Re: [PATCH 04/15] kasan: arm64: x86: risc-v: Make special tags arch specific

[Palmer Dabbelt <palmer@dabbelt.com>]

On Tue, 04 Feb 2025 09:33:45 PST (-0800), maciej.wieczor-retman@intel.com wrote:
> 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.
> - Max value. 0xFD is the highest value that can be randomly generated
>   for a new tag.
>
> 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 tags arch specific for x86, risc-v and arm64. On x86 the values
> just lose the top 4 bits.
>
> Replace hardcoded kernel tag value and tag width with macros in KASAN's
> non-arch specific code.
>
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
> ---
>  MAINTAINERS                         |  2 +-
>  arch/arm64/include/asm/kasan-tags.h |  9 +++++++++
>  arch/riscv/include/asm/kasan-tags.h | 12 ++++++++++++
>  arch/riscv/include/asm/kasan.h      |  4 ----
>  arch/x86/include/asm/kasan-tags.h   |  9 +++++++++
>  include/linux/kasan-tags.h          | 12 +++++++++++-
>  include/linux/kasan.h               |  4 +++-
>  include/linux/mm.h                  |  6 +++---
>  include/linux/page-flags-layout.h   |  7 +------
>  9 files changed, 49 insertions(+), 16 deletions(-)
>  create mode 100644 arch/arm64/include/asm/kasan-tags.h
>  create mode 100644 arch/riscv/include/asm/kasan-tags.h
>  create mode 100644 arch/x86/include/asm/kasan-tags.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index b878ddc99f94..45671faa3b6f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -12227,7 +12227,7 @@ L:	kasan-dev@googlegroups.com
>  S:	Maintained
>  B:	https://bugzilla.kernel.org/buglist.cgi?component=Sanitizers&product=Memory%20Management
>  F:	Documentation/dev-tools/kasan.rst
> -F:	arch/*/include/asm/*kasan.h
> +F:	arch/*/include/asm/*kasan*.h
>  F:	arch/*/mm/kasan_init*
>  F:	include/linux/kasan*.h
>  F:	lib/Kconfig.kasan
> diff --git a/arch/arm64/include/asm/kasan-tags.h b/arch/arm64/include/asm/kasan-tags.h
> new file mode 100644
> index 000000000000..9e835da95f6b
> --- /dev/null
> +++ b/arch/arm64/include/asm/kasan-tags.h
> @@ -0,0 +1,9 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_KASAN_TAGS_H
> +#define __ASM_KASAN_TAGS_H
> +
> +#define KASAN_TAG_KERNEL	0xFF /* native kernel pointers tag */
> +
> +#define KASAN_TAG_WIDTH 8
> +
> +#endif /* ASM_KASAN_TAGS_H */
> diff --git a/arch/riscv/include/asm/kasan-tags.h b/arch/riscv/include/asm/kasan-tags.h
> new file mode 100644
> index 000000000000..83d7dcc8af74
> --- /dev/null
> +++ b/arch/riscv/include/asm/kasan-tags.h
> @@ -0,0 +1,12 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_KASAN_TAGS_H
> +#define __ASM_KASAN_TAGS_H
> +
> +#ifdef CONFIG_KASAN_SW_TAGS
> +#define KASAN_TAG_KERNEL	0x7f /* native kernel pointers tag */
> +#endif
> +
> +#define KASAN_TAG_WIDTH 8
> +
> +#endif /* ASM_KASAN_TAGS_H */
> +
> diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
> index f6b378ba936d..27938e0d5233 100644
> --- a/arch/riscv/include/asm/kasan.h
> +++ b/arch/riscv/include/asm/kasan.h
> @@ -41,10 +41,6 @@
>
>  #define KASAN_SHADOW_OFFSET	_AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
>
> -#ifdef CONFIG_KASAN_SW_TAGS
> -#define KASAN_TAG_KERNEL	0x7f /* native kernel pointers tag */
> -#endif
> -
>  #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)
> diff --git a/arch/x86/include/asm/kasan-tags.h b/arch/x86/include/asm/kasan-tags.h
> new file mode 100644
> index 000000000000..68ba385bc75c
> --- /dev/null
> +++ b/arch/x86/include/asm/kasan-tags.h
> @@ -0,0 +1,9 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_KASAN_TAGS_H
> +#define __ASM_KASAN_TAGS_H
> +
> +#define KASAN_TAG_KERNEL	0xF /* native kernel pointers tag */
> +
> +#define KASAN_TAG_WIDTH		4
> +
> +#endif /* ASM_KASAN_TAGS_H */
> diff --git a/include/linux/kasan-tags.h b/include/linux/kasan-tags.h
> index e07c896f95d3..b4aacfa8709b 100644
> --- a/include/linux/kasan-tags.h
> +++ b/include/linux/kasan-tags.h
> @@ -2,7 +2,17 @@
>  #ifndef _LINUX_KASAN_TAGS_H
>  #define _LINUX_KASAN_TAGS_H
>
> -#include <asm/kasan.h>
> +#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
> +#include <asm/kasan-tags.h>
> +#endif
> +
> +#ifdef CONFIG_KASAN_SW_TAGS_DENSE
> +#define KASAN_TAG_WIDTH		4
> +#endif
> +
> +#ifndef KASAN_TAG_WIDTH
> +#define KASAN_TAG_WIDTH		0
> +#endif
>
>  #ifndef KASAN_TAG_KERNEL
>  #define KASAN_TAG_KERNEL	0xFF /* native kernel pointers tag */
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 5a3e9bec21c2..83146367170a 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -88,7 +88,9 @@ static inline u8 kasan_get_shadow_tag(const void *addr)
>
>  #ifdef CONFIG_KASAN_SW_TAGS
>  /* This matches KASAN_TAG_INVALID. */
> -#define KASAN_SHADOW_INIT 0xFE
> +#ifndef KASAN_SHADOW_INIT
> +#define KASAN_SHADOW_INIT KASAN_TAG_INVALID
> +#endif
>  #else
>  #define KASAN_SHADOW_INIT 0
>  #endif
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 61fff5d34ed5..ddca2f63a5f6 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1813,7 +1813,7 @@ static inline u8 page_kasan_tag(const struct page *page)
>
>  	if (kasan_enabled()) {
>  		tag = (page->flags >> KASAN_TAG_PGSHIFT) & KASAN_TAG_MASK;
> -		tag ^= 0xff;
> +		tag ^= KASAN_TAG_KERNEL;
>  	}
>
>  	return tag;
> @@ -1826,7 +1826,7 @@ static inline void page_kasan_tag_set(struct page *page, u8 tag)
>  	if (!kasan_enabled())
>  		return;
>
> -	tag ^= 0xff;
> +	tag ^= KASAN_TAG_KERNEL;
>  	old_flags = READ_ONCE(page->flags);
>  	do {
>  		flags = old_flags;
> @@ -1845,7 +1845,7 @@ static inline void page_kasan_tag_reset(struct page *page)
>
>  static inline u8 page_kasan_tag(const struct page *page)
>  {
> -	return 0xff;
> +	return KASAN_TAG_KERNEL;
>  }
>
>  static inline void page_kasan_tag_set(struct page *page, u8 tag) { }
> diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
> index 7d79818dc065..ac3576f409ad 100644
> --- a/include/linux/page-flags-layout.h
> +++ b/include/linux/page-flags-layout.h
> @@ -3,6 +3,7 @@
>  #define PAGE_FLAGS_LAYOUT_H
>
>  #include <linux/numa.h>
> +#include <linux/kasan-tags.h>
>  #include <generated/bounds.h>
>
>  /*
> @@ -72,12 +73,6 @@
>  #define NODE_NOT_IN_PAGE_FLAGS	1
>  #endif
>
> -#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
> -#define KASAN_TAG_WIDTH 8
> -#else
> -#define KASAN_TAG_WIDTH 0
> -#endif
> -
>  #ifdef CONFIG_NUMA_BALANCING
>  #define LAST__PID_SHIFT 8
>  #define LAST__PID_MASK  ((1 << LAST__PID_SHIFT)-1)

Acked-by: Palmer Dabbelt <palmer@rivosinc.com> # RISC-V

Probably best to keep this along with the rest of the patches, but LMK 
if you want me to point something at the RISC-V tree.