Commit a27a8816 authored by Catalin Marinas's avatar Catalin Marinas
Browse files

Merge branch 'for-next/pac-set-get-enabled-keys' into for-next/core 

* for-next/pac-set-get-enabled-keys:
  : Introduce arm64 prctl(PR_PAC_{SET,GET}_ENABLED_KEYS).
  arm64: pac: Optimize kernel entry/exit key installation code paths
  arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS)
  arm64: mte: make the per-task SCTLR_EL1 field usable elsewhere
parents 604df13d b90e4839

Documentation/arm64/pointer-authentication.rst

+34 −0
Original line number Diff line number Diff line
@@ -107,3 +107,37 @@ filter out the Pointer Authentication system key registers from 
KVM_GET/SET_REG_* ioctls and mask those features from cpufeature ID

register. Any attempt to use the Pointer Authentication instructions will

result in an UNDEFINED exception being injected into the guest.





Enabling and disabling keys

---------------------------



The prctl PR_PAC_SET_ENABLED_KEYS allows the user program to control which

PAC keys are enabled in a particular task. It takes two arguments, the

first being a bitmask of PR_PAC_APIAKEY, PR_PAC_APIBKEY, PR_PAC_APDAKEY

and PR_PAC_APDBKEY specifying which keys shall be affected by this prctl,

and the second being a bitmask of the same bits specifying whether the key

should be enabled or disabled. For example::



  prctl(PR_PAC_SET_ENABLED_KEYS,

        PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY | PR_PAC_APDBKEY,

        PR_PAC_APIBKEY, 0, 0);



disables all keys except the IB key.



The main reason why this is useful is to enable a userspace ABI that uses PAC

instructions to sign and authenticate function pointers and other pointers

exposed outside of the function, while still allowing binaries conforming to

the ABI to interoperate with legacy binaries that do not sign or authenticate

pointers.



The idea is that a dynamic loader or early startup code would issue this

prctl very early after establishing that a process may load legacy binaries,

but before executing any PAC instructions.



For compatibility with previous kernel versions, processes start up with IA,

IB, DA and DB enabled, and are reset to this state on exec(). Processes created

via fork() and clone() inherit the key enabled state from the calling process.



It is recommended to avoid disabling the IA key, as this has higher performance

overhead than disabling any of the other keys.

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/mte.h

+2 −2
Original line number Diff line number Diff line
@@ -39,7 +39,7 @@ void mte_free_tag_storage(char *storage); 


void mte_sync_tags(pte_t *ptep, pte_t pte);

void mte_copy_page_tags(void *kto, const void *kfrom);

void flush_mte_state(void);

void mte_thread_init_user(void);

void mte_thread_switch(struct task_struct *next);

void mte_suspend_enter(void);

void mte_suspend_exit(void);
@@ -59,7 +59,7 @@ static inline void mte_sync_tags(pte_t *ptep, pte_t pte) 
static inline void mte_copy_page_tags(void *kto, const void *kfrom)

{

}

static inline void flush_mte_state(void)

static inline void mte_thread_init_user(void)

{

}

static inline void mte_thread_switch(struct task_struct *next)

arch/arm64/include/asm/pointer_auth.h

+51 −10
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
#define __ASM_POINTER_AUTH_H



#include <linux/bitops.h>

#include <linux/prctl.h>

#include <linux/random.h>



#include <asm/cpufeature.h>
@@ -34,6 +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()) {
@@ -45,14 +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)

{
@@ -71,6 +86,10 @@ static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kerne 


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,

				    unsigned long enabled);

extern int ptrauth_get_enabled_keys(struct task_struct *tsk);



static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)

{

	return ptrauth_clear_pac(ptr);
@@ -85,8 +104,23 @@ static __always_inline void ptrauth_enable(void) 
	isb();

}



#define ptrauth_thread_init_user(tsk)					\

	ptrauth_keys_init_user(&(tsk)->thread.keys_user)

#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);            \

									       \

		/* enable all keys */                                          \

		if (system_supports_address_auth())                            \

			set_task_sctlr_el1(current->thread.sctlr_user |        \

					   SCTLR_ELx_ENIA | SCTLR_ELx_ENIB |   \

					   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)				\
@@ -95,10 +129,17 @@ static __always_inline void ptrauth_enable(void) 
#else /* CONFIG_ARM64_PTR_AUTH */

#define ptrauth_enable()

#define ptrauth_prctl_reset_keys(tsk, arg)	(-EINVAL)

#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_thread_init_user(tsk)

#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 */



#define PR_PAC_ENABLED_KEYS_MASK                                               \

	(PR_PAC_APIAKEY | PR_PAC_APIBKEY | PR_PAC_APDAKEY | PR_PAC_APDBKEY)



#endif /* __ASM_POINTER_AUTH_H */

arch/arm64/include/asm/processor.h

+12 −1
Original line number Diff line number Diff line
@@ -151,11 +151,15 @@ struct thread_struct { 
	struct ptrauth_keys_kernel	keys_kernel;

#endif

#ifdef CONFIG_ARM64_MTE

	u64			sctlr_tcf0;

	u64			gcr_user_excl;

#endif

	u64			sctlr_user;

};



#define SCTLR_USER_MASK                                                        \

	(SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | SCTLR_ELx_ENDA | SCTLR_ELx_ENDB |   \

	 SCTLR_EL1_TCF0_MASK)



static inline void arch_thread_struct_whitelist(unsigned long *offset,

						unsigned long *size)

{
@@ -247,6 +251,8 @@ extern void release_thread(struct task_struct *); 


unsigned long get_wchan(struct task_struct *p);



void set_task_sctlr_el1(u64 sctlr);



/* Thread switching */

extern struct task_struct *cpu_switch_to(struct task_struct *prev,

					 struct task_struct *next);
@@ -301,6 +307,11 @@ extern void __init minsigstksz_setup(void); 
/* PR_PAC_RESET_KEYS prctl */

#define PAC_RESET_KEYS(tsk, arg)	ptrauth_prctl_reset_keys(tsk, arg)



/* PR_PAC_{SET,GET}_ENABLED_KEYS prctl */

#define PAC_SET_ENABLED_KEYS(tsk, keys, enabled)				\

	ptrauth_set_enabled_keys(tsk, keys, enabled)

#define PAC_GET_ENABLED_KEYS(tsk) ptrauth_get_enabled_keys(tsk)



#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI

/* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */

long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg);