arm64: initialize and switch ptrauth kernel keys

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>

diff --git a/arch/arm64/include/asm/asm_pointer_auth.h b/arch/arm64/include/asm/asm_pointer_auth.h
index 3482348..d3f4aee 100644 (file)
--- a/arch/arm64/include/asm/asm_pointer_auth.h
+++ b/arch/arm64/include/asm/asm_pointer_auth.h
@@ -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 */

diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index dabe026..aa956ca 100644 (file)
--- 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()) {
@@ -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 */

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 496a928..4c77da5 100644 (file)
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -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
 };
 

diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index 8d66497..40d5ba0 100644 (file)
--- a/arch/arm64/include/asm/smp.h
+++ b/arch/arm64/include/asm/smp.h
@@ -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;
 };
 

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 7b1ea2a..9981a0a 100644 (file)
--- 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]));
@@ -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;

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 684e475..3dad2d0 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -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)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 6140e79..7db0302 100644 (file)
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -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;

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index d4ed9a1..0890341 100644 (file)
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -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) {

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 4cf19a2..5a11a89 100644 (file)
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -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