Commit b90e4839 authored by Peter Collingbourne's avatar Peter Collingbourne Committed by Catalin Marinas
Browse files

arm64: pac: Optimize kernel entry/exit key installation code paths 



The kernel does not use any keys besides IA so we don't need to
install IB/DA/DB/GA on kernel exit if we arrange to install them
on task switch instead, which we can expect to happen an order of
magnitude less often.

Furthermore we can avoid installing the user IA in the case where the
user task has IA disabled and just leave the kernel IA installed. This
also lets us avoid needing to install IA on kernel entry.

On an Apple M1 under a hypervisor, the overhead of kernel entry/exit
has been measured to be reduced by 15.6ns in the case where IA is
enabled, and 31.9ns in the case where IA is disabled.

Signed-off-by: default avatarPeter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/Ieddf6b580d23c9e0bed45a822dabe72d2ffc9a8e
Link: https://lore.kernel.org/r/2d653d055f38f779937f2b92f8ddd5cf9e4af4f4.1616123271.git.pcc@google.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 20169862

arch/arm64/include/asm/asm_pointer_auth.h

+1 −19
Original line number Diff line number Diff line
@@ -13,30 +13,12 @@ 
 * 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

	.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_nosync tsk, tmp1, tmp2, tmp3

arch/arm64/include/asm/pointer_auth.h

+29 −7
Original line number Diff line number Diff line
@@ -35,6 +35,25 @@ struct ptrauth_keys_kernel { 
	struct ptrauth_key apia;

};



#define __ptrauth_key_install_nosync(k, v)			\

do {								\

	struct ptrauth_key __pki_v = (v);			\

	write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1);	\

	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\

} while (0)



static inline void ptrauth_keys_install_user(struct ptrauth_keys_user *keys)

{

	if (system_supports_address_auth()) {

		__ptrauth_key_install_nosync(APIB, keys->apib);

		__ptrauth_key_install_nosync(APDA, keys->apda);

		__ptrauth_key_install_nosync(APDB, keys->apdb);

	}



	if (system_supports_generic_auth())

		__ptrauth_key_install_nosync(APGA, keys->apga);

}



static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)

{

	if (system_supports_address_auth()) {
@@ -46,14 +65,9 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys) 


	if (system_supports_generic_auth())

		get_random_bytes(&keys->apga, sizeof(keys->apga));

}



#define __ptrauth_key_install_nosync(k, v)			\

do {								\

	struct ptrauth_key __pki_v = (v);			\

	write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1);	\

	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\

} while (0)

	ptrauth_keys_install_user(keys);

}



static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)

{
@@ -90,6 +104,9 @@ static __always_inline void ptrauth_enable(void) 
	isb();

}



#define ptrauth_suspend_exit()                                                 \

	ptrauth_keys_install_user(&current->thread.keys_user)



#define ptrauth_thread_init_user()                                             \

	do {                                                                   \

		ptrauth_keys_init_user(&current->thread.keys_user);            \
@@ -101,6 +118,9 @@ static __always_inline void ptrauth_enable(void) 
					   SCTLR_ELx_ENDA | SCTLR_ELx_ENDB);   \

	} while (0)



#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)				\
@@ -112,8 +132,10 @@ static __always_inline void ptrauth_enable(void) 
#define ptrauth_set_enabled_keys(tsk, keys, enabled)	(-EINVAL)

#define ptrauth_get_enabled_keys(tsk)	(-EINVAL)

#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 */

arch/arm64/kernel/asm-offsets.c

+0 −4
Original line number Diff line number Diff line
@@ -148,10 +148,6 @@ int main(void) 
#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

arch/arm64/kernel/entry.S

+19 −14
Original line number Diff line number Diff line
@@ -247,21 +247,26 @@ alternative_else_nop_endif 
	check_mte_async_tcf x19, x22

	apply_ssbd 1, x22, x23



	ptrauth_keys_install_kernel_nosync tsk, x20, x22, x23



#ifdef CONFIG_ARM64_PTR_AUTH

alternative_if ARM64_HAS_ADDRESS_AUTH

	/*

	 * Enable IA for in-kernel PAC if the task had it disabled. Although

	 * this could be implemented with an unconditional MRS which would avoid

	 * a load, this was measured to be slower on Cortex-A75 and Cortex-A76.

	 *

	 * Install the kernel IA key only if IA was enabled in the task. If IA

	 * was disabled on kernel exit then we would have left the kernel IA

	 * installed so there is no need to install it again.

	 */

	ldr	x0, [tsk, THREAD_SCTLR_USER]

	tbnz	x0, SCTLR_ELx_ENIA_SHIFT, 1f

	tbz	x0, SCTLR_ELx_ENIA_SHIFT, 1f

	__ptrauth_keys_install_kernel_nosync tsk, x20, x22, x23

	b	2f

1:

	mrs	x0, sctlr_el1

	orr	x0, x0, SCTLR_ELx_ENIA

	msr	sctlr_el1, x0

1:

2:

	isb

alternative_else_nop_endif

#endif
@@ -368,24 +373,24 @@ alternative_else_nop_endif 
3:

	scs_save tsk, x0



	/*

	 * No kernel C function calls after this as user keys are set and IA may

	 * be disabled.

	 */

	ptrauth_keys_install_user tsk, x0, x1, x2



#ifdef CONFIG_ARM64_PTR_AUTH

alternative_if ARM64_HAS_ADDRESS_AUTH

	/*

	 * IA was enabled for in-kernel PAC. Disable it now if needed.

	 * All other per-task SCTLR bits were updated on task switch.

	 * IA was enabled for in-kernel PAC. Disable it now if needed, or

	 * alternatively install the user's IA. All other per-task keys and

	 * SCTLR bits were updated on task switch.

	 *

	 * No kernel C function calls after this.

	 */

	ldr	x0, [tsk, THREAD_SCTLR_USER]

	tbnz	x0, SCTLR_ELx_ENIA_SHIFT, 1f

	tbz	x0, SCTLR_ELx_ENIA_SHIFT, 1f

	__ptrauth_keys_install_user tsk, x0, x1, x2

	b	2f

1:

	mrs	x0, sctlr_el1

	bic	x0, x0, SCTLR_ELx_ENIA

	msr	sctlr_el1, x0

1:

2:

alternative_else_nop_endif

#endif

arch/arm64/kernel/pointer_auth.c

+1 −0
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg) 
		get_random_bytes(&keys->apdb, sizeof(keys->apdb));

	if (arg & PR_PAC_APGAKEY)

		get_random_bytes(&keys->apga, sizeof(keys->apga));

	ptrauth_keys_install_user(keys);



	return 0;

}