191 lines
6.3 KiB
Plaintext
191 lines
6.3 KiB
Plaintext
What: /sys/kernel/security/*/ima/policy
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Date: May 2008
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Contact: Mimi Zohar <zohar@us.ibm.com>
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Description:
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The Trusted Computing Group(TCG) runtime Integrity
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Measurement Architecture(IMA) maintains a list of hash
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values of executables and other sensitive system files
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loaded into the run-time of this system. At runtime,
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the policy can be constrained based on LSM specific data.
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Policies are loaded into the securityfs file ima/policy
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by opening the file, writing the rules one at a time and
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then closing the file. The new policy takes effect after
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the file ima/policy is closed.
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IMA appraisal, if configured, uses these file measurements
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for local measurement appraisal.
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::
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rule format: action [condition ...]
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action: measure | dont_measure | appraise | dont_appraise |
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audit | hash | dont_hash
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condition:= base | lsm [option]
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base: [[func=] [mask=] [fsmagic=] [fsuuid=] [fsname=]
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[uid=] [euid=] [gid=] [egid=]
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[fowner=] [fgroup=]]
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lsm: [[subj_user=] [subj_role=] [subj_type=]
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[obj_user=] [obj_role=] [obj_type=]]
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option: [digest_type=] [template=] [permit_directio]
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[appraise_type=] [appraise_flag=]
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[appraise_algos=] [keyrings=]
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base:
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func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
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[FIRMWARE_CHECK]
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[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
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[KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA]
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[SETXATTR_CHECK][MMAP_CHECK_REQPROT]
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mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
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[[^]MAY_EXEC]
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fsmagic:= hex value
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fsuuid:= file system UUID (e.g 8bcbe394-4f13-4144-be8e-5aa9ea2ce2f6)
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uid:= decimal value
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euid:= decimal value
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gid:= decimal value
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egid:= decimal value
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fowner:= decimal value
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fgroup:= decimal value
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lsm: are LSM specific
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option:
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appraise_type:= [imasig] | [imasig|modsig] | [sigv3]
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where 'imasig' is the original or the signature
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format v2.
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where 'modsig' is an appended signature,
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where 'sigv3' is the signature format v3. (Currently
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limited to fsverity digest based signatures
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stored in security.ima xattr. Requires
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specifying "digest_type=verity" first.)
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appraise_flag:= [check_blacklist]
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Currently, blacklist check is only for files signed with appended
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signature.
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digest_type:= verity
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Require fs-verity's file digest instead of the
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regular IMA file hash.
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keyrings:= list of keyrings
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(eg, .builtin_trusted_keys|.ima). Only valid
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when action is "measure" and func is KEY_CHECK.
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template:= name of a defined IMA template type
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(eg, ima-ng). Only valid when action is "measure".
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pcr:= decimal value
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label:= [selinux]|[kernel_info]|[data_label]
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data_label:= a unique string used for grouping and limiting critical data.
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For example, "selinux" to measure critical data for SELinux.
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appraise_algos:= comma-separated list of hash algorithms
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For example, "sha256,sha512" to only accept to appraise
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files where the security.ima xattr was hashed with one
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of these two algorithms.
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default policy:
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# PROC_SUPER_MAGIC
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dont_measure fsmagic=0x9fa0
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dont_appraise fsmagic=0x9fa0
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# SYSFS_MAGIC
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dont_measure fsmagic=0x62656572
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dont_appraise fsmagic=0x62656572
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# DEBUGFS_MAGIC
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dont_measure fsmagic=0x64626720
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dont_appraise fsmagic=0x64626720
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# TMPFS_MAGIC
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dont_measure fsmagic=0x01021994
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dont_appraise fsmagic=0x01021994
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# RAMFS_MAGIC
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dont_appraise fsmagic=0x858458f6
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# DEVPTS_SUPER_MAGIC
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dont_measure fsmagic=0x1cd1
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dont_appraise fsmagic=0x1cd1
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# BINFMTFS_MAGIC
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dont_measure fsmagic=0x42494e4d
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dont_appraise fsmagic=0x42494e4d
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# SECURITYFS_MAGIC
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dont_measure fsmagic=0x73636673
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dont_appraise fsmagic=0x73636673
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# SELINUX_MAGIC
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dont_measure fsmagic=0xf97cff8c
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dont_appraise fsmagic=0xf97cff8c
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# CGROUP_SUPER_MAGIC
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dont_measure fsmagic=0x27e0eb
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dont_appraise fsmagic=0x27e0eb
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# NSFS_MAGIC
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dont_measure fsmagic=0x6e736673
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dont_appraise fsmagic=0x6e736673
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measure func=BPRM_CHECK
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measure func=FILE_MMAP mask=MAY_EXEC
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measure func=FILE_CHECK mask=MAY_READ uid=0
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measure func=MODULE_CHECK
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measure func=FIRMWARE_CHECK
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appraise fowner=0
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The default policy measures all executables in bprm_check,
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all files mmapped executable in file_mmap, and all files
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open for read by root in do_filp_open. The default appraisal
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policy appraises all files owned by root.
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Examples of LSM specific definitions:
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SELinux::
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dont_measure obj_type=var_log_t
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dont_appraise obj_type=var_log_t
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dont_measure obj_type=auditd_log_t
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dont_appraise obj_type=auditd_log_t
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measure subj_user=system_u func=FILE_CHECK mask=MAY_READ
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measure subj_role=system_r func=FILE_CHECK mask=MAY_READ
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Smack::
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measure subj_user=_ func=FILE_CHECK mask=MAY_READ
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Example of measure rules using alternate PCRs::
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measure func=KEXEC_KERNEL_CHECK pcr=4
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measure func=KEXEC_INITRAMFS_CHECK pcr=5
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Example of appraise rule allowing modsig appended signatures:
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appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig
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Example of measure rule using KEY_CHECK to measure all keys:
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measure func=KEY_CHECK
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Example of measure rule using KEY_CHECK to only measure
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keys added to .builtin_trusted_keys or .ima keyring:
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measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima
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Example of the special SETXATTR_CHECK appraise rule, that
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restricts the hash algorithms allowed when writing to the
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security.ima xattr of a file:
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appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512
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Example of a 'measure' rule requiring fs-verity's digests
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with indication of type of digest in the measurement list.
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measure func=FILE_CHECK digest_type=verity \
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template=ima-ngv2
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Example of 'measure' and 'appraise' rules requiring fs-verity
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signatures (format version 3) stored in security.ima xattr.
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The 'measure' rule specifies the 'ima-sigv3' template option,
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which includes the indication of type of digest and the file
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signature in the measurement list.
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measure func=BPRM_CHECK digest_type=verity \
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template=ima-sigv3
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The 'appraise' rule specifies the type and signature format
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version (sigv3) required.
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appraise func=BPRM_CHECK digest_type=verity \
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appraise_type=sigv3
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All of these policy rules could, for example, be constrained
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either based on a filesystem's UUID (fsuuid) or based on LSM
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labels.
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