1 What: /sys/kernel/security/*/ima/policy 2 Date: May 2008 3 Contact: Mimi Zohar <zohar@us.ibm.com> 4 Description: 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 | hash | dont_hash 24 condition:= base | lsm [option] 25 base: [[func=] [mask=] [fsmagic=] [fsuuid=] [fsname=] 26 [uid=] [euid=] [gid=] [egid=] 27 [fowner=] [fgroup=]] 28 lsm: [[subj_user=] [subj_role=] [subj_type=] 29 [obj_user=] [obj_role=] [obj_type=]] 30 option: [digest_type=] [template=] [permit_directio] 31 [appraise_type=] [appraise_flag=] 32 [appraise_algos=] [keyrings=] 33 base: 34 func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK] 35 [FIRMWARE_CHECK] 36 [KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK] 37 [KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA] 38 [SETXATTR_CHECK][MMAP_CHECK_REQPROT] 39 mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND] 40 [[^]MAY_EXEC] 41 fsmagic:= hex value 42 fsuuid:= file system UUID (e.g 8bcbe394-4f13-4144-be8e-5aa9ea2ce2f6) 43 uid:= decimal value 44 euid:= decimal value 45 gid:= decimal value 46 egid:= decimal value 47 fowner:= decimal value 48 fgroup:= decimal value 49 lsm: are LSM specific 50 option: 51 appraise_type:= [imasig] | [imasig|modsig] | [sigv3] 52 where 'imasig' is the original or the signature 53 format v2. 54 where 'modsig' is an appended signature, 55 where 'sigv3' is the signature format v3. (Currently 56 limited to fsverity digest based signatures 57 stored in security.ima xattr. Requires 58 specifying "digest_type=verity" first.) 59 60 appraise_flag:= [check_blacklist] 61 Currently, blacklist check is only for files signed with appended 62 signature. 63 digest_type:= verity 64 Require fs-verity's file digest instead of the 65 regular IMA file hash. 66 keyrings:= list of keyrings 67 (eg, .builtin_trusted_keys|.ima). Only valid 68 when action is "measure" and func is KEY_CHECK. 69 template:= name of a defined IMA template type 70 (eg, ima-ng). Only valid when action is "measure". 71 pcr:= decimal value 72 label:= [selinux]|[kernel_info]|[data_label] 73 data_label:= a unique string used for grouping and limiting critical data. 74 For example, "selinux" to measure critical data for SELinux. 75 appraise_algos:= comma-separated list of hash algorithms 76 For example, "sha256,sha512" to only accept to appraise 77 files where the security.ima xattr was hashed with one 78 of these two algorithms. 79 80 default policy: 81 # PROC_SUPER_MAGIC 82 dont_measure fsmagic=0x9fa0 83 dont_appraise fsmagic=0x9fa0 84 # SYSFS_MAGIC 85 dont_measure fsmagic=0x62656572 86 dont_appraise fsmagic=0x62656572 87 # DEBUGFS_MAGIC 88 dont_measure fsmagic=0x64626720 89 dont_appraise fsmagic=0x64626720 90 # TMPFS_MAGIC 91 dont_measure fsmagic=0x01021994 92 dont_appraise fsmagic=0x01021994 93 # RAMFS_MAGIC 94 dont_appraise fsmagic=0x858458f6 95 # DEVPTS_SUPER_MAGIC 96 dont_measure fsmagic=0x1cd1 97 dont_appraise fsmagic=0x1cd1 98 # BINFMTFS_MAGIC 99 dont_measure fsmagic=0x42494e4d 100 dont_appraise fsmagic=0x42494e4d 101 # SECURITYFS_MAGIC 102 dont_measure fsmagic=0x73636673 103 dont_appraise fsmagic=0x73636673 104 # SELINUX_MAGIC 105 dont_measure fsmagic=0xf97cff8c 106 dont_appraise fsmagic=0xf97cff8c 107 # CGROUP_SUPER_MAGIC 108 dont_measure fsmagic=0x27e0eb 109 dont_appraise fsmagic=0x27e0eb 110 # NSFS_MAGIC 111 dont_measure fsmagic=0x6e736673 112 dont_appraise fsmagic=0x6e736673 113 114 measure func=BPRM_CHECK 115 measure func=FILE_MMAP mask=MAY_EXEC 116 measure func=FILE_CHECK mask=MAY_READ uid=0 117 measure func=MODULE_CHECK 118 measure func=FIRMWARE_CHECK 119 appraise fowner=0 120 121 The default policy measures all executables in bprm_check, 122 all files mmapped executable in file_mmap, and all files 123 open for read by root in do_filp_open. The default appraisal 124 policy appraises all files owned by root. 125 126 Examples of LSM specific definitions: 127 128 SELinux:: 129 130 dont_measure obj_type=var_log_t 131 dont_appraise obj_type=var_log_t 132 dont_measure obj_type=auditd_log_t 133 dont_appraise obj_type=auditd_log_t 134 measure subj_user=system_u func=FILE_CHECK mask=MAY_READ 135 measure subj_role=system_r func=FILE_CHECK mask=MAY_READ 136 137 Smack:: 138 139 measure subj_user=_ func=FILE_CHECK mask=MAY_READ 140 141 Example of measure rules using alternate PCRs:: 142 143 measure func=KEXEC_KERNEL_CHECK pcr=4 144 measure func=KEXEC_INITRAMFS_CHECK pcr=5 145 146 Example of appraise rule allowing modsig appended signatures: 147 148 appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig 149 150 Example of measure rule using KEY_CHECK to measure all keys: 151 152 measure func=KEY_CHECK 153 154 Example of measure rule using KEY_CHECK to only measure 155 keys added to .builtin_trusted_keys or .ima keyring: 156 157 measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima 158 159 Example of the special SETXATTR_CHECK appraise rule, that 160 restricts the hash algorithms allowed when writing to the 161 security.ima xattr of a file: 162 163 appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512 164 165 Example of a 'measure' rule requiring fs-verity's digests 166 with indication of type of digest in the measurement list. 167 168 measure func=FILE_CHECK digest_type=verity \ 169 template=ima-ngv2 170 171 Example of 'measure' and 'appraise' rules requiring fs-verity 172 signatures (format version 3) stored in security.ima xattr. 173 174 The 'measure' rule specifies the 'ima-sigv3' template option, 175 which includes the indication of type of digest and the file 176 signature in the measurement list. 177 178 measure func=BPRM_CHECK digest_type=verity \ 179 template=ima-sigv3 180 181 182 The 'appraise' rule specifies the type and signature format 183 version (sigv3) required. 184 185 appraise func=BPRM_CHECK digest_type=verity \ 186 appraise_type=sigv3 187 188 All of these policy rules could, for example, be constrained 189 either based on a filesystem's UUID (fsuuid) or based on LSM 190 labels. 191