[RFC][PATCH 3/7] ima: Introduce diglim and appraise_diglim policies
Roberto Sassu
roberto.sassu at huawei.com
Thu Sep 30 11:55:29 UTC 2021
Introduce two new hardcoded policies, 'diglim' and 'appraise_diglim' to
measure and appraise digest lists and related files.
In particular, the 'diglim' policy adds the new rule:
measure func=DIGEST_LIST_CHECK pcr=<PCR value> use_diglim
where PCR value is 11 or the one chosen with the ima_diglim_pcr= kernel
option. It also adds the use_diglim directive to existing selected rules
with hooks BPRM_CHECK, CREDS_CHECK, MMAP_CHECK, FILE_CHECK, MODULE_CHECK,
FIRMWARE_CHECK and DIGEST_LIST_CHECK.
A rule with the DIGEST_LIST_CHECK hook is sufficient to cover all aspects
of the digest list loading process. For direct upload, the kernel reads the
file with type READING_DIGEST_LIST, which is mapped to that hook. For
upload by a user space parser, DIGLIM LSM performs a second read for every
file opened by the parser (including the executable), also with type
READING_DIGEST_LIST.
The 'appraise_diglim' policy adds the new rule:
appraise func=DIGEST_LIST_CHECK appraise_type=imasig|modsig use_diglim
and, like for the 'diglim' policy, adds the use_diglim directive for the
selected IMA rules with action appraise.
Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
---
.../admin-guide/kernel-parameters.txt | 19 +++-
security/integrity/ima/ima_policy.c | 102 +++++++++++++++++-
2 files changed, 119 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e0db162ba202..fa4959a321d8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1835,6 +1835,13 @@
Use the canonical format for the binary runtime
measurements, instead of host native format.
+ ima_diglim_pcr=
+ [IMA]
+ Format: 0 - 23
+ default: 11
+ Define the PCR to be used for measurement entries
+ created with the diglim IMA policy.
+
ima_hash= [IMA]
Format: { md5 | sha1 | rmd160 | sha256 | sha384
| sha512 | ... }
@@ -1846,7 +1853,8 @@
ima_policy= [IMA]
The builtin policies to load during IMA setup.
Format: "tcb | appraise_tcb | secure_boot |
- fail_securely | critical_data"
+ fail_securely | critical_data | diglim |
+ appraise_diglim"
The "tcb" policy measures all programs exec'd, files
mmap'd for exec, and all files opened with the read
@@ -1860,6 +1868,11 @@
the tmpfs filesystem, for the "ima_tcb", "tcb" and
"exec_tcb" policies.
+ The "diglim" policy enables measurement of
+ DIGLIM-related files (e.g. digest lists, parsers) and
+ usage of DIGLIM for measurement (exec, mmap, open,
+ firmware and module loading).
+
The "appraise_tcb" policy appraises the integrity of
all files owned by root.
@@ -1876,6 +1889,10 @@
rule for the tmpfs and ramfs filesystems for the
"appraise_tcb" and "appraise_exec_tcb" policies.
+ The "appraise_diglim" policy enables appraisal of
+ DIGLIM-related files and usage of DIGLIM for appraisal
+ (exec, mmap, open, firmware and module loading).
+
The "secure_boot" policy appraises the integrity
of files (eg. kexec kernel image, kernel modules,
firmware, policy, etc) based on file signatures.
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index dfab21aeb7e1..5e1532abca5d 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -162,6 +162,10 @@ static struct ima_rule_entry default_measurement_rules[] __ro_after_init = {
{.action = MEASURE, .func = POLICY_CHECK, .flags = IMA_FUNC},
};
+static struct ima_rule_entry diglim_measure_rule __ro_after_init = {
+ .action = MEASURE, .func = DIGEST_LIST_CHECK, .flags = IMA_FUNC
+};
+
static struct ima_rule_entry default_appraise_rules[] __ro_after_init = {
{.action = DONT_APPRAISE, .fsmagic = PROC_SUPER_MAGIC, .flags = IMA_FSMAGIC},
{.action = DONT_APPRAISE, .fsmagic = SYSFS_MAGIC, .flags = IMA_FSMAGIC},
@@ -228,6 +232,11 @@ static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
};
+static struct ima_rule_entry diglim_appraise_rule __ro_after_init = {
+ .action = APPRAISE, .func = DIGEST_LIST_CHECK,
+ .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED
+};
+
static struct ima_rule_entry critical_data_rules[] __ro_after_init = {
{.action = MEASURE, .func = CRITICAL_DATA, .flags = IMA_FUNC},
};
@@ -253,9 +262,12 @@ static int __init default_measure_policy_setup(char *str)
__setup("ima_tcb", default_measure_policy_setup);
static unsigned int ima_measure_skip_flags __initdata;
+static unsigned int ima_measure_diglim __initdata;
static unsigned int ima_appraise_skip_flags __initdata;
+static unsigned int ima_diglim_pcr __initdata = 11;
static bool ima_use_appraise_tcb __initdata;
static bool ima_use_appraise_exec_immutable __initdata;
+static bool ima_use_appraise_diglim __initdata;
static bool ima_use_secure_boot __initdata;
static bool ima_use_critical_data __initdata;
static bool ima_fail_unverifiable_sigs __ro_after_init;
@@ -273,7 +285,9 @@ static int __init policy_setup(char *str)
else if ((strcmp(p, "exec_tcb") == 0) && !ima_policy) {
ima_policy = DEFAULT_TCB;
ima_measure_skip_flags |= IMA_SKIP_OPEN;
- } else if (strcmp(p, "appraise_tcb") == 0)
+ } else if (strcmp(p, "diglim") == 0)
+ ima_measure_diglim = true;
+ else if (strcmp(p, "appraise_tcb") == 0)
ima_use_appraise_tcb = true;
else if ((strcmp(p, "appraise_tmpfs") == 0))
ima_appraise_skip_flags |= IMA_SKIP_TMPFS;
@@ -282,6 +296,8 @@ static int __init policy_setup(char *str)
ima_appraise_skip_flags |= IMA_SKIP_OPEN;
} else if (strcmp(p, "appraise_exec_immutable") == 0)
ima_use_appraise_exec_immutable = true;
+ else if (strcmp(p, "appraise_diglim") == 0)
+ ima_use_appraise_diglim = true;
else if (strcmp(p, "secure_boot") == 0)
ima_use_secure_boot = true;
else if (strcmp(p, "critical_data") == 0)
@@ -303,6 +319,28 @@ static int __init default_appraise_policy_setup(char *str)
}
__setup("ima_appraise_tcb", default_appraise_policy_setup);
+static int __init default_diglim_pcr_setup(char *str)
+{
+ unsigned int pcr;
+ int ret;
+
+ ret = kstrtouint(str, 10, &pcr);
+ if (ret < 0 || pcr > 23) {
+ pr_err("Invalid value for ima_diglim_pcr=\n");
+ return 1;
+ }
+
+ /* Using the default IMA PCR is forbidden. */
+ if (ret == CONFIG_IMA_MEASURE_PCR_IDX) {
+ pr_err("Default IMA PCR cannot be used for ima_diglim_pcr=\n");
+ return 1;
+ }
+
+ ima_diglim_pcr = pcr;
+ return 1;
+}
+__setup("ima_diglim_pcr=", default_diglim_pcr_setup);
+
static struct ima_rule_opt_list *ima_alloc_rule_opt_list(const substring_t *src)
{
struct ima_rule_opt_list *opt_list;
@@ -812,6 +850,61 @@ void ima_update_policy_flags(void)
ima_policy_flag = new_policy_flag;
}
+/*
+ * Add the IMA_USE_DIGLIM_MEASURE and IMA_USE_DIGLIM_APPRAISE flags to the
+ * initial policy depending on the options in the kernel command line, and set
+ * the correct PCR for the measure rules.
+ */
+static void __init ima_add_diglim_flag(void)
+{
+ struct ima_rule_entry *entry;
+
+ if (!IS_ENABLED(CONFIG_DIGLIM))
+ return;
+
+ if (!ima_measure_diglim && !ima_use_appraise_diglim)
+ return;
+
+ list_for_each_entry(entry, ima_rules, list) {
+ if (entry->action != IMA_MEASURE &&
+ entry->action != IMA_APPRAISE)
+ continue;
+
+ if (entry->action == IMA_MEASURE && !ima_measure_diglim)
+ continue;
+
+ if (entry->action == IMA_APPRAISE &&
+ !ima_use_appraise_diglim)
+ continue;
+
+ switch (entry->func) {
+ case BPRM_CHECK:
+ fallthrough;
+ case CREDS_CHECK:
+ fallthrough;
+ case MMAP_CHECK:
+ fallthrough;
+ case FILE_CHECK:
+ fallthrough;
+ case MODULE_CHECK:
+ fallthrough;
+ case FIRMWARE_CHECK:
+ fallthrough;
+ case DIGEST_LIST_CHECK:
+ if (entry->action == IMA_MEASURE) {
+ entry->flags |= IMA_USE_DIGLIM_MEASURE;
+ entry->flags |= IMA_PCR;
+ entry->pcr = ima_diglim_pcr;
+ } else {
+ entry->flags |= IMA_USE_DIGLIM_APPRAISE;
+ }
+ break;
+ default:
+ break;
+ }
+ }
+}
+
static int ima_appraise_flag(enum ima_hooks func)
{
if (func == MODULE_CHECK)
@@ -989,7 +1082,14 @@ void __init ima_init_policy(void)
atomic_set(&ima_setxattr_allowed_hash_algorithms, 0);
+ if (ima_measure_diglim)
+ add_rules(&diglim_measure_rule, 1, IMA_DEFAULT_POLICY, 0);
+
+ if (ima_use_appraise_diglim)
+ add_rules(&diglim_appraise_rule, 1, IMA_DEFAULT_POLICY, 0);
+
ima_update_policy_flags();
+ ima_add_diglim_flag();
}
/* Make sure we have a valid policy, at least containing some rules. */
--
2.32.0
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