Re: [PATCH v5 5/6] arm64: mte: Expose execution mode

MTE enabled arm64 HW can be configured in synchronous or asynchronous
tagging mode of execution.
In synchronous mode, an exception is triggered if a tag check fault
occurs.
In asynchronous mode, if a tag check fault occurs, the TFSR_EL1 register
is updated asynchronously. The kernel checks the corresponding bits
periodically.

Introduce an API that exposes the mode of execution to the kernel.

Note: This API will be used by KASAN KUNIT tests to forbid the execution
when async mode is enable.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
 arch/arm64/include/asm/memory.h    | 1 +
 arch/arm64/include/asm/mte-kasan.h | 6 ++++++
 arch/arm64/kernel/mte.c            | 8 ++++++++
 3 files changed, 15 insertions(+)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index df96b9c10b81..1d4eef519fa6 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h

@@ -233,6 +233,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
 #ifdef CONFIG_KASAN_HW_TAGS
 #define arch_enable_tagging_sync()             mte_enable_kernel_sync()
 #define arch_enable_tagging_async()            mte_enable_kernel_async()
+#define arch_is_mode_sync()                    mte_is_mode_sync()
 #define arch_set_tagging_report_once(state)    mte_set_report_once(state)
 #define arch_init_tags(max_tag)                        mte_init_tags(max_tag)
 #define arch_get_random_tag()                  mte_get_random_tag()

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 76b6a5988ce5..c216160e805c 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h

@@ -31,6 +31,7 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);

 void mte_enable_kernel_sync(void);
 void mte_enable_kernel_async(void);
+bool mte_is_mode_sync(void);
 void mte_init_tags(u64 max_tag);

 void mte_set_report_once(bool state);

@@ -64,6 +65,11 @@ static inline void mte_enable_kernel_sync(void)
 {
 }

+static inline bool mte_is_mode_sync(void)
+{
+       return false;
+}
+
 static inline void mte_init_tags(u64 max_tag)
 {
 }

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 7763ac1f2917..1cc3fc173b97 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c

@@ -26,6 +26,7 @@
 u64 gcr_kernel_excl __ro_after_init;

 static bool report_fault_once = true;
+static bool __mte_mode_sync = true;

 static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
 {

@@ -169,9 +170,16 @@ void mte_enable_kernel_sync(void)

 void mte_enable_kernel_async(void)
 {
+       __mte_mode_sync = false;
+
        __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);
 }

+bool mte_is_mode_sync(void)
+{
+       return __mte_mode_sync;
+}
+
 void mte_set_report_once(bool state)
 {
        WRITE_ONCE(report_fault_once, state);
--

2.30.0