[PATCH v7 0/3] add new ima hook ima_kexec_cmdline to measure kexec boot cmdline args

Prakhar Srivastava
2019-06-07T00:23:58Z

The motive behind the patch series is to measure the boot cmdline args
used for soft reboot/kexec case.

For secure boot attestation, it is necessary to measure the kernel
command line and the kernel version. For cold boot, the boot loader
can be enhanced to measure these parameters.
(https://mjg59.dreamwidth.org/48897.html)
However, for attestation across soft reboot boundary, these values
also need to be measured during kexec_file_load.

Currently for Kexec(kexec_file_load)/soft reboot scenario the boot cmdline
args for the next kernel are not measured. For
normal case of boot/hardreboot the cmdline args are measured into the TPM.
The hash of boot command line is calculated and added to the current
running kernel's measurement list.
On a soft reboot like kexec, no cmdline arguments measurement takes place.

To achive the above the patch series does the following
-adds a new ima hook: ima_kexec_cmdline which measures the cmdline args
into the ima log, behind a new ima policy entry KEXEC_CMDLINE.
-since the cmldine args cannot be appraised, a new template field(buf) is
added. The template field contains the buffer passed(cmldine args), which
can be used to appraise/attest at a later stage.
-call the ima_kexec_cmdline(...) hook from kexec_file_load call.

The ima logs need to be carried over to the next kernel, which will be followed
up by other patchsets for x86_64 and arm64.

The kexec cmdline hash can be verified using
sudo cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements |
grep kexec-cmdline | cut -d' ' -f 6 | xxd -r -p | sha256sum

Changelog:
V7:
- rebased to next-queued-testing
https://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git/log/?h=next-queued-testing

V6:
-add a new ima hook and policy to measure the cmdline
args(ima_kexec_cmdline)
-add a new template field buf to contain the buffer measured.
[suggested by Mimi Zohar]
add new fields to ima_event_data to store/read buffer data.
[suggested by Roberto]
-call ima_kexec_cmdline from kexec_file_load path

v5:
-add a new ima hook and policy to measure the cmdline
args(ima_kexec_cmdline)
-add a new template field buf to contain the buffer measured.
[suggested by Mimi Zohar]
-call ima_kexec_cmdline from kexec_file_load path

v4:
- per feedback from LSM community, removed the LSM hook and renamed the
IMA policy to KEXEC_CMDLINE

v3: (rebase changes to next-general)
- Add policy checks for buffer[suggested by Mimi Zohar]
- use the IMA_XATTR to add buffer
- Add kexec_cmdline used for kexec file load
- Add an LSM hook to allow usage by other LSM.[suggestd by Mimi Zohar]

v2:
- Add policy checks for buffer[suggested by Mimi Zohar]
- Add an LSM hook to allow usage by other LSM.[suggestd by Mimi Zohar]
- use the IMA_XATTR to add buffer instead of sig template

v1:
-Add kconfigs to control the ima_buffer_check
-measure the cmdline args suffixed with the kernel file name
-add the buffer to the template sig field.

Prakhar Srivastava (3):
Add a new ima hook ima_kexec_cmdline to measure cmdline args
add a new ima template field buf
call ima_kexec_cmdline to measure the cmdline args

Documentation/ABI/testing/ima_policy | 1 +
Documentation/security/IMA-templates.rst | 2 +-
include/linux/ima.h | 2 +
kernel/kexec_file.c | 8 ++-
security/integrity/ima/ima.h | 3 +
security/integrity/ima/ima_api.c | 5 +-
security/integrity/ima/ima_init.c | 2 +-
security/integrity/ima/ima_main.c | 80 +++++++++++++++++++++++
security/integrity/ima/ima_policy.c | 9 +++
security/integrity/ima/ima_template.c | 2 +
security/integrity/ima/ima_template_lib.c | 20 ++++++
security/integrity/ima/ima_template_lib.h | 4 ++
12 files changed, 131 insertions(+), 7 deletions(-)

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2.17.1