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arm64: initialize and switch ptrauth kernel keys

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Set up keys to use pointer authentication within the kernel. The kernel
will be compiled with APIAKey instructions, the other keys are currently
unused. Each task is given its own APIAKey, which is initialized during
fork. The key is changed during context switch and on kernel entry from
EL0.

The keys for idle threads need to be set before calling any C functions,
because it is not possible to enter and exit a function with different
keys.

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
[Amit: Modified secondary cores key structure, comments]
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Kristina Martsenko 2020-03-13 14:34:56 +05:30 committed by Catalin Marinas
parent 6982934e19
commit 33e4523498
9 changed files with 62 additions and 0 deletions
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14
arch/arm64/include/asm/asm_pointer_auth.h
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@ -39,11 +39,25 @@ alternative_if ARM64_HAS_GENERIC_AUTH
alternative_else_nop_endif
.endm
.macro ptrauth_keys_install_kernel tsk, tmp1, tmp2, tmp3
alternative_if ARM64_HAS_ADDRESS_AUTH
mov \tmp1, #THREAD_KEYS_KERNEL
add \tmp1, \tsk, \tmp1
ldp \tmp2, \tmp3, [\tmp1, #PTRAUTH_KERNEL_KEY_APIA]
msr_s SYS_APIAKEYLO_EL1, \tmp2
msr_s SYS_APIAKEYHI_EL1, \tmp3
isb
alternative_else_nop_endif
.endm
#else /* CONFIG_ARM64_PTR_AUTH */
.macro ptrauth_keys_install_user 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 */

13
arch/arm64/include/asm/pointer_auth.h
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@ -30,6 +30,10 @@ struct ptrauth_keys_user {
struct ptrauth_key apga;
};
struct ptrauth_keys_kernel {
struct ptrauth_key apia;
};
static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
{
if (system_supports_address_auth()) {
@ -50,6 +54,12 @@ do { \
write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1); \
} while (0)
static inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
{
if (system_supports_address_auth())
get_random_bytes(&keys->apia, sizeof(keys->apia));
}
extern int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg);
/*
@ -66,11 +76,14 @@ static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
#define ptrauth_thread_init_user(tsk) \
ptrauth_keys_init_user(&(tsk)->thread.keys_user)
#define ptrauth_thread_init_kernel(tsk) \
ptrauth_keys_init_kernel(&(tsk)->thread.keys_kernel)
#else /* CONFIG_ARM64_PTR_AUTH */
#define ptrauth_prctl_reset_keys(tsk, arg) (-EINVAL)
#define ptrauth_strip_insn_pac(lr) (lr)
#define ptrauth_thread_init_user(tsk)
#define ptrauth_thread_init_kernel(tsk)
#endif /* CONFIG_ARM64_PTR_AUTH */
#endif /* __ASM_POINTER_AUTH_H */

1
arch/arm64/include/asm/processor.h
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@ -147,6 +147,7 @@ struct thread_struct {
struct debug_info debug; /* debugging */
#ifdef CONFIG_ARM64_PTR_AUTH
struct ptrauth_keys_user keys_user;
struct ptrauth_keys_kernel keys_kernel;
#endif
};

4
arch/arm64/include/asm/smp.h
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@ -38,6 +38,7 @@
#include <linux/threads.h>
#include <linux/cpumask.h>
#include <linux/thread_info.h>
#include <asm/pointer_auth.h>
DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number);
@ -95,6 +96,9 @@ asmlinkage void secondary_start_kernel(void);
struct secondary_data {
void *stack;
struct task_struct *task;
#ifdef CONFIG_ARM64_PTR_AUTH
struct ptrauth_keys_kernel ptrauth_key;
#endif
long status;
};

5
arch/arm64/kernel/asm-offsets.c
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@ -42,6 +42,7 @@ int main(void)
DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context));
#ifdef CONFIG_ARM64_PTR_AUTH
DEFINE(THREAD_KEYS_USER, offsetof(struct task_struct, thread.keys_user));
DEFINE(THREAD_KEYS_KERNEL, offsetof(struct task_struct, thread.keys_kernel));
#endif
BLANK();
DEFINE(S_X0, offsetof(struct pt_regs, regs[0]));
@ -91,6 +92,9 @@ int main(void)
BLANK();
DEFINE(CPU_BOOT_STACK, offsetof(struct secondary_data, stack));
DEFINE(CPU_BOOT_TASK, offsetof(struct secondary_data, task));
#ifdef CONFIG_ARM64_PTR_AUTH
DEFINE(CPU_BOOT_PTRAUTH_KEY, offsetof(struct secondary_data, ptrauth_key));
#endif
BLANK();
#ifdef CONFIG_KVM_ARM_HOST
DEFINE(VCPU_CONTEXT, offsetof(struct kvm_vcpu, arch.ctxt));
@ -137,6 +141,7 @@ int main(void)
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
return 0;

3
arch/arm64/kernel/entry.S
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@ -178,6 +178,7 @@ alternative_cb_end
apply_ssbd 1, x22, x23
ptrauth_keys_install_kernel tsk, x20, x22, x23
.else
add x21, sp, #S_FRAME_SIZE
get_current_task tsk
@ -342,6 +343,7 @@ alternative_else_nop_endif
msr cntkctl_el1, x1
4:
#endif
/* No kernel C function calls after this as user keys are set. */
ptrauth_keys_install_user tsk, x0, x1, x2
apply_ssbd 0, x0, x1
@ -898,6 +900,7 @@ ENTRY(cpu_switch_to)
ldr lr, [x8]
mov sp, x9
msr sp_el0, x1
ptrauth_keys_install_kernel x1, x8, x9, x10
ret
ENDPROC(cpu_switch_to)
NOKPROBE(cpu_switch_to)

2
arch/arm64/kernel/process.c
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@ -376,6 +376,8 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long stack_start,
*/
fpsimd_flush_task_state(p);
ptrauth_thread_init_kernel(p);
if (likely(!(p->flags & PF_KTHREAD))) {
*childregs = *current_pt_regs();
childregs->regs[0] = 0;

8
arch/arm64/kernel/smp.c
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@ -112,6 +112,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
*/
secondary_data.task = idle;
secondary_data.stack = task_stack_page(idle) + THREAD_SIZE;
#if defined(CONFIG_ARM64_PTR_AUTH)
secondary_data.ptrauth_key.apia.lo = idle->thread.keys_kernel.apia.lo;
secondary_data.ptrauth_key.apia.hi = idle->thread.keys_kernel.apia.hi;
#endif
update_cpu_boot_status(CPU_MMU_OFF);
__flush_dcache_area(&secondary_data, sizeof(secondary_data));
@ -138,6 +142,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
secondary_data.task = NULL;
secondary_data.stack = NULL;
#if defined(CONFIG_ARM64_PTR_AUTH)
secondary_data.ptrauth_key.apia.lo = 0;
secondary_data.ptrauth_key.apia.hi = 0;
#endif
__flush_dcache_area(&secondary_data, sizeof(secondary_data));
status = READ_ONCE(secondary_data.status);
if (ret && status) {

12
arch/arm64/mm/proc.S
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@ -485,6 +485,10 @@ SYM_FUNC_START(__cpu_setup)
ubfx x2, x2, #ID_AA64ISAR1_APA_SHIFT, #8
cbz x2, 3f
/*
* The primary cpu keys are reset here and can be
* re-initialised with some proper values later.
*/
msr_s SYS_APIAKEYLO_EL1, xzr
msr_s SYS_APIAKEYHI_EL1, xzr
@ -497,6 +501,14 @@ alternative_if_not ARM64_HAS_ADDRESS_AUTH
b 3f
alternative_else_nop_endif
/* Install ptrauth key for secondary cpus */
adr_l x2, secondary_data
ldr x3, [x2, #CPU_BOOT_TASK] // get secondary_data.task
cbz x3, 2f // check for slow booting cpus
ldp x3, x4, [x2, #CPU_BOOT_PTRAUTH_KEY]
msr_s SYS_APIAKEYLO_EL1, x3
msr_s SYS_APIAKEYHI_EL1, x4
2: /* Enable ptrauth instructions */
ldr x2, =SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | \
SCTLR_ELx_ENDA | SCTLR_ELx_ENDB