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Subject[RFC 16/17] arm64: initialize and switch ptrauth kernel keys
Date
Set up keys to use pointer auth in the kernel. Each task has its own
APIAKey, which is initialized during fork. The key is changed during
context switch and on kernel entry from EL0.

A function that changes the key cannot return, so inline such functions.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
---
arch/arm64/include/asm/pointer_auth.h | 9 ++++++++-
arch/arm64/include/asm/ptrauth-asm.h | 13 +++++++++++++
arch/arm64/include/asm/thread_info.h | 1 +
arch/arm64/kernel/asm-offsets.c | 1 +
arch/arm64/kernel/entry.S | 4 ++++
arch/arm64/kernel/process.c | 3 +++
arch/arm64/kernel/smp.c | 3 +++
7 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index 0634f06c3af2..e94ca7df8dab 100644
--- a/arch/arm64/include/asm/pointer_auth.h
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -50,12 +50,13 @@ do { \
write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1); \
} while (0)

-static inline void ptrauth_keys_switch(struct ptrauth_keys *keys)
+static __always_inline void ptrauth_keys_switch(struct ptrauth_keys *keys)
{
if (!cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH))
return;

__ptrauth_key_install(APIA, keys->apia);
+ isb();
}

static __always_inline void ptrauth_cpu_enable(void)
@@ -85,11 +86,17 @@ static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)

#define ptrauth_task_init_user(tsk) \
ptrauth_keys_init(&(tsk)->thread_info.keys_user)
+#define ptrauth_task_init_kernel(tsk) \
+ ptrauth_keys_init(&(tsk)->thread_info.keys_kernel)
+#define ptrauth_task_switch(tsk) \
+ ptrauth_keys_switch(&(tsk)->thread_info.keys_kernel)

#else /* CONFIG_ARM64_PTR_AUTH */
#define __no_ptrauth
#define ptrauth_strip_insn_pac(lr) (lr)
#define ptrauth_task_init_user(tsk)
+#define ptrauth_task_init_kernel(tsk)
+#define ptrauth_task_switch(tsk)
#define ptrauth_cpu_enable(tsk)
#endif /* CONFIG_ARM64_PTR_AUTH */

diff --git a/arch/arm64/include/asm/ptrauth-asm.h b/arch/arm64/include/asm/ptrauth-asm.h
index f50bdfc4046c..3ef1cc8903d5 100644
--- a/arch/arm64/include/asm/ptrauth-asm.h
+++ b/arch/arm64/include/asm/ptrauth-asm.h
@@ -16,11 +16,24 @@ alternative_if ARM64_HAS_ADDRESS_AUTH
alternative_else_nop_endif
.endm

+ .macro ptrauth_keys_install_kernel tsk, tmp
+alternative_if ARM64_HAS_ADDRESS_AUTH
+ ldr \tmp, [\tsk, #(TSK_TI_KEYS_KERNEL + PTRAUTH_KEY_APIALO)]
+ msr_s SYS_APIAKEYLO_EL1, \tmp
+ ldr \tmp, [\tsk, #(TSK_TI_KEYS_KERNEL + PTRAUTH_KEY_APIAHI)]
+ msr_s SYS_APIAKEYHI_EL1, \tmp
+ isb
+alternative_else_nop_endif
+ .endm
+
#else /* CONFIG_ARM64_PTR_AUTH */

.macro ptrauth_keys_install_user tsk, tmp
.endm

+ .macro ptrauth_keys_install_kernel tsk, tmp
+ .endm
+
#endif /* CONFIG_ARM64_PTR_AUTH */

#endif /* __ASM_PTRAUTH_ASM_H */
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index ea9272fb52d4..e3ec5345addc 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -46,6 +46,7 @@ struct thread_info {
int preempt_count; /* 0 => preemptable, <0 => bug */
#ifdef CONFIG_ARM64_PTR_AUTH
struct ptrauth_keys keys_user;
+ struct ptrauth_keys keys_kernel;
#endif
};

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index b6be0dd037fd..6c61c9722b47 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -47,6 +47,7 @@ int main(void)
#endif
#ifdef CONFIG_ARM64_PTR_AUTH
DEFINE(TSK_TI_KEYS_USER, offsetof(struct task_struct, thread_info.keys_user));
+ DEFINE(TSK_TI_KEYS_KERNEL, offsetof(struct task_struct, thread_info.keys_kernel));
#endif
DEFINE(TSK_STACK, offsetof(struct task_struct, stack));
BLANK();
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 1e925f6d2978..a4503da445f7 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -250,6 +250,10 @@ alternative_else_nop_endif
msr sp_el0, tsk
.endif

+ .if \el == 0
+ ptrauth_keys_install_kernel tsk, x20
+ .endif
+
/*
* Registers that may be useful after this macro is invoked:
*
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 857ae05cd04c..a866996610de 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -330,6 +330,8 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
*/
fpsimd_flush_task_state(p);

+ ptrauth_task_init_kernel(p);
+
if (likely(!(p->flags & PF_KTHREAD))) {
*childregs = *current_pt_regs();
childregs->regs[0] = 0;
@@ -426,6 +428,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
contextidr_thread_switch(next);
entry_task_switch(next);
uao_thread_switch(next);
+ ptrauth_task_switch(next);

/*
* Complete any pending TLB or cache maintenance on this CPU in case
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 09690024dce8..d952dd62c780 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -212,6 +212,7 @@ asmlinkage notrace void secondary_start_kernel(void)
*/
check_local_cpu_capabilities();

+ ptrauth_task_switch(current);
ptrauth_cpu_enable();

if (cpu_ops[cpu]->cpu_postboot)
@@ -418,6 +419,8 @@ void __init __no_ptrauth smp_prepare_boot_cpu(void)
jump_label_init();
cpuinfo_store_boot_cpu();

+ ptrauth_task_init_kernel(current);
+ ptrauth_task_switch(current);
ptrauth_cpu_enable();
}

--
2.11.0
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