| Message ID | 1571300065-10236-8-git-send-email-amit.kachhap@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: return address signing | expand |
Hi Amit, On 17/10/2019 09:14, Amit Daniel Kachhap wrote: > From: Kristina Martsenko <kristina.martsenko@arm.com> > > 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. > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 8ec792d..c12c98d 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -145,6 +145,7 @@ 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 > }; > > diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h > index 46e2b05..2294e93 100644 > --- a/arch/arm64/include/asm/smp.h > +++ b/arch/arm64/include/asm/smp.h > @@ -88,6 +88,8 @@ asmlinkage void secondary_start_kernel(void); > struct secondary_data { > void *stack; > struct task_struct *task; > + unsigned long ptrauth_key_lo; > + unsigned long ptrauth_key_hi; How come this isn't a struct ptrauth_keys_kernel, like the thread struct? Everywhere else you ldp it as one 128 bit quantity, here its split into lo/hi and loaded independently. I think this is safe for big-endian... but it hurts to think about it. I'd like the lo/hi not to matter, its a randomly generated key, as long as we always read it from memory and write it to the CPU registers in the same way, it doesn't matter which bits end up in the hi/lo registers. > long status; > }; > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 157c811..e518511 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -858,6 +858,16 @@ alternative_endif > orr x2, x2, x1 // primary || system_supports_address_auth() > cbz x2, 3f > > + /* Install ptrauth key */ > + mov x3, xzr > + mov x4, xzr > + cbnz x1, 1f > + adr_l x2, secondary_data > + ldr x3, [x2, CPU_BOOT_PTRAUTH_KEY_LO] > + ldr x4, [x2, CPU_BOOT_PTRAUTH_KEY_HI] > +1: msr_s SYS_APIAKEYLO_EL1, x3 > + msr_s SYS_APIAKEYHI_EL1, x4 Why do we store zero to those registers if !system_supports_address_auth()? Is this for the boot CPU? It would be good to keep the code accessing secondary_data together. The boot-cpu's values are always going to come from somewhere funny, so it makes sense to keep the secondarys separate. (We test values from secondary_data in case the cpu-online code has given up on us. I don't think we can test the PTRAUTH_KEY against 0 for too-slow secondaries, as 0 may be the random key we generated). This assembly function is a bit of a swiss-army-knife, it does everything to do with ptrauth. The code-patching makes it difficult to work out what happens. In general I think it would be simpler if these functions did one thing, even if there ends up being more code overall. Thanks, James
Hi James, On 10/23/19 11:05 PM, James Morse wrote: > Hi Amit, > > On 17/10/2019 09:14, Amit Daniel Kachhap wrote: >> From: Kristina Martsenko <kristina.martsenko@arm.com> >> >> 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. > > >> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h >> index 8ec792d..c12c98d 100644 >> --- a/arch/arm64/include/asm/processor.h >> +++ b/arch/arm64/include/asm/processor.h >> @@ -145,6 +145,7 @@ 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 >> }; >> >> diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h >> index 46e2b05..2294e93 100644 >> --- a/arch/arm64/include/asm/smp.h >> +++ b/arch/arm64/include/asm/smp.h >> @@ -88,6 +88,8 @@ asmlinkage void secondary_start_kernel(void); >> struct secondary_data { >> void *stack; >> struct task_struct *task; >> + unsigned long ptrauth_key_lo; >> + unsigned long ptrauth_key_hi; > > How come this isn't a struct ptrauth_keys_kernel, like the thread struct? > Everywhere else you ldp it as one 128 bit quantity, here its split into lo/hi and loaded > independently. It can be updated to struct ptrauth_keys_kernel. > > I think this is safe for big-endian... but it hurts to think about it. > > I'd like the lo/hi not to matter, its a randomly generated key, as long as we always read > it from memory and write it to the CPU registers in the same way, it doesn't matter which > bits end up in the hi/lo registers. > > >> long status; >> }; >> > >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> index 157c811..e518511 100644 >> --- a/arch/arm64/kernel/head.S >> +++ b/arch/arm64/kernel/head.S >> @@ -858,6 +858,16 @@ alternative_endif >> orr x2, x2, x1 // primary || system_supports_address_auth() >> cbz x2, 3f >> >> + /* Install ptrauth key */ >> + mov x3, xzr >> + mov x4, xzr >> + cbnz x1, 1f >> + adr_l x2, secondary_data >> + ldr x3, [x2, CPU_BOOT_PTRAUTH_KEY_LO] >> + ldr x4, [x2, CPU_BOOT_PTRAUTH_KEY_HI] >> +1: msr_s SYS_APIAKEYLO_EL1, x3 >> + msr_s SYS_APIAKEYHI_EL1, x4 > > Why do we store zero to those registers if !system_supports_address_auth()? > Is this for the boot CPU? Yes. This is a limitation in the current implementation. Is it better to leave it uninitialized here? > > It would be good to keep the code accessing secondary_data together. The boot-cpu's values > are always going to come from somewhere funny, so it makes sense to keep the secondarys > separate. ok. > > (We test values from secondary_data in case the cpu-online code has given up on us. I > don't think we can test the PTRAUTH_KEY against 0 for too-slow secondaries, as 0 may be > the random key we generated). Ok thanks for the details. After looking at the code, it seems secondary_data.ptrauth_key_lo/hi is not required as secondary_data.task.thread.keys_kernel.apia.lo can fetch us the same information. > > This assembly function is a bit of a swiss-army-knife, it does everything to do with > ptrauth. The code-patching makes it difficult to work out what happens. In general I think > it would be simpler if these functions did one thing, even if there ends up being more ok I will try to simplify them in next iteration. Thanks, Amit > > > Thanks, > > James >
diff --git a/arch/arm64/include/asm/asm_pointer_auth.h b/arch/arm64/include/asm/asm_pointer_auth.h index 3d39788..172548a 100644 --- a/arch/arm64/include/asm/asm_pointer_auth.h +++ b/arch/arm64/include/asm/asm_pointer_auth.h @@ -35,11 +35,25 @@ alternative_if ARM64_HAS_GENERIC_AUTH alternative_else_nop_endif .endm + .macro ptrauth_keys_install_kernel tsk, tmp1, tmp2, tmp3 + mov \tmp1, #THREAD_KEYS_KERNEL + add \tmp1, \tsk, \tmp1 +alternative_if ARM64_HAS_ADDRESS_AUTH + 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 */ diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h index cc42145..599dd09 100644 --- a/arch/arm64/include/asm/pointer_auth.h +++ b/arch/arm64/include/asm/pointer_auth.h @@ -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()) { @@ -43,6 +47,12 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys) get_random_bytes(&keys->apga, sizeof(keys->apga)); } +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); /* @@ -59,11 +69,14 @@ 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 */ diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 8ec792d..c12c98d 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -145,6 +145,7 @@ 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 }; diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h index 46e2b05..2294e93 100644 --- a/arch/arm64/include/asm/smp.h +++ b/arch/arm64/include/asm/smp.h @@ -88,6 +88,8 @@ asmlinkage void secondary_start_kernel(void); struct secondary_data { void *stack; struct task_struct *task; + unsigned long ptrauth_key_lo; + unsigned long ptrauth_key_hi; long status; }; diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index cf15182..78ab279 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -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])); @@ -90,6 +91,8 @@ int main(void) BLANK(); DEFINE(CPU_BOOT_STACK, offsetof(struct secondary_data, stack)); DEFINE(CPU_BOOT_TASK, offsetof(struct secondary_data, task)); + DEFINE(CPU_BOOT_PTRAUTH_KEY_LO, offsetof(struct secondary_data, ptrauth_key_lo)); + DEFINE(CPU_BOOT_PTRAUTH_KEY_HI, offsetof(struct secondary_data, ptrauth_key_hi)); BLANK(); #ifdef CONFIG_KVM_ARM_HOST DEFINE(VCPU_CONTEXT, offsetof(struct kvm_vcpu, arch.ctxt)); @@ -136,6 +139,7 @@ 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; diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index b6272a3..0619065 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -173,6 +173,7 @@ 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 @@ -1155,6 +1157,7 @@ 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) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 157c811..e518511 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -858,6 +858,16 @@ alternative_endif orr x2, x2, x1 // primary || system_supports_address_auth() cbz x2, 3f + /* Install ptrauth key */ + mov x3, xzr + mov x4, xzr + cbnz x1, 1f + adr_l x2, secondary_data + ldr x3, [x2, CPU_BOOT_PTRAUTH_KEY_LO] + ldr x4, [x2, CPU_BOOT_PTRAUTH_KEY_HI] +1: msr_s SYS_APIAKEYLO_EL1, x3 + msr_s SYS_APIAKEYHI_EL1, x4 + /* Enable ptrauth instructions */ ldr x2, =SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | \ SCTLR_ELx_ENDA | SCTLR_ELx_ENDB diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 5b2b158..b737f55 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -376,6 +376,8 @@ int copy_thread(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; diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index a6a5f24..230d21f 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -110,6 +110,10 @@ 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_lo = idle->thread.keys_kernel.apia.lo; + secondary_data.ptrauth_key_hi = idle->thread.keys_kernel.apia.hi; +#endif update_cpu_boot_status(CPU_MMU_OFF); __flush_dcache_area(&secondary_data, sizeof(secondary_data)); @@ -136,6 +140,8 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) secondary_data.task = NULL; secondary_data.stack = NULL; + secondary_data.ptrauth_key_lo = 0; + secondary_data.ptrauth_key_hi = 0; __flush_dcache_area(&secondary_data, sizeof(secondary_data)); status = READ_ONCE(secondary_data.status); if (ret && status) {