xref: /kernel/linux/linux-6.6/Documentation/ABI/testing/ima_policy (revision 62306a36)

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:	[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.