Re: [PATCH v5 00/10] ima: carry the measurement list across kexec
From: Mimi Zohar
Date: Thu Sep 29 2016 - 18:10:39 EST
On Thu, 2016-09-29 at 16:37 -0500, Eric W. Biederman wrote:
> Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> writes:
> > The TPM PCRs are only reset on a hard reboot. In order to validate a
> > TPM's quote after a soft reboot (eg. kexec -e), the IMA measurement list
> > of the running kernel must be saved and then restored on the subsequent
> > boot, possibly of a different architecture.
> > The existing securityfs binary_runtime_measurements file conveniently
> > provides a serialized format of the IMA measurement list. This patch
> > set serializes the measurement list in this format and restores it.
> > Up to now, the binary_runtime_measurements was defined as architecture
> > native format. The assumption being that userspace could and would
> > handle any architecture conversions. With the ability of carrying the
> > measurement list across kexec, possibly from one architecture to a
> > different one, the per boot architecture information is lost and with it
> > the ability of recalculating the template digest hash. To resolve this
> > problem, without breaking the existing ABI, this patch set introduces
> > the boot command line option "ima_canonical_fmt", which is arbitrarily
> > defined as little endian.
> > The need for this boot command line option will be limited to the
> > existing version 1 format of the binary_runtime_measurements.
> > Subsequent formats will be defined as canonical format (eg. TPM 2.0
> > support for larger digests).
> > A simplified method of Thiago Bauermann's "kexec buffer handover" patch
> > series for carrying the IMA measurement list across kexec is included
> > in this patch set. The simplified method requires all file measurements
> > be taken prior to executing the kexec load, as subsequent measurements
> > will not be carried across the kexec and restored.
> So I just went through the kexec portions of this and I don't see
> anything particularly worrying.
> I have one thing that I think could be improved, but is not wrong.
> Having both receiving and transmitting the ima measurments both under
> HAVE_IMA_KEXEC seems wrong. There may be people who want to receive the
> measurment list but don't want to support kexec'ing other kernels or the
> other way around. I can very much see bootloaders that expect they will
> be the first kernel to not want to compile in the extra code for
> receiving the measurment list.
> But again that is a nit, and not a problem.
Right, some kernels will want to carry the measurement list across kexec
and have it restored on the kexec'ed kernel, whiles others won't. The
CONFIG_IMA_KEXEC. enables "dumping" the IMA measurement list to be
carried across kexec.
> So for the series, from the kexec point of view.
> Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> > These patches can also be found in the next-kexec-restore branch of:
> > git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git
> > Changelog v5:
> > - Included patches from Thiago Bauermann's "kexec buffer handover"
> > patch series for carrying the IMA measurement list across kexec.
> > - Added CONFIG_HAVE_IMA_KEXEC
> > - Renamed functions to variations of ima_kexec_buffer instead of
> > variations of kexec_handover_buffer
> > Changelog v4:
> > - Fixed "spinlock bad magic" BUG - reported by Dmitry Vyukov
> > - Rebased on Thiago Bauermann's v5 patch set
> > - Removed the skip_checksum initialization
> > Changelog v3:
> > - Cleaned up the code for calculating the requested kexec segment size
> > needed for the IMA measurement list, limiting the segment size to half
> > of the totalram_pages.
> > - Fixed kernel test robot reports as enumerated in the respective
> > patch changelog.
> > Changelog v2:
> > - Canonical measurement list support added
> > - Redefined the ima_kexec_hdr struct to use well defined sizes
> > Andreas Steffen (1):
> > ima: platform-independent hash value
> > Mimi Zohar (7):
> > ima: on soft reboot, restore the measurement list
> > ima: permit duplicate measurement list entries
> > ima: maintain memory size needed for serializing the measurement list
> > ima: on soft reboot, save the measurement list
> > ima: store the builtin/custom template definitions in a list
> > ima: support restoring multiple template formats
> > ima: define a canonical binary_runtime_measurements list format
> > Thiago Jung Bauermann (2):
> > powerpc: ima: Get the kexec buffer passed by the previous kernel
> > powerpc: ima: Send the kexec buffer to the next kernel
> > Documentation/kernel-parameters.txt | 4 +
> > arch/Kconfig | 3 +
> > arch/powerpc/Kconfig | 1 +
> > arch/powerpc/include/asm/ima.h | 29 +++
> > arch/powerpc/include/asm/kexec.h | 16 +-
> > arch/powerpc/kernel/Makefile | 4 +
> > arch/powerpc/kernel/ima_kexec.c | 223 +++++++++++++++++++++++
> > arch/powerpc/kernel/kexec_elf_64.c | 2 +-
> > arch/powerpc/kernel/machine_kexec_64.c | 116 ++++++------
> > include/linux/ima.h | 12 ++
> > kernel/kexec_file.c | 4 +
> > security/integrity/ima/Kconfig | 12 ++
> > security/integrity/ima/Makefile | 1 +
> > security/integrity/ima/ima.h | 31 ++++
> > security/integrity/ima/ima_crypto.c | 6 +-
> > security/integrity/ima/ima_fs.c | 30 ++-
> > security/integrity/ima/ima_init.c | 2 +
> > security/integrity/ima/ima_kexec.c | 168 +++++++++++++++++
> > security/integrity/ima/ima_main.c | 1 +
> > security/integrity/ima/ima_queue.c | 76 +++++++-
> > security/integrity/ima/ima_template.c | 293 ++++++++++++++++++++++++++++--
> > security/integrity/ima/ima_template_lib.c | 7 +-
> > 22 files changed, 952 insertions(+), 89 deletions(-)
> > create mode 100644 arch/powerpc/include/asm/ima.h
> > create mode 100644 arch/powerpc/kernel/ima_kexec.c
> > create mode 100644 security/integrity/ima/ima_kexec.c
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