1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
|
What: 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: [[appraise_type=]] [template=] [permit_directio]
[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]
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]
appraise_flag:= [check_blacklist]
Currently, blacklist check is only for files signed with appended
signature.
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
|