arch/arm64/include/asm/uaccess.h |  1 +
>  include/linux/kasan-tags.h       | 13 ++++++++-----
>  3 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h
> index e1b57c13f8a4..4ab419df8b93 100644
> --- a/arch/arm64/include/asm/kasan.h
> +++ b/arch/arm64/include/asm/kasan.h
> @@ -6,8 +6,10 @@
>
>  #include <linux/linkage.h>
>  #include <asm/memory.h>
> -#include <asm/mte-kasan.h>
> -#include <asm/pgtable-types.h>
> +
> +#ifdef CONFIG_KASAN_HW_TAGS
> +#define KASAN_TAG_MIN                  0xF0 /* minimum value for random tags */
> +#endif
>
>  #define arch_kasan_set_tag(addr, tag)  __tag_set(addr, tag)
>  #define arch_kasan_reset_tag(addr)     __tag_reset(addr)
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 28f665e0975a..56a09f412272 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -22,6 +22,7 @@
>  #include <asm/cpufeature.h>
>  #include <asm/mmu.h>
>  #include <asm/mte.h>
> +#include <asm/mte-kasan.h>
>  #include <asm/ptrace.h>
>  #include <asm/memory.h>
>  #include <asm/extable.h>
> diff --git a/include/linux/kasan-tags.h b/include/linux/kasan-tags.h
> index 4f85f562512c..e07c896f95d3 100644
> --- a/include/linux/kasan-tags.h
> +++ b/include/linux/kasan-tags.h
> @@ -2,13 +2,16 @@
>  #ifndef _LINUX_KASAN_TAGS_H
>  #define _LINUX_KASAN_TAGS_H
>
> +#include <asm/kasan.h>
> +
> +#ifndef KASAN_TAG_KERNEL
>  #define KASAN_TAG_KERNEL       0xFF /* native kernel pointers tag */
> -#define KASAN_TAG_INVALID      0xFE /* inaccessible memory tag */
> -#define KASAN_TAG_MAX          0xFD /* maximum value for random tags */
> +#endif
> +
> +#define KASAN_TAG_INVALID      (KASAN_TAG_KERNEL - 1) /* inaccessible memory tag */
> +#define KASAN_TAG_MAX          (KASAN_TAG_KERNEL - 2) /* maximum value for random tags */
>
> -#ifdef CONFIG_KASAN_HW_TAGS
> -#define KASAN_TAG_MIN          0xF0 /* minimum value for random tags */
> -#else
> +#ifndef KASAN_TAG_MIN
>  #define KASAN_TAG_MIN          0x00 /* minimum value for random tags */
>  #endif
>
> --
> 2.45.1
>

Reviewed-by: Andrey Konovalov <andreyknvl at gmail.com>