arm64: mte: Enable async tag check fault

MTE provides a mode that asynchronously updates the TFSR_EL1 register
when a tag check exception is detected.

To take advantage of this mode the kernel has to verify the status of
the register at:
  1. Context switching
  2. Return to user/EL0 (Not required in entry from EL0 since the kernel
  did not run)
  3. Kernel entry from EL1
  4. Kernel exit to EL1

If the register is non-zero a trace is reported.

Add the required features for EL1 detection and reporting.

Note: ITFSB bit is set in the SCTLR_EL1 register hence it guaranties that
the indirect writes to TFSR_EL1 are synchronized at exception entry to
EL1. On the context switch path the synchronization is guarantied by the
dsb() in __switch_to().
The dsb(nsh) in mte_check_tfsr_exit() is provisional pending
confirmation by the architects.

Cc: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/r/20210315132019.33202-8-vincenzo.frascino@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 8603c6636a7d..9a929620ca5d 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -98,11 +98,40 @@ static inline bool system_uses_mte_async_mode(void)
 {
 	return static_branch_unlikely(&mte_async_mode);
 }
+
+void mte_check_tfsr_el1(void);
+
+static inline void mte_check_tfsr_entry(void)
+{
+	mte_check_tfsr_el1();
+}
+
+static inline void mte_check_tfsr_exit(void)
+{
+	/*
+	 * The asynchronous faults are sync'ed automatically with
+	 * TFSR_EL1 on kernel entry but for exit an explicit dsb()
+	 * is required.
+	 */
+	dsb(nsh);
+	isb();
+
+	mte_check_tfsr_el1();
+}
 #else
 static inline bool system_uses_mte_async_mode(void)
 {
 	return false;
 }
+static inline void mte_check_tfsr_el1(void)
+{
+}
+static inline void mte_check_tfsr_entry(void)
+{
+}
+static inline void mte_check_tfsr_exit(void)
+{
+}
 #endif /* CONFIG_KASAN_HW_TAGS */
 
 #endif /* __ASSEMBLY__ */