arm64: initialize and switch ptrauth kernel keys

Set up keys to use pointer authentication within the kernel. The kernel
will be compiled with APIAKey instructions, the other keys are currently
unused. Each task is given its own APIAKey, which is initialized during
fork. The key is changed during context switch and on kernel entry from
EL0.

The keys for idle threads need to be set before calling any C functions,
because it is not possible to enter and exit a function with different
keys.

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
[Amit: Modified secondary cores key structure, comments]
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

4 files changed, 32 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/asm_pointer_auth.h b/arch/arm64/include/asm/asm_pointer_auth.h
index 3482348ec07f..d3f4aee42851 100644
--- a/arch/arm64/include/asm/asm_pointer_auth.h
+++ b/arch/arm64/include/asm/asm_pointer_auth.h
@@ -39,11 +39,25 @@ alternative_if ARM64_HAS_GENERIC_AUTH
 alternative_else_nop_endif
 	.endm
 
+	.macro ptrauth_keys_install_kernel tsk, 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
+	isb
+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, tmp1, tmp2, tmp3
+	.endm
+
 #endif /* CONFIG_ARM64_PTR_AUTH */
 
 #endif /* __ASM_ASM_POINTER_AUTH_H */
diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index dabe026ca8ca..aa956ca5f2c2 100644
--- a/arch/arm64/include/asm/pointer_auth.h
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -30,6 +30,10 @@ struct ptrauth_keys_user {
 	struct ptrauth_key apga;
 };
 
+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()) {
@@ -50,6 +54,12 @@ do {								\
 	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
 } while (0)
 
+static inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
+{
+	if (system_supports_address_auth())
+		get_random_bytes(&keys->apia, sizeof(keys->apia));
+}
+
 extern int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg);
 
 /*
@@ -66,11 +76,14 @@ static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
 
 #define ptrauth_thread_init_user(tsk)					\
 	ptrauth_keys_init_user(&(tsk)->thread.keys_user)
+#define ptrauth_thread_init_kernel(tsk)					\
+	ptrauth_keys_init_kernel(&(tsk)->thread.keys_kernel)
 
 #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_init_kernel(tsk)
 #endif /* CONFIG_ARM64_PTR_AUTH */
 
 #endif /* __ASM_POINTER_AUTH_H */
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 496a92873290..4c77da5dc819 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -147,6 +147,7 @@ struct thread_struct {
 	struct debug_info	debug;		/* debugging */
 #ifdef CONFIG_ARM64_PTR_AUTH
 	struct ptrauth_keys_user	keys_user;
+	struct ptrauth_keys_kernel	keys_kernel;
 #endif
 };
 
diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index 8d66497d8157..40d5ba029615 100644
--- a/arch/arm64/include/asm/smp.h
+++ b/arch/arm64/include/asm/smp.h
@@ -38,6 +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);
 
@@ -95,6 +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;
 };