linux-kernel - Re: [PATCH 0/5] MODSIGN: Use PKCS#7 for module signatures

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Date:	Mon, 24 Nov 2014 14:33:38 +0200
From:	Dmitry Kasatkin <d.kasatkin@...sung.com>
To:	David Howells <dhowells@...hat.com>, mmarek@...e.cz,
	rusty@...tcorp.com.au, vgoyal@...hat.com
Cc:	keyrings@...ux-nfs.org, linux-security-module@...r.kernel.org,
	zohar@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] MODSIGN: Use PKCS#7 for module signatures

On 20/11/14 18:53, David Howells wrote:
> Here's a set of patches that does the following:
>
>  (1) Extracts both parts of an X.509 AuthorityKeyIdentifier (AKID) extension.
>      We already extract the bit that can match the subjectKeyIdentifier (SKID)
>      of the parent X.509 cert, but we currently ignore the bits that can match
>      the issuer and serialNumber.
>
>      Looks up an X.509 cert by issuer and serialNumber if those are provided in
>      the AKID.  If the keyIdentifier is also provided, checks that the
>      subjectKeyIdentifier of the cert found matches that also.
>
>      If no issuer and serialNumber are provided in the AKID, looks up an X.509
>      cert by SKID using the AKID keyIdentifier.
>
>      This allows module signing to be done with certificates that don't have an
>      SKID by which they can be looked up.
>
>  (2) Makes use of the PKCS#7 facility to provide module signatures.
>
>      sign-file is replaced with a program that generates a PKCS#7 message that
>      has no X.509 certs embedded and that has detached data (the module
>      content) and adds it onto the message with magic string and descriptor.

Why do you highlight that X509 is not embedded?
Current module signing does not embed X509 also.

- Dmitry

>  (3) The PKCS#7 message (and matching X.509 cert) supply all the information
>      that is needed to select the X.509 cert to be used to verify the signature
>      by standard means (including selection of digest algorithm and public key
>      algorithm).  No kernel-specific magic values are required.
>
> Note that the revised sign-file program no longer supports the "-s <signature>"
> option as I'm not sure what the best way to deal with this is.  Do we generate
> a PKCS#7 cert from the signature given, or do we get given a PKCS#7 cert?  I
> lean towards the latter.
>
> They can be found here also:
>
> 	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=modsign-pkcs7
>
> These patches are based on the security tree's next branch.
>
> David
> ---
> David Howells (5):
>       X.509: Extract both parts of the AuthorityKeyIdentifier
>       X.509: Support X.509 lookup by Issuer+Serial form AuthorityKeyIdentifier
>       PKCS#7: Allow detached data to be supplied for signature checking purposes
>       MODSIGN: Provide a utility to append a PKCS#7 signature to a module
>       MODSIGN: Use PKCS#7 messages as module signatures
>
>
>  crypto/asymmetric_keys/Makefile           |    8 -
>  crypto/asymmetric_keys/pkcs7_trust.c      |   10 -
>  crypto/asymmetric_keys/pkcs7_verify.c     |   81 ++++--
>  crypto/asymmetric_keys/x509_akid.asn1     |   35 ++
>  crypto/asymmetric_keys/x509_cert_parser.c |  142 ++++++----
>  crypto/asymmetric_keys/x509_parser.h      |    3 
>  crypto/asymmetric_keys/x509_public_key.c  |   85 ++++--
>  include/crypto/pkcs7.h                    |    3 
>  include/crypto/public_key.h               |    4 
>  init/Kconfig                              |    1 
>  kernel/module_signing.c                   |  220 +++------------
>  scripts/Makefile                          |    2 
>  scripts/sign-file                         |  421 -----------------------------
>  scripts/sign-file.c                       |  189 +++++++++++++
>  14 files changed, 505 insertions(+), 699 deletions(-)
>  create mode 100644 crypto/asymmetric_keys/x509_akid.asn1
>  delete mode 100755 scripts/sign-file
>  create mode 100755 scripts/sign-file.c
>
> --
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