Merge branch 'for-next/kernel-ptrauth' into for-next/core

* for-next/kernel-ptrauth:
  : Return address signing - in-kernel support
  arm64: Kconfig: verify binutils support for ARM64_PTR_AUTH
  lkdtm: arm64: test kernel pointer authentication
  arm64: compile the kernel with ptrauth return address signing
  kconfig: Add support for 'as-option'
  arm64: suspend: restore the kernel ptrauth keys
  arm64: __show_regs: strip PAC from lr in printk
  arm64: unwind: strip PAC from kernel addresses
  arm64: mask PAC bits of __builtin_return_address
  arm64: initialize ptrauth keys for kernel booting task
  arm64: initialize and switch ptrauth kernel keys
  arm64: enable ptrauth earlier
  arm64: cpufeature: handle conflicts based on capability
  arm64: cpufeature: Move cpu capability helpers inside C file
  arm64: ptrauth: Add bootup/runtime flags for __cpu_setup
  arm64: install user ptrauth keys at kernel exit time
  arm64: rename ptrauth key structures to be user-specific
  arm64: cpufeature: add pointer auth meta-capabilities
  arm64: cpufeature: Fix meta-capability cpufeature check

arch/arm64/Kconfig

@@ -118,6 +118,7 @@ config ARM64
 	select HAVE_ALIGNED_STRUCT_PAGE if SLUB
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_BITREVERSE
+	select HAVE_ARCH_COMPILER_H
 	select HAVE_ARCH_HUGE_VMAP
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
@@ -1501,6 +1502,9 @@ config ARM64_PTR_AUTH
 	bool "Enable support for pointer authentication"
 	default y
 	depends on !KVM || ARM64_VHE
+	depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC
+	depends on CC_IS_GCC || (CC_IS_CLANG && AS_HAS_CFI_NEGATE_RA_STATE)
+	depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
 	help
 	  Pointer authentication (part of the ARMv8.3 Extensions) provides
 	  instructions for signing and authenticating pointers against secret
@@ -1508,16 +1512,45 @@ config ARM64_PTR_AUTH
 	  and other attacks.
 
 	  This option enables these instructions at EL0 (i.e. for userspace).
-
 	  Choosing this option will cause the kernel to initialise secret keys
 	  for each process at exec() time, with these keys being
 	  context-switched along with the process.
 
+	  If the compiler supports the -mbranch-protection or
+	  -msign-return-address flag (e.g. GCC 7 or later), then this option
+	  will also cause the kernel itself to be compiled with return address
+	  protection. In this case, and if the target hardware is known to
+	  support pointer authentication, then CONFIG_STACKPROTECTOR can be
+	  disabled with minimal loss of protection.
+
 	  The feature is detected at runtime. If the feature is not present in
 	  hardware it will not be advertised to userspace/KVM guest nor will it
 	  be enabled. However, KVM guest also require VHE mode and hence
 	  CONFIG_ARM64_VHE=y option to use this feature.
 
+	  If the feature is present on the boot CPU but not on a late CPU, then
+	  the late CPU will be parked. Also, if the boot CPU does not have
+	  address auth and the late CPU has then the late CPU will still boot
+	  but with the feature disabled. On such a system, this option should
+	  not be selected.
+
+	  This feature works with FUNCTION_GRAPH_TRACER option only if
+	  DYNAMIC_FTRACE_WITH_REGS is enabled.
+
+config CC_HAS_BRANCH_PROT_PAC_RET
+	# GCC 9 or later, clang 8 or later
+	def_bool $(cc-option,-mbranch-protection=pac-ret+leaf)
+
+config CC_HAS_SIGN_RETURN_ADDRESS
+	# GCC 7, 8
+	def_bool $(cc-option,-msign-return-address=all)
+
+config AS_HAS_PAC
+	def_bool $(as-option,-Wa$(comma)-march=armv8.3-a)
+
+config AS_HAS_CFI_NEGATE_RA_STATE
+	def_bool $(as-instr,.cfi_startproc\n.cfi_negate_ra_state\n.cfi_endproc\n)
+
 endmenu
 
 menu "ARMv8.4 architectural features"

arch/arm64/Makefile

@@ -65,6 +65,17 @@ stack_protector_prepare: prepare0
 					include/generated/asm-offsets.h))
 endif
 
+ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
+branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all
+branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
+# -march=armv8.3-a enables the non-nops instructions for PAC, to avoid the
+# compiler to generate them and consequently to break the single image contract
+# we pass it only to the assembler. This option is utilized only in case of non
+# integrated assemblers.
+branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a
+KBUILD_CFLAGS += $(branch-prot-flags-y)
+endif
+
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__

arch/arm64/include/asm/asm_pointer_auth.h

@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_ASM_POINTER_AUTH_H
+#define __ASM_ASM_POINTER_AUTH_H
+
+#include <asm/alternative.h>
+#include <asm/asm-offsets.h>
+#include <asm/cpufeature.h>
+#include <asm/sysreg.h>
+
+#ifdef CONFIG_ARM64_PTR_AUTH
+/*
+ * thread.keys_user.ap* as offset exceeds the #imm offset range
+ * 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
+	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 tsk, sync, tmp1, tmp2, tmp3
+alternative_if ARM64_HAS_ADDRESS_AUTH
+	mov	\tmp1, #THREAD_KEYS_KERNEL
+	add	\tmp1, \tsk, \tmp1
+	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_KERNEL_KEY_APIA]
+	msr_s	SYS_APIAKEYLO_EL1, \tmp2
+	msr_s	SYS_APIAKEYHI_EL1, \tmp3
+	.if     \sync == 1
+	isb
+	.endif
+alternative_else_nop_endif
+	.endm
+
+#else /* CONFIG_ARM64_PTR_AUTH */
+
+	.macro ptrauth_keys_install_user tsk, tmp1, tmp2, tmp3
+	.endm
+
+	.macro ptrauth_keys_install_kernel tsk, sync, tmp1, tmp2, tmp3
+	.endm
+
+#endif /* CONFIG_ARM64_PTR_AUTH */
+
+#endif /* __ASM_ASM_POINTER_AUTH_H */

arch/arm64/include/asm/compiler.h

@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_COMPILER_H
+#define __ASM_COMPILER_H
+
+#if defined(CONFIG_ARM64_PTR_AUTH)
+
+/*
+ * The EL0/EL1 pointer bits used by a pointer authentication code.
+ * This is dependent on TBI0/TBI1 being enabled, or bits 63:56 would also apply.
+ */
+#define ptrauth_user_pac_mask()		GENMASK_ULL(54, vabits_actual)
+#define ptrauth_kernel_pac_mask()	GENMASK_ULL(63, vabits_actual)
+
+/* Valid for EL0 TTBR0 and EL1 TTBR1 instruction pointers */
+#define ptrauth_clear_pac(ptr)						\
+	((ptr & BIT_ULL(55)) ? (ptr | ptrauth_kernel_pac_mask()) :	\
+			       (ptr & ~ptrauth_user_pac_mask()))
+
+#define __builtin_return_address(val)					\
+	(void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val)))
+
+#endif /* CONFIG_ARM64_PTR_AUTH */
+
+#endif /* __ASM_COMPILER_H */

arch/arm64/include/asm/cpucaps.h

@@ -59,7 +59,9 @@
 #define ARM64_HAS_E0PD				49
 #define ARM64_HAS_RNG				50
 #define ARM64_HAS_AMU_EXTN			51
+#define ARM64_HAS_ADDRESS_AUTH			52
+#define ARM64_HAS_GENERIC_AUTH			53
 
-#define ARM64_NCAPS				52
+#define ARM64_NCAPS				54
 
 #endif /* __ASM_CPUCAPS_H */

arch/arm64/include/asm/cpufeature.h

@@ -208,6 +208,10 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
  *     In some non-typical cases either both (a) and (b), or neither,
  *     should be permitted. This can be described by including neither
  *     or both flags in the capability's type field.
+ *
+ *     In case of a conflict, the CPU is prevented from booting. If the
+ *     ARM64_CPUCAP_PANIC_ON_CONFLICT flag is specified for the capability,
+ *     then a kernel panic is triggered.
  */
 
 
@@ -240,6 +244,8 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
 #define ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU	((u16)BIT(4))
 /* Is it safe for a late CPU to miss this capability when system has it */
 #define ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU	((u16)BIT(5))
+/* Panic when a conflict is detected */
+#define ARM64_CPUCAP_PANIC_ON_CONFLICT		((u16)BIT(6))
 
 /*
  * CPU errata workarounds that need to be enabled at boot time if one or
@@ -279,9 +285,20 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
 
 /*
  * CPU feature used early in the boot based on the boot CPU. All secondary
- * CPUs must match the state of the capability as detected by the boot CPU.
+ * CPUs must match the state of the capability as detected by the boot CPU. In
+ * case of a conflict, a kernel panic is triggered.
  */
-#define ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE ARM64_CPUCAP_SCOPE_BOOT_CPU
+#define ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE		\
+	(ARM64_CPUCAP_SCOPE_BOOT_CPU | ARM64_CPUCAP_PANIC_ON_CONFLICT)
+
+/*
+ * CPU feature used early in the boot based on the boot CPU. It is safe for a
+ * late CPU to have this feature even though the boot CPU hasn't enabled it,
+ * although the feature will not be used by Linux in this case. If the boot CPU
+ * has enabled this feature already, then every late CPU must have it.
+ */
+#define ARM64_CPUCAP_BOOT_CPU_FEATURE                  \
+	(ARM64_CPUCAP_SCOPE_BOOT_CPU | ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU)
 
 struct arm64_cpu_capabilities {
 	const char *desc;
@@ -340,18 +357,6 @@ static inline int cpucap_default_scope(const struct arm64_cpu_capabilities *cap)
 	return cap->type & ARM64_CPUCAP_SCOPE_MASK;
 }
 
-static inline bool
-cpucap_late_cpu_optional(const struct arm64_cpu_capabilities *cap)
-{
-	return !!(cap->type & ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU);
-}
-
-static inline bool
-cpucap_late_cpu_permitted(const struct arm64_cpu_capabilities *cap)
-{
-	return !!(cap->type & ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU);
-}
-
 /*
  * Generic helper for handling capabilties with multiple (match,enable) pairs
  * of call backs, sharing the same capability bit.
@@ -654,15 +659,13 @@ static inline bool system_supports_cnp(void)
 static inline bool system_supports_address_auth(void)
 {
 	return IS_ENABLED(CONFIG_ARM64_PTR_AUTH) &&
-		(cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH_ARCH) ||
+		cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH);
-		 cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH_IMP_DEF));
 }
 
 static inline bool system_supports_generic_auth(void)
 {
 	return IS_ENABLED(CONFIG_ARM64_PTR_AUTH) &&
-		(cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH_ARCH) ||
+		cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH);
-		 cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH_IMP_DEF));
 }
 
 static inline bool system_uses_irq_prio_masking(void)

arch/arm64/include/asm/pointer_auth.h

@@ -22,7 +22,7 @@ struct ptrauth_key {
  * We give each process its own keys, which are shared by all threads. The keys
  * are inherited upon fork(), and reinitialised upon exec*().
  */
-struct ptrauth_keys {
+struct ptrauth_keys_user {
 	struct ptrauth_key apia;
 	struct ptrauth_key apib;
 	struct ptrauth_key apda;
@@ -30,7 +30,11 @@ struct ptrauth_keys {
 	struct ptrauth_key apga;
 };
 
-static inline void ptrauth_keys_init(struct ptrauth_keys *keys)
+struct ptrauth_keys_kernel {
+	struct ptrauth_key apia;
+};
+
+static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
 {
 	if (system_supports_address_auth()) {
 		get_random_bytes(&keys->apia, sizeof(keys->apia));
@@ -50,48 +54,38 @@ do {								\
 	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
 } while (0)
 
-static inline void ptrauth_keys_switch(struct ptrauth_keys *keys)
+static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
 {
-	if (system_supports_address_auth()) {
+	if (system_supports_address_auth())
-		__ptrauth_key_install(APIA, keys->apia);
+		get_random_bytes(&keys->apia, sizeof(keys->apia));
-		__ptrauth_key_install(APIB, keys->apib);
+}
-		__ptrauth_key_install(APDA, keys->apda);
-		__ptrauth_key_install(APDB, keys->apdb);
-	}
 
-	if (system_supports_generic_auth())
+static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kernel *keys)
-		__ptrauth_key_install(APGA, keys->apga);
+{
+	if (system_supports_address_auth())
+		__ptrauth_key_install(APIA, keys->apia);
 }
 
 extern int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg);
 
-/*
- * The EL0 pointer bits used by a pointer authentication code.
- * This is dependent on TBI0 being enabled, or bits 63:56 would also apply.
- */
-#define ptrauth_user_pac_mask()	GENMASK(54, vabits_actual)
-
-/* Only valid for EL0 TTBR0 instruction pointers */
 static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
 {
-	return ptr & ~ptrauth_user_pac_mask();
+	return ptrauth_clear_pac(ptr);
 }
 
 #define ptrauth_thread_init_user(tsk)					\
-do {									\
+	ptrauth_keys_init_user(&(tsk)->thread.keys_user)
-	struct task_struct *__ptiu_tsk = (tsk);				\
+#define ptrauth_thread_init_kernel(tsk)					\
-	ptrauth_keys_init(&__ptiu_tsk->thread.keys_user);		\
+	ptrauth_keys_init_kernel(&(tsk)->thread.keys_kernel)
-	ptrauth_keys_switch(&__ptiu_tsk->thread.keys_user);		\
+#define ptrauth_thread_switch_kernel(tsk)				\
-} while (0)
+	ptrauth_keys_switch_kernel(&(tsk)->thread.keys_kernel)
-
-#define ptrauth_thread_switch(tsk)	\
-	ptrauth_keys_switch(&(tsk)->thread.keys_user)
 
 #else /* CONFIG_ARM64_PTR_AUTH */
 #define ptrauth_prctl_reset_keys(tsk, arg)	(-EINVAL)
 #define ptrauth_strip_insn_pac(lr)	(lr)
 #define ptrauth_thread_init_user(tsk)
-#define ptrauth_thread_switch(tsk)
+#define ptrauth_thread_init_kernel(tsk)
+#define ptrauth_thread_switch_kernel(tsk)
 #endif /* CONFIG_ARM64_PTR_AUTH */
 
 #endif /* __ASM_POINTER_AUTH_H */

arch/arm64/include/asm/processor.h

@@ -146,7 +146,8 @@ struct thread_struct {
 	unsigned long		fault_code;	/* ESR_EL1 value */
 	struct debug_info	debug;		/* debugging */
 #ifdef CONFIG_ARM64_PTR_AUTH
-	struct ptrauth_keys	keys_user;
+	struct ptrauth_keys_user	keys_user;
+	struct ptrauth_keys_kernel	keys_kernel;
 #endif
 };
 

arch/arm64/include/asm/smp.h

@@ -23,6 +23,14 @@
 #define CPU_STUCK_REASON_52_BIT_VA	(UL(1) << CPU_STUCK_REASON_SHIFT)
 #define CPU_STUCK_REASON_NO_GRAN	(UL(2) << CPU_STUCK_REASON_SHIFT)
 
+/* Possible options for __cpu_setup */
+/* Option to setup primary cpu */
+#define ARM64_CPU_BOOT_PRIMARY		(1)
+/* Option to setup secondary cpus */
+#define ARM64_CPU_BOOT_SECONDARY	(2)
+/* Option to setup cpus for different cpu run time services */
+#define ARM64_CPU_RUNTIME		(3)
+
 #ifndef __ASSEMBLY__
 
 #include <asm/percpu.h>
@@ -30,6 +38,7 @@
 #include <linux/threads.h>
 #include <linux/cpumask.h>
 #include <linux/thread_info.h>
+#include <asm/pointer_auth.h>
 
 DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number);
 
@@ -87,6 +96,9 @@ asmlinkage void secondary_start_kernel(void);
 struct secondary_data {
 	void *stack;
 	struct task_struct *task;
+#ifdef CONFIG_ARM64_PTR_AUTH
+	struct ptrauth_keys_kernel ptrauth_key;
+#endif
 	long status;
 };
 

arch/arm64/include/asm/stackprotector.h

@@ -15,6 +15,7 @@
 
 #include <linux/random.h>
 #include <linux/version.h>
+#include <asm/pointer_auth.h>
 
 extern unsigned long __stack_chk_guard;
 
@@ -26,6 +27,7 @@ extern unsigned long __stack_chk_guard;
  */
 static __always_inline void boot_init_stack_canary(void)
 {
+#if defined(CONFIG_STACKPROTECTOR)
 	unsigned long canary;
 
 	/* Try to get a semi random initial value. */
@@ -36,6 +38,9 @@ static __always_inline void boot_init_stack_canary(void)
 	current->stack_canary = canary;
 	if (!IS_ENABLED(CONFIG_STACKPROTECTOR_PER_TASK))
 		__stack_chk_guard = current->stack_canary;
+#endif
+	ptrauth_thread_init_kernel(current);
+	ptrauth_thread_switch_kernel(current);
 }
 
 #endif	/* _ASM_STACKPROTECTOR_H */

arch/arm64/kernel/asm-offsets.c

@@ -40,6 +40,10 @@ int main(void)
 #endif
   BLANK();
   DEFINE(THREAD_CPU_CONTEXT,	offsetof(struct task_struct, thread.cpu_context));
+#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));
+#endif
   BLANK();
   DEFINE(S_X0,			offsetof(struct pt_regs, regs[0]));
   DEFINE(S_X2,			offsetof(struct pt_regs, regs[2]));
@@ -88,6 +92,9 @@ int main(void)
   BLANK();
   DEFINE(CPU_BOOT_STACK,	offsetof(struct secondary_data, stack));
   DEFINE(CPU_BOOT_TASK,		offsetof(struct secondary_data, task));
+#ifdef CONFIG_ARM64_PTR_AUTH
+  DEFINE(CPU_BOOT_PTRAUTH_KEY,	offsetof(struct secondary_data, ptrauth_key));
+#endif
   BLANK();
 #ifdef CONFIG_KVM_ARM_HOST
   DEFINE(VCPU_CONTEXT,		offsetof(struct kvm_vcpu, arch.ctxt));
@@ -127,6 +134,15 @@ int main(void)
 #ifdef CONFIG_ARM_SDE_INTERFACE
   DEFINE(SDEI_EVENT_INTREGS,	offsetof(struct sdei_registered_event, interrupted_regs));
   DEFINE(SDEI_EVENT_PRIORITY,	offsetof(struct sdei_registered_event, priority));
+#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
   return 0;
 }

arch/arm64/kernel/cpufeature.c

@@ -116,6 +116,8 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
 
 static void cpu_enable_cnp(struct arm64_cpu_capabilities const *cap);
 
+static bool __system_matches_cap(unsigned int n);
+
 /*
  * NOTE: Any changes to the visibility of features should be kept in
  * sync with the documentation of the CPU feature register ABI.
@@ -1368,10 +1370,18 @@ static void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused)
 #endif /* CONFIG_ARM64_RAS_EXTN */
 
 #ifdef CONFIG_ARM64_PTR_AUTH
-static void cpu_enable_address_auth(struct arm64_cpu_capabilities const *cap)
+static bool has_address_auth(const struct arm64_cpu_capabilities *entry,
+			     int __unused)
 {
-	sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ENIA | SCTLR_ELx_ENIB |
+	return __system_matches_cap(ARM64_HAS_ADDRESS_AUTH_ARCH) ||
-				       SCTLR_ELx_ENDA | SCTLR_ELx_ENDB);
+	       __system_matches_cap(ARM64_HAS_ADDRESS_AUTH_IMP_DEF);
+}
+
+static bool has_generic_auth(const struct arm64_cpu_capabilities *entry,
+			     int __unused)
+{
+	return __system_matches_cap(ARM64_HAS_GENERIC_AUTH_ARCH) ||
+	       __system_matches_cap(ARM64_HAS_GENERIC_AUTH_IMP_DEF);
 }
 #endif /* CONFIG_ARM64_PTR_AUTH */
 
@@ -1399,6 +1409,25 @@ static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
 }
 #endif
 
+/* Internal helper functions to match cpu capability type */
+static bool
+cpucap_late_cpu_optional(const struct arm64_cpu_capabilities *cap)
+{
+	return !!(cap->type & ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU);
+}
+
+static bool
+cpucap_late_cpu_permitted(const struct arm64_cpu_capabilities *cap)
+{
+	return !!(cap->type & ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU);
+}
+
+static bool
+cpucap_panic_on_conflict(const struct arm64_cpu_capabilities *cap)
+{
+	return !!(cap->type & ARM64_CPUCAP_PANIC_ON_CONFLICT);
+}
+
 static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "GIC system register CPU interface",
@@ -1662,24 +1691,27 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "Address authentication (architected algorithm)",
 		.capability = ARM64_HAS_ADDRESS_AUTH_ARCH,
-		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
 		.sys_reg = SYS_ID_AA64ISAR1_EL1,
 		.sign = FTR_UNSIGNED,
 		.field_pos = ID_AA64ISAR1_APA_SHIFT,
 		.min_field_value = ID_AA64ISAR1_APA_ARCHITECTED,
 		.matches = has_cpuid_feature,
-		.cpu_enable = cpu_enable_address_auth,
 	},
 	{
 		.desc = "Address authentication (IMP DEF algorithm)",
 		.capability = ARM64_HAS_ADDRESS_AUTH_IMP_DEF,
-		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
 		.sys_reg = SYS_ID_AA64ISAR1_EL1,
 		.sign = FTR_UNSIGNED,
 		.field_pos = ID_AA64ISAR1_API_SHIFT,
 		.min_field_value = ID_AA64ISAR1_API_IMP_DEF,
 		.matches = has_cpuid_feature,
-		.cpu_enable = cpu_enable_address_auth,
+	},
+	{
+		.capability = ARM64_HAS_ADDRESS_AUTH,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
+		.matches = has_address_auth,
 	},
 	{
 		.desc = "Generic authentication (architected algorithm)",
@@ -1701,6 +1733,11 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.min_field_value = ID_AA64ISAR1_GPI_IMP_DEF,
 		.matches = has_cpuid_feature,
 	},
+	{
+		.capability = ARM64_HAS_GENERIC_AUTH,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_generic_auth,
+	},
 #endif /* CONFIG_ARM64_PTR_AUTH */
 #ifdef CONFIG_ARM64_PSEUDO_NMI
 	{
@@ -2050,10 +2087,8 @@ static void __init enable_cpu_capabilities(u16 scope_mask)
  * Run through the list of capabilities to check for conflicts.
  * If the system has already detected a capability, take necessary
  * action on this CPU.
- *
- * Returns "false" on conflicts.
  */
-static bool verify_local_cpu_caps(u16 scope_mask)
+static void verify_local_cpu_caps(u16 scope_mask)
 {
 	int i;
 	bool cpu_has_cap, system_has_cap;
@@ -2098,10 +2133,12 @@ static bool verify_local_cpu_caps(u16 scope_mask)
 		pr_crit("CPU%d: Detected conflict for capability %d (%s), System: %d, CPU: %d\n",
 			smp_processor_id(), caps->capability,
 			caps->desc, system_has_cap, cpu_has_cap);
-		return false;
-	}
 
-	return true;
+		if (cpucap_panic_on_conflict(caps))
+			cpu_panic_kernel();
+		else
+			cpu_die_early();
+	}
 }
 
 /*
@@ -2111,12 +2148,8 @@ static bool verify_local_cpu_caps(u16 scope_mask)
 static void check_early_cpu_features(void)
 {
 	verify_cpu_asid_bits();
-	/*
+
-	 * Early features are used by the kernel already. If there
+	verify_local_cpu_caps(SCOPE_BOOT_CPU);
-	 * is a conflict, we cannot proceed further.
-	 */
-	if (!verify_local_cpu_caps(SCOPE_BOOT_CPU))
-		cpu_panic_kernel();
 }
 
 static void
@@ -2164,8 +2197,7 @@ static void verify_local_cpu_capabilities(void)
 	 * check_early_cpu_features(), as they need to be verified
 	 * on all secondary CPUs.
 	 */
-	if (!verify_local_cpu_caps(SCOPE_ALL & ~SCOPE_BOOT_CPU))
+	verify_local_cpu_caps(SCOPE_ALL & ~SCOPE_BOOT_CPU);
-		cpu_die_early();
 
 	verify_local_elf_hwcaps(arm64_elf_hwcaps);
 
@@ -2216,6 +2248,23 @@ bool this_cpu_has_cap(unsigned int n)
 	return false;
 }
 
+/*
+ * This helper function is used in a narrow window when,
+ * - The system wide safe registers are set with all the SMP CPUs and,
+ * - The SYSTEM_FEATURE cpu_hwcaps may not have been set.
+ * In all other cases cpus_have_{const_}cap() should be used.
+ */
+static bool __system_matches_cap(unsigned int n)
+{
+	if (n < ARM64_NCAPS) {
+		const struct arm64_cpu_capabilities *cap = cpu_hwcaps_ptrs[n];
+
+		if (cap)
+			return cap->matches(cap, SCOPE_SYSTEM);
+	}
+	return false;
+}
+
 void cpu_set_feature(unsigned int num)
 {
 	WARN_ON(num >= MAX_CPU_FEATURES);
@@ -2288,7 +2337,7 @@ void __init setup_cpu_features(void)
 static bool __maybe_unused
 cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
 {
-	return (cpus_have_const_cap(ARM64_HAS_PAN) && !cpus_have_const_cap(ARM64_HAS_UAO));
+	return (__system_matches_cap(ARM64_HAS_PAN) && !__system_matches_cap(ARM64_HAS_UAO));
 }
 
 static void __maybe_unused cpu_enable_cnp(struct arm64_cpu_capabilities const *cap)

arch/arm64/kernel/entry.S

@@ -14,6 +14,7 @@
 #include <asm/alternative.h>
 #include <asm/assembler.h>
 #include <asm/asm-offsets.h>
+#include <asm/asm_pointer_auth.h>
 #include <asm/cpufeature.h>
 #include <asm/errno.h>
 #include <asm/esr.h>
@@ -177,6 +178,7 @@ alternative_cb_end
 
 	apply_ssbd 1, x22, x23
 
+	ptrauth_keys_install_kernel tsk, 1, x20, x22, x23
 	.else
 	add	x21, sp, #S_FRAME_SIZE
 	get_current_task tsk
@@ -341,6 +343,9 @@ alternative_else_nop_endif
 	msr	cntkctl_el1, x1
 4:
 #endif
+	/* No kernel C function calls after this as user keys are set. */
+	ptrauth_keys_install_user tsk, x0, x1, x2
+
 	apply_ssbd 0, x0, x1
 	.endif
 
@@ -895,6 +900,7 @@ SYM_FUNC_START(cpu_switch_to)
 	ldr	lr, [x8]
 	mov	sp, x9
 	msr	sp_el0, x1
+	ptrauth_keys_install_kernel x1, 1, x8, x9, x10
 	ret
 SYM_FUNC_END(cpu_switch_to)
 NOKPROBE(cpu_switch_to)

arch/arm64/kernel/head.S

@@ -118,6 +118,7 @@ SYM_CODE_START(stext)
 	 * On return, the CPU will be ready for the MMU to be turned on and
 	 * the TCR will have been set.
 	 */
+	mov	x0, #ARM64_CPU_BOOT_PRIMARY
 	bl	__cpu_setup			// initialise processor
 	b	__primary_switch
 SYM_CODE_END(stext)
@@ -716,6 +717,7 @@ SYM_FUNC_START_LOCAL(secondary_startup)
 	 * Common entry point for secondary CPUs.
 	 */
 	bl	__cpu_secondary_check52bitva
+	mov	x0, #ARM64_CPU_BOOT_SECONDARY
 	bl	__cpu_setup			// initialise processor
 	adrp	x1, swapper_pg_dir
 	bl	__enable_mmu

arch/arm64/kernel/pointer_auth.c

@@ -9,7 +9,7 @@
 
 int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg)
 {
-	struct ptrauth_keys *keys = &tsk->thread.keys_user;
+	struct ptrauth_keys_user *keys = &tsk->thread.keys_user;
 	unsigned long addr_key_mask = PR_PAC_APIAKEY | PR_PAC_APIBKEY |
 				      PR_PAC_APDAKEY | PR_PAC_APDBKEY;
 	unsigned long key_mask = addr_key_mask | PR_PAC_APGAKEY;
@@ -18,8 +18,7 @@ int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg)
 		return -EINVAL;
 
 	if (!arg) {
-		ptrauth_keys_init(keys);
+		ptrauth_keys_init_user(keys);
-		ptrauth_keys_switch(keys);
 		return 0;
 	}
 
@@ -41,7 +40,5 @@ int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg)
 	if (arg & PR_PAC_APGAKEY)
 		get_random_bytes(&keys->apga, sizeof(keys->apga));
 
-	ptrauth_keys_switch(keys);
-
 	return 0;
 }

arch/arm64/kernel/process.c

@@ -262,7 +262,7 @@ void __show_regs(struct pt_regs *regs)
 
 	if (!user_mode(regs)) {
 		printk("pc : %pS\n", (void *)regs->pc);
-		printk("lr : %pS\n", (void *)lr);
+		printk("lr : %pS\n", (void *)ptrauth_strip_insn_pac(lr));
 	} else {
 		printk("pc : %016llx\n", regs->pc);
 		printk("lr : %016llx\n", lr);
@@ -376,6 +376,8 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long stack_start,
 	 */
 	fpsimd_flush_task_state(p);
 
+	ptrauth_thread_init_kernel(p);
+
 	if (likely(!(p->flags & PF_KTHREAD))) {
 		*childregs = *current_pt_regs();
 		childregs->regs[0] = 0;
@@ -512,7 +514,6 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	contextidr_thread_switch(next);
 	entry_task_switch(next);
 	uao_thread_switch(next);
-	ptrauth_thread_switch(next);
 	ssbs_thread_switch(next);
 
 	/*

arch/arm64/kernel/ptrace.c

@@ -999,7 +999,7 @@ static struct ptrauth_key pac_key_from_user(__uint128_t ukey)
 }
 
 static void pac_address_keys_to_user(struct user_pac_address_keys *ukeys,
-				     const struct ptrauth_keys *keys)
+				     const struct ptrauth_keys_user *keys)
 {
 	ukeys->apiakey = pac_key_to_user(&keys->apia);
 	ukeys->apibkey = pac_key_to_user(&keys->apib);
@@ -1007,7 +1007,7 @@ static void pac_address_keys_to_user(struct user_pac_address_keys *ukeys,
 	ukeys->apdbkey = pac_key_to_user(&keys->apdb);
 }
 
-static void pac_address_keys_from_user(struct ptrauth_keys *keys,
+static void pac_address_keys_from_user(struct ptrauth_keys_user *keys,
 				       const struct user_pac_address_keys *ukeys)
 {
 	keys->apia = pac_key_from_user(ukeys->apiakey);
@@ -1021,7 +1021,7 @@ static int pac_address_keys_get(struct task_struct *target,
 				unsigned int pos, unsigned int count,
 				void *kbuf, void __user *ubuf)
 {
-	struct ptrauth_keys *keys = &target->thread.keys_user;
+	struct ptrauth_keys_user *keys = &target->thread.keys_user;
 	struct user_pac_address_keys user_keys;
 
 	if (!system_supports_address_auth())
@@ -1038,7 +1038,7 @@ static int pac_address_keys_set(struct task_struct *target,
 				unsigned int pos, unsigned int count,
 				const void *kbuf, const void __user *ubuf)
 {
-	struct ptrauth_keys *keys = &target->thread.keys_user;
+	struct ptrauth_keys_user *keys = &target->thread.keys_user;
 	struct user_pac_address_keys user_keys;
 	int ret;
 
@@ -1056,12 +1056,12 @@ static int pac_address_keys_set(struct task_struct *target,
 }
 
 static void pac_generic_keys_to_user(struct user_pac_generic_keys *ukeys,
-				     const struct ptrauth_keys *keys)
+				     const struct ptrauth_keys_user *keys)
 {
 	ukeys->apgakey = pac_key_to_user(&keys->apga);
 }
 
-static void pac_generic_keys_from_user(struct ptrauth_keys *keys,
+static void pac_generic_keys_from_user(struct ptrauth_keys_user *keys,
 				       const struct user_pac_generic_keys *ukeys)
 {
 	keys->apga = pac_key_from_user(ukeys->apgakey);
@@ -1072,7 +1072,7 @@ static int pac_generic_keys_get(struct task_struct *target,
 				unsigned int pos, unsigned int count,
 				void *kbuf, void __user *ubuf)
 {
-	struct ptrauth_keys *keys = &target->thread.keys_user;
+	struct ptrauth_keys_user *keys = &target->thread.keys_user;
 	struct user_pac_generic_keys user_keys;
 
 	if (!system_supports_generic_auth())
@@ -1089,7 +1089,7 @@ static int pac_generic_keys_set(struct task_struct *target,
 				unsigned int pos, unsigned int count,
 				const void *kbuf, const void __user *ubuf)
 {
-	struct ptrauth_keys *keys = &target->thread.keys_user;
+	struct ptrauth_keys_user *keys = &target->thread.keys_user;
 	struct user_pac_generic_keys user_keys;
 	int ret;
 

arch/arm64/kernel/sleep.S

@@ -3,6 +3,7 @@
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
 #include <asm/assembler.h>
+#include <asm/smp.h>
 
 	.text
 /*
@@ -99,6 +100,7 @@ ENDPROC(__cpu_suspend_enter)
 	.pushsection ".idmap.text", "awx"
 ENTRY(cpu_resume)
 	bl	el2_setup		// if in EL2 drop to EL1 cleanly
+	mov	x0, #ARM64_CPU_RUNTIME
 	bl	__cpu_setup
 	/* enable the MMU early - so we can access sleep_save_stash by va */
 	adrp	x1, swapper_pg_dir

arch/arm64/kernel/smp.c

@@ -114,6 +114,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	 */
 	secondary_data.task = idle;
 	secondary_data.stack = task_stack_page(idle) + THREAD_SIZE;
+#if defined(CONFIG_ARM64_PTR_AUTH)
+	secondary_data.ptrauth_key.apia.lo = idle->thread.keys_kernel.apia.lo;
+	secondary_data.ptrauth_key.apia.hi = idle->thread.keys_kernel.apia.hi;
+#endif
 	update_cpu_boot_status(CPU_MMU_OFF);
 	__flush_dcache_area(&secondary_data, sizeof(secondary_data));
 
@@ -136,6 +140,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	pr_crit("CPU%u: failed to come online\n", cpu);
 	secondary_data.task = NULL;
 	secondary_data.stack = NULL;
+#if defined(CONFIG_ARM64_PTR_AUTH)
+	secondary_data.ptrauth_key.apia.lo = 0;
+	secondary_data.ptrauth_key.apia.hi = 0;
+#endif
 	__flush_dcache_area(&secondary_data, sizeof(secondary_data));
 	status = READ_ONCE(secondary_data.status);
 	if (status == CPU_MMU_OFF)

arch/arm64/kernel/stacktrace.c

@@ -14,6 +14,7 @@
 #include <linux/stacktrace.h>
 
 #include <asm/irq.h>
+#include <asm/pointer_auth.h>
 #include <asm/stack_pointer.h>
 #include <asm/stacktrace.h>
 
@@ -86,7 +87,7 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	if (tsk->ret_stack &&
-			(frame->pc == (unsigned long)return_to_handler)) {
+		(ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
 		struct ftrace_ret_stack *ret_stack;
 		/*
 		 * This is a case where function graph tracer has
@@ -101,6 +102,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 	}
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
+	frame->pc = ptrauth_strip_insn_pac(frame->pc);
+
 	/*
 	 * Frames created upon entry from EL0 have NULL FP and PC values, so
 	 * don't bother reporting these. Frames created by __noreturn functions

arch/arm64/mm/proc.S

@@ -11,11 +11,13 @@
 #include <linux/linkage.h>
 #include <asm/assembler.h>
 #include <asm/asm-offsets.h>
+#include <asm/asm_pointer_auth.h>
 #include <asm/hwcap.h>
 #include <asm/pgtable.h>
 #include <asm/pgtable-hwdef.h>
 #include <asm/cpufeature.h>
 #include <asm/alternative.h>
+#include <asm/smp.h>
 
 #ifdef CONFIG_ARM64_64K_PAGES
 #define TCR_TG_FLAGS	TCR_TG0_64K | TCR_TG1_64K
@@ -137,6 +139,7 @@ alternative_if ARM64_HAS_RAS_EXTN
 	msr_s	SYS_DISR_EL1, xzr
 alternative_else_nop_endif
 
+	ptrauth_keys_install_kernel x14, 0, x1, x2, x3
 	isb
 	ret
 SYM_FUNC_END(cpu_do_resume)
@@ -381,32 +384,32 @@ SYM_FUNC_END(idmap_kpti_install_ng_mappings)
 /*
  *	__cpu_setup
  *
- *	Initialise the processor for turning the MMU on.  Return in x0 the
+ *	Initialise the processor for turning the MMU on.
- *	value of the SCTLR_EL1 register.
+ *
+ * Input:
+ *	x0 with a flag ARM64_CPU_BOOT_PRIMARY/ARM64_CPU_BOOT_SECONDARY/ARM64_CPU_RUNTIME.
+ * Output:
+ *	Return in x0 the value of the SCTLR_EL1 register.
  */
 	.pushsection ".idmap.text", "awx"
 SYM_FUNC_START(__cpu_setup)
 	tlbi	vmalle1				// Invalidate local TLB
 	dsb	nsh
 
-	mov	x0, #3 << 20
+	mov	x1, #3 << 20
-	msr	cpacr_el1, x0			// Enable FP/ASIMD
+	msr	cpacr_el1, x1			// Enable FP/ASIMD
-	mov	x0, #1 << 12			// Reset mdscr_el1 and disable
+	mov	x1, #1 << 12			// Reset mdscr_el1 and disable
-	msr	mdscr_el1, x0			// access to the DCC from EL0
+	msr	mdscr_el1, x1			// access to the DCC from EL0
 	isb					// Unmask debug exceptions now,
 	enable_dbg				// since this is per-cpu
-	reset_pmuserenr_el0 x0			// Disable PMU access from EL0
+	reset_pmuserenr_el0 x1			// Disable PMU access from EL0
-	reset_amuserenr_el0 x0			// Disable AMU access from EL0
+	reset_amuserenr_el0 x1			// Disable AMU access from EL0
 
 	/*
 	 * Memory region attributes
 	 */
 	mov_q	x5, MAIR_EL1_SET
 	msr	mair_el1, x5
-	/*
-	 * Prepare SCTLR
-	 */
-	mov_q	x0, SCTLR_EL1_SET
 	/*
 	 * Set/prepare TCR and TTBR. We use 512GB (39-bit) address range for
 	 * both user and kernel.
@@ -443,5 +446,51 @@ SYM_FUNC_START(__cpu_setup)
 1:
 #endif	/* CONFIG_ARM64_HW_AFDBM */
 	msr	tcr_el1, x10
+	mov	x1, x0
+	/*
+	 * Prepare SCTLR
+	 */
+	mov_q	x0, SCTLR_EL1_SET
+
+#ifdef CONFIG_ARM64_PTR_AUTH
+	/* No ptrauth setup for run time cpus */
+	cmp	x1, #ARM64_CPU_RUNTIME
+	b.eq	3f
+
+	/* Check if the CPU supports ptrauth */
+	mrs	x2, id_aa64isar1_el1
+	ubfx	x2, x2, #ID_AA64ISAR1_APA_SHIFT, #8
+	cbz	x2, 3f
+
+	/*
+	 * The primary cpu keys are reset here and can be
+	 * re-initialised with some proper values later.
+	 */
+	msr_s	SYS_APIAKEYLO_EL1, xzr
+	msr_s	SYS_APIAKEYHI_EL1, xzr
+
+	/* Just enable ptrauth for primary cpu */
+	cmp	x1, #ARM64_CPU_BOOT_PRIMARY
+	b.eq	2f
+
+	/* if !system_supports_address_auth() then skip enable */
+alternative_if_not ARM64_HAS_ADDRESS_AUTH
+	b	3f
+alternative_else_nop_endif
+
+	/* Install ptrauth key for secondary cpus */
+	adr_l	x2, secondary_data
+	ldr	x3, [x2, #CPU_BOOT_TASK]	// get secondary_data.task
+	cbz	x3, 2f				// check for slow booting cpus
+	ldp	x3, x4, [x2, #CPU_BOOT_PTRAUTH_KEY]
+	msr_s	SYS_APIAKEYLO_EL1, x3
+	msr_s	SYS_APIAKEYHI_EL1, x4
+
+2:	/* Enable ptrauth instructions */
+	ldr	x2, =SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | \
+		     SCTLR_ELx_ENDA | SCTLR_ELx_ENDB
+	orr	x0, x0, x2
+3:
+#endif
 	ret					// return to head.S
 SYM_FUNC_END(__cpu_setup)

drivers/misc/lkdtm/bugs.c

@@ -378,3 +378,39 @@ void lkdtm_DOUBLE_FAULT(void)
 	pr_err("XFAIL: this test is ia32-only\n");
 #endif
 }
+
+#ifdef CONFIG_ARM64_PTR_AUTH
+static noinline void change_pac_parameters(void)
+{
+	/* Reset the keys of current task */
+	ptrauth_thread_init_kernel(current);
+	ptrauth_thread_switch_kernel(current);
+}
+
+#define CORRUPT_PAC_ITERATE	10
+noinline void lkdtm_CORRUPT_PAC(void)
+{
+	int i;
+
+	if (!system_supports_address_auth()) {
+		pr_err("FAIL: arm64 pointer authentication feature not present\n");
+		return;
+	}
+
+	pr_info("Change the PAC parameters to force function return failure\n");
+	/*
+	 * Pac is a hash value computed from input keys, return address and
+	 * stack pointer. As pac has fewer bits so there is a chance of
+	 * collision, so iterate few times to reduce the collision probability.
+	 */
+	for (i = 0; i < CORRUPT_PAC_ITERATE; i++)
+		change_pac_parameters();
+
+	pr_err("FAIL: %s test failed. Kernel may be unstable from here\n", __func__);
+}
+#else /* !CONFIG_ARM64_PTR_AUTH */
+noinline void lkdtm_CORRUPT_PAC(void)
+{
+	pr_err("FAIL: arm64 pointer authentication config disabled\n");
+}
+#endif

drivers/misc/lkdtm/core.c

@@ -116,6 +116,7 @@ static const struct crashtype crashtypes[] = {
 	CRASHTYPE(STACK_GUARD_PAGE_LEADING),
 	CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
 	CRASHTYPE(UNSET_SMEP),
+	CRASHTYPE(CORRUPT_PAC),
 	CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
 	CRASHTYPE(OVERWRITE_ALLOCATION),
 	CRASHTYPE(WRITE_AFTER_FREE),

drivers/misc/lkdtm/lkdtm.h

@@ -31,6 +31,7 @@ void lkdtm_UNSET_SMEP(void);
 #ifdef CONFIG_X86_32
 void lkdtm_DOUBLE_FAULT(void);
 #endif
+void lkdtm_CORRUPT_PAC(void);
 
 /* lkdtm_heap.c */
 void __init lkdtm_heap_init(void);

include/linux/stackprotector.h

@@ -6,7 +6,7 @@
 #include <linux/sched.h>
 #include <linux/random.h>
 
-#ifdef CONFIG_STACKPROTECTOR
+#if defined(CONFIG_STACKPROTECTOR) || defined(CONFIG_ARM64_PTR_AUTH)
 # include <asm/stackprotector.h>
 #else
 static inline void boot_init_stack_canary(void)

scripts/Kconfig.include

@@ -31,6 +31,12 @@ cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -S -x c /dev/null -o /de
 # Return y if the linker supports <flag>, n otherwise
 ld-option = $(success,$(LD) -v $(1))
 
+# $(as-option,<flag>)
+# /dev/zero is used as output instead of /dev/null as some assembler cribs when
+# both input and output are same. Also both of them have same write behaviour so
+# can be easily substituted.
+as-option = $(success, $(CC) $(CLANG_FLAGS) $(1) -c -x assembler /dev/null -o /dev/zero)
+
 # $(as-instr,<instr>)
 # Return y if the assembler supports <instr>, n otherwise
 as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler -o /dev/null -)