IBM updates Linux IMA to improve boot security

Thiago Jung Bauermann of IBM has submitted a 6-part patch to the Linux-IMA-devel/Linux-Kernel lists, with some improvements to Linux IMA for OpenPOWER secure/trusted boot. Including comments from parts 1 and 6 of the patch, see the full patch for full details.

Appended signatures support for IMA appraisal

On the OpenPOWER platform, secure boot and trusted boot are being implemented using IMA for taking measurements and verifying signatures. Since the kernel image on Power servers is an ELF binary, kernels are signed using the scripts/sign-file tool and thus use the same signature format as signed kernel modules. This patch series adds support in IMA for verifying those signatures. It adds flexibility to OpenPOWER secure boot, because it can boot kernels with the signature appended to them as well as kernels where the signature is stored in the IMA extended attribute. The first four patches are cleanups and improvements that can be taken independently from the others (and from each other as well). The last two are the ones actually focused on this feature. […] This patch introduces the appended_imasig keyword to the IMA policy syntax to specify that a given hook should expect the file to have the IMA signature appended to it. Here is how it can be used in a rule:

appraise func=KEXEC_KERNEL_CHECK appraise_type=appended_imasig
appraise func=KEXEC_KERNEL_CHECK appraise_type=appended_imasig|imasig

In the second form, IMA will accept either an appended signature or a signature stored in the extended attribute. In that case, it will first check whether there is an appended signature, and if not it will read it from the extended attribute. The format of the appended signature is the same used for signed kernel modules. This means that the file can be signed with the scripts/sign-file tool, with a command line such as this:

$ sign-file sha256 privkey_ima.pem x509_ima.der vmlinux

This code only works for files that are hashed from a memory buffer, not for files that are read from disk at the time of hash calculation. In other words, only hooks that use kernel_read_file can support appended signatures. The change in CONFIG_INTEGRITY_SIGNATURE to select CONFIG_KEYS instead of depending on it is to avoid a dependency recursion in CONFIG_IMA_APPRAISE_APPENDED_SIG, because CONFIG_MODULE_SIG_FORMAT selects CONFIG_KEYS and Kconfig complains that CONFIG_INTEGRITY_SIGNATURE depends on it.



new Linux-IMA patchset closes multiple measurement/appraisal gaps

Mimi Zohar and Dmitry Kasatkin have created a new patchset for Linux IMA which:

“closes a number of measurement/appraisal gaps by defining a generic function named ima_read_and_process_file() for measuring and appraising files read by the kernel (eg. kexec image and initramfs, firmware, IMA policy). To differentiate between callers of ima_read_and_process_file() in the IMA policy, a new enumeration is defined named ima_read_hooks, which initially includes KEXEC_CHECK, INITRAMFS_CHECK, FIRMWARE_CHECK, and POLICY_CHECK.

separate ‘security.ima’ reading functionality from collect
load policy using path
update appraise flags after policy update completes
measure and appraise kexec image and initramfs
measure and appraise firmware (improvement)
measure and appraise the IMA policy itself
require signed IMA policy

 Documentation/ABI/testing/ima_policy      |  2 +-
 drivers/base/firmware_class.c             | 15 +++++–
 include/linux/ima.h                       | 12 +++++
 kernel/kexec_file.c                       | 28 +++++++—–
 security/integrity/digsig.c               |  2 +-
 security/integrity/iint.c                 | 24 +++++++—
 security/integrity/ima/ima.h              | 24 +++++—–
 security/integrity/ima/ima_api.c          | 51 +++++++++++++++——
 security/integrity/ima/ima_appraise.c     | 40 +++++++++++——
 security/integrity/ima/ima_crypto.c       | 56 ++++++++++++++++——–
 security/integrity/ima/ima_fs.c           | 45 ++++++++++++++++++-
 security/integrity/ima/ima_init.c         |  2 +-
 security/integrity/ima/ima_main.c         | 55 ++++++++++++++++++—–
 security/integrity/ima/ima_policy.c       | 73 ++++++++++++++++++++++++——-
 security/integrity/ima/ima_template.c     |  2 –
 security/integrity/ima/ima_template_lib.c |  3 +-
 security/integrity/integrity.h            | 14 +++—
 17 files changed, 329 insertions(+), 119 deletions(-)

More information:


RMS on Free Hardware from LibrePlanet 2015

The Free Software Foundation has released some of the videos from LibrePlanet 2015. The presentation from RMS is described as:

Free software, free hardware, and other things by Richard Stallman, founder of the Free Software Foundation. Richard gives his take on some major issues facing the world of free software and explains how the free software philosophy extends to hardware.

It is a 45-minute video, the first 23 minutes are presentation, the remainder are QA. Video is here:

I have few questions of my own, from watching it:

At the beginning, he mentions that remote attestation of TPM doesn’t work, without any details on why he thinks that. I don’t understand what he’s talking about, there are multiple TNC implemenations, as well as non-TNC equivalent solutions that use TPM for network attestation. Linux-based Chrome OS, StrongSwan for Linux, Linux-IMA or OpenAttestation (OAT) for example.
If someone has more background on his perspective on remote attestation of TPM doesn’t work, please speak up. Heck, even the UEFI firmware on most modern systems have TNC support. IMO, it would have been more interesting to hear a discussion about new TPM 2.0 features, as well as TrustZone on ARM, and how that impacts various Free Software/Firmware/Hardware movements.

Later, he talks about “Free Hardware” term, which AFAICT isn’t that well-defined, and recommends using GPLv3 for hardware, and doesn’t mention OSHWA license, except to say that the alternatives offer no value. I am not sure that the existing OSHWA has the same opinion as RMS with his “Free Hardware” perspective, see March-April thread on the OSHWA list. IMO, Free Hardware -vs- Open Hardware needs some clarification. I guess, like with software, we’ll have the Open camps and the Free camp, with FSF as the Free owner and OSHWA instead of OSI for the Open camps, in addition to the Closed camps. However, unlike ISVs, I’ve never met an OEM or IHV that likes the GPL, so any Free Hardware will likely have to be community-funded, like Novena; I hope the FSF plans community-funded Free Hardware in the coming months.