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ima: define a set of appraisal rules requiring file signatures

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The builtin "ima_appraise_tcb" policy should require file signatures for
at least a few of the hooks (eg. kernel modules, firmware, and the kexec
kernel image), but changing it would break the existing userspace/kernel
ABI.

This patch defines a new builtin policy named "secure_boot", which
can be specified on the "ima_policy=" boot command line, independently
or in conjunction with the "ima_appraise_tcb" policy, by specifing
ima_policy="appraise_tcb | secure_boot".  The new appraisal rules
requiring file signatures will be added prior to the "ima_appraise_tcb"
rules.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

Changelog:
- Reference secure boot in the new builtin policy name. (Thiago Bauermann)
This commit is contained in:
Mimi Zohar 2017-04-21 18:58:27 -04:00
parent 33ce9549cf
commit 503ceaef8e
2 changed files with 30 additions and 2 deletions
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6
Documentation/admin-guide/kernel-parameters.txt
View File

@ -1478,7 +1478,7 @@
ima_policy= [IMA]
The builtin policies to load during IMA setup.
Format: "tcb | appraise_tcb"
Format: "tcb | appraise_tcb | secure_boot"
The "tcb" policy measures all programs exec'd, files
mmap'd for exec, and all files opened with the read
@ -1489,6 +1489,10 @@
all files owned by root. (This is the equivalent
of ima_appraise_tcb.)
The "secure_boot" policy appraises the integrity
of files (eg. kexec kernel image, kernel modules,
firmware, policy, etc) based on file signatures.
ima_tcb [IMA] Deprecated. Use ima_policy= instead.
Load a policy which meets the needs of the Trusted
Computing Base. This means IMA will measure all

26
security/integrity/ima/ima_policy.c
View File

@ -153,6 +153,17 @@ static struct ima_rule_entry default_appraise_rules[] __ro_after_init = {
#endif
};
static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
{.action = APPRAISE, .func = MODULE_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
{.action = APPRAISE, .func = FIRMWARE_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
{.action = APPRAISE, .func = KEXEC_KERNEL_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
{.action = APPRAISE, .func = POLICY_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
};
static LIST_HEAD(ima_default_rules);
static LIST_HEAD(ima_policy_rules);
static LIST_HEAD(ima_temp_rules);
@ -171,6 +182,7 @@ static int __init default_measure_policy_setup(char *str)
__setup("ima_tcb", default_measure_policy_setup);
static bool ima_use_appraise_tcb __initdata;
static bool ima_use_secure_boot __initdata;
static int __init policy_setup(char *str)
{
char *p;
@ -182,6 +194,8 @@ static int __init policy_setup(char *str)
ima_policy = DEFAULT_TCB;
else if (strcmp(p, "appraise_tcb") == 0)
ima_use_appraise_tcb = 1;
else if (strcmp(p, "secure_boot") == 0)
ima_use_secure_boot = 1;
}
return 1;
@ -410,12 +424,14 @@ void ima_update_policy_flag(void)
*/
void __init ima_init_policy(void)
{
int i, measure_entries, appraise_entries;
int i, measure_entries, appraise_entries, secure_boot_entries;
/* if !ima_policy set entries = 0 so we load NO default rules */
measure_entries = ima_policy ? ARRAY_SIZE(dont_measure_rules) : 0;
appraise_entries = ima_use_appraise_tcb ?
ARRAY_SIZE(default_appraise_rules) : 0;
secure_boot_entries = ima_use_secure_boot ?
ARRAY_SIZE(secure_boot_rules) : 0;
for (i = 0; i < measure_entries; i++)
list_add_tail(&dont_measure_rules[i].list, &ima_default_rules);
@ -434,6 +450,14 @@ void __init ima_init_policy(void)
break;
}
/*
* Insert the appraise rules requiring file signatures, prior to
* any other appraise rules.
*/
for (i = 0; i < secure_boot_entries; i++)
list_add_tail(&secure_boot_rules[i].list,
&ima_default_rules);
for (i = 0; i < appraise_entries; i++) {
list_add_tail(&default_appraise_rules[i].list,
&ima_default_rules);