[PATCH v2 4/9] kasan: sw_tags: Support tag widths less than 8 bits

Samuel Holland
2024-10-22T02:14:10Z

Allow architectures to override KASAN_TAG_KERNEL in asm/kasan.h. This
is needed on RISC-V, which supports 57-bit virtual addresses and 7-bit
pointer tags. For consistency, move the arm64 MTE definition of
KASAN_TAG_MIN to asm/kasan.h, since it is also architecture-dependent;
RISC-V's equivalent extension is expected to support 7-bit hardware
memory tags.

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

(no changes since v1)

arch/arm64/include/asm/kasan.h | 6 ++++--
arch/arm64/include/asm/uaccess.h | 1 +
include/linux/kasan-tags.h | 13 ++++++++-----
3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h
index e1b57c13f8a4..4ab419df8b93 100644
--- a/arch/arm64/include/asm/kasan.h
+++ b/arch/arm64/include/asm/kasan.h
@@ -6,8 +6,10 @@

#include <linux/linkage.h>
#include <asm/memory.h>
-#include <asm/mte-kasan.h>
-#include <asm/pgtable-types.h>
+
+#ifdef CONFIG_KASAN_HW_TAGS
+#define KASAN_TAG_MIN 0xF0 /* minimum value for random tags */
+#endif

#define arch_kasan_set_tag(addr, tag) __tag_set(addr, tag)
#define arch_kasan_reset_tag(addr) __tag_reset(addr)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 1aa4ecb73429..8f700a7dd2cd 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -22,6 +22,7 @@
#include <asm/cpufeature.h>
#include <asm/mmu.h>
#include <asm/mte.h>
+#include <asm/mte-kasan.h>
#include <asm/ptrace.h>
#include <asm/memory.h>
#include <asm/extable.h>
diff --git a/include/linux/kasan-tags.h b/include/linux/kasan-tags.h
index 4f85f562512c..e07c896f95d3 100644
--- a/include/linux/kasan-tags.h
+++ b/include/linux/kasan-tags.h
@@ -2,13 +2,16 @@
#ifndef _LINUX_KASAN_TAGS_H
#define _LINUX_KASAN_TAGS_H

+#include <asm/kasan.h>
+
+#ifndef KASAN_TAG_KERNEL
#define KASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */
-#define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
-#define KASAN_TAG_MAX 0xFD /* maximum value for random tags */
+#endif
+
+#define KASAN_TAG_INVALID (KASAN_TAG_KERNEL - 1) /* inaccessible memory tag */
+#define KASAN_TAG_MAX (KASAN_TAG_KERNEL - 2) /* maximum value for random tags */

-#ifdef CONFIG_KASAN_HW_TAGS
-#define KASAN_TAG_MIN 0xF0 /* minimum value for random tags */
-#else
+#ifndef KASAN_TAG_MIN
#define KASAN_TAG_MIN 0x00 /* minimum value for random tags */
#endif

--
2.45.1