arm64: Conditionally configure PTR_AUTH key of the kernel.

If the kernel is not compiled with CONFIG_ARM64_PTR_AUTH_KERNEL=y,
then no PACI/AUTI instructions are expected while the kernel is running
so the kernel's key will not be used. Write of a system registers
is expensive therefore avoid if not required.

Signed-off-by: Daniel Kiss <daniel.kiss@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210613092632.93591-3-daniel.kiss@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 33 insertions, 26 deletions

diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index d50416be99be..28a78b67d9b4 100644
--- a/arch/arm64/include/asm/pointer_auth.h
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -31,10 +31,6 @@ struct ptrauth_keys_user {
 	struct ptrauth_key apga;
 };
 
-struct ptrauth_keys_kernel {
-	struct ptrauth_key apia;
-};
-
 #define __ptrauth_key_install_nosync(k, v)			\
 do {								\
 	struct ptrauth_key __pki_v = (v);			\
@@ -42,6 +38,29 @@ do {								\
 	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
 } while (0)
 
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
+
+struct ptrauth_keys_kernel {
+	struct ptrauth_key apia;
+};
+
+static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
+{
+	if (system_supports_address_auth())
+		get_random_bytes(&keys->apia, sizeof(keys->apia));
+}
+
+static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kernel *keys)
+{
+	if (!system_supports_address_auth())
+		return;
+
+	__ptrauth_key_install_nosync(APIA, keys->apia);
+	isb();
+}
+
+#endif /* CONFIG_ARM64_PTR_AUTH_KERNEL */
+
 static inline void ptrauth_keys_install_user(struct ptrauth_keys_user *keys)
 {
 	if (system_supports_address_auth()) {
@@ -69,21 +88,6 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
 	ptrauth_keys_install_user(keys);
 }
 
-static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
-{
-	if (system_supports_address_auth())
-		get_random_bytes(&keys->apia, sizeof(keys->apia));
-}
-
-static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kernel *keys)
-{
-	if (!system_supports_address_auth())
-		return;
-
-	__ptrauth_key_install_nosync(APIA, keys->apia);
-	isb();
-}
-
 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,
@@ -121,11 +125,6 @@ static __always_inline void ptrauth_enable(void)
 #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)				\
-	ptrauth_keys_switch_kernel(&(tsk)->thread.keys_kernel)
-
 #else /* CONFIG_ARM64_PTR_AUTH */
 #define ptrauth_enable()
 #define ptrauth_prctl_reset_keys(tsk, arg)	(-EINVAL)
@@ -134,11 +133,19 @@ static __always_inline void ptrauth_enable(void)
 #define ptrauth_strip_insn_pac(lr)	(lr)
 #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 */
 
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
+#define ptrauth_thread_init_kernel(tsk)					\
+	ptrauth_keys_init_kernel(&(tsk)->thread.keys_kernel)
+#define ptrauth_thread_switch_kernel(tsk)				\
+	ptrauth_keys_switch_kernel(&(tsk)->thread.keys_kernel)
+#else
+#define ptrauth_thread_init_kernel(tsk)
+#define ptrauth_thread_switch_kernel(tsk)
+#endif /* CONFIG_ARM64_PTR_AUTH_KERNEL */
+
 #define PR_PAC_ENABLED_KEYS_MASK                                               \
 	(PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY | PR_PAC_APDBKEY)