Re: [PATCH v3 1/4] kasan, arm64: Add KASAN light mode

Architectures supported by KASAN HW can provide a light mode of
execution. On an MTE enabled arm64 hw for example this can be identified
with the asynch mode of execution.
In this mode, if a tag check fault occurs, the TFSR_EL1 register is
updated asynchronously. The kernel checks the corresponding bits
periodically.

KASAN requires a specific mode of execution to make use of this hw feature.

Add KASAN HW light execution mode.

Note: This patch adds the KASAN_ARG_MODE_LIGHT config option and the
"light" kernel command line option to enable the described feature.
This patch introduces the kasan_def.h header to make easier to propagate
the relevant enumerations to the architectural code.

Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <redacted>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <redacted>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
 arch/arm64/include/asm/memory.h    |  2 +-
 arch/arm64/include/asm/mte-kasan.h |  5 +++--
 arch/arm64/kernel/mte.c            |  2 +-
 include/linux/kasan.h              |  1 +
 include/linux/kasan_def.h          | 10 ++++++++++
 mm/kasan/hw_tags.c                 | 19 ++++++++++++++++++-
 mm/kasan/kasan.h                   |  2 +-
 7 files changed, 35 insertions(+), 6 deletions(-)
 create mode 100644 include/linux/kasan_def.h

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 18fce223b67b..3a7c5beb7096 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h

@@ -231,7 +231,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
 }

 #ifdef CONFIG_KASAN_HW_TAGS
-#define arch_enable_tagging()                  mte_enable_kernel()
+#define arch_enable_tagging(mode)              mte_enable_kernel(mode)
 #define arch_init_tags(max_tag)                        mte_init_tags(max_tag)
 #define arch_get_random_tag()                  mte_get_random_tag()
 #define arch_get_mem_tag(addr)                 mte_get_mem_tag(addr)

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 26349a4b5e2e..5402f4c8e88d 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h

@@ -9,6 +9,7 @@

 #ifndef __ASSEMBLY__

+#include <linux/kasan_def.h>
 #include <linux/types.h>

 /*

@@ -29,7 +30,7 @@ u8 mte_get_mem_tag(void *addr);
 u8 mte_get_random_tag(void);
 void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);

-void mte_enable_kernel(void);
+void mte_enable_kernel(enum kasan_hw_tags_mode mode);
 void mte_init_tags(u64 max_tag);

 #else /* CONFIG_ARM64_MTE */

@@ -52,7 +53,7 @@ static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
        return addr;
 }

-static inline void mte_enable_kernel(void)
+static inline void mte_enable_kernel(enum kasan_hw_tags_mode mode)
 {
 }

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index dc9ada64feed..53a6d734e29b 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c

@@ -151,7 +151,7 @@ void mte_init_tags(u64 max_tag)
        write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
 }

-void mte_enable_kernel(void)
+void mte_enable_kernel(enum kasan_hw_tags_mode mode)
 {
        /* Enable MTE Sync Mode for EL1. */
        sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 5e0655fb2a6f..026031444217 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h

@@ -2,6 +2,7 @@
 #ifndef _LINUX_KASAN_H
 #define _LINUX_KASAN_H

+#include <linux/kasan_def.h>
 #include <linux/static_key.h>
 #include <linux/types.h>

diff --git a/include/linux/kasan_def.h b/include/linux/kasan_def.h
new file mode 100644
index 000000000000..0a55400809c9
--- /dev/null
+++ b/include/linux/kasan_def.h

@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_KASAN_DEF_H
+#define _LINUX_KASAN_DEF_H
+
+enum kasan_hw_tags_mode {
+       KASAN_HW_TAGS_SYNC,
+       KASAN_HW_TAGS_ASYNC,
+};
+
+#endif /* _LINUX_KASAN_DEF_H */

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 55bd6f09c70f..6c3b0742f639 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c

@@ -22,6 +22,7 @@
 enum kasan_arg_mode {
        KASAN_ARG_MODE_DEFAULT,
        KASAN_ARG_MODE_OFF,
+       KASAN_ARG_MODE_LIGHT,
        KASAN_ARG_MODE_PROD,
        KASAN_ARG_MODE_FULL,
 };

@@ -60,6 +61,8 @@ static int __init early_kasan_mode(char *arg)

        if (!strcmp(arg, "off"))
                kasan_arg_mode = KASAN_ARG_MODE_OFF;
+       else if (!strcmp(arg, "light"))
+               kasan_arg_mode = KASAN_ARG_MODE_LIGHT;