Merge branch 'for-next/mte' into for-next/core

* for-next/mte:
  kasan: Extend KASAN mode kernel parameter
  arm64: mte: Add asymmetric mode support
  arm64: mte: CPU feature detection for Asymm MTE
  arm64: mte: Bitfield definitions for Asymm MTE
  kasan: Remove duplicate of kasan_flag_async
  arm64: kasan: mte: move GCR_EL1 switch to task switch when KASAN disabled

Documentation/dev-tools/kasan.rst

@@ -194,14 +194,17 @@ additional boot parameters that allow disabling KASAN or controlling features:
 
 - ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).
 
-- ``kasan.mode=sync`` or ``=async`` controls whether KASAN is configured in
-  synchronous or asynchronous mode of execution (default: ``sync``).
+- ``kasan.mode=sync``, ``=async`` or ``=asymm`` controls whether KASAN
+  is configured in synchronous, asynchronous or asymmetric mode of
+  execution (default: ``sync``).
   Synchronous mode: a bad access is detected immediately when a tag
   check fault occurs.
   Asynchronous mode: a bad access detection is delayed. When a tag check
   fault occurs, the information is stored in hardware (in the TFSR_EL1
   register for arm64). The kernel periodically checks the hardware and
   only reports tag faults during these checks.
+  Asymmetric mode: a bad access is detected synchronously on reads and
+  asynchronously on writes.
 
 - ``kasan.stacktrace=off`` or ``=on`` disables or enables alloc and free stack
   traces collection (default: ``on``).

arch/arm64/include/asm/memory.h

@@ -243,6 +243,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
 #ifdef CONFIG_KASAN_HW_TAGS
 #define arch_enable_tagging_sync()		mte_enable_kernel_sync()
 #define arch_enable_tagging_async()		mte_enable_kernel_async()
+#define arch_enable_tagging_asymm()		mte_enable_kernel_asymm()
 #define arch_force_async_tag_fault()		mte_check_tfsr_exit()
 #define arch_get_random_tag()			mte_get_random_tag()
 #define arch_get_mem_tag(addr)			mte_get_mem_tag(addr)

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

@@ -130,6 +130,7 @@ 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);
 
 #else /* CONFIG_ARM64_MTE */
 
@@ -161,6 +162,10 @@ static inline void mte_enable_kernel_async(void)
 {
 }
 
+static inline void mte_enable_kernel_asymm(void)
+{
+}
+
 #endif /* CONFIG_ARM64_MTE */
 
 #endif /* __ASSEMBLY__ */

arch/arm64/include/asm/mte.h

@@ -88,11 +88,11 @@ static inline int mte_ptrace_copy_tags(struct task_struct *child,
 
 #ifdef CONFIG_KASAN_HW_TAGS
 /* Whether the MTE asynchronous mode is enabled. */
-DECLARE_STATIC_KEY_FALSE(mte_async_mode);
+DECLARE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
 
-static inline bool system_uses_mte_async_mode(void)
+static inline bool system_uses_mte_async_or_asymm_mode(void)
 {
-	return static_branch_unlikely(&mte_async_mode);
+	return static_branch_unlikely(&mte_async_or_asymm_mode);
 }
 
 void mte_check_tfsr_el1(void);
@@ -121,7 +121,7 @@ static inline void mte_check_tfsr_exit(void)
 	mte_check_tfsr_el1();
 }
 #else
-static inline bool system_uses_mte_async_mode(void)
+static inline bool system_uses_mte_async_or_asymm_mode(void)
 {
 	return false;
 }

arch/arm64/include/asm/sysreg.h

@@ -626,6 +626,7 @@
 #define SCTLR_ELx_TCF_NONE	(UL(0x0) << SCTLR_ELx_TCF_SHIFT)
 #define SCTLR_ELx_TCF_SYNC	(UL(0x1) << SCTLR_ELx_TCF_SHIFT)
 #define SCTLR_ELx_TCF_ASYNC	(UL(0x2) << SCTLR_ELx_TCF_SHIFT)
+#define SCTLR_ELx_TCF_ASYMM	(UL(0x3) << SCTLR_ELx_TCF_SHIFT)
 #define SCTLR_ELx_TCF_MASK	(UL(0x3) << SCTLR_ELx_TCF_SHIFT)
 
 #define SCTLR_ELx_ENIA_SHIFT	31
@@ -671,6 +672,7 @@
 #define SCTLR_EL1_TCF0_NONE	(UL(0x0) << SCTLR_EL1_TCF0_SHIFT)
 #define SCTLR_EL1_TCF0_SYNC	(UL(0x1) << SCTLR_EL1_TCF0_SHIFT)
 #define SCTLR_EL1_TCF0_ASYNC	(UL(0x2) << SCTLR_EL1_TCF0_SHIFT)
+#define SCTLR_EL1_TCF0_ASYMM	(UL(0x3) << SCTLR_EL1_TCF0_SHIFT)
 #define SCTLR_EL1_TCF0_MASK	(UL(0x3) << SCTLR_EL1_TCF0_SHIFT)
 
 #define SCTLR_EL1_BT1		(BIT(36))
@@ -812,6 +814,7 @@
 #define ID_AA64PFR1_MTE_NI		0x0
 #define ID_AA64PFR1_MTE_EL0		0x1
 #define ID_AA64PFR1_MTE			0x2
+#define ID_AA64PFR1_MTE_ASYMM		0x3
 
 /* id_aa64zfr0 */
 #define ID_AA64ZFR0_F64MM_SHIFT		56

arch/arm64/include/asm/uaccess.h

@@ -191,13 +191,13 @@ static inline void __uaccess_enable_tco(void)
  */
 static inline void __uaccess_disable_tco_async(void)
 {
-	if (system_uses_mte_async_mode())
+	if (system_uses_mte_async_or_asymm_mode())
 		 __uaccess_disable_tco();
 }
 
 static inline void __uaccess_enable_tco_async(void)
 {
-	if (system_uses_mte_async_mode())
+	if (system_uses_mte_async_or_asymm_mode())
 		__uaccess_enable_tco();
 }
 

arch/arm64/kernel/cpufeature.c

@@ -2331,6 +2331,16 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.sign = FTR_UNSIGNED,
 		.cpu_enable = cpu_enable_mte,
 	},
+	{
+		.desc = "Asymmetric MTE Tag Check Fault",
+		.capability = ARM64_MTE_ASYMM,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
+		.matches = has_cpuid_feature,
+		.sys_reg = SYS_ID_AA64PFR1_EL1,
+		.field_pos = ID_AA64PFR1_MTE_SHIFT,
+		.min_field_value = ID_AA64PFR1_MTE_ASYMM,
+		.sign = FTR_UNSIGNED,
+	},
 #endif /* CONFIG_ARM64_MTE */
 	{
 		.desc = "RCpc load-acquire (LDAPR)",

arch/arm64/kernel/entry.S

@@ -168,20 +168,20 @@ alternative_else_nop_endif
 
 	.macro mte_set_kernel_gcr, tmp, tmp2
 #ifdef CONFIG_KASAN_HW_TAGS
-alternative_if_not ARM64_MTE
+alternative_cb	kasan_hw_tags_enable
 	b	1f
-alternative_else_nop_endif
+alternative_cb_end
 	mov	\tmp, KERNEL_GCR_EL1
 	msr_s	SYS_GCR_EL1, \tmp
 1:
 #endif
 	.endm
 
 	.macro mte_set_user_gcr, tsk, tmp, tmp2
-#ifdef CONFIG_ARM64_MTE
-alternative_if_not ARM64_MTE
+#ifdef CONFIG_KASAN_HW_TAGS
+alternative_cb	kasan_hw_tags_enable
 	b	1f
-alternative_else_nop_endif
+alternative_cb_end
 	ldr	\tmp, [\tsk, #THREAD_MTE_CTRL]
 
 	mte_set_gcr \tmp, \tmp2

arch/arm64/kernel/mte.c

@@ -26,9 +26,12 @@
 static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred);
 
 #ifdef CONFIG_KASAN_HW_TAGS
-/* Whether the MTE asynchronous mode is enabled. */
-DEFINE_STATIC_KEY_FALSE(mte_async_mode);
-EXPORT_SYMBOL_GPL(mte_async_mode);
+/*
+ * The asynchronous and asymmetric MTE modes have the same behavior for
+ * store operations. This flag is set when either of these modes is enabled.
+ */
+DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
+EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode);
 #endif
 
 static void mte_sync_page_tags(struct page *page, pte_t old_pte,
@@ -116,7 +119,7 @@ void mte_enable_kernel_sync(void)
 	 * Make sure we enter this function when no PE has set
 	 * async mode previously.
 	 */
-	WARN_ONCE(system_uses_mte_async_mode(),
+	WARN_ONCE(system_uses_mte_async_or_asymm_mode(),
 			"MTE async mode enabled system wide!");
 
 	__mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
@@ -134,8 +137,34 @@ void mte_enable_kernel_async(void)
 	 * mode in between sync and async, this strategy needs
 	 * to be reviewed.
 	 */
-	if (!system_uses_mte_async_mode())
-		static_branch_enable(&mte_async_mode);
+	if (!system_uses_mte_async_or_asymm_mode())
+		static_branch_enable(&mte_async_or_asymm_mode);
+}
+
+void mte_enable_kernel_asymm(void)
+{
+	if (cpus_have_cap(ARM64_MTE_ASYMM)) {
+		__mte_enable_kernel("asymmetric", SCTLR_ELx_TCF_ASYMM);
+
+		/*
+		 * MTE asymm mode behaves as async mode for store
+		 * operations. The mode is set system wide by the
+		 * first PE that executes this function.
+		 *
+		 * Note: If in future KASAN acquires a runtime switching
+		 * mode in between sync and async, this strategy needs
+		 * to be reviewed.
+		 */
+		if (!system_uses_mte_async_or_asymm_mode())
+			static_branch_enable(&mte_async_or_asymm_mode);
+	} else {
+		/*
+		 * If the CPU does not support MTE asymmetric mode the
+		 * kernel falls back on synchronous mode which is the
+		 * default for kasan=on.
+		 */
+		mte_enable_kernel_sync();
+	}
 }
 #endif
 
@@ -179,6 +208,30 @@ static void mte_update_sctlr_user(struct task_struct *task)
 	task->thread.sctlr_user = sctlr;
 }
 
+static void mte_update_gcr_excl(struct task_struct *task)
+{
+	/*
+	 * SYS_GCR_EL1 will be set to current->thread.mte_ctrl value by
+	 * mte_set_user_gcr() in kernel_exit, but only if KASAN is enabled.
+	 */
+	if (kasan_hw_tags_enabled())
+		return;
+
+	write_sysreg_s(
+		((task->thread.mte_ctrl >> MTE_CTRL_GCR_USER_EXCL_SHIFT) &
+		 SYS_GCR_EL1_EXCL_MASK) | SYS_GCR_EL1_RRND,
+		SYS_GCR_EL1);
+}
+
+void __init kasan_hw_tags_enable(struct alt_instr *alt, __le32 *origptr,
+				 __le32 *updptr, int nr_inst)
+{
+	BUG_ON(nr_inst != 1); /* Branch -> NOP */
+
+	if (kasan_hw_tags_enabled())
+		*updptr = cpu_to_le32(aarch64_insn_gen_nop());
+}
+
 void mte_thread_init_user(void)
 {
 	if (!system_supports_mte())
@@ -198,6 +251,7 @@ void mte_thread_switch(struct task_struct *next)
 		return;
 
 	mte_update_sctlr_user(next);
+	mte_update_gcr_excl(next);
 
 	/*
 	 * Check if an async tag exception occurred at EL1.
@@ -243,6 +297,7 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 	if (task == current) {
 		preempt_disable();
 		mte_update_sctlr_user(task);
+		mte_update_gcr_excl(task);
 		update_sctlr_el1(task->thread.sctlr_user);
 		preempt_enable();
 	}

arch/arm64/tools/cpucaps

@@ -40,6 +40,7 @@ HW_DBM
 KVM_PROTECTED_MODE
 MISMATCHED_CACHE_TYPE
 MTE
+MTE_ASYMM
 SPECTRE_V2
 SPECTRE_V3A
 SPECTRE_V4

include/linux/kasan.h

@@ -89,7 +89,7 @@ static __always_inline bool kasan_enabled(void)
 	return static_branch_likely(&kasan_flag_enabled);
 }
 
-static inline bool kasan_has_integrated_init(void)
+static inline bool kasan_hw_tags_enabled(void)
 {
 	return kasan_enabled();
 }
@@ -104,7 +104,7 @@ static inline bool kasan_enabled(void)
 	return IS_ENABLED(CONFIG_KASAN);
 }
 
-static inline bool kasan_has_integrated_init(void)
+static inline bool kasan_hw_tags_enabled(void)
 {
 	return false;
 }
@@ -125,6 +125,11 @@ static __always_inline void kasan_free_pages(struct page *page,
 
 #endif /* CONFIG_KASAN_HW_TAGS */
 
+static inline bool kasan_has_integrated_init(void)
+{
+	return kasan_hw_tags_enabled();
+}
+
 #ifdef CONFIG_KASAN
 
 struct kasan_cache {

lib/test_kasan.c

@@ -88,7 +88,7 @@ static void kasan_test_exit(struct kunit *test)
  */
 #define KUNIT_EXPECT_KASAN_FAIL(test, expression) do {			\
 	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS) &&				\
-	    !kasan_async_mode_enabled())				\
+	    kasan_sync_fault_possible())				\
 		migrate_disable();					\
 	KUNIT_EXPECT_FALSE(test, READ_ONCE(fail_data.report_found));	\
 	barrier();							\

mm/kasan/hw_tags.c

@@ -29,6 +29,7 @@ enum kasan_arg_mode {
 	KASAN_ARG_MODE_DEFAULT,
 	KASAN_ARG_MODE_SYNC,
 	KASAN_ARG_MODE_ASYNC,
+	KASAN_ARG_MODE_ASYMM,
 };
 
 enum kasan_arg_stacktrace {
@@ -45,9 +46,9 @@ static enum kasan_arg_stacktrace kasan_arg_stacktrace __ro_after_init;
 DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
 EXPORT_SYMBOL(kasan_flag_enabled);
 
-/* Whether the asynchronous mode is enabled. */
-bool kasan_flag_async __ro_after_init;
-EXPORT_SYMBOL_GPL(kasan_flag_async);
+/* Whether the selected mode is synchronous/asynchronous/asymmetric.*/
+enum kasan_mode kasan_mode __ro_after_init;
+EXPORT_SYMBOL_GPL(kasan_mode);
 
 /* Whether to collect alloc/free stack traces. */
 DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
@@ -69,7 +70,7 @@ static int __init early_kasan_flag(char *arg)
 }
 early_param("kasan", early_kasan_flag);
 
-/* kasan.mode=sync/async */
+/* kasan.mode=sync/async/asymm */
 static int __init early_kasan_mode(char *arg)
 {
 	if (!arg)
@@ -79,6 +80,8 @@ static int __init early_kasan_mode(char *arg)
 		kasan_arg_mode = KASAN_ARG_MODE_SYNC;
 	else if (!strcmp(arg, "async"))
 		kasan_arg_mode = KASAN_ARG_MODE_ASYNC;
+	else if (!strcmp(arg, "asymm"))
+		kasan_arg_mode = KASAN_ARG_MODE_ASYMM;
 	else
 		return -EINVAL;
 
@@ -116,11 +119,13 @@ void kasan_init_hw_tags_cpu(void)
 		return;
 
 	/*
-	 * Enable async mode only when explicitly requested through
-	 * the command line.
+	 * Enable async or asymm modes only when explicitly requested
+	 * through the command line.
 	 */
 	if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
 		hw_enable_tagging_async();
+	else if (kasan_arg_mode == KASAN_ARG_MODE_ASYMM)
+		hw_enable_tagging_asymm();
 	else
 		hw_enable_tagging_sync();
 }
@@ -143,15 +148,19 @@ void __init kasan_init_hw_tags(void)
 	case KASAN_ARG_MODE_DEFAULT:
 		/*
 		 * Default to sync mode.
-		 * Do nothing, kasan_flag_async keeps its default value.
 		 */
-		break;
+		fallthrough;
 	case KASAN_ARG_MODE_SYNC:
-		/* Do nothing, kasan_flag_async keeps its default value. */
+		/* Sync mode enabled. */
+		kasan_mode = KASAN_MODE_SYNC;
 		break;
 	case KASAN_ARG_MODE_ASYNC:
 		/* Async mode enabled. */
-		kasan_flag_async = true;
+		kasan_mode = KASAN_MODE_ASYNC;
+		break;
+	case KASAN_ARG_MODE_ASYMM:
+		/* Asymm mode enabled. */
+		kasan_mode = KASAN_MODE_ASYMM;
 		break;
 	}