xref: /linux/Documentation/ABI/testing/ima_policy (revision 4d7d9486c04d917265f64c55bd23b2cc4fe7749c)

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 | dont_audit | hash | dont_hash
		  condition:= base | lsm  [option]
			base:	[[func=] [mask=] [fsmagic=] [fsuuid=] [fsname=]
				[fs_subtype=]
				[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.

			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
			# CONFIGFS_MAGIC
			dont_measure fsmagic=0x62656570
			dont_appraise fsmagic=0x62656570

			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

		Example of a regular IMA file hash 'appraise' rule requiring
		signature version 3 format stored in security.ima xattr.

			appraise func=BPRM_CHECK 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.