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Subject[PATCH v3 1/4] kasan, arm64: Add KASAN light mode
Date
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 <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
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;
else if (!strcmp(arg, "prod"))
kasan_arg_mode = KASAN_ARG_MODE_PROD;
else if (!strcmp(arg, "full"))
@@ -105,9 +108,21 @@ static int __init early_kasan_fault(char *arg)
}
early_param("kasan.fault", early_kasan_fault);

+static inline int hw_init_mode(enum kasan_arg_mode mode)
+{
+ switch (mode) {
+ case KASAN_ARG_MODE_LIGHT:
+ return KASAN_HW_TAGS_ASYNC;
+ default:
+ return KASAN_HW_TAGS_SYNC;
+ }
+}
+
/* kasan_init_hw_tags_cpu() is called for each CPU. */
void kasan_init_hw_tags_cpu(void)
{
+ enum kasan_hw_tags_mode hw_mode;
+
/*
* There's no need to check that the hardware is MTE-capable here,
* as this function is only called for MTE-capable hardware.
@@ -118,7 +133,8 @@ void kasan_init_hw_tags_cpu(void)
return;

hw_init_tags(KASAN_TAG_MAX);
- hw_enable_tagging();
+ hw_mode = hw_init_mode(kasan_arg_mode);
+ hw_enable_tagging(hw_mode);
}

/* kasan_init_hw_tags() is called once on boot CPU. */
@@ -145,6 +161,7 @@ void __init kasan_init_hw_tags(void)
case KASAN_ARG_MODE_OFF:
/* If KASAN is disabled, do nothing. */
return;
+ case KASAN_ARG_MODE_LIGHT:
case KASAN_ARG_MODE_PROD:
static_branch_enable(&kasan_flag_enabled);
break;
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index cc4d9e1d49b1..78c09279327e 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -284,7 +284,7 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
#define arch_set_mem_tag_range(addr, size, tag) ((void *)(addr))
#endif

-#define hw_enable_tagging() arch_enable_tagging()
+#define hw_enable_tagging(mode) arch_enable_tagging(mode)
#define hw_init_tags(max_tag) arch_init_tags(max_tag)
#define hw_get_random_tag() arch_get_random_tag()
#define hw_get_mem_tag(addr) arch_get_mem_tag(addr)
--
2.30.0
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