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

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Date:	Thu, 28 Feb 2013 23:48:06 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	David Howells <dhowells@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, jwboyer@...hat.com,
	pjones@...hat.com, vgoyal@...hat.com, mjg59@...f.ucam.org,
	keescook@...omium.org, keyrings@...ux-nfs.org,
	linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
	Florian Weimer <fw@...eb.enyo.de>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [GIT PULL] Load keys from signed PE binaries

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

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