[PATCH v6 2/2] arm64: Conditionally configure PTR_AUTH key of the kernel.
Daniel Kiss
daniel.kiss at arm.com
Sun Jun 13 02:26:32 PDT 2021
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 at arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
---
arch/arm64/Kconfig | 2 +-
arch/arm64/include/asm/asm_pointer_auth.h | 49 +++++++++++--------
arch/arm64/include/asm/pointer_auth.h | 59 +++++++++++++----------
arch/arm64/include/asm/processor.h | 2 +
arch/arm64/kernel/asm-offsets.c | 2 +
5 files changed, 67 insertions(+), 47 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 489e3e42320f..dabe9b81012f 100644
--- 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 8ca2dc0661ee..f1bba5fc61c4 100644
--- 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 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)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 9df3feeee890..e7d50c6f700d 100644
--- 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 03420b89c602..c9e72d92606f 100644
--- 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;
--
2.25.1
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