On Tue, Feb 18, 2025 at 9:18 AM Maciej Wieczor-Retman
<maciej.wieczor-retman@xxxxxxxxx> wrote:
>
> KASAN's software tag-based mode needs multiple macros/functions to
> handle tag and pointer interactions - mainly to set and retrieve 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>
> ---
> arch/x86/include/asm/kasan.h | 32 ++++++++++++++++++++++++++++++--
> 1 file changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
> index de75306b932e..8829337a75fa 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 +26,33 @@
> KASAN_SHADOW_SCALE_SHIFT)))
>
> #ifndef __ASSEMBLY__
> +#include <linux/bitops.h>
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
> +
> +#define arch_kasan_set_tag(addr, tag) __tag_set(addr, tag)
But __tag_set is defined below. I think these need to be reordered.
> +#define arch_kasan_reset_tag(addr) __tag_reset(addr)
> +#define arch_kasan_get_tag(addr) __tag_get(addr)
> +
> +#ifdef CONFIG_KASAN_SW_TAGS
> +
> +#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 */
>
> #ifdef CONFIG_KASAN
> +
> +static inline const void *__tag_set(const void *addr, u8 tag)
A bit weird that __tag_set is defined under CONFIG_KASAN:
CONFIG_KASAN_SW_TAGS (or no condition, like on arm64) would make more
sense.
> +{
> + u64 __addr = (u64)addr & ~__tag_shifted(KASAN_TAG_KERNEL);
> + return (const void *)(__addr | __tag_shifted(tag));
> +}
> +
> 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 +61,9 @@ 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 /* __ASSEMBLY__ */
>
> #endif
> --
> 2.47.1
>
