Re: [edk2] [PATCH 0/2] UefiCpuPkg: Add RSB stuffing before rsm instruction

2018-08-16 Thread Laszlo Ersek 
On 08/16/18 05:07, Wu, Hao A wrote:

> I have filed a Bugzilla for adding $(INC)-like support when compiling
> .NASM files:
> 
> https://bugzilla.tianocore.org/show_bug.cgi?id=1085
> 
> After some discussion with the BaseTools owners, some investigation is
> needed for the above support. Hence, I plan to perform a 2-stage change
> when extracting the common RSB stuffing logics to INC file: [...]

I've also filed 
now (and assigned it to you, if that's OK with you). BZ#1085 should
track the BaseTools update, and then BZ#1091 should take advantage of it
in UefiCpuPkg, for unifying the .inc files.

I've also set up the dependency between the BZs accordingly.

Thanks!
Laszlo
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Re: [edk2] [PATCH 0/2] UefiCpuPkg: Add RSB stuffing before rsm instruction

2018-08-16 Thread Laszlo Ersek 
On 08/16/18 05:07, Wu, Hao A wrote:
>> -Original Message-
>> From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Laszlo
>> Ersek
>> Sent: Friday, August 10, 2018 11:06 PM

>> (2) If I understand correctly, the same pattern is used everywhere -- a
>> loop body is executed 32 times, and in the loop body, we jump (via
>> subroutine calls) twice, and each call is followed by a "trap" for
>> speculative execution. At the end of the loop, we forcefully unwind the
>> stack, and then we proceed to RSM.
>>
>> I think this should be implemented with a lot less code duplication.
>> NASM supports macros with labels that are local to macro *invocation*
>> (not macro *definition*); please see the %%skip example here:
>>
>>   https://www.nasm.us/doc/nasmdoc4.html
>>   4.3.2 Macro-Local Labels
>>
>> In addition, it should be possible to pass parameters to macros, such as:
>> - the register to use as counter (eax vs. rax),
>> - the stack pointer to restore (esp vs. rsp),
>> - the size of a stack frame (4 vs. 8)
>>
>> Using all those tools, it should be possible to define the macro only
>> once, in a UefiCpuPkg-level ".inc" file (for example,
>> "UefiCpuPkg/Include/StuffRsb.inc"), and then only invoke the macro near
>> all 10 RSM instructions:
> 
> Yes. Extracting the common logic to a INC file is a good idea.
> 
> However, I found that when compiling .NASM files, the current build rule
> does not support including files other than the .NASM file directory.
> So including a package-level INC file is not supported at this moment.
> 
> I have filed a Bugzilla for adding $(INC)-like support when compiling
> .NASM files:
> 
> https://bugzilla.tianocore.org/show_bug.cgi?id=1085
> 
> After some discussion with the BaseTools owners, some investigation is
> needed for the above support. Hence, I plan to perform a 2-stage change
> when extracting the common RSB stuffing logics to INC file:
> 
> 1. Duplicate the INC file and place them together with the NASM files that
> uses the RSB stuffing logics.
> 
> 2. After NASM compiling support the $(INC)-like feature, propose another
> patch to remove those duplicated INC files and create one under
> UefiCpuPkg/Include/.
> 
> Please help to share your thought on this. Thanks in advance.

Sounds good to me. This approach still eliminates as much code
duplication as it is possible at the current level of BaseTools support.
Also we'll have a reminder (a BZ) for completing the unification.

Thanks!
Laszlo
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Re: [edk2] [PATCH 0/2] UefiCpuPkg: Add RSB stuffing before rsm instruction

2018-08-15 Thread Wu, Hao A 
> -Original Message-
> From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Laszlo
> Ersek
> Sent: Friday, August 10, 2018 11:06 PM
> To: Wu, Hao A; edk2-devel@lists.01.org
> Cc: Yao, Jiewen; Dong, Eric
> Subject: Re: [edk2] [PATCH 0/2] UefiCpuPkg: Add RSB stuffing before rsm
> instruction
> 
> On 08/10/18 03:43, Hao Wu wrote:
> > The series will add RSB stuffing logics to avoid RSB underflow on return
> > from SMM (rsm instruction).
> >
> > Cc: Jiewen Yao 
> > Cc: Eric Dong 
> > Cc: Laszlo Ersek 
> >
> > Hao Wu (2):
> >   UefiCpuPkg/SmmCpuFeaturesLib: Add RSB stuffing before rsm instruction
> >   UefiCpuPkg/PiSmmCpuDxeSmm: Add RSB stuffing before rsm instruction
> >
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/Ia32/SmiEntry.nasm | 20
> +
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/Ia32/SmiException.nasm | 44
> ++--
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/X64/SmiEntry.nasm  | 20
> +
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/X64/SmiException.nasm  | 42
> ++-
> >  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmiEntry.nasm| 20
> +
> >  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm | 21
> ++
> >  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm | 20
> +
> >  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmInit.nasm  | 20
> +
> >  8 files changed, 202 insertions(+), 5 deletions(-)
> >
> 
> I haven't tested this patch set yet; first I'd like to make some comments:
> 
> (1) I think the commit messages are very lacking. Please explain
> *precisely* why the Return Stack Buffer has to be stuffed before RSM.
> 
> (1a) To my understanding, speculation is micro-architectural (and not
> architectural) state, therefore it makes no sense to say that "RSB is
> left in a state that application program or operating-system does
> not expect". Applications and operating systems can only have
> expectations for architectural state, and not for micro-architectural state.
> 
> (1b) Furthermore, to my understanding, speculation can be abused by
> training the predictor in a non-privileged context, then calling into a
> higher privilege level, where the previous (unprivileged) training will
> lead to the speculative execution of privileged code, for example
> bypassing range checks. In turn, the result of those (invalid and
> speculative) privileged operations can be sniffed from
> micro-architectural state, such as timing memory accesses (to see
> whether something has been cached or not by the speculative privileged
> execution).
> 
> Is this correct more or less? If so, then why are we stuffing the RSB
> just before we *leave* the privileged mode (=SMM) for the less
> privileged mode (=ring 0, IIUC)? Shouldn't we kill the "external
> training" of the predictor right after we *enter* SMM?
> 
> (1c) Or, perhaps, in this kind of attack, the RSB is not used for
> triggering speculative execution in the more privileged mode, but to
> *leak* information from the more privileged mode to the less privileged
> mode. IOW, the RSB is what is used by the attacker as the "read end" of
> the side-channel; perhaps by timing returns (in non-privileged code)
> that reflect the training that the predictor picked up while in SMM.
> 
> Now, if that's the case, then the current commit messages are even more
> confusing; they should state, "System Management Interrupt (SMI)
> handlers can leave the Return Stack Buffer (RSB) in a state that leaks
> information to malicious code that runs with lesser privileges".
> Because, the point is not whether the OS or the app find the state
> "unexpected" (a benign OS or app won't care at all); the point is that a
> malicious OS or app will *definitely* expect some leaked information,
> and we must prevent that.
> 
> 
> I imagine that I'm pretty confused about this. Please document the exact
> threat that the RSB stuffing is supposed to mitigate. I know I can find
> long articles and blogs about this. The commit messages should
> nonetheless provide a good concise summary.

Thanks Laszlo,

I will update the commit log message to better clarify the purpose of the
series.

> 
> 
> (2) If I understand correctly, the same pattern is used everywhere -- a
> loop body is executed 32 times, and in the loop body, we jump (via
> subroutine calls) twice, and each call is followed by a "trap" for
> speculative execution. At the end of the loop, we forcefully unwind the
> stack, and then we proceed to RSM.
> 
> I think this should be implemented with a lo

Re: [edk2] [PATCH 0/2] UefiCpuPkg: Add RSB stuffing before rsm instruction

2018-08-15 Thread Yao, Jiewen 
Thank you Laszlo, for your feedback.

The public document is at 
https://software.intel.com/security-software-guidance/insights/host-firmware-speculative-execution-side-channel-mitigation
the "Branch target injection mitigation" section

I agree with you that we should add those info in the commit message.

Thank you
Yao Jiewen


> -Original Message-
> From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of
> Laszlo Ersek
> Sent: Friday, August 10, 2018 11:06 PM
> To: Wu, Hao A ; edk2-devel@lists.01.org
> Cc: Yao, Jiewen ; Dong, Eric 
> Subject: Re: [edk2] [PATCH 0/2] UefiCpuPkg: Add RSB stuffing before rsm
> instruction
> 
> On 08/10/18 03:43, Hao Wu wrote:
> > The series will add RSB stuffing logics to avoid RSB underflow on return
> > from SMM (rsm instruction).
> >
> > Cc: Jiewen Yao 
> > Cc: Eric Dong 
> > Cc: Laszlo Ersek 
> >
> > Hao Wu (2):
> >   UefiCpuPkg/SmmCpuFeaturesLib: Add RSB stuffing before rsm instruction
> >   UefiCpuPkg/PiSmmCpuDxeSmm: Add RSB stuffing before rsm instruction
> >
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/Ia32/SmiEntry.nasm | 20
> +
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/Ia32/SmiException.nasm | 44
> ++--
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/X64/SmiEntry.nasm  | 20
> +
> >  UefiCpuPkg/Library/SmmCpuFeaturesLib/X64/SmiException.nasm  | 42
> ++-
> >  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmiEntry.nasm|
> 20 +
> >  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm |
> 21 ++
> >  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm |
> 20 +
> >  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmInit.nasm  |
> 20 +
> >  8 files changed, 202 insertions(+), 5 deletions(-)
> >
> 
> I haven't tested this patch set yet; first I'd like to make some comments:
> 
> (1) I think the commit messages are very lacking. Please explain
> *precisely* why the Return Stack Buffer has to be stuffed before RSM.
> 
> (1a) To my understanding, speculation is micro-architectural (and not
> architectural) state, therefore it makes no sense to say that "RSB is
> left in a state that application program or operating-system does
> not expect". Applications and operating systems can only have
> expectations for architectural state, and not for micro-architectural state.
> 
> (1b) Furthermore, to my understanding, speculation can be abused by
> training the predictor in a non-privileged context, then calling into a
> higher privilege level, where the previous (unprivileged) training will
> lead to the speculative execution of privileged code, for example
> bypassing range checks. In turn, the result of those (invalid and
> speculative) privileged operations can be sniffed from
> micro-architectural state, such as timing memory accesses (to see
> whether something has been cached or not by the speculative privileged
> execution).
> 
> Is this correct more or less? If so, then why are we stuffing the RSB
> just before we *leave* the privileged mode (=SMM) for the less
> privileged mode (=ring 0, IIUC)? Shouldn't we kill the "external
> training" of the predictor right after we *enter* SMM?
> 
> (1c) Or, perhaps, in this kind of attack, the RSB is not used for
> triggering speculative execution in the more privileged mode, but to
> *leak* information from the more privileged mode to the less privileged
> mode. IOW, the RSB is what is used by the attacker as the "read end" of
> the side-channel; perhaps by timing returns (in non-privileged code)
> that reflect the training that the predictor picked up while in SMM.
> 
> Now, if that's the case, then the current commit messages are even more
> confusing; they should state, "System Management Interrupt (SMI)
> handlers can leave the Return Stack Buffer (RSB) in a state that leaks
> information to malicious code that runs with lesser privileges".
> Because, the point is not whether the OS or the app find the state
> "unexpected" (a benign OS or app won't care at all); the point is that a
> malicious OS or app will *definitely* expect some leaked information,
> and we must prevent that.
> 
> 
> I imagine that I'm pretty confused about this. Please document the exact
> threat that the RSB stuffing is supposed to mitigate. I know I can find
> long articles and blogs about this. The commit messages should
> nonetheless provide a good concise summary.
> 
> 
> (2) If I understand correctly, the same pattern is used everywhere -- a
> loop body is executed 32 times, and in the loop body, we jump (via
> sub

Re: [edk2] [PATCH 0/2] UefiCpuPkg: Add RSB stuffing before rsm instruction

2018-08-10 Thread Laszlo Ersek 
On 08/10/18 03:43, Hao Wu wrote:
> The series will add RSB stuffing logics to avoid RSB underflow on return
> from SMM (rsm instruction).
> 
> Cc: Jiewen Yao 
> Cc: Eric Dong 
> Cc: Laszlo Ersek 
> 
> Hao Wu (2):
>   UefiCpuPkg/SmmCpuFeaturesLib: Add RSB stuffing before rsm instruction
>   UefiCpuPkg/PiSmmCpuDxeSmm: Add RSB stuffing before rsm instruction
> 
>  UefiCpuPkg/Library/SmmCpuFeaturesLib/Ia32/SmiEntry.nasm | 20 +
>  UefiCpuPkg/Library/SmmCpuFeaturesLib/Ia32/SmiException.nasm | 44 
> ++--
>  UefiCpuPkg/Library/SmmCpuFeaturesLib/X64/SmiEntry.nasm  | 20 +
>  UefiCpuPkg/Library/SmmCpuFeaturesLib/X64/SmiException.nasm  | 42 
> ++-
>  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmiEntry.nasm| 20 +
>  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm | 21 ++
>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm | 20 +
>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmInit.nasm  | 20 +
>  8 files changed, 202 insertions(+), 5 deletions(-)
> 

I haven't tested this patch set yet; first I'd like to make some comments:

(1) I think the commit messages are very lacking. Please explain
*precisely* why the Return Stack Buffer has to be stuffed before RSM.

(1a) To my understanding, speculation is micro-architectural (and not
architectural) state, therefore it makes no sense to say that "RSB is
left in a state that application program or operating-system does
not expect". Applications and operating systems can only have
expectations for architectural state, and not for micro-architectural state.

(1b) Furthermore, to my understanding, speculation can be abused by
training the predictor in a non-privileged context, then calling into a
higher privilege level, where the previous (unprivileged) training will
lead to the speculative execution of privileged code, for example
bypassing range checks. In turn, the result of those (invalid and
speculative) privileged operations can be sniffed from
micro-architectural state, such as timing memory accesses (to see
whether something has been cached or not by the speculative privileged
execution).

Is this correct more or less? If so, then why are we stuffing the RSB
just before we *leave* the privileged mode (=SMM) for the less
privileged mode (=ring 0, IIUC)? Shouldn't we kill the "external
training" of the predictor right after we *enter* SMM?

(1c) Or, perhaps, in this kind of attack, the RSB is not used for
triggering speculative execution in the more privileged mode, but to
*leak* information from the more privileged mode to the less privileged
mode. IOW, the RSB is what is used by the attacker as the "read end" of
the side-channel; perhaps by timing returns (in non-privileged code)
that reflect the training that the predictor picked up while in SMM.

Now, if that's the case, then the current commit messages are even more
confusing; they should state, "System Management Interrupt (SMI)
handlers can leave the Return Stack Buffer (RSB) in a state that leaks
information to malicious code that runs with lesser privileges".
Because, the point is not whether the OS or the app find the state
"unexpected" (a benign OS or app won't care at all); the point is that a
malicious OS or app will *definitely* expect some leaked information,
and we must prevent that.


I imagine that I'm pretty confused about this. Please document the exact
threat that the RSB stuffing is supposed to mitigate. I know I can find
long articles and blogs about this. The commit messages should
nonetheless provide a good concise summary.


(2) If I understand correctly, the same pattern is used everywhere -- a
loop body is executed 32 times, and in the loop body, we jump (via
subroutine calls) twice, and each call is followed by a "trap" for
speculative execution. At the end of the loop, we forcefully unwind the
stack, and then we proceed to RSM.

I think this should be implemented with a lot less code duplication.
NASM supports macros with labels that are local to macro *invocation*
(not macro *definition*); please see the %%skip example here:

  https://www.nasm.us/doc/nasmdoc4.html
  4.3.2 Macro-Local Labels

In addition, it should be possible to pass parameters to macros, such as:
- the register to use as counter (eax vs. rax),
- the stack pointer to restore (esp vs. rsp),
- the size of a stack frame (4 vs. 8)

Using all those tools, it should be possible to define the macro only
once, in a UefiCpuPkg-level ".inc" file (for example,
"UefiCpuPkg/Include/StuffRsb.inc"), and then only invoke the macro near
all 10 RSM instructions:

-
%define RSB_STUFF_ENTRIES 0x20

; @param 1: register to use as counter (eax vs. rax)
; @param 2: stack pointer to restore (esp vs. rsp)
; @param 3: the size of a stack frame (4 vs. 8)
%macro StuffRsb 3
  mov %1, RSB_STUFF_ENTRIES / 2
  %%Unroll1:
  call%%Unroll2
  %%SpecTrap1:
  pause
  lfence
  jmp %%SpecTrap1
  %%Unroll2: