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* [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
@ 2020-07-09 19:50 Florian Fainelli
  2020-07-11  0:28 ` Sasha Levin
  2020-07-20 13:04 ` Greg KH
  0 siblings, 2 replies; 4+ messages in thread
From: Florian Fainelli @ 2020-07-09 19:50 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Nick Desaulniers, Florian Fainelli, Fangrui Song,
	Catalin Marinas, Will Deacon, open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 KVM/arm64, Mark Brown,
	Kristina Martsenko, Sami Tolvanen, Marc Zyngier, Will Deacon,
	Ard Biesheuvel

From: Will Deacon <will.deacon@arm.com>

commit 679db70801da9fda91d26caf13bf5b5ccc74e8e8 upstream

Some CPUs can speculate past an ERET instruction and potentially perform
speculative accesses to memory before processing the exception return.
Since the register state is often controlled by a lower privilege level
at the point of an ERET, this could potentially be used as part of a
side-channel attack.

This patch emits an SB sequence after each ERET so that speculation is
held up on exception return.

Signed-off-by: Will Deacon <will.deacon@arm.com>
[florian: Adjust hyp-entry.S to account for the label
 added change to hyp/entry.S]
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
Changes in v2:

- added missing hunk in hyp/entry.S per Will's feedback

 arch/arm64/kernel/entry.S      | 2 ++
 arch/arm64/kvm/hyp/entry.S     | 2 ++
 arch/arm64/kvm/hyp/hyp-entry.S | 4 ++++
 3 files changed, 8 insertions(+)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ca978d7d98eb..3408c782702c 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -255,6 +255,7 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
 	.else
 	eret
 	.endif
+	sb
 	.endm
 
 	.macro	get_thread_info, rd
@@ -945,6 +946,7 @@ __ni_sys_trace:
 	mrs	x30, far_el1
 	.endif
 	eret
+	sb
 	.endm
 
 	.align	11
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index a360ac6e89e9..93704e6894d2 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -83,6 +83,7 @@ ENTRY(__guest_enter)
 
 	// Do not touch any register after this!
 	eret
+	sb
 ENDPROC(__guest_enter)
 
 ENTRY(__guest_exit)
@@ -195,4 +196,5 @@ alternative_endif
 	ldp	x0, x1, [sp], #16
 
 	eret
+	sb
 ENDPROC(__fpsimd_guest_restore)
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index bf4988f9dae8..3675e7f0ab72 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -97,6 +97,7 @@ el1_sync:				// Guest trapped into EL2
 	do_el2_call
 
 2:	eret
+	sb
 
 el1_hvc_guest:
 	/*
@@ -147,6 +148,7 @@ wa_epilogue:
 	mov	x0, xzr
 	add	sp, sp, #16
 	eret
+	sb
 
 el1_trap:
 	get_vcpu_ptr	x1, x0
@@ -198,6 +200,7 @@ el2_error:
 	b.ne	__hyp_panic
 	mov	x0, #(1 << ARM_EXIT_WITH_SERROR_BIT)
 	eret
+	sb
 
 ENTRY(__hyp_do_panic)
 	mov	lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
@@ -206,6 +209,7 @@ ENTRY(__hyp_do_panic)
 	ldr	lr, =panic
 	msr	elr_el2, lr
 	eret
+	sb
 ENDPROC(__hyp_do_panic)
 
 ENTRY(__hyp_panic)
-- 
2.17.1

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^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-07-09 19:50 [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction Florian Fainelli
@ 2020-07-11  0:28 ` Sasha Levin
  2020-07-20 13:04 ` Greg KH
  1 sibling, 0 replies; 4+ messages in thread
From: Sasha Levin @ 2020-07-11  0:28 UTC (permalink / raw)
  To: Florian Fainelli
  Cc: Nick Desaulniers, Fangrui Song, Catalin Marinas, Will Deacon,
	open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, Sami Tolvanen, Marc Zyngier, Kristina Martsenko,
	Will Deacon, Ard Biesheuvel, linux-arm-kernel

On Thu, Jul 09, 2020 at 12:50:23PM -0700, Florian Fainelli wrote:
>From: Will Deacon <will.deacon@arm.com>
>
>commit 679db70801da9fda91d26caf13bf5b5ccc74e8e8 upstream
>
>Some CPUs can speculate past an ERET instruction and potentially perform
>speculative accesses to memory before processing the exception return.
>Since the register state is often controlled by a lower privilege level
>at the point of an ERET, this could potentially be used as part of a
>side-channel attack.
>
>This patch emits an SB sequence after each ERET so that speculation is
>held up on exception return.
>
>Signed-off-by: Will Deacon <will.deacon@arm.com>
>[florian: Adjust hyp-entry.S to account for the label
> added change to hyp/entry.S]
>Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

I've queued it up, thanks!

-- 
Thanks,
Sasha
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-07-09 19:50 [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction Florian Fainelli
  2020-07-11  0:28 ` Sasha Levin
@ 2020-07-20 13:04 ` Greg KH
  2020-07-20 18:26   ` Florian Fainelli
  1 sibling, 1 reply; 4+ messages in thread
From: Greg KH @ 2020-07-20 13:04 UTC (permalink / raw)
  To: Florian Fainelli
  Cc: Nick Desaulniers, Fangrui Song, Catalin Marinas, Will Deacon,
	open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, Sami Tolvanen, Marc Zyngier, Kristina Martsenko,
	Will Deacon, Ard Biesheuvel, linux-arm-kernel

On Thu, Jul 09, 2020 at 12:50:23PM -0700, Florian Fainelli wrote:
> From: Will Deacon <will.deacon@arm.com>
> 
> commit 679db70801da9fda91d26caf13bf5b5ccc74e8e8 upstream
> 
> Some CPUs can speculate past an ERET instruction and potentially perform
> speculative accesses to memory before processing the exception return.
> Since the register state is often controlled by a lower privilege level
> at the point of an ERET, this could potentially be used as part of a
> side-channel attack.
> 
> This patch emits an SB sequence after each ERET so that speculation is
> held up on exception return.
> 
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> [florian: Adjust hyp-entry.S to account for the label
>  added change to hyp/entry.S]
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
> Changes in v2:
> 
> - added missing hunk in hyp/entry.S per Will's feedback

What about 4.19.y and 4.14.y trees?  I can't take something for 4.9.y
and then have a regression if someone moves to a newer release, right?

thanks,

greg k-h
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-07-20 13:04 ` Greg KH
@ 2020-07-20 18:26   ` Florian Fainelli
  0 siblings, 0 replies; 4+ messages in thread
From: Florian Fainelli @ 2020-07-20 18:26 UTC (permalink / raw)
  To: Greg KH
  Cc: Nick Desaulniers, Fangrui Song, Catalin Marinas, Will Deacon,
	open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, Sami Tolvanen, Marc Zyngier, Kristina Martsenko,
	Will Deacon, Ard Biesheuvel, linux-arm-kernel

On 7/20/20 6:04 AM, Greg KH wrote:
> On Thu, Jul 09, 2020 at 12:50:23PM -0700, Florian Fainelli wrote:
>> From: Will Deacon <will.deacon@arm.com>
>>
>> commit 679db70801da9fda91d26caf13bf5b5ccc74e8e8 upstream
>>
>> Some CPUs can speculate past an ERET instruction and potentially perform
>> speculative accesses to memory before processing the exception return.
>> Since the register state is often controlled by a lower privilege level
>> at the point of an ERET, this could potentially be used as part of a
>> side-channel attack.
>>
>> This patch emits an SB sequence after each ERET so that speculation is
>> held up on exception return.
>>
>> Signed-off-by: Will Deacon <will.deacon@arm.com>
>> [florian: Adjust hyp-entry.S to account for the label
>>  added change to hyp/entry.S]
>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>> ---
>> Changes in v2:
>>
>> - added missing hunk in hyp/entry.S per Will's feedback
> 
> What about 4.19.y and 4.14.y trees?  I can't take something for 4.9.y
> and then have a regression if someone moves to a newer release, right?

Sure, send you candidates for 4.14 and 4.19.
-- 
Florian
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kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

^ permalink raw reply	[flat|nested] 4+ messages in thread

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-- links below jump to the message on this page --
2020-07-09 19:50 [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction Florian Fainelli
2020-07-11  0:28 ` Sasha Levin
2020-07-20 13:04 ` Greg KH
2020-07-20 18:26   ` Florian Fainelli

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