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arm64: sync kernel APIAKey when installing

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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: 2832158233 ("arm64: initialize ptrauth keys for kernel booting task")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: Will Deacon <will@kernel.org>
Cc: Amit Daniel Kachhap <amit.kachhap@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2020-04-21 13:10:14 +01:00 committed by Catalin Marinas
parent ae83d0b416
commit 3fabb43818
1 changed files with 6 additions and 3 deletions
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9
arch/arm64/include/asm/pointer_auth.h
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@ -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);