1What: /sys/kernel/security/*/ima/policy 2Date: May 2008 3Contact: Mimi Zohar <zohar@us.ibm.com> 4Description: 5 The Trusted Computing Group(TCG) runtime Integrity 6 Measurement Architecture(IMA) maintains a list of hash 7 values of executables and other sensitive system files 8 loaded into the run-time of this system. At runtime, 9 the policy can be constrained based on LSM specific data. 10 Policies are loaded into the securityfs file ima/policy 11 by opening the file, writing the rules one at a time and 12 then closing the file. The new policy takes effect after 13 the file ima/policy is closed. 14 15 IMA appraisal, if configured, uses these file measurements 16 for local measurement appraisal. 17 18 :: 19 20 rule format: action [condition ...] 21 22 action: measure | dont_measure | appraise | dont_appraise | 23 audit | dont_audit | hash | dont_hash 24 condition:= base | lsm [option] 25 base: [[func=] [mask=] [fsmagic=] [fsuuid=] [fsname=] 26 [fs_subtype=] 27 [uid=] [euid=] [gid=] [egid=] 28 [fowner=] [fgroup=]] 29 lsm: [[subj_user=] [subj_role=] [subj_type=] 30 [obj_user=] [obj_role=] [obj_type=]] 31 option: [digest_type=] [template=] [permit_directio] 32 [appraise_type=] [appraise_flag=] 33 [appraise_algos=] [keyrings=] 34 base: 35 func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK] 36 [FIRMWARE_CHECK] 37 [KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK] 38 [KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA] 39 [SETXATTR_CHECK][MMAP_CHECK_REQPROT] 40 mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND] 41 [[^]MAY_EXEC] 42 fsmagic:= hex value 43 fsuuid:= file system UUID (e.g 8bcbe394-4f13-4144-be8e-5aa9ea2ce2f6) 44 uid:= decimal value 45 euid:= decimal value 46 gid:= decimal value 47 egid:= decimal value 48 fowner:= decimal value 49 fgroup:= decimal value 50 lsm: are LSM specific 51 option: 52 appraise_type:= [imasig] | [imasig|modsig] | [sigv3] 53 where 'imasig' is the original or the signature 54 format v2. 55 where 'modsig' is an appended signature, 56 where 'sigv3' is the signature format v3. (Currently 57 limited to fsverity digest based signatures 58 stored in security.ima xattr. Requires 59 specifying "digest_type=verity" first.) 60 61 appraise_flag:= [check_blacklist] (deprecated) 62 Setting the check_blacklist flag is no longer necessary. 63 All appraisal functions set it by default. 64 digest_type:= verity 65 Require fs-verity's file digest instead of the 66 regular IMA file hash. 67 keyrings:= list of keyrings 68 (eg, .builtin_trusted_keys|.ima). Only valid 69 when action is "measure" and func is KEY_CHECK. 70 template:= name of a defined IMA template type 71 (eg, ima-ng). Only valid when action is "measure". 72 pcr:= decimal value 73 label:= [selinux]|[kernel_info]|[data_label] 74 data_label:= a unique string used for grouping and limiting critical data. 75 For example, "selinux" to measure critical data for SELinux. 76 appraise_algos:= comma-separated list of hash algorithms 77 For example, "sha256,sha512" to only accept to appraise 78 files where the security.ima xattr was hashed with one 79 of these two algorithms. 80 81 default policy: 82 # PROC_SUPER_MAGIC 83 dont_measure fsmagic=0x9fa0 84 dont_appraise fsmagic=0x9fa0 85 # SYSFS_MAGIC 86 dont_measure fsmagic=0x62656572 87 dont_appraise fsmagic=0x62656572 88 # DEBUGFS_MAGIC 89 dont_measure fsmagic=0x64626720 90 dont_appraise fsmagic=0x64626720 91 # TMPFS_MAGIC 92 dont_measure fsmagic=0x01021994 93 dont_appraise fsmagic=0x01021994 94 # RAMFS_MAGIC 95 dont_appraise fsmagic=0x858458f6 96 # DEVPTS_SUPER_MAGIC 97 dont_measure fsmagic=0x1cd1 98 dont_appraise fsmagic=0x1cd1 99 # BINFMTFS_MAGIC 100 dont_measure fsmagic=0x42494e4d 101 dont_appraise fsmagic=0x42494e4d 102 # SECURITYFS_MAGIC 103 dont_measure fsmagic=0x73636673 104 dont_appraise fsmagic=0x73636673 105 # SELINUX_MAGIC 106 dont_measure fsmagic=0xf97cff8c 107 dont_appraise fsmagic=0xf97cff8c 108 # CGROUP_SUPER_MAGIC 109 dont_measure fsmagic=0x27e0eb 110 dont_appraise fsmagic=0x27e0eb 111 # NSFS_MAGIC 112 dont_measure fsmagic=0x6e736673 113 dont_appraise fsmagic=0x6e736673 114 115 measure func=BPRM_CHECK 116 measure func=FILE_MMAP mask=MAY_EXEC 117 measure func=FILE_CHECK mask=MAY_READ uid=0 118 measure func=MODULE_CHECK 119 measure func=FIRMWARE_CHECK 120 appraise fowner=0 121 122 The default policy measures all executables in bprm_check, 123 all files mmapped executable in file_mmap, and all files 124 open for read by root in do_filp_open. The default appraisal 125 policy appraises all files owned by root. 126 127 Examples of LSM specific definitions: 128 129 SELinux:: 130 131 dont_measure obj_type=var_log_t 132 dont_appraise obj_type=var_log_t 133 dont_measure obj_type=auditd_log_t 134 dont_appraise obj_type=auditd_log_t 135 measure subj_user=system_u func=FILE_CHECK mask=MAY_READ 136 measure subj_role=system_r func=FILE_CHECK mask=MAY_READ 137 138 Smack:: 139 140 measure subj_user=_ func=FILE_CHECK mask=MAY_READ 141 142 Example of measure rules using alternate PCRs:: 143 144 measure func=KEXEC_KERNEL_CHECK pcr=4 145 measure func=KEXEC_INITRAMFS_CHECK pcr=5 146 147 Example of appraise rule allowing modsig appended signatures: 148 149 appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig 150 151 Example of measure rule using KEY_CHECK to measure all keys: 152 153 measure func=KEY_CHECK 154 155 Example of measure rule using KEY_CHECK to only measure 156 keys added to .builtin_trusted_keys or .ima keyring: 157 158 measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima 159 160 Example of the special SETXATTR_CHECK appraise rule, that 161 restricts the hash algorithms allowed when writing to the 162 security.ima xattr of a file: 163 164 appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512 165 166 Example of a 'measure' rule requiring fs-verity's digests 167 with indication of type of digest in the measurement list. 168 169 measure func=FILE_CHECK digest_type=verity \ 170 template=ima-ngv2 171 172 Example of 'measure' and 'appraise' rules requiring fs-verity 173 signatures (format version 3) stored in security.ima xattr. 174 175 The 'measure' rule specifies the 'ima-sigv3' template option, 176 which includes the indication of type of digest and the file 177 signature in the measurement list. 178 179 measure func=BPRM_CHECK digest_type=verity \ 180 template=ima-sigv3 181 182 183 The 'appraise' rule specifies the type and signature format 184 version (sigv3) required. 185 186 appraise func=BPRM_CHECK digest_type=verity \ 187 appraise_type=sigv3 188 189 All of these policy rules could, for example, be constrained 190 either based on a filesystem's UUID (fsuuid) or based on LSM 191 labels. 192