arm64: mte: rename TCO routines

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>

1 files changed, 81 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 9f79425fc65a..2e98028c1965 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -13,9 +13,74 @@
 
 #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,
@@ -138,6 +203,22 @@ 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;