From 3fabb43818c9bfe7c4084badfa21d4e8187021a6 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Tue, 21 Apr 2020 13:10:14 +0100 Subject: [PATCH] arm64: sync kernel APIAKey when installing A direct write to a APxxKey_EL1 register requires a context synchronization event to ensure that indirect reads made by subsequent instructions (e.g. AUTIASP, PACIASP) observe the new value. When we initialize the boot task's APIAKey in boot_init_stack_canary() via ptrauth_keys_switch_kernel() we miss the necessary ISB, and so there is a window where instructions are not guaranteed to use the new APIAKey value. This has been observed to result in boot-time crashes where PACIASP and AUTIASP within a function used a mixture of the old and new key values. Fix this by having ptrauth_keys_switch_kernel() synchronize the new key value with an ISB. At the same time, __ptrauth_key_install() is renamed to __ptrauth_key_install_nosync() so that it is obvious that this performs no synchronization itself. Fixes: 28321582334c261c ("arm64: initialize ptrauth keys for kernel booting task") Signed-off-by: Mark Rutland Reported-by: Will Deacon Cc: Amit Daniel Kachhap Cc: Marc Zyngier Signed-off-by: Catalin Marinas Tested-by: Will Deacon --- arch/arm64/include/asm/pointer_auth.h | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h index 70c47156e54b..c6b4f0603024 100644 --- a/arch/arm64/include/asm/pointer_auth.h +++ b/arch/arm64/include/asm/pointer_auth.h @@ -47,7 +47,7 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys) get_random_bytes(&keys->apga, sizeof(keys->apga)); } -#define __ptrauth_key_install(k, v) \ +#define __ptrauth_key_install_nosync(k, v) \ do { \ struct ptrauth_key __pki_v = (v); \ write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1); \ @@ -62,8 +62,11 @@ static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kernel *keys) { - if (system_supports_address_auth()) - __ptrauth_key_install(APIA, keys->apia); + if (!system_supports_address_auth()) + return; + + __ptrauth_key_install_nosync(APIA, keys->apia); + isb(); } extern int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg);