Re: [GIT PULL] Load keys from signed PE binaries

Jiri Kosina
2013-02-28T22:48:19Z

On Thu, 21 Feb 2013, David Howells wrote:

> The way we have come up with to get around this is to embed an X.509
> certificate containing the key in a section called ".keylist" in an EFI PE
> binary and then get the binary signed by Microsoft. The key can then be passed
> to the kernel by passing the signed binary:
>
> keyctl padd asymmetric "" {ID of .system_keyring} <pekey.efi.signed

Please let me take this back to square one for a very short moment.

I completely fail to understand how your security model is dealing with
this scenario:

- Mr. Evil Blackhat creates EFI PE binary from "int main() { return 42; }"
(psuedo)code
- Mr. Evil Blackhat puts his own key into .keylist section of this binary
- Mr. Evil Blackhat goes through the $99 process of having this binary
signed by Microsoft. They don't have a slightest reason not to sign it,
as the binary obviously can't be used to run backdoored Windows
- Mr. Evil Blackhat then uses keyctl to process this signed binary
- Mr. Evil Blackhat modprobes i_own_your_ring0.ko which is signed by
his key, and he instantly has his code running in your SecureBoot
environment

Let me formulate my point more clearly -- Microsoft very likely going to
sign hello world EFI PE binary, no matter the contents of .keylist
section, as they don't give a damn about this section, as it has zero
semantic value to them, right?

They sign the binary. By signing the binary, they are *NOT* establishing
cryptographic chain of trust to the key stored in .keylist, but your
patchset seems to imply so.

What am I missing?

Thanks,

--
Jiri Kosina
SUSE Labs