Merge branch 'for-next/pac-set-get-enabled-keys' into for-next/core

* for-next/pac-set-get-enabled-keys:
  : Introduce arm64 prctl(PR_PAC_{SET,GET}_ENABLED_KEYS).
  arm64: pac: Optimize kernel entry/exit key installation code paths
  arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS)
  arm64: mte: make the per-task SCTLR_EL1 field usable elsewhere

Documentation/arm64/pointer-authentication.rst

@@ -107,3 +107,37 @@ filter out the Pointer Authentication system key registers from
 KVM_GET/SET_REG_* ioctls and mask those features from cpufeature ID
 register. Any attempt to use the Pointer Authentication instructions will
 result in an UNDEFINED exception being injected into the guest.
+
+
+Enabling and disabling keys
+---------------------------
+
+The prctl PR_PAC_SET_ENABLED_KEYS allows the user program to control which
+PAC keys are enabled in a particular task. It takes two arguments, the
+first being a bitmask of PR_PAC_APIAKEY, PR_PAC_APIBKEY, PR_PAC_APDAKEY
+and PR_PAC_APDBKEY specifying which keys shall be affected by this prctl,
+and the second being a bitmask of the same bits specifying whether the key
+should be enabled or disabled. For example::
+
+  prctl(PR_PAC_SET_ENABLED_KEYS,
+        PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY | PR_PAC_APDBKEY,
+        PR_PAC_APIBKEY, 0, 0);
+
+disables all keys except the IB key.
+
+The main reason why this is useful is to enable a userspace ABI that uses PAC
+instructions to sign and authenticate function pointers and other pointers
+exposed outside of the function, while still allowing binaries conforming to
+the ABI to interoperate with legacy binaries that do not sign or authenticate
+pointers.
+
+The idea is that a dynamic loader or early startup code would issue this
+prctl very early after establishing that a process may load legacy binaries,
+but before executing any PAC instructions.
+
+For compatibility with previous kernel versions, processes start up with IA,
+IB, DA and DB enabled, and are reset to this state on exec(). Processes created
+via fork() and clone() inherit the key enabled state from the calling process.
+
+It is recommended to avoid disabling the IA key, as this has higher performance
+overhead than disabling any of the other keys.

arch/arm64/include/asm/asm_pointer_auth.h

@@ -13,30 +13,12 @@
  * so use the base value of ldp as thread.keys_user and offset as
  * thread.keys_user.ap*.
  */
-	.macro ptrauth_keys_install_user tsk, tmp1, tmp2, tmp3
+	.macro __ptrauth_keys_install_user tsk, tmp1, tmp2, tmp3
 	mov	\tmp1, #THREAD_KEYS_USER
 	add	\tmp1, \tsk, \tmp1
-alternative_if_not ARM64_HAS_ADDRESS_AUTH
-	b	.Laddr_auth_skip_\@
-alternative_else_nop_endif
 	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APIA]
 	msr_s	SYS_APIAKEYLO_EL1, \tmp2
 	msr_s	SYS_APIAKEYHI_EL1, \tmp3
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APIB]
-	msr_s	SYS_APIBKEYLO_EL1, \tmp2
-	msr_s	SYS_APIBKEYHI_EL1, \tmp3
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APDA]
-	msr_s	SYS_APDAKEYLO_EL1, \tmp2
-	msr_s	SYS_APDAKEYHI_EL1, \tmp3
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APDB]
-	msr_s	SYS_APDBKEYLO_EL1, \tmp2
-	msr_s	SYS_APDBKEYHI_EL1, \tmp3
-.Laddr_auth_skip_\@:
-alternative_if ARM64_HAS_GENERIC_AUTH
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APGA]
-	msr_s	SYS_APGAKEYLO_EL1, \tmp2
-	msr_s	SYS_APGAKEYHI_EL1, \tmp3
-alternative_else_nop_endif
 	.endm
 
 	.macro __ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3

arch/arm64/include/asm/mte.h

@@ -39,7 +39,7 @@ void mte_free_tag_storage(char *storage);
 
 void mte_sync_tags(pte_t *ptep, pte_t pte);
 void mte_copy_page_tags(void *kto, const void *kfrom);
-void flush_mte_state(void);
+void mte_thread_init_user(void);
 void mte_thread_switch(struct task_struct *next);
 void mte_suspend_enter(void);
 void mte_suspend_exit(void);
@@ -59,7 +59,7 @@ static inline void mte_sync_tags(pte_t *ptep, pte_t pte)
 static inline void mte_copy_page_tags(void *kto, const void *kfrom)
 {
 }
-static inline void flush_mte_state(void)
+static inline void mte_thread_init_user(void)
 {
 }
 static inline void mte_thread_switch(struct task_struct *next)

arch/arm64/include/asm/pointer_auth.h

@@ -3,6 +3,7 @@
 #define __ASM_POINTER_AUTH_H
 
 #include <linux/bitops.h>
+#include <linux/prctl.h>
 #include <linux/random.h>
 
 #include <asm/cpufeature.h>
@@ -34,6 +35,25 @@ struct ptrauth_keys_kernel {
 	struct ptrauth_key apia;
 };
 
+#define __ptrauth_key_install_nosync(k, v)			\
+do {								\
+	struct ptrauth_key __pki_v = (v);			\
+	write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1);	\
+	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
+} while (0)
+
+static inline void ptrauth_keys_install_user(struct ptrauth_keys_user *keys)
+{
+	if (system_supports_address_auth()) {
+		__ptrauth_key_install_nosync(APIB, keys->apib);
+		__ptrauth_key_install_nosync(APDA, keys->apda);
+		__ptrauth_key_install_nosync(APDB, keys->apdb);
+	}
+
+	if (system_supports_generic_auth())
+		__ptrauth_key_install_nosync(APGA, keys->apga);
+}
+
 static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
 {
 	if (system_supports_address_auth()) {
@@ -45,14 +65,9 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
 
 	if (system_supports_generic_auth())
 		get_random_bytes(&keys->apga, sizeof(keys->apga));
-}
 
-#define __ptrauth_key_install_nosync(k, v)			\
-do {								\
-	struct ptrauth_key __pki_v = (v);			\
-	write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1);	\
-	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
-} while (0)
+	ptrauth_keys_install_user(keys);
+}
 
 static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
 {
@@ -71,6 +86,10 @@ static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kerne
 
 extern int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg);
 
+extern int ptrauth_set_enabled_keys(struct task_struct *tsk, unsigned long keys,
+				    unsigned long enabled);
+extern int ptrauth_get_enabled_keys(struct task_struct *tsk);
+
 static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
 {
 	return ptrauth_clear_pac(ptr);
@@ -85,8 +104,23 @@ static __always_inline void ptrauth_enable(void)
 	isb();
 }
 
-#define ptrauth_thread_init_user(tsk)					\
-	ptrauth_keys_init_user(&(tsk)->thread.keys_user)
+#define ptrauth_suspend_exit()                                                 \
+	ptrauth_keys_install_user(&current->thread.keys_user)
+
+#define ptrauth_thread_init_user()                                             \
+	do {                                                                   \
+		ptrauth_keys_init_user(&current->thread.keys_user);            \
+									       \
+		/* enable all keys */                                          \
+		if (system_supports_address_auth())                            \
+			set_task_sctlr_el1(current->thread.sctlr_user |        \
+					   SCTLR_ELx_ENIA | SCTLR_ELx_ENIB |   \
+					   SCTLR_ELx_ENDA | SCTLR_ELx_ENDB);   \
+	} while (0)
+
+#define ptrauth_thread_switch_user(tsk)                                        \
+	ptrauth_keys_install_user(&(tsk)->thread.keys_user)
+
 #define ptrauth_thread_init_kernel(tsk)					\
 	ptrauth_keys_init_kernel(&(tsk)->thread.keys_kernel)
 #define ptrauth_thread_switch_kernel(tsk)				\
@@ -95,10 +129,17 @@ static __always_inline void ptrauth_enable(void)
 #else /* CONFIG_ARM64_PTR_AUTH */
 #define ptrauth_enable()
 #define ptrauth_prctl_reset_keys(tsk, arg)	(-EINVAL)
+#define ptrauth_set_enabled_keys(tsk, keys, enabled)	(-EINVAL)
+#define ptrauth_get_enabled_keys(tsk)	(-EINVAL)
 #define ptrauth_strip_insn_pac(lr)	(lr)
-#define ptrauth_thread_init_user(tsk)
+#define ptrauth_suspend_exit()
+#define ptrauth_thread_init_user()
 #define ptrauth_thread_init_kernel(tsk)
+#define ptrauth_thread_switch_user(tsk)
 #define ptrauth_thread_switch_kernel(tsk)
 #endif /* CONFIG_ARM64_PTR_AUTH */
 
+#define PR_PAC_ENABLED_KEYS_MASK                                               \
+	(PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY | PR_PAC_APDBKEY)
+
 #endif /* __ASM_POINTER_AUTH_H */

arch/arm64/include/asm/processor.h

@@ -151,11 +151,15 @@ struct thread_struct {
 	struct ptrauth_keys_kernel	keys_kernel;
 #endif
 #ifdef CONFIG_ARM64_MTE
-	u64			sctlr_tcf0;
 	u64			gcr_user_excl;
 #endif
+	u64			sctlr_user;
 };
 
+#define SCTLR_USER_MASK                                                        \
+	(SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | SCTLR_ELx_ENDA | SCTLR_ELx_ENDB |   \
+	 SCTLR_EL1_TCF0_MASK)
+
 static inline void arch_thread_struct_whitelist(unsigned long *offset,
 						unsigned long *size)
 {
@@ -247,6 +251,8 @@ extern void release_thread(struct task_struct *);
 
 unsigned long get_wchan(struct task_struct *p);
 
+void set_task_sctlr_el1(u64 sctlr);
+
 /* Thread switching */
 extern struct task_struct *cpu_switch_to(struct task_struct *prev,
 					 struct task_struct *next);
@@ -301,6 +307,11 @@ extern void __init minsigstksz_setup(void);
 /* PR_PAC_RESET_KEYS prctl */
 #define PAC_RESET_KEYS(tsk, arg)	ptrauth_prctl_reset_keys(tsk, arg)
 
+/* PR_PAC_{SET,GET}_ENABLED_KEYS prctl */
+#define PAC_SET_ENABLED_KEYS(tsk, keys, enabled)				\
+	ptrauth_set_enabled_keys(tsk, keys, enabled)
+#define PAC_GET_ENABLED_KEYS(tsk) ptrauth_get_enabled_keys(tsk)
+
 #ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
 /* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */
 long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg);

arch/arm64/include/asm/sysreg.h

@@ -571,8 +571,10 @@
 #define SCTLR_ELx_TCF_ASYNC	(UL(0x2) << SCTLR_ELx_TCF_SHIFT)
 #define SCTLR_ELx_TCF_MASK	(UL(0x3) << SCTLR_ELx_TCF_SHIFT)
 
+#define SCTLR_ELx_ENIA_SHIFT	31
+
 #define SCTLR_ELx_ITFSB	(BIT(37))
-#define SCTLR_ELx_ENIA	(BIT(31))
+#define SCTLR_ELx_ENIA	(BIT(SCTLR_ELx_ENIA_SHIFT))
 #define SCTLR_ELx_ENIB	(BIT(30))
 #define SCTLR_ELx_ENDA	(BIT(27))
 #define SCTLR_ELx_EE    (BIT(25))

arch/arm64/kernel/asm-offsets.c

@@ -43,6 +43,7 @@ int main(void)
 #endif
   BLANK();
   DEFINE(THREAD_CPU_CONTEXT,	offsetof(struct task_struct, thread.cpu_context));
+  DEFINE(THREAD_SCTLR_USER,	offsetof(struct task_struct, thread.sctlr_user));
 #ifdef CONFIG_ARM64_PTR_AUTH
   DEFINE(THREAD_KEYS_USER,	offsetof(struct task_struct, thread.keys_user));
   DEFINE(THREAD_KEYS_KERNEL,	offsetof(struct task_struct, thread.keys_kernel));
@@ -149,10 +150,6 @@ int main(void)
 #endif
 #ifdef CONFIG_ARM64_PTR_AUTH
   DEFINE(PTRAUTH_USER_KEY_APIA,		offsetof(struct ptrauth_keys_user, apia));
-  DEFINE(PTRAUTH_USER_KEY_APIB,		offsetof(struct ptrauth_keys_user, apib));
-  DEFINE(PTRAUTH_USER_KEY_APDA,		offsetof(struct ptrauth_keys_user, apda));
-  DEFINE(PTRAUTH_USER_KEY_APDB,		offsetof(struct ptrauth_keys_user, apdb));
-  DEFINE(PTRAUTH_USER_KEY_APGA,		offsetof(struct ptrauth_keys_user, apga));
   DEFINE(PTRAUTH_KERNEL_KEY_APIA,	offsetof(struct ptrauth_keys_kernel, apia));
   BLANK();
 #endif

arch/arm64/kernel/entry.S

@@ -247,7 +247,29 @@ alternative_else_nop_endif
 	check_mte_async_tcf x19, x22
 	apply_ssbd 1, x22, x23
 
-	ptrauth_keys_install_kernel tsk, x20, x22, x23
+#ifdef CONFIG_ARM64_PTR_AUTH
+alternative_if ARM64_HAS_ADDRESS_AUTH
+	/*
+	 * Enable IA for in-kernel PAC if the task had it disabled. Although
+	 * this could be implemented with an unconditional MRS which would avoid
+	 * a load, this was measured to be slower on Cortex-A75 and Cortex-A76.
+	 *
+	 * Install the kernel IA key only if IA was enabled in the task. If IA
+	 * was disabled on kernel exit then we would have left the kernel IA
+	 * installed so there is no need to install it again.
+	 */
+	ldr	x0, [tsk, THREAD_SCTLR_USER]
+	tbz	x0, SCTLR_ELx_ENIA_SHIFT, 1f
+	__ptrauth_keys_install_kernel_nosync tsk, x20, x22, x23
+	b	2f
+1:
+	mrs	x0, sctlr_el1
+	orr	x0, x0, SCTLR_ELx_ENIA
+	msr	sctlr_el1, x0
+2:
+	isb
+alternative_else_nop_endif
+#endif
 
 	mte_set_kernel_gcr x22, x23
 
@@ -351,8 +373,26 @@ alternative_else_nop_endif
 3:
 	scs_save tsk, x0
 
-	/* No kernel C function calls after this as user keys are set. */
-	ptrauth_keys_install_user tsk, x0, x1, x2
+#ifdef CONFIG_ARM64_PTR_AUTH
+alternative_if ARM64_HAS_ADDRESS_AUTH
+	/*
+	 * IA was enabled for in-kernel PAC. Disable it now if needed, or
+	 * alternatively install the user's IA. All other per-task keys and
+	 * SCTLR bits were updated on task switch.
+	 *
+	 * No kernel C function calls after this.
+	 */
+	ldr	x0, [tsk, THREAD_SCTLR_USER]
+	tbz	x0, SCTLR_ELx_ENIA_SHIFT, 1f
+	__ptrauth_keys_install_user tsk, x0, x1, x2
+	b	2f
+1:
+	mrs	x0, sctlr_el1
+	bic	x0, x0, SCTLR_ELx_ENIA
+	msr	sctlr_el1, x0
+2:
+alternative_else_nop_endif
+#endif
 
 	mte_set_user_gcr tsk, x0, x1
 

arch/arm64/kernel/mte.c

@@ -185,26 +185,6 @@ void mte_check_tfsr_el1(void)
 }
 #endif
 
-static void update_sctlr_el1_tcf0(u64 tcf0)
-{
-	/* ISB required for the kernel uaccess routines */
-	sysreg_clear_set(sctlr_el1, SCTLR_EL1_TCF0_MASK, tcf0);
-	isb();
-}
-
-static void set_sctlr_el1_tcf0(u64 tcf0)
-{
-	/*
-	 * mte_thread_switch() checks current->thread.sctlr_tcf0 as an
-	 * optimisation. Disable preemption so that it does not see
-	 * the variable update before the SCTLR_EL1.TCF0 one.
-	 */
-	preempt_disable();
-	current->thread.sctlr_tcf0 = tcf0;
-	update_sctlr_el1_tcf0(tcf0);
-	preempt_enable();
-}
-
 static void update_gcr_el1_excl(u64 excl)
 {
 
@@ -227,7 +207,7 @@ static void set_gcr_el1_excl(u64 excl)
 	 */
 }
 
-void flush_mte_state(void)
+void mte_thread_init_user(void)
 {
 	if (!system_supports_mte())
 		return;
@@ -237,31 +217,22 @@ void flush_mte_state(void)
 	write_sysreg_s(0, SYS_TFSRE0_EL1);
 	clear_thread_flag(TIF_MTE_ASYNC_FAULT);
 	/* disable tag checking */
-	set_sctlr_el1_tcf0(SCTLR_EL1_TCF0_NONE);
+	set_task_sctlr_el1((current->thread.sctlr_user & ~SCTLR_EL1_TCF0_MASK) |
+			   SCTLR_EL1_TCF0_NONE);
 	/* reset tag generation mask */
 	set_gcr_el1_excl(SYS_GCR_EL1_EXCL_MASK);
 }
 
 void mte_thread_switch(struct task_struct *next)
 {
-	if (!system_supports_mte())
-		return;
-
-	/* avoid expensive SCTLR_EL1 accesses if no change */
-	if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
-		update_sctlr_el1_tcf0(next->thread.sctlr_tcf0);
-	else
-		isb();
-
 	/*
 	 * Check if an async tag exception occurred at EL1.
 	 *
 	 * Note: On the context switch path we rely on the dsb() present
 	 * in __switch_to() to guarantee that the indirect writes to TFSR_EL1
 	 * are synchronized before this point.
-	 * isb() above is required for the same reason.
-	 *
 	 */
+	isb();
 	mte_check_tfsr_el1();
 }
 
@@ -291,7 +262,7 @@ void mte_suspend_exit(void)
 
 long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 {
-	u64 tcf0;
+	u64 sctlr = task->thread.sctlr_user & ~SCTLR_EL1_TCF0_MASK;
 	u64 gcr_excl = ~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
 		       SYS_GCR_EL1_EXCL_MASK;
 
@@ -300,23 +271,23 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 
 	switch (arg & PR_MTE_TCF_MASK) {
 	case PR_MTE_TCF_NONE:
-		tcf0 = SCTLR_EL1_TCF0_NONE;
+		sctlr |= SCTLR_EL1_TCF0_NONE;
 		break;
 	case PR_MTE_TCF_SYNC:
-		tcf0 = SCTLR_EL1_TCF0_SYNC;
+		sctlr |= SCTLR_EL1_TCF0_SYNC;
 		break;
 	case PR_MTE_TCF_ASYNC:
-		tcf0 = SCTLR_EL1_TCF0_ASYNC;
+		sctlr |= SCTLR_EL1_TCF0_ASYNC;
 		break;
 	default:
 		return -EINVAL;
 	}
 
 	if (task != current) {
-		task->thread.sctlr_tcf0 = tcf0;
+		task->thread.sctlr_user = sctlr;
 		task->thread.gcr_user_excl = gcr_excl;
 	} else {
-		set_sctlr_el1_tcf0(tcf0);
+		set_task_sctlr_el1(sctlr);
 		set_gcr_el1_excl(gcr_excl);
 	}
 
@@ -333,7 +304,7 @@ long get_mte_ctrl(struct task_struct *task)
 
 	ret = incl << PR_MTE_TAG_SHIFT;
 
-	switch (task->thread.sctlr_tcf0) {
+	switch (task->thread.sctlr_user & SCTLR_EL1_TCF0_MASK) {
 	case SCTLR_EL1_TCF0_NONE:
 		ret |= PR_MTE_TCF_NONE;
 		break;

arch/arm64/kernel/pointer_auth.c

@@ -43,6 +43,69 @@ int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg)
 		get_random_bytes(&keys->apdb, sizeof(keys->apdb));
 	if (arg & PR_PAC_APGAKEY)
 		get_random_bytes(&keys->apga, sizeof(keys->apga));
+	ptrauth_keys_install_user(keys);
 
 	return 0;
 }
+
+static u64 arg_to_enxx_mask(unsigned long arg)
+{
+	u64 sctlr_enxx_mask = 0;
+
+	WARN_ON(arg & ~PR_PAC_ENABLED_KEYS_MASK);
+	if (arg & PR_PAC_APIAKEY)
+		sctlr_enxx_mask |= SCTLR_ELx_ENIA;
+	if (arg & PR_PAC_APIBKEY)
+		sctlr_enxx_mask |= SCTLR_ELx_ENIB;
+	if (arg & PR_PAC_APDAKEY)
+		sctlr_enxx_mask |= SCTLR_ELx_ENDA;
+	if (arg & PR_PAC_APDBKEY)
+		sctlr_enxx_mask |= SCTLR_ELx_ENDB;
+	return sctlr_enxx_mask;
+}
+
+int ptrauth_set_enabled_keys(struct task_struct *tsk, unsigned long keys,
+			     unsigned long enabled)
+{
+	u64 sctlr = tsk->thread.sctlr_user;
+
+	if (!system_supports_address_auth())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(tsk)))
+		return -EINVAL;
+
+	if ((keys & ~PR_PAC_ENABLED_KEYS_MASK) || (enabled & ~keys))
+		return -EINVAL;
+
+	sctlr &= ~arg_to_enxx_mask(keys);
+	sctlr |= arg_to_enxx_mask(enabled);
+	if (tsk == current)
+		set_task_sctlr_el1(sctlr);
+	else
+		tsk->thread.sctlr_user = sctlr;
+
+	return 0;
+}
+
+int ptrauth_get_enabled_keys(struct task_struct *tsk)
+{
+	int retval = 0;
+
+	if (!system_supports_address_auth())
+		return -EINVAL;
+
+	if (is_compat_thread(task_thread_info(tsk)))
+		return -EINVAL;
+
+	if (tsk->thread.sctlr_user & SCTLR_ELx_ENIA)
+		retval |= PR_PAC_APIAKEY;
+	if (tsk->thread.sctlr_user & SCTLR_ELx_ENIB)
+		retval |= PR_PAC_APIBKEY;
+	if (tsk->thread.sctlr_user & SCTLR_ELx_ENDA)
+		retval |= PR_PAC_APDAKEY;
+	if (tsk->thread.sctlr_user & SCTLR_ELx_ENDB)
+		retval |= PR_PAC_APDBKEY;
+
+	return retval;
+}

arch/arm64/kernel/process.c

@@ -339,7 +339,6 @@ void flush_thread(void)
 	tls_thread_flush();
 	flush_ptrace_hw_breakpoint(current);
 	flush_tagged_addr_state();
-	flush_mte_state();
 }
 
 void release_thread(struct task_struct *dead_task)
@@ -529,6 +528,31 @@ static void erratum_1418040_thread_switch(struct task_struct *prev,
 	write_sysreg(val, cntkctl_el1);
 }
 
+static void update_sctlr_el1(u64 sctlr)
+{
+	/*
+	 * EnIA must not be cleared while in the kernel as this is necessary for
+	 * in-kernel PAC. It will be cleared on kernel exit if needed.
+	 */
+	sysreg_clear_set(sctlr_el1, SCTLR_USER_MASK & ~SCTLR_ELx_ENIA, sctlr);
+
+	/* ISB required for the kernel uaccess routines when setting TCF0. */
+	isb();
+}
+
+void set_task_sctlr_el1(u64 sctlr)
+{
+	/*
+	 * __switch_to() checks current->thread.sctlr as an
+	 * optimisation. Disable preemption so that it does not see
+	 * the variable update before the SCTLR_EL1 one.
+	 */
+	preempt_disable();
+	current->thread.sctlr_user = sctlr;
+	update_sctlr_el1(sctlr);
+	preempt_enable();
+}
+
 /*
  * Thread switching.
  */
@@ -544,6 +568,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	entry_task_switch(next);
 	ssbs_thread_switch(next);
 	erratum_1418040_thread_switch(prev, next);
+	ptrauth_thread_switch_user(next);
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case
@@ -559,6 +584,9 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	 * registers.
 	 */
 	mte_thread_switch(next);
+	/* avoid expensive SCTLR_EL1 accesses if no change */
+	if (prev->thread.sctlr_user != next->thread.sctlr_user)
+		update_sctlr_el1(next->thread.sctlr_user);
 
 	/* the actual thread switch */
 	last = cpu_switch_to(prev, next);
@@ -608,7 +636,8 @@ void arch_setup_new_exec(void)
 {
 	current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
 
-	ptrauth_thread_init_user(current);
+	ptrauth_thread_init_user();
+	mte_thread_init_user();
 
 	if (task_spec_ssb_noexec(current)) {
 		arch_prctl_spec_ctrl_set(current, PR_SPEC_STORE_BYPASS,

arch/arm64/kernel/ptrace.c

@@ -909,6 +909,38 @@ static int pac_mask_get(struct task_struct *target,
 	return membuf_write(&to, &uregs, sizeof(uregs));
 }
 
+static int pac_enabled_keys_get(struct task_struct *target,
+				const struct user_regset *regset,
+				struct membuf to)
+{
+	long enabled_keys = ptrauth_get_enabled_keys(target);
+
+	if (IS_ERR_VALUE(enabled_keys))
+		return enabled_keys;
+
+	return membuf_write(&to, &enabled_keys, sizeof(enabled_keys));
+}
+
+static int pac_enabled_keys_set(struct task_struct *target,
+				const struct user_regset *regset,
+				unsigned int pos, unsigned int count,
+				const void *kbuf, const void __user *ubuf)
+{
+	int ret;
+	long enabled_keys = ptrauth_get_enabled_keys(target);
+
+	if (IS_ERR_VALUE(enabled_keys))
+		return enabled_keys;
+
+	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &enabled_keys, 0,
+				 sizeof(long));
+	if (ret)
+		return ret;
+
+	return ptrauth_set_enabled_keys(target, PR_PAC_ENABLED_KEYS_MASK,
+					enabled_keys);
+}
+
 #ifdef CONFIG_CHECKPOINT_RESTORE
 static __uint128_t pac_key_to_user(const struct ptrauth_key *key)
 {
@@ -1074,6 +1106,7 @@ enum aarch64_regset {
 #endif
 #ifdef CONFIG_ARM64_PTR_AUTH
 	REGSET_PAC_MASK,
+	REGSET_PAC_ENABLED_KEYS,
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	REGSET_PACA_KEYS,
 	REGSET_PACG_KEYS,
@@ -1160,6 +1193,14 @@ static const struct user_regset aarch64_regsets[] = {
 		.regset_get = pac_mask_get,
 		/* this cannot be set dynamically */
 	},
+	[REGSET_PAC_ENABLED_KEYS] = {
+		.core_note_type = NT_ARM_PAC_ENABLED_KEYS,
+		.n = 1,
+		.size = sizeof(long),
+		.align = sizeof(long),
+		.regset_get = pac_enabled_keys_get,
+		.set = pac_enabled_keys_set,
+	},
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	[REGSET_PACA_KEYS] = {
 		.core_note_type = NT_ARM_PACA_KEYS,

arch/arm64/kernel/suspend.c

@@ -74,8 +74,9 @@ void notrace __cpu_suspend_exit(void)
 	 */
 	spectre_v4_enable_mitigation(NULL);
 
-	/* Restore additional MTE-specific configuration */
+	/* Restore additional feature-specific configuration */
 	mte_suspend_exit();
+	ptrauth_suspend_exit();
 }
 
 /*

include/uapi/linux/elf.h

@@ -426,6 +426,7 @@ typedef struct elf64_shdr {
 #define NT_ARM_PACA_KEYS	0x407	/* ARM pointer authentication address keys */
 #define NT_ARM_PACG_KEYS	0x408	/* ARM pointer authentication generic key */
 #define NT_ARM_TAGGED_ADDR_CTRL	0x409	/* arm64 tagged address control (prctl()) */
+#define NT_ARM_PAC_ENABLED_KEYS	0x40a	/* arm64 ptr auth enabled keys (prctl()) */
 #define NT_ARC_V2	0x600		/* ARCv2 accumulator/extra registers */
 #define NT_VMCOREDD	0x700		/* Vmcore Device Dump Note */
 #define NT_MIPS_DSP	0x800		/* MIPS DSP ASE registers */

include/uapi/linux/prctl.h

@@ -255,4 +255,8 @@ struct prctl_mm_map {
 # define SYSCALL_DISPATCH_FILTER_ALLOW	0
 # define SYSCALL_DISPATCH_FILTER_BLOCK	1
 
+/* Set/get enabled arm64 pointer authentication keys */
+#define PR_PAC_SET_ENABLED_KEYS		60
+#define PR_PAC_GET_ENABLED_KEYS		61
+
 #endif /* _LINUX_PRCTL_H */

kernel/sys.c

@@ -119,6 +119,12 @@
 #ifndef PAC_RESET_KEYS
 # define PAC_RESET_KEYS(a, b)	(-EINVAL)
 #endif
+#ifndef PAC_SET_ENABLED_KEYS
+# define PAC_SET_ENABLED_KEYS(a, b, c)	(-EINVAL)
+#endif
+#ifndef PAC_GET_ENABLED_KEYS
+# define PAC_GET_ENABLED_KEYS(a)	(-EINVAL)
+#endif
 #ifndef SET_TAGGED_ADDR_CTRL
 # define SET_TAGGED_ADDR_CTRL(a)	(-EINVAL)
 #endif
@@ -2497,6 +2503,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			return -EINVAL;
 		error = PAC_RESET_KEYS(me, arg2);
 		break;
+	case PR_PAC_SET_ENABLED_KEYS:
+		if (arg4 || arg5)
+			return -EINVAL;
+		error = PAC_SET_ENABLED_KEYS(me, arg2, arg3);
+		break;
+	case PR_PAC_GET_ENABLED_KEYS:
+		if (arg2 || arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = PAC_GET_ENABLED_KEYS(me);
+		break;
 	case PR_SET_TAGGED_ADDR_CTRL:
 		if (arg3 || arg4 || arg5)
 			return -EINVAL;