What: /sys/kernel/security/*/ima/policy Date: May 2008 Contact: Mimi Zohar 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: [digest_type=] [template=] [permit_directio] [appraise_type=] [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][MMAP_CHECK_REQPROT] 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] | [sigv3] where 'imasig' is the original or the signature format v2. where 'modsig' is an appended signature, where 'sigv3' is the signature format v3. (Currently limited to fsverity digest based signatures stored in security.ima xattr. Requires specifying "digest_type=verity" first.) appraise_flag:= [check_blacklist] (deprecated) Setting the check_blacklist flag is no longer necessary. All appraisal functions set it by default. digest_type:= verity Require fs-verity's file digest instead of the regular IMA file hash. 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 Example of a 'measure' rule requiring fs-verity's digests with indication of type of digest in the measurement list. measure func=FILE_CHECK digest_type=verity \ template=ima-ngv2 Example of 'measure' and 'appraise' rules requiring fs-verity signatures (format version 3) stored in security.ima xattr. The 'measure' rule specifies the 'ima-sigv3' template option, which includes the indication of type of digest and the file signature in the measurement list. measure func=BPRM_CHECK digest_type=verity \ template=ima-sigv3 The 'appraise' rule specifies the type and signature format version (sigv3) required. appraise func=BPRM_CHECK digest_type=verity \ appraise_type=sigv3 All of these policy rules could, for example, be constrained either based on a filesystem's UUID (fsuuid) or based on LSM labels.