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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; 12+ 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] 12+ 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; 12+ 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] 12+ 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; 12+ 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] 12+ 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
  2020-08-06 20:00     ` Florian Fainelli
  0 siblings, 1 reply; 12+ 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
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-07-20 18:26   ` Florian Fainelli
@ 2020-08-06 20:00     ` Florian Fainelli
  2020-08-07 13:14       ` Greg KH
  0 siblings, 1 reply; 12+ messages in thread
From: Florian Fainelli @ 2020-08-06 20:00 UTC (permalink / raw)
  To: Greg KH, Will Deacon, Will Deacon
  Cc: Nick Desaulniers, Fangrui Song, Catalin Marinas,
	Kristina Martsenko, open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, linux-arm-kernel, Sami Tolvanen, Marc Zyngier,
	Ard Biesheuvel



On 7/20/2020 11:26 AM, Florian Fainelli wrote:
> 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.

Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?

https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/

Thanks
-- 
Florian
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-08-06 20:00     ` Florian Fainelli
@ 2020-08-07 13:14       ` Greg KH
  2020-08-07 18:17         ` Florian Fainelli
  2020-08-21 16:03         ` Will Deacon
  0 siblings, 2 replies; 12+ messages in thread
From: Greg KH @ 2020-08-07 13:14 UTC (permalink / raw)
  To: Florian Fainelli
  Cc: Nick Desaulniers, Fangrui Song, Marc Zyngier, Will Deacon,
	open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, Sami Tolvanen, Catalin Marinas, Kristina Martsenko,
	Will Deacon, Ard Biesheuvel, linux-arm-kernel

On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
> 
> 
> On 7/20/2020 11:26 AM, Florian Fainelli wrote:
> > 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.
> 
> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
> 
> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/

Nope, I was waiting for Will's "ack" for these.

thanks,

greg k-h
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^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-08-07 13:14       ` Greg KH
@ 2020-08-07 18:17         ` Florian Fainelli
  2020-08-13 20:52           ` Florian Fainelli
  2020-08-21 16:03         ` Will Deacon
  1 sibling, 1 reply; 12+ messages in thread
From: Florian Fainelli @ 2020-08-07 18:17 UTC (permalink / raw)
  To: Greg KH, Will Deacon, Will Deacon
  Cc: Nick Desaulniers, Fangrui Song, Catalin Marinas,
	Kristina Martsenko, open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, linux-arm-kernel, Sami Tolvanen, Marc Zyngier,
	Ard Biesheuvel



On 8/7/2020 6:14 AM, Greg KH wrote:
> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
>>
>>
>> On 7/20/2020 11:26 AM, Florian Fainelli wrote:
>>> 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.
>>
>> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
>>
>> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
>> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
>> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/
> 
> Nope, I was waiting for Will's "ack" for these.

OK, Will, can you review those? Thanks
-- 
Florian
_______________________________________________
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^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-08-07 18:17         ` Florian Fainelli
@ 2020-08-13 20:52           ` Florian Fainelli
  0 siblings, 0 replies; 12+ messages in thread
From: Florian Fainelli @ 2020-08-13 20:52 UTC (permalink / raw)
  To: Greg KH, Will Deacon, Will Deacon
  Cc: Nick Desaulniers, Fangrui Song, Catalin Marinas,
	Kristina Martsenko, open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, linux-arm-kernel, Sami Tolvanen, Marc Zyngier,
	Ard Biesheuvel



On 8/7/2020 11:17 AM, Florian Fainelli wrote:
> 
> 
> On 8/7/2020 6:14 AM, Greg KH wrote:
>> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
>>>
>>>
>>> On 7/20/2020 11:26 AM, Florian Fainelli wrote:
>>>> 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.
>>>
>>> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
>>>
>>> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
>>> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
>>> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/
>>
>> Nope, I was waiting for Will's "ack" for these.
> 
> OK, Will, can you review those? Thanks

Will, can you please review those patches?
-- 
Florian
_______________________________________________
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kvmarm@lists.cs.columbia.edu
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^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-08-07 13:14       ` Greg KH
  2020-08-07 18:17         ` Florian Fainelli
@ 2020-08-21 16:03         ` Will Deacon
  2020-08-21 17:16           ` Florian Fainelli
  1 sibling, 1 reply; 12+ messages in thread
From: Will Deacon @ 2020-08-21 16:03 UTC (permalink / raw)
  To: Greg KH
  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, Sami Tolvanen, Marc Zyngier, Kristina Martsenko,
	Ard Biesheuvel, linux-arm-kernel

On Fri, Aug 07, 2020 at 03:14:29PM +0200, Greg KH wrote:
> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
> > 
> > 
> > On 7/20/2020 11:26 AM, Florian Fainelli wrote:
> > > 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.
> > 
> > Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
> > 
> > https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
> > https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
> > https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/
> 
> Nope, I was waiting for Will's "ack" for these.

This patch doesn't even build for me (the 'sb' macro is not defined in 4.9),
and I really wonder why we bother backporting it at all. Nobody's ever shown
it to be a problem in practice, and it's clear that this is just being
submitted to tick a box rather than anything else (otherwise it would build,
right?).

So I'm not going to Ack any of them. As with a lot of this side-channel
stuff the cure is far worse than the disease.

Will
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^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-08-21 16:03         ` Will Deacon
@ 2020-08-21 17:16           ` Florian Fainelli
  2020-08-24 16:32             ` Will Deacon
  0 siblings, 1 reply; 12+ messages in thread
From: Florian Fainelli @ 2020-08-21 17:16 UTC (permalink / raw)
  To: Will Deacon, 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,
	Ard Biesheuvel, linux-arm-kernel

On 8/21/20 9:03 AM, Will Deacon wrote:
> On Fri, Aug 07, 2020 at 03:14:29PM +0200, Greg KH wrote:
>> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
>>>
>>>
>>> On 7/20/2020 11:26 AM, Florian Fainelli wrote:
>>>> 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.
>>>
>>> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
>>>
>>> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
>>> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
>>> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/
>>
>> Nope, I was waiting for Will's "ack" for these.
> 
> This patch doesn't even build for me (the 'sb' macro is not defined in 4.9),
> and I really wonder why we bother backporting it at all. Nobody's ever shown
> it to be a problem in practice, and it's clear that this is just being
> submitted to tick a box rather than anything else (otherwise it would build,
> right?).

Doh, I completely missed submitting the patch this depended on that's
why I did not notice the build failure locally, sorry about that, what a
shame.

Would not be the same "tick a box" argument be used against your
original submission then? Sure, I have not been able to demonstrate in
real life this was a problem, however the same can be said about a lot
security related fixes.

What if it becomes exploitable in the future, would not it be nice to
have it in a 6 year LTS kernel?

> 
> So I'm not going to Ack any of them. As with a lot of this side-channel
> stuff the cure is far worse than the disease.
Assuming that my v3 does build correctly, which it will, would you be
keen on changing your position?
-- 
Florian
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kvmarm@lists.cs.columbia.edu
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^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-08-21 17:16           ` Florian Fainelli
@ 2020-08-24 16:32             ` Will Deacon
  2020-08-24 16:42               ` Florian Fainelli
  0 siblings, 1 reply; 12+ messages in thread
From: Will Deacon @ 2020-08-24 16:32 UTC (permalink / raw)
  To: Florian Fainelli
  Cc: Nick Desaulniers, Catalin Marinas, Fangrui Song, Marc Zyngier,
	Will Deacon, open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, Sami Tolvanen, Greg KH, Kristina Martsenko,
	Ard Biesheuvel, linux-arm-kernel

Hi Florian,

On Fri, Aug 21, 2020 at 10:16:23AM -0700, Florian Fainelli wrote:
> On 8/21/20 9:03 AM, Will Deacon wrote:
> > On Fri, Aug 07, 2020 at 03:14:29PM +0200, Greg KH wrote:
> >> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
> >>> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
> >>>
> >>> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
> >>> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
> >>> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/
> >>
> >> Nope, I was waiting for Will's "ack" for these.
> > 
> > This patch doesn't even build for me (the 'sb' macro is not defined in 4.9),
> > and I really wonder why we bother backporting it at all. Nobody's ever shown
> > it to be a problem in practice, and it's clear that this is just being
> > submitted to tick a box rather than anything else (otherwise it would build,
> > right?).
> 
> Doh, I completely missed submitting the patch this depended on that's
> why I did not notice the build failure locally, sorry about that, what a
> shame.
> 
> Would not be the same "tick a box" argument be used against your
> original submission then? Sure, I have not been able to demonstrate in
> real life this was a problem, however the same can be said about a lot
> security related fixes.

Sort of, although I wrote the original patch because it was dead easy to do
and saved having to think too much about the problem, whereas the complexity
of backporting largerly diminishes that imo.

> What if it becomes exploitable in the future, would not it be nice to
> have it in a 6 year LTS kernel?

Even if people are stuck on an old LTS, they should still be taking the
regular updates for it, and we would obviously need to backport the fix if
it turned out to be exploitable (and hey, we could even test it then!).

> > So I'm not going to Ack any of them. As with a lot of this side-channel
> > stuff the cure is far worse than the disease.
> Assuming that my v3 does build correctly, which it will, would you be
> keen on changing your position?

Note that I'm not trying to block this patch from going in, I'm just saying
that I'm not supportive of it. Perhaps somebody from Arm can review it if
they think it's worth the effort.

Will
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction
  2020-08-24 16:32             ` Will Deacon
@ 2020-08-24 16:42               ` Florian Fainelli
  0 siblings, 0 replies; 12+ messages in thread
From: Florian Fainelli @ 2020-08-24 16:42 UTC (permalink / raw)
  To: Will Deacon
  Cc: Nick Desaulniers, Catalin Marinas, Fangrui Song, Marc Zyngier,
	Will Deacon, open list, stable,
	open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64),
	Mark Brown, Sami Tolvanen, Greg KH, Kristina Martsenko,
	Ard Biesheuvel, linux-arm-kernel



On 8/24/2020 9:32 AM, Will Deacon wrote:
> Hi Florian,
> 
> On Fri, Aug 21, 2020 at 10:16:23AM -0700, Florian Fainelli wrote:
>> On 8/21/20 9:03 AM, Will Deacon wrote:
>>> On Fri, Aug 07, 2020 at 03:14:29PM +0200, Greg KH wrote:
>>>> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
>>>>> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
>>>>>
>>>>> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
>>>>> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
>>>>> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/
>>>>
>>>> Nope, I was waiting for Will's "ack" for these.
>>>
>>> This patch doesn't even build for me (the 'sb' macro is not defined in 4.9),
>>> and I really wonder why we bother backporting it at all. Nobody's ever shown
>>> it to be a problem in practice, and it's clear that this is just being
>>> submitted to tick a box rather than anything else (otherwise it would build,
>>> right?).
>>
>> Doh, I completely missed submitting the patch this depended on that's
>> why I did not notice the build failure locally, sorry about that, what a
>> shame.
>>
>> Would not be the same "tick a box" argument be used against your
>> original submission then? Sure, I have not been able to demonstrate in
>> real life this was a problem, however the same can be said about a lot
>> security related fixes.
> 
> Sort of, although I wrote the original patch because it was dead easy to do
> and saved having to think too much about the problem, whereas the complexity
> of backporting largerly diminishes that imo.
> 
>> What if it becomes exploitable in the future, would not it be nice to
>> have it in a 6 year LTS kernel?
> 
> Even if people are stuck on an old LTS, they should still be taking the
> regular updates for it, and we would obviously need to backport the fix if
> it turned out to be exploitable (and hey, we could even test it then!).
> 
>>> So I'm not going to Ack any of them. As with a lot of this side-channel
>>> stuff the cure is far worse than the disease.
>> Assuming that my v3 does build correctly, which it will, would you be
>> keen on changing your position?
> 
> Note that I'm not trying to block this patch from going in, I'm just saying
> that I'm not supportive of it. Perhaps somebody from Arm can review it if
> they think it's worth the effort.

How about I submit the actual full series (two patches) and we take the 
discussion from there?

Thanks for responding!
-- 
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] 12+ messages in thread

end of thread, back to index

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- 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
2020-08-06 20:00     ` Florian Fainelli
2020-08-07 13:14       ` Greg KH
2020-08-07 18:17         ` Florian Fainelli
2020-08-13 20:52           ` Florian Fainelli
2020-08-21 16:03         ` Will Deacon
2020-08-21 17:16           ` Florian Fainelli
2020-08-24 16:32             ` Will Deacon
2020-08-24 16:42               ` Florian Fainelli

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