Re: [PATCH 04/15] kasan: arm64: x86: risc-v: Make special tags arch specific
From: Palmer Dabbelt
Date: Wed Feb 05 2025 - 15:20:23 EST
On Tue, 04 Feb 2025 09:33:45 PST (-0800), maciej.wieczor-retman@xxxxxxxxx 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@xxxxxxxxx>
---
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@xxxxxxxxxxxxxxxx
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@xxxxxxxxxxxx> # 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.