* [PATCH] arm64: sync kernel APIAKey when installing
@ 2020-04-21 12:10 Mark Rutland
2020-04-21 12:31 ` Will Deacon
0 siblings, 1 reply; 3+ messages in thread
From: Mark Rutland @ 2020-04-21 12:10 UTC (permalink / raw)
To: linux-arm-kernel, will
Cc: Mark Rutland, Amit Daniel Kachhap, Marc Zyngier, Catalin Marinas
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 <mark.rutland@arm.com>
Reported-by: Will Deacon <will@kernel.org>
Cc: Amit Daniel Kachhap <amit.kachhap@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
---
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);
--
2.11.0
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] arm64: sync kernel APIAKey when installing
2020-04-21 12:10 [PATCH] arm64: sync kernel APIAKey when installing Mark Rutland
@ 2020-04-21 12:31 ` Will Deacon
2020-04-21 13:31 ` Catalin Marinas
0 siblings, 1 reply; 3+ messages in thread
From: Will Deacon @ 2020-04-21 12:31 UTC (permalink / raw)
To: Mark Rutland
Cc: Amit Daniel Kachhap, Catalin Marinas, linux-arm-kernel, Marc Zyngier
On Tue, Apr 21, 2020 at 01:10:14PM +0100, Mark Rutland wrote:
> 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 <mark.rutland@arm.com>
> Reported-by: Will Deacon <will@kernel.org>
> Cc: Amit Daniel Kachhap <amit.kachhap@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/include/asm/pointer_auth.h | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
Tested-by: Will Deacon <will@kernel.org>
Catalin -- please can you queue this for -rc3?
Cheers,
Will
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] arm64: sync kernel APIAKey when installing
2020-04-21 12:31 ` Will Deacon
@ 2020-04-21 13:31 ` Catalin Marinas
0 siblings, 0 replies; 3+ messages in thread
From: Catalin Marinas @ 2020-04-21 13:31 UTC (permalink / raw)
To: Will Deacon
Cc: Mark Rutland, Amit Daniel Kachhap, linux-arm-kernel, Marc Zyngier
On Tue, Apr 21, 2020 at 01:31:51PM +0100, Will Deacon wrote:
> On Tue, Apr 21, 2020 at 01:10:14PM +0100, Mark Rutland wrote:
> > 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 <mark.rutland@arm.com>
> > Reported-by: Will Deacon <will@kernel.org>
> > Cc: Amit Daniel Kachhap <amit.kachhap@arm.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Marc Zyngier <maz@kernel.org>
> > ---
> > arch/arm64/include/asm/pointer_auth.h | 9 ++++++---
> > 1 file changed, 6 insertions(+), 3 deletions(-)
>
> Tested-by: Will Deacon <will@kernel.org>
>
> Catalin -- please can you queue this for -rc3?
I will. Thanks.
--
Catalin
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-04-21 12:10 [PATCH] arm64: sync kernel APIAKey when installing Mark Rutland
2020-04-21 12:31 ` Will Deacon
2020-04-21 13:31 ` Catalin Marinas
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