BACKPORT: arm64: mte: rename TCO routines

(Backport: no real conflicts, neighboring lines changed.)

The TCO related routines are used in uaccess methods and
load_unaligned_zeropad() but are unrelated to both even if the naming
suggest otherwise.

Improve the readability of the code moving the away from uaccess.h and
pre-pending them with "mte".

[andreyknvl@google.com: drop __ from mte_disable/enable_tco names]
  Link: https://lkml.kernel.org/r/74d26337b2360733956114069e96ff11c296a944.1680114854.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/a48e7adce1248c0f9603a457776d59daa0ef734b.1678491668.git.andreyknvl@google.com
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Weizhao Ouyang <ouyangweizhao@zeku.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Bug: 254721825
(cherry picked from commit 2cc029a084)
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Change-Id: Icb37f3338fd99204bc1029f7cf8e1165a311a2fa

arch/arm64/include/asm/mte-kasan.h

@@ -12,8 +12,73 @@
 
 #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.
@@ -137,6 +202,22 @@ void mte_enable_kernel_asymm(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;

arch/arm64/include/asm/mte.h

@@ -145,14 +145,6 @@ static inline void mte_disable_tco_entry(struct task_struct *task)
 }
 
 #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);
-}
-
 void mte_check_tfsr_el1(void);
 
 static inline void mte_check_tfsr_entry(void)
@@ -179,10 +171,6 @@ static inline void mte_check_tfsr_exit(void)
 	mte_check_tfsr_el1();
 }
 #else
-static inline bool system_uses_mte_async_or_asymm_mode(void)
-{
-	return false;
-}
 static inline void mte_check_tfsr_el1(void)
 {
 }

arch/arm64/include/asm/uaccess.h

@@ -208,7 +208,7 @@ static inline void __uaccess_enable_tco_async(void)
 
 static inline void uaccess_disable_privileged(void)
 {
-	__uaccess_disable_tco();
+	mte_disable_tco();
 
 	if (uaccess_ttbr0_disable())
 		return;
@@ -218,7 +218,7 @@ static inline void uaccess_disable_privileged(void)
 
 static inline void uaccess_enable_privileged(void)
 {
-	__uaccess_enable_tco();
+	mte_enable_tco();
 
 	if (uaccess_ttbr0_enable())
 		return;
@@ -332,8 +332,8 @@ do {									\
 #define get_user	__get_user
 
 /*
- * We must not call into the scheduler between __uaccess_enable_tco_async() and
- * __uaccess_disable_tco_async(). As `dst` and `src` may contain blocking
+ * We must not call into the scheduler between __mte_enable_tco_async() and
+ * __mte_disable_tco_async(). As `dst` and `src` may contain blocking
  * functions, we must evaluate these outside of the critical section.
  */
 #define __get_kernel_nofault(dst, src, type, err_label)			\
@@ -342,10 +342,10 @@ do {									\
 	__typeof__(src) __gkn_src = (src);				\
 	int __gkn_err = 0;						\
 									\
-	__uaccess_enable_tco_async();					\
+	__mte_enable_tco_async();					\
 	__raw_get_mem("ldr", *((type *)(__gkn_dst)),			\
 		      (__force type *)(__gkn_src), __gkn_err);		\
-	__uaccess_disable_tco_async();					\
+	__mte_disable_tco_async();					\
 									\
 	if (unlikely(__gkn_err))					\
 		goto err_label;						\
@@ -423,8 +423,8 @@ do {									\
 #define put_user	__put_user
 
 /*
- * We must not call into the scheduler between __uaccess_enable_tco_async() and
- * __uaccess_disable_tco_async(). As `dst` and `src` may contain blocking
+ * We must not call into the scheduler between __mte_enable_tco_async() and
+ * __mte_disable_tco_async(). As `dst` and `src` may contain blocking
  * functions, we must evaluate these outside of the critical section.
  */
 #define __put_kernel_nofault(dst, src, type, err_label)			\
@@ -433,10 +433,10 @@ do {									\
 	__typeof__(src) __pkn_src = (src);				\
 	int __pkn_err = 0;						\
 									\
-	__uaccess_enable_tco_async();					\
+	__mte_enable_tco_async();					\
 	__raw_put_mem("str", *((type *)(__pkn_src)),			\
 		      (__force type *)(__pkn_dst), __pkn_err);		\
-	__uaccess_disable_tco_async();					\
+	__mte_disable_tco_async();					\
 									\
 	if (unlikely(__pkn_err))					\
 		goto err_label;						\

arch/arm64/include/asm/word-at-a-time.h

@@ -55,7 +55,7 @@ static inline unsigned long load_unaligned_zeropad(const void *addr)
 {
 	unsigned long ret, tmp;
 
-	__uaccess_enable_tco_async();
+	__mte_enable_tco_async();
 
 	/* Load word from unaligned pointer addr */
 	asm(
@@ -78,7 +78,7 @@ static inline unsigned long load_unaligned_zeropad(const void *addr)
 	: "=&r" (ret), "=&r" (tmp)
 	: "r" (addr), "Q" (*(unsigned long *)addr));
 
-	__uaccess_disable_tco_async();
+	__mte_disable_tco_async();
 
 	return ret;
 }