linux-kernel - [PATCH v7 04/15] x86/kasan: Add arch specific kasan functions

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Message-ID: <406416dea492be82578c2cf4ee70e45d98200081.1765386422.git.m.wieczorretman@pm.me>
Date: Wed, 10 Dec 2025 17:29:03 +0000
From: Maciej Wieczor-Retman <m.wieczorretman@...me>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Axel Rasmussen <axelrasmussen@...gle.com>, Yuanchu Xie <yuanchu@...gle.com>, Wei Xu <weixugc@...gle.com>
Cc: m.wieczorretman@...me, Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v7 04/15] x86/kasan: Add arch specific kasan functions

From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>

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@...el.com>
---
Changelog v7:
- Add KASAN_TAG_BYTE_MASK to avoid circular includes and avoid removing
  KASAN_TAG_MASK from mmzone.h.
- Remove Andrey's Acked-by tag.

Changelog v6:
- Remove empty line after ifdef CONFIG_KASAN_SW_TAGS
- Add ifdef 64 bit to avoid problems in vdso32.
- Add Andrey's Acked-by tag.

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 | 42 ++++++++++++++++++++++++++++++++++--
 include/linux/kasan-tags.h   |  2 ++
 include/linux/mmzone.h       |  2 +-
 3 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
index d7e33c7f096b..eab12527ed7f 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 +26,43 @@
 						  KASAN_SHADOW_SCALE_SHIFT)))
 
 #ifndef __ASSEMBLER__
+#include <linux/bitops.h>
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+
+#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_64BIT
+static inline void *__tag_set(const void *__addr, u8 tag)
+{
+	u64 addr = (u64)__addr;
+
+	addr &= ~__tag_shifted(KASAN_TAG_BYTE_MASK);
+	addr |= __tag_shifted(tag & KASAN_TAG_BYTE_MASK);
+
+	return (void *)addr;
+}
+#else
+static inline void *__tag_set(void *__addr, u8 tag)
+{
+	return __addr;
+}
+#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)
 
 #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 +71,9 @@ 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
diff --git a/include/linux/kasan-tags.h b/include/linux/kasan-tags.h
index ad5c11950233..e4f26bec3673 100644
--- a/include/linux/kasan-tags.h
+++ b/include/linux/kasan-tags.h
@@ -10,6 +10,8 @@
 #define KASAN_TAG_WIDTH		0
 #endif
 
+#define KASAN_TAG_BYTE_MASK	((1UL << KASAN_TAG_WIDTH) - 1)
+
 #ifndef KASAN_TAG_KERNEL
 #define KASAN_TAG_KERNEL	0xFF /* native kernel pointers tag */
 #endif
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 7fb7331c5725..aa35f8331a4b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1181,7 +1181,7 @@ static inline bool zone_is_empty(const struct zone *zone)
 #define NODES_MASK		((1UL << NODES_WIDTH) - 1)
 #define SECTIONS_MASK		((1UL << SECTIONS_WIDTH) - 1)
 #define LAST_CPUPID_MASK	((1UL << LAST_CPUPID_SHIFT) - 1)
-#define KASAN_TAG_MASK		((1UL << KASAN_TAG_WIDTH) - 1)
+#define KASAN_TAG_MASK		KASAN_TAG_BYTE_MASK
 #define ZONEID_MASK		((1UL << ZONEID_SHIFT) - 1)
 
 static inline enum zone_type memdesc_zonenum(memdesc_flags_t flags)
-- 
2.52.0