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. 57 58 appraise_flag:= [check_blacklist] (deprecated) 59 Setting the check_blacklist flag is no longer necessary. 60 All appraisal functions set it by default. 61 digest_type:= verity 62 Require fs-verity's file digest instead of the 63 regular IMA file hash. 64 keyrings:= list of keyrings 65 (eg, .builtin_trusted_keys|.ima). Only valid 66 when action is "measure" and func is KEY_CHECK. 67 template:= name of a defined IMA template type 68 (eg, ima-ng). Only valid when action is "measure". 69 pcr:= decimal value 70 label:= [selinux]|[kernel_info]|[data_label] 71 data_label:= a unique string used for grouping and limiting critical data. 72 For example, "selinux" to measure critical data for SELinux. 73 appraise_algos:= comma-separated list of hash algorithms 74 For example, "sha256,sha512" to only accept to appraise 75 files where the security.ima xattr was hashed with one 76 of these two algorithms. 77 78 default policy: 79 # PROC_SUPER_MAGIC 80 dont_measure fsmagic=0x9fa0 81 dont_appraise fsmagic=0x9fa0 82 # SYSFS_MAGIC 83 dont_measure fsmagic=0x62656572 84 dont_appraise fsmagic=0x62656572 85 # DEBUGFS_MAGIC 86 dont_measure fsmagic=0x64626720 87 dont_appraise fsmagic=0x64626720 88 # TMPFS_MAGIC 89 dont_measure fsmagic=0x01021994 90 dont_appraise fsmagic=0x01021994 91 # RAMFS_MAGIC 92 dont_appraise fsmagic=0x858458f6 93 # DEVPTS_SUPER_MAGIC 94 dont_measure fsmagic=0x1cd1 95 dont_appraise fsmagic=0x1cd1 96 # BINFMTFS_MAGIC 97 dont_measure fsmagic=0x42494e4d 98 dont_appraise fsmagic=0x42494e4d 99 # SECURITYFS_MAGIC 100 dont_measure fsmagic=0x73636673 101 dont_appraise fsmagic=0x73636673 102 # SELINUX_MAGIC 103 dont_measure fsmagic=0xf97cff8c 104 dont_appraise fsmagic=0xf97cff8c 105 # CGROUP_SUPER_MAGIC 106 dont_measure fsmagic=0x27e0eb 107 dont_appraise fsmagic=0x27e0eb 108 # NSFS_MAGIC 109 dont_measure fsmagic=0x6e736673 110 dont_appraise fsmagic=0x6e736673 111 112 measure func=BPRM_CHECK 113 measure func=FILE_MMAP mask=MAY_EXEC 114 measure func=FILE_CHECK mask=MAY_READ uid=0 115 measure func=MODULE_CHECK 116 measure func=FIRMWARE_CHECK 117 appraise fowner=0 118 119 The default policy measures all executables in bprm_check, 120 all files mmapped executable in file_mmap, and all files 121 open for read by root in do_filp_open. The default appraisal 122 policy appraises all files owned by root. 123 124 Examples of LSM specific definitions: 125 126 SELinux:: 127 128 dont_measure obj_type=var_log_t 129 dont_appraise obj_type=var_log_t 130 dont_measure obj_type=auditd_log_t 131 dont_appraise obj_type=auditd_log_t 132 measure subj_user=system_u func=FILE_CHECK mask=MAY_READ 133 measure subj_role=system_r func=FILE_CHECK mask=MAY_READ 134 135 Smack:: 136 137 measure subj_user=_ func=FILE_CHECK mask=MAY_READ 138 139 Example of measure rules using alternate PCRs:: 140 141 measure func=KEXEC_KERNEL_CHECK pcr=4 142 measure func=KEXEC_INITRAMFS_CHECK pcr=5 143 144 Example of appraise rule allowing modsig appended signatures: 145 146 appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig 147 148 Example of measure rule using KEY_CHECK to measure all keys: 149 150 measure func=KEY_CHECK 151 152 Example of measure rule using KEY_CHECK to only measure 153 keys added to .builtin_trusted_keys or .ima keyring: 154 155 measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima 156 157 Example of the special SETXATTR_CHECK appraise rule, that 158 restricts the hash algorithms allowed when writing to the 159 security.ima xattr of a file: 160 161 appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512 162 163 Example of a 'measure' rule requiring fs-verity's digests 164 with indication of type of digest in the measurement list. 165 166 measure func=FILE_CHECK digest_type=verity \ 167 template=ima-ngv2 168 169 Example of 'measure' and 'appraise' rules requiring fs-verity 170 signatures (format version 3) stored in security.ima xattr. 171 172 The 'measure' rule specifies the 'ima-sigv3' template option, 173 which includes the indication of type of digest and the file 174 signature in the measurement list. 175 176 measure func=BPRM_CHECK digest_type=verity \ 177 template=ima-sigv3 178 179 180 The 'appraise' rule specifies the type and signature format 181 version (sigv3) required. 182 183 appraise func=BPRM_CHECK digest_type=verity \ 184 appraise_type=sigv3 185 186 Example of a regular IMA file hash 'appraise' rule requiring 187 signature version 3 format stored in security.ima xattr. 188 189 appraise func=BPRM_CHECK appraise_type=sigv3 190 191 All of these policy rules could, for example, be constrained 192 either based on a filesystem's UUID (fsuuid) or based on LSM 193 labels. 194