Re: [PATCH v13 1/7] arm64: mte: Add asynchronous mode support

On 2/12/21 9:21 PM, Andrey Konovalov wrote:

On Thu, Feb 11, 2021 at 4:34 PM Vincenzo Frascino
[off-list ref] wrote:

quoted

MTE provides an asynchronous mode for detecting tag exceptions. In
particular instead of triggering a fault the arm64 core updates a
register which is checked by the kernel after the asynchronous tag
check fault has occurred.

Add support for MTE asynchronous mode.

The exception handling mechanism will be added with a future patch.

Note: KASAN HW activates async mode via kasan.mode kernel parameter.
The default mode is set to synchronous.
The code that verifies the status of TFSR_EL1 will be added with a
future patch.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Andrey Konovalov <redacted>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
 arch/arm64/include/asm/memory.h    |  3 ++-
 arch/arm64/include/asm/mte-kasan.h |  9 +++++++--
 arch/arm64/kernel/mte.c            | 19 ++++++++++++++++---
 3 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index c759faf7a1ff..91515383d763 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h

@@ -243,7 +243,8 @@ 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_sync()             mte_enable_kernel_sync()
+#define arch_enable_tagging_async()            mte_enable_kernel_async()

We need to update KASAN usage of arch_enable_tagging() to
arch_enable_tagging_sync() in this patch as well. Otherwise, this
leaves KASAN broken between this patch and the next one.

Yes you are right, still can't explain why it did bysect cleanly though.
I will introduce temporarily here:

#define arch_enable_tagging() arch_enable_tagging_sync()

and remove it again in the respective kasan patch.

quoted

 #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 7ab500e2ad17..4acf8bf41cad 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h

@@ -77,7 +77,8 @@ static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
        } while (curr != end);
 }

-void mte_enable_kernel(void);
+void mte_enable_kernel_sync(void);
+void mte_enable_kernel_async(void);
 void mte_init_tags(u64 max_tag);

 void mte_set_report_once(bool state);

@@ -104,7 +105,11 @@ static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
 {
 }

-static inline void mte_enable_kernel(void)
+static inline void mte_enable_kernel_sync(void)
+{
+}
+
+static inline void mte_enable_kernel_async(void)
 {
 }

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index a66c2806fc4d..706b7ab75f31 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c

@@ -107,13 +107,26 @@ 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)
+static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
 {
        /* Enable MTE Sync Mode for EL1. */
-       sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
+       sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf);
        isb();
+
+       pr_info_once("MTE: enabled in %s mode at EL1\n", mode);
+}
+
+void mte_enable_kernel_sync(void)
+{
+       __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
+}
+EXPORT_SYMBOL_GPL(mte_enable_kernel_sync);
+
+void mte_enable_kernel_async(void)
+{
+       __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);
 }
-EXPORT_SYMBOL_GPL(mte_enable_kernel);
+EXPORT_SYMBOL_GPL(mte_enable_kernel_async);

 void mte_set_report_once(bool state)
 {
--

2.30.0

-- 
Regards,
Vincenzo

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