On Mon, Aug 25, 2025 at 10:27 PM Maciej Wieczor-Retman
<maciej.wieczor-retman@xxxxxxxxx> wrote:
>
> KASAN's software tag-based mode needs multiple macros/functions to
> handle tag and pointer interactions - to set, retrieve and reset tags
> from the top bits of a pointer.
>
> Mimic functions currently used by arm64 but change the tag's position to
> bits [60:57] in the pointer.
>
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
> ---
> Changelog v4:
> - Rewrite __tag_set() without pointless casts and make it more readable.
>
> Changelog v3:
> - Reorder functions so that __tag_*() etc are above the
> arch_kasan_*() ones.
> - Remove CONFIG_KASAN condition from __tag_set()
>
> arch/x86/include/asm/kasan.h | 36 ++++++++++++++++++++++++++++++++++--
> 1 file changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
> index d7e33c7f096b..1963eb2fcff3 100644
> --- a/arch/x86/include/asm/kasan.h
> +++ b/arch/x86/include/asm/kasan.h
> @@ -3,6 +3,8 @@
> #define _ASM_X86_KASAN_H
>
> #include <linux/const.h>
> +#include <linux/kasan-tags.h>
> +#include <linux/types.h>
> #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
> #define KASAN_SHADOW_SCALE_SHIFT 3
>
> @@ -24,8 +26,37 @@
> KASAN_SHADOW_SCALE_SHIFT)))
>
> #ifndef __ASSEMBLER__
> +#include <linux/bitops.h>
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
> +
> +#ifdef CONFIG_KASAN_SW_TAGS
> +
Nit: can remove this empty line.
> +#define __tag_shifted(tag) FIELD_PREP(GENMASK_ULL(60, 57), tag)
> +#define __tag_reset(addr) (sign_extend64((u64)(addr), 56))
> +#define __tag_get(addr) ((u8)FIELD_GET(GENMASK_ULL(60, 57), (u64)addr))
> +#else
> +#define __tag_shifted(tag) 0UL
> +#define __tag_reset(addr) (addr)
> +#define __tag_get(addr) 0
> +#endif /* CONFIG_KASAN_SW_TAGS */
> +
> +static inline void *__tag_set(const void *__addr, u8 tag)
> +{
> + u64 addr = (u64)__addr;
> +
> + addr &= ~__tag_shifted(KASAN_TAG_MASK);
> + addr |= __tag_shifted(tag);
> +
> + return (void *)addr;
> +}
> +
> +#define arch_kasan_set_tag(addr, tag) __tag_set(addr, tag)
> +#define arch_kasan_reset_tag(addr) __tag_reset(addr)
> +#define arch_kasan_get_tag(addr) __tag_get(addr)
>
> #ifdef CONFIG_KASAN
> +
> void __init kasan_early_init(void);
> void __init kasan_init(void);
> void __init kasan_populate_shadow_for_vaddr(void *va, size_t size, int nid);
> @@ -34,8 +65,9 @@ static inline void kasan_early_init(void) { }
> static inline void kasan_init(void) { }
> static inline void kasan_populate_shadow_for_vaddr(void *va, size_t size,
> int nid) { }
> -#endif
>
> -#endif
> +#endif /* CONFIG_KASAN */
> +
> +#endif /* __ASSEMBLER__ */
>
> #endif
> --
> 2.50.1
>
Acked-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
