[v2,05/14] kasan: arm64: x86: Make special tags arch specific

Commit Message

Maciej Wieczor-Retman Feb. 18, 2025, 8:15 a.m. UTC

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 native kernel tag arch specific for x86 and arm64.

Replace hardcoded kernel tag value and tag width with macros in KASAN's
non-arch specific code.

Signed-off-by: Maciej Wieczor-Retman <[e-mail]>
---
Changelog v2:
- Remove risc-v from the patch.

 MAINTAINERS                         | 2 +-
 arch/arm64/include/asm/kasan-tags.h | 9 +++++++++
 arch/x86/include/asm/kasan-tags.h   | 9 +++++++++
 include/linux/kasan-tags.h          | 8 +++++++-
 include/linux/kasan.h               | 4 +++-
 include/linux/mm.h                  | 6 +++---
 include/linux/page-flags-layout.h   | 7 +------
 7 files changed, 33 insertions(+), 12 deletions(-)
 create mode 100644 arch/arm64/include/asm/kasan-tags.h
 create mode 100644 arch/x86/include/asm/kasan-tags.h

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index 896a307fa065..37971952c24b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12478,7 +12478,7 @@  L:	[e-mail]
 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/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..ad5c11950233 100644
--- a/include/linux/kasan-tags.h
+++ b/include/linux/kasan-tags.h
@@ -2,7 +2,13 @@ 
 #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
+
+#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 b396feca714f..54481f8c30c5 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -40,7 +40,9 @@  typedef unsigned int __bitwise kasan_vmalloc_flags_t;
 
 #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 7b1068ddcbb7..0b1d21864294 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1824,7 +1824,7 @@  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;
@@ -1837,7 +1837,7 @@  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;
@@ -1856,7 +1856,7 @@  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 4f5c9e979bb9..b2cc4cb870e0 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)