Re: [edk2-devel] [PATCH v1 0/4] Don't require self-signed PK in setup mode

["Jan Bobek" <jbobek@nvidia.com>]

Hi Sean,

> From looking over the patch 1/4 email i have a concern.
>
> In AuthService.c on the conditional change you made. Aren't we losing
> a case where we are evaluating a nonPK payload signed by the PK?
> Given the system is in SetupMode that means there is no PK but is this
> the conditional path that is used when installing Secure boot keys in
> reverse (DBX,DX,KEK,PK) order?

Thanks for sharing your concern! They way I think about the change is
that I've replaced the expression

    IsPk

with

    FeaturePcdGet (PcdRequireSelfSignedPk) && IsPk

and nothing else. When you look at it this way, it's fairly easy to
break down how it affects the logic:

1. Assume PcdRequireSelfSignedPk is TRUE. In this case, the two
   expressions are exactly the same and no change in behavior occurs,
   just as we want.

2. Assume IsPk is FALSE. In this case, both expressions evaluate to
   FALSE, no matter what the PCD is configured to. That's also good,
   because we don't want to change how non-PK payloads are handled.

3. In fact, the only change in behavior that occurs is when
   PcdRequireSelfSignedPk is FALSE and IsPk is TRUE; here the former
   expression would be TRUE, whereas the latter is FALSE. That's exactly
   what we want: we wish to enter the first block of the if-else branch
   (which changes the variable similarly to when we're in custom mode)
   rather than falling through to the third block (which checks the
   self-signature).

To directly answer your question, I don't think the behavior changes at
all when processing non-PK payloads, by virtue of IsPk being FALSE and
what I said in point (2.) above.

Additionally, yes, the first block of the if-else branch is exactly the
path that's taken when enrolling KEK/DB/DBX in Setup mode, and one that
has always been available even without Custom mode. It used to be that
you couldn't use this path to enroll PK without Custom mode (precisely
because of !IsPk in the condition), but I'm hoping to enable this path
with my patch.

Let me know if I haven't answered or misunderstood your question.

> Is there testing you have done?  This code should be pretty easy to do
> host based unit testing on. Any chance you have authored that to
> confirm use cases are not unexpectedly impacted?  Example of host
> based unit test of library is here:
> edk2/SecurityPkg/Library/SecureBootVariableLib/UnitTest at master ·
> tianocore/edk2
> (github.com)<https://github.com/tianocore/edk2/tree/master/SecurityPkg/Library/SecureBootVariableLib/UnitTest>

I've done an ad-hoc test by commenting out the switch to/from Custom
mode in EnrollFromDefaultKeysApp from SecurityPkg, booting in Setup mode
and using the modified app to enroll the keys. You could do a similar
test from the OS, but in my case this was more straightforward.

I am aware of the host-based unit testing library in edk2, and I agree
that it would be great to have the code in AuthVariableLib tested for
all the different cases. However, I don't have any such tests right now,
and while I'm willing to potentially look into writing some, I'd have to
do it more or less on the side, meaning it could take a while.

Best,
-Jan

> On 1/22/2023 10:13 PM, Yao, Jiewen wrote:
>
> Hi Sean
> I would like to hear your feedback, since it is a little different from the original MSFT patch.
>
> Would you please take a look?
>
> Thank you
> Yao, Jiewen
>
>
>
> -----Original Message-----
> From: Jan Bobek <jbobek@nvidia.com><mailto:jbobek@nvidia.com>
> Sent: Saturday, January 21, 2023 6:59 AM
> To: devel@edk2.groups.io<mailto:devel@edk2.groups.io>
> Cc: Jan Bobek <jbobek@nvidia.com><mailto:jbobek@nvidia.com>; Laszlo Ersek <lersek@redhat.com><mailto:lersek@redhat.com>; Yao,
> Jiewen <jiewen.yao@intel.com><mailto:jiewen.yao@intel.com>
> Subject: [PATCH v1 0/4] Don't require self-signed PK in setup mode
>
> Hi all,
>
> I'm sending out v1 of my patch series that addresses a UEFI spec
> non-compliance when enrolling PK in setup mode. Additional info can be
> found in bugzilla [1]; the changes are split into 4 patches as
> suggested by Laszlo Ersek in comment #4.
>
> I've based my work on the patch by Matthew Carlson; I've credited him
> with co-authorship of the first patch even though in the end I decided
> to do the implementation a bit differently.
>
> Comments & reviews welcome!
>
> Cheers,
> -Jan
>
> References:
> 1. https://bugzilla.tianocore.org/show_bug.cgi?id=2506
>
> Jan Bobek (4):
>  SecurityPkg: limit verification of enrolled PK in setup mode
>  OvmfPkg: require self-signed PK when secure boot is enabled
>  ArmVirtPkg: require self-signed PK when secure boot is enabled
>  SecurityPkg: don't require PK to be self-signed by default
>
> SecurityPkg/SecurityPkg.dec                             | 7 +++++++
> ArmVirtPkg/ArmVirtCloudHv.dsc                           | 4 ++++
> ArmVirtPkg/ArmVirtQemu.dsc                              | 4 ++++
> ArmVirtPkg/ArmVirtQemuKernel.dsc                        | 4 ++++
> OvmfPkg/Bhyve/BhyveX64.dsc                              | 3 +++
> OvmfPkg/CloudHv/CloudHvX64.dsc                          | 3 +++
> OvmfPkg/IntelTdx/IntelTdxX64.dsc                        | 3 +++
> OvmfPkg/Microvm/MicrovmX64.dsc                          | 3 +++
> OvmfPkg/OvmfPkgIa32.dsc                                 | 3 +++
> OvmfPkg/OvmfPkgIa32X64.dsc                              | 3 +++
> OvmfPkg/OvmfPkgX64.dsc                                  | 3 +++
> SecurityPkg/Library/AuthVariableLib/AuthVariableLib.inf | 3 +++
> SecurityPkg/Library/AuthVariableLib/AuthService.c       | 9 +++++++--
> 13 files changed, 50 insertions(+), 2 deletions(-)