[PATCH v3 0/6] ima: provide signature based 'init' appraisal

From: Dmitry Kasatkin
Date: Fri Oct 10 2014 - 10:10:08 EST

Currently secure IMA/EVM initialization has to be done from the initramfs,
embedded in the signed kernel image. Many systems do not want to use
initramfs or usage of embedded initramfs makes it difficult to have
multi-target kernels.

This is a very simple patchset which makes it possible to perform secure
initialization by requiring initial user-space to be signed.

It does it by:
- introducing a hook to load keys
- loading IMA signed public key certificate into the '.ima' trusted keyring
- making default IMA appraisal policy to require everything to be signed

When builtin initramfs is not in use, keys cannot be read from initcalls,
because root filesystem is not yet mounted. In order to read keys before
executing init process, ima_prepare_keys() hook is introduced. Reading
public keys from the kernel is justified because signature verification
key is needed in order to verify anything else which is read from the
file system. Public keys are X509 certificates and itself signed by the
trusted key from the .system keyring. Kernel BIG KEYS support is an example
of reading keys directly by the kernel.

CONFIG_IMA_APPRAISE_SIGNED_INIT kernel option is provided to make the IMA
default appraisal policy to required signature validation. Signed init
process need to initialize EVM key and load appropriate IMA policy which
would not require everything to be signed.

Unless real '/sbin/init' is signed, a simple and practical way is to place
all signed programs, libraries, scripts and configuration files under
dedicated directory, for example '/ima', and run signed init process by
providing a kernel command line parameter 'init=/ima/init'.

In the first post of these patches Andrew Morton noted that
integrity_read_file() is a very simple open-file-and-slurp-it-into-memory
and if there are other similar functions that can be made in ./lib.
I found out that only sound:sound_firmware.c:do_mod_firmware_load(),
which is enabled by CONFIG_SOUND_PRIME which is related to deprecated OSS
interface and is not enabled anymore in latest Ubuntu kernels, at least.
So I am keeping integrity_read_file() in integrity subsystem.

cpio based initramfs currently does not support extended attributes.
There is an initial agreement to introduce light-weight tar parser to
the kernel to support extended attributes which will make it possible to
use IMA appraisal with external initramfs. It will benefit from this
patchset and allow to update initramfs with signed files also on the
running system as distros do.

Changes in v3:
* ima_prepare_keys() renamed to integrity_load_keys() to be the hook
for both modules of integrity subsystem IMA/EVM.
* removed unnecessary configuration options and declared init functions
with '__init'.
* updated to lately introduced 'ima_policy_flag' variable to disabled and
enable IMA appraisal.
* separated key loading patch from policy change patch
* added patch which refactor vfs_read(). Agreed with Mimi to offer to
move calling file operations hooks to a separate helper function which
is then used by vfs_read() and integrity_kernel_read(). Applying this
patch does not affect functionality and can be applied if agreed so.

Changes in v2:
* ima_kernel_read() moved as integrity_kernel_read() from ima_crypto.c to
iint.c for use by integrity_read_file. The reason for keeping internal
version is because 'integrity' version does not call fsnotify_access(),
add_rchar() and inc_syscr().
* integrity_read_file() moved from digsig.c to iint.c because it is used
by IMA crypto subsystem and should not depend on digsig support being


Dmitry Kasatkin (6):
integrity: provide integrity_read_file()
integrity: provide x509 certificate loading from the kernel
ima: load x509 certificate from the kernel
integrity: provide hook to load keys when rootfs is ready
ima: require signature based appraisal
VFS: refactor vfs_read()

fs/read_write.c | 24 ++++++++---
include/linux/fs.h | 1 +
include/linux/integrity.h | 6 +++
init/main.c | 6 ++-
security/integrity/digsig.c | 37 +++++++++++++++-
security/integrity/iint.c | 85 +++++++++++++++++++++++++++++++++++++
security/integrity/ima/Kconfig | 22 ++++++++++
security/integrity/ima/ima_crypto.c | 35 ++-------------
security/integrity/ima/ima_init.c | 17 ++++++++
security/integrity/ima/ima_policy.c | 5 +++
security/integrity/integrity.h | 14 ++++++
11 files changed, 212 insertions(+), 40 deletions(-)


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