[edk2-devel] [GSoC proposal] Secure Image Loader

Thu Apr 8 16:06:25 UTC 2021

We use the loader code in userspace anyway for fuzzing and such. I also 
want to build a database of all sorts of UEFI binaries some time before 
the merge to confirm they are all accepted (Windows / macOS / Linux 
bootloaders, tools like memtest, drivers like iPXE). As part of that, 
I'm sure we can have a userspace tool that uses the code to emit parsing 
information.

But as the EDK II build system is very... not so userspace friendly, I 
will not promise it will be very nice. :)

Best regards,
Marvin

On 08.04.21 16:13, Andrew (EFI) Fish wrote:
> At a minimum it would be nice if we had a tool that would point out the security faults with a given PE/COFF file layout.
>
> Sent from my iPhone
>
>> On Apr 8, 2021, at 4:16 AM, Laszlo Ersek <lersek at redhat.com> wrote:
>>
>> On 04/06/21 12:06, Marvin Häuser wrote:
>>> Good day Nate,
>>>
>>> Comments are inline.
>>>
>>> Best regards,
>>> Marvin
>>>
>>>> On 06.04.21 11:41, Nate DeSimone wrote:
>>>> Hi Marvin,
>>>>
>>>> Great to meet you and welcome back! Glad you hear you are interested!
>>>> Completing a formal verification of a PE/COFF loader is certainly
>>>> impressive. Was this done with some sort of automated theorem proving?
>>>> It would seem a rather arduous task doing an inductive proof for an
>>>> algorithm like that by hand!
>>> I would call it "semi-automated", a great deal of intermediate goals
>>> (preconditions, postconditions, invariants, assertions, ...) were
>>> required to show all interesting properties. But yes, the actual proof
>>> steps are automated by common SMT solvers. It was done using the
>>> AstraVer Toolset and ACSL, latter basically a language to express logic
>>> statements with C-like syntax.
>>>
>>>> I completely agree with you that getting a formally verified PE/COFF
>>>> loader into mainline is undoubtably valuable and would pay security
>>>> dividends for years to come.
>>> I'm glad to hear that. :)
>>>
>>>> Admittedly, this is an area of computer science that I don't have a
>>>> great deal of experience with. The furthest I have gone on this topic
>>>> is writing out proofs for simple algorithms on exams in my Algorithms
>>>> class in college. Regardless you have a much better idea of what the
>>>> current status is of the work that you and Vitaly have done. I guess
>>>> my only question is do you think there is sufficient work remaining to
>>>> fill the 10 week GSoC development window?
>>> Please don't get me wrong, but I would be surprised if the UEFI
>>> specification changes I'd like to discuss alone would be completed
>>> within 10 weeks, let alone implementation throughout the codebase. While
>>> I think the plain amount of code may be a bit less than say a
>>> MinPlatform port, the changes are much deeper and require much more
>>> caution to avoid regressions (e.g. by invalidating undocumented
>>> assertions). This sadly is not a matter of just replacing the underlying
>>> library implementation or "plug-in and play" at all. It furthermore
>>> affects many parts of the stack, the core dispatchers used for all
>>> platforms, image emulation (EBC), UEFI userland emulation (EmuPkg), and
>>> so on. I was rather worried the scope is too broad time-wise, but it can
>>> be narrowed/widened as you see fit really. This is one of *the* core
>>> components used on millions of device, and many package maintainers need
>>> to review and validate the changes, this must really be done right the
>>> first try. :)
>>>
>>>> Certainly we can use some of that time to perform the code reviews you
>>>> mention and write up formal ECRs for the UEFI spec changes that you
>>>> believe are needed.
>>> I believed that was part of the workload, yes, but even without it I
>>> think there is plenty to do.
>>>
>>>> Thank you for sending the application and alerting us to the great
>>>> work you and Vitaly have done! I'll read your paper more closely and
>>>> come back with any questions I still have.
>>> Thank you, I will gladly explain anything unclear. Just try to not give
>>> Laszlo too many flashbacks. :)
>> I haven't commented yet in this thread, as I thought my stance on this
>> undertaking was (or should be) obvious.
>>
>> I very much welcome a replacement for the PE/COFF parser (as I consider
>> its security issues unfixable in an incremental manner). From my reading
>> of Marvin's and Vitaly's paper (draft), they have my full trust, and I'm
>> ready to put their upcoming code to use in ArmVirtPkg and OvmfPkg with
>> minimal actual code review. If fixing the pervasive security problems
>> around this area cannot avoid spiraling out to other core code in edk2,
>> such as dispatchers, and even to the PI / UEFI specs, so be it.
>>
>> Regarding GSoC itself: as I stated elsewhere previously, I support
>> edk2's participation in GSoC, while at the same time I'm not
>> volunteering for mentorship at all. I'm uncertain if GSoC is the best
>> framework for upstreaming such a large undertaking, but if it can help,
>> we should use it as much as possible.
>>
>> Thanks
>> Laszlo
>>
>>
>>
>>
>>
>>>> With Best Regards,
>>>> Nate
>>>>
>>>>> -----Original Message-----
>>>>> From: devel at edk2.groups.io <devel at edk2.groups.io> On Behalf Of Marvin
>>>>> Häuser
>>>>> Sent: Sunday, April 4, 2021 4:02 PM
>>>>> To: devel at edk2.groups.io; Laszlo Ersek <lersek at redhat.com>; Andrew Fish
>>>>> <afish at apple.com>; Kinney, Michael D <michael.d.kinney at intel.com>
>>>>> Subject: [edk2-devel] [GSoC proposal] Secure Image Loader
>>>>>
>>>>> Good day everyone,
>>>>>
>>>>> I'll keep the introduction brief because I've been around for a while
>>>>> now. :) I'm
>>>>> Marvin Häuser, a third-year Computer Science student from TU
>>>>> Kaiserslautern,
>>>>> Germany. Late last year, my colleague Vitaly from ISP RAS and me
>>>>> introduced a
>>>>> formally verified Image Loader for UEFI usage at ISP RAS Open[1] due
>>>>> to various
>>>>> defects we outlined in the corresponding paper. Thank you once again
>>>>> Laszlo
>>>>> for your *incredible* review work on the publication part.
>>>>>
>>>>> I now want to make an effort to mainline it, preferably as part of
>>>>> the current
>>>>> Google Summer of Code event. To be clear, my internship at ISP RAS has
>>>>> concluded, and while Vitaly will be available for design discussion,
>>>>> he has other
>>>>> priorities at the moment and the practical part will be on me. I have
>>>>> previously
>>>>> submitted a proposal via the GSoC website for your review.
>>>>>
>>>>> There are many things to consider:
>>>>> 1. The Image Loader is a core component, and there needs to be a
>>>>> significant
>>>>> level of quality and security assurance.
>>>>> 2. Being consumed by many packages, the proposed patch set will take
>>>>> a lot of
>>>>> time to review and integrate.
>>>>> 3. During my initial exploration, I discovered defective PPIs and
>>>>> protocols (e.g.
>>>>> returning data with no corresponding size) originating from the UEFI
>>>>> PI and
>>>>> UEFI specifications. Changes need to be discussed, settled on, and
>>>>> submitted to
>>>>> the UEFI Forum.
>>>>> 4. Some UEFI APIs like the Security Architecture protocols are
>>>>> inconveniently
>>>>> abstract, see 5.
>>>>> 5. Some of the current code does not use the existing context, or
>>>>> accesses it
>>>>> outside of the exposed APIs. The control flow of the dispatchers may
>>>>> need to be
>>>>> adapted to make the context available to appropriate APIs.
>>>>>
>>>>> But obviously there are not only unpleasant considerations:
>>>>> A. The Image Loader is mostly formally verified, and only very few
>>>>> changes will
>>>>> be required from the last proven state. This gives a lot of trust in
>>>>> its correctness
>>>>> and safety.
>>>>> B. All outlined defects that are of critical nature have been fixed
>>>>> successfully.
>>>>> C. The Image Loader has been tested with real-world code loading
>>>>> real-world
>>>>> OSes on thousands of machines in the past few months, including
>>>>> rejecting
>>>>> malformed images (configurable by PCD).
>>>>> D. The new APIs will centralise everything PE, reducing code
>>>>> duplication and
>>>>> potentially unsafe operations.
>>>>> E. Centralising and reduced parse duplication may improve overall boot
>>>>> performance.
>>>>> F. The code has been coverage-tested to not contain dead code.
>>>>> G. The code has been fuzz-tested including sanitizers to not invoke
>>>>> undefined
>>>>> behaviour.
>>>>> H. I already managed to identify a malformed image in OVMF with its help
>>>>> (incorrectly reported section alignment of an Intel IPXE driver). A
>>>>> fix will be
>>>>> submitted shortly.
>>>>> I. I plan to support PE section permissions, allowing for read-only data
>>>>> segments when enabled.
>>>>>
>>>>> There are likely more points for both lists, but I hope this gives a
>>>>> decent
>>>>> starting point for discussion. What are your thoughts on the matter?
>>>>> I strongly
>>>>> encourage everyone to read the section regarding defects of our
>>>>> publication[2]
>>>>> to better understand the motivation. The vague points above can of
>>>>> course be
>>>>> elaborated in due time, as you see fit.
>>>>>
>>>>> Thank you for your time!
>>>>>
>>>>> Best regards,
>>>>> Marvin
>>>>>
>>>>>
>>>>> [1] https://github.com/mhaeuser/ISPRASOpen-SecurePE
>>>>> [2] https://arxiv.org/pdf/2012.05471.pdf
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>>
>>
>>
>> 
>>
>>

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