1 files changed, 89 insertions, 2 deletions

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 9f79425fc65a..352139271918 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -9,13 +9,78 @@
 #include <asm/cputype.h>
 #include <asm/mte-def.h>
 
-#ifndef __ASSEMBLY__
+#ifndef __ASSEMBLER__
 
 #include <linux/types.h>
 
+#ifdef CONFIG_KASAN_HW_TAGS
+
+/* Whether the MTE asynchronous mode is enabled. */
+DECLARE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
+
+static inline bool system_uses_mte_async_or_asymm_mode(void)
+{
+	return static_branch_unlikely(&mte_async_or_asymm_mode);
+}
+
+#else /* CONFIG_KASAN_HW_TAGS */
+
+static inline bool system_uses_mte_async_or_asymm_mode(void)
+{
+	return false;
+}
+
+#endif /* CONFIG_KASAN_HW_TAGS */
+
 #ifdef CONFIG_ARM64_MTE
 
 /*
+ * The Tag Check Flag (TCF) mode for MTE is per EL, hence TCF0
+ * affects EL0 and TCF affects EL1 irrespective of which TTBR is
+ * used.
+ * The kernel accesses TTBR0 usually with LDTR/STTR instructions
+ * when UAO is available, so these would act as EL0 accesses using
+ * TCF0.
+ * However futex.h code uses exclusives which would be executed as
+ * EL1, this can potentially cause a tag check fault even if the
+ * user disables TCF0.
+ *
+ * To address the problem we set the PSTATE.TCO bit in uaccess_enable()
+ * and reset it in uaccess_disable().
+ *
+ * The Tag check override (TCO) bit disables temporarily the tag checking
+ * preventing the issue.
+ */
+static inline void mte_disable_tco(void)
+{
+	asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(0),
+				 ARM64_MTE, CONFIG_KASAN_HW_TAGS));
+}
+
+static inline void mte_enable_tco(void)
+{
+	asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(1),
+				 ARM64_MTE, CONFIG_KASAN_HW_TAGS));
+}
+
+/*
+ * These functions disable tag checking only if in MTE async mode
+ * since the sync mode generates exceptions synchronously and the
+ * nofault or load_unaligned_zeropad can handle them.
+ */
+static inline void __mte_disable_tco_async(void)
+{
+	if (system_uses_mte_async_or_asymm_mode())
+		mte_disable_tco();
+}
+
+static inline void __mte_enable_tco_async(void)
+{
+	if (system_uses_mte_async_or_asymm_mode())
+		mte_enable_tco();
+}
+
+/*
  * These functions are meant to be only used from KASAN runtime through
  * the arch_*() interface defined in asm/memory.h.
  * These functions don't include system_supports_mte() checks,
@@ -135,9 +200,26 @@ static inline 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);
 void mte_enable_kernel_asymm(void);
+int mte_enable_kernel_store_only(void);
 
 #else /* CONFIG_ARM64_MTE */
 
+static inline void mte_disable_tco(void)
+{
+}
+
+static inline void mte_enable_tco(void)
+{
+}
+
+static inline void __mte_disable_tco_async(void)
+{
+}
+
+static inline void __mte_enable_tco_async(void)
+{
+}
+
 static inline u8 mte_get_ptr_tag(void *ptr)
 {
 	return 0xFF;
@@ -170,8 +252,13 @@ static inline void mte_enable_kernel_asymm(void)
 {
 }
 
+static inline int mte_enable_kernel_store_only(void)
+{
+	return -EINVAL;
+}
+
 #endif /* CONFIG_ARM64_MTE */
 
-#endif /* __ASSEMBLY__ */
+#endif /* __ASSEMBLER__ */
 
 #endif /* __ASM_MTE_KASAN_H  */