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What: /sys/kernel/security/*/ima/policy
Date: May 2008
Contact: Mimi Zohar <zohar@us.ibm.com>
Description:
The Trusted Computing Group(TCG) runtime Integrity
Measurement Architecture(IMA) maintains a list of hash
values of executables and other sensitive system files
loaded into the run-time of this system. At runtime,
the policy can be constrained based on LSM specific data.
Policies are loaded into the securityfs file ima/policy
by opening the file, writing the rules one at a time and
then closing the file. The new policy takes effect after
the file ima/policy is closed.
IMA appraisal, if configured, uses these file measurements
for local measurement appraisal.
::
rule format: action [condition ...]
action: measure | dont_measure | appraise | dont_appraise |
audit | hash | dont_hash
condition:= base | lsm [option]
base: [[func=] [mask=] [fsmagic=] [fsuuid=] [fsname=]
[uid=] [euid=] [gid=] [egid=]
[fowner=] [fgroup=]]
lsm: [[subj_user=] [subj_role=] [subj_type=]
[obj_user=] [obj_role=] [obj_type=]]
option: [[appraise_type=]] [template=] [permit_directio]
[appraise_flag=] [appraise_algos=] [keyrings=]
base:
func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
[KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA]
[SETXATTR_CHECK]
mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
[[^]MAY_EXEC]
fsmagic:= hex value
fsuuid:= file system UUID (e.g 8bcbe394-4f13-4144-be8e-5aa9ea2ce2f6)
uid:= decimal value
euid:= decimal value
gid:= decimal value
egid:= decimal value
fowner:= decimal value
fgroup:= decimal value
lsm: are LSM specific
option:
appraise_type:= [imasig] [imasig|modsig]
appraise_flag:= [check_blacklist]
Currently, blacklist check is only for files signed with appended
signature.
keyrings:= list of keyrings
(eg, .builtin_trusted_keys|.ima). Only valid
when action is "measure" and func is KEY_CHECK.
template:= name of a defined IMA template type
(eg, ima-ng). Only valid when action is "measure".
pcr:= decimal value
label:= [selinux]|[kernel_info]|[data_label]
data_label:= a unique string used for grouping and limiting critical data.
For example, "selinux" to measure critical data for SELinux.
appraise_algos:= comma-separated list of hash algorithms
For example, "sha256,sha512" to only accept to appraise
files where the security.ima xattr was hashed with one
of these two algorithms.
default policy:
# PROC_SUPER_MAGIC
dont_measure fsmagic=0x9fa0
dont_appraise fsmagic=0x9fa0
# SYSFS_MAGIC
dont_measure fsmagic=0x62656572
dont_appraise fsmagic=0x62656572
# DEBUGFS_MAGIC
dont_measure fsmagic=0x64626720
dont_appraise fsmagic=0x64626720
# TMPFS_MAGIC
dont_measure fsmagic=0x01021994
dont_appraise fsmagic=0x01021994
# RAMFS_MAGIC
dont_appraise fsmagic=0x858458f6
# DEVPTS_SUPER_MAGIC
dont_measure fsmagic=0x1cd1
dont_appraise fsmagic=0x1cd1
# BINFMTFS_MAGIC
dont_measure fsmagic=0x42494e4d
dont_appraise fsmagic=0x42494e4d
# SECURITYFS_MAGIC
dont_measure fsmagic=0x73636673
dont_appraise fsmagic=0x73636673
# SELINUX_MAGIC
dont_measure fsmagic=0xf97cff8c
dont_appraise fsmagic=0xf97cff8c
# CGROUP_SUPER_MAGIC
dont_measure fsmagic=0x27e0eb
dont_appraise fsmagic=0x27e0eb
# NSFS_MAGIC
dont_measure fsmagic=0x6e736673
dont_appraise fsmagic=0x6e736673
measure func=BPRM_CHECK
measure func=FILE_MMAP mask=MAY_EXEC
measure func=FILE_CHECK mask=MAY_READ uid=0
measure func=MODULE_CHECK
measure func=FIRMWARE_CHECK
appraise fowner=0
The default policy measures all executables in bprm_check,
all files mmapped executable in file_mmap, and all files
open for read by root in do_filp_open. The default appraisal
policy appraises all files owned by root.
Examples of LSM specific definitions:
SELinux::
dont_measure obj_type=var_log_t
dont_appraise obj_type=var_log_t
dont_measure obj_type=auditd_log_t
dont_appraise obj_type=auditd_log_t
measure subj_user=system_u func=FILE_CHECK mask=MAY_READ
measure subj_role=system_r func=FILE_CHECK mask=MAY_READ
Smack::
measure subj_user=_ func=FILE_CHECK mask=MAY_READ
Example of measure rules using alternate PCRs::
measure func=KEXEC_KERNEL_CHECK pcr=4
measure func=KEXEC_INITRAMFS_CHECK pcr=5
Example of appraise rule allowing modsig appended signatures:
appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig
Example of measure rule using KEY_CHECK to measure all keys:
measure func=KEY_CHECK
Example of measure rule using KEY_CHECK to only measure
keys added to .builtin_trusted_keys or .ima keyring:
measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima
Example of the special SETXATTR_CHECK appraise rule, that
restricts the hash algorithms allowed when writing to the
security.ima xattr of a file:
appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512
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