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>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 489e3e42320f1c0f65e51b669089fd0346b249ea..dabe9b81012f81f8565890ae388293196fd23ed5 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1503,7 +1503,7 @@ config ARM64_PTR_AUTH
          not be selected.
 
 config ARM64_PTR_AUTH_KERNEL
-       bool
+       bool "Use pointer authentication for kernel"
        default y
        depends on ARM64_PTR_AUTH
        depends on (CC_HAS_SIGN_RETURN_ADDRESS || CC_HAS_BRANCH_PROT_PAC_RET) && AS_HAS_PAC

diff --git a/arch/arm64/include/asm/asm_pointer_auth.h b/arch/arm64/include/asm/asm_pointer_auth.h
index 8ca2dc0661ee298a503d6f794ec8bfff95932da2..f1bba5fc61c49f326dc42f27485a07988b1f84fc 100644 (file)
--- a/arch/arm64/include/asm/asm_pointer_auth.h
+++ b/arch/arm64/include/asm/asm_pointer_auth.h
@@ -7,19 +7,7 @@
 #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
-       ldp     \tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APIA]
-       msr_s   SYS_APIAKEYLO_EL1, \tmp2
-       msr_s   SYS_APIAKEYHI_EL1, \tmp3
-       .endm
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
 
        .macro __ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3
        mov     \tmp1, #THREAD_KEYS_KERNEL
@@ -42,6 +30,33 @@ alternative_if ARM64_HAS_ADDRESS_AUTH
 alternative_else_nop_endif
        .endm
 
+#else /* CONFIG_ARM64_PTR_AUTH_KERNEL */
+
+       .macro __ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3
+       .endm
+
+       .macro ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3
+       .endm
+
+       .macro ptrauth_keys_install_kernel tsk, tmp1, tmp2, tmp3
+       .endm
+
+#endif /* CONFIG_ARM64_PTR_AUTH_KERNEL */
+
+#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
+       ldp     \tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APIA]
+       msr_s   SYS_APIAKEYLO_EL1, \tmp2
+       msr_s   SYS_APIAKEYHI_EL1, \tmp3
+       .endm
+
        .macro __ptrauth_keys_init_cpu tsk, tmp1, tmp2, tmp3
        mrs     \tmp1, id_aa64isar1_el1
        ubfx    \tmp1, \tmp1, #ID_AA64ISAR1_APA_SHIFT, #8
@@ -64,17 +79,11 @@ alternative_else_nop_endif
 .Lno_addr_auth\@:
        .endm
 
-#else /* CONFIG_ARM64_PTR_AUTH */
+#else /* !CONFIG_ARM64_PTR_AUTH */
 
        .macro ptrauth_keys_install_user tsk, tmp1, tmp2, tmp3
        .endm
 
-       .macro ptrauth_keys_install_kernel_nosync 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 d50416be99be0bf0d903f0a985b476546bc83d63..28a78b67d9b40753d0a0228e6c990a504ce64ffe 100644 (file)
--- 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)
 

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 9df3feeee8909b5a0794a8d15c6331d855e072f4..e7d50c6f700d36fd5f561ae87928e078279f3b3c 100644 (file)
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -148,8 +148,10 @@ struct thread_struct {
        struct debug_info       debug;          /* debugging */
 #ifdef CONFIG_ARM64_PTR_AUTH
        struct ptrauth_keys_user        keys_user;
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
        struct ptrauth_keys_kernel      keys_kernel;
 #endif
+#endif
 #ifdef CONFIG_ARM64_MTE
        u64                     gcr_user_excl;
 #endif

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 03420b89c60296c691133075aa8d4112f4d60e19..c9e72d92606fb1e56fce2dc3805f9516e568f1e2 100644 (file)
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -155,7 +155,9 @@ int main(void)
 #endif
 #ifdef CONFIG_ARM64_PTR_AUTH
   DEFINE(PTRAUTH_USER_KEY_APIA,                offsetof(struct ptrauth_keys_user, apia));
+#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
   DEFINE(PTRAUTH_KERNEL_KEY_APIA,      offsetof(struct ptrauth_keys_kernel, apia));
+#endif
   BLANK();
 #endif
   return 0;