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ima: add build time policy 

IMA by default does not measure, appraise or audit files, but can be
enabled at runtime by specifying a builtin policy on the boot command line
or by loading a custom policy.

This patch defines a build time policy, which verifies kernel modules,
firmware, kexec image, and/or the IMA policy signatures.  This build time
policy is automatically enabled at runtime and persists after loading a
custom policy.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>
This commit is contained in:
Mimi Zohar 2018-07-13 14:06:01 -04:00 committed by James Morris
parent fed2512a7c
commit ef96837b0d
2 changed files with 101 additions and 3 deletions
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58
security/integrity/ima/Kconfig
View File

@ -156,6 +156,64 @@ config IMA_APPRAISE
<http://linux-ima.sourceforge.net>
If unsure, say N.
config IMA_APPRAISE_BUILD_POLICY
bool "IMA build time configured policy rules"
depends on IMA_APPRAISE && INTEGRITY_ASYMMETRIC_KEYS
default n
help
This option defines an IMA appraisal policy at build time, which
is enforced at run time without having to specify a builtin
policy name on the boot command line. The build time appraisal
policy rules persist after loading a custom policy.
Depending on the rules configured, this policy may require kernel
modules, firmware, the kexec kernel image, and/or the IMA policy
to be signed. Unsigned files might prevent the system from
booting or applications from working properly.
config IMA_APPRAISE_REQUIRE_FIRMWARE_SIGS
bool "Appraise firmware signatures"
depends on IMA_APPRAISE_BUILD_POLICY
default n
help
This option defines a policy requiring all firmware to be signed,
including the regulatory.db. If both this option and
CFG80211_REQUIRE_SIGNED_REGDB are enabled, then both signature
verification methods are necessary.
config IMA_APPRAISE_REQUIRE_KEXEC_SIGS
bool "Appraise kexec kernel image signatures"
depends on IMA_APPRAISE_BUILD_POLICY
default n
help
Enabling this rule will require all kexec'ed kernel images to
be signed and verified by a public key on the trusted IMA
keyring.
Kernel image signatures can not be verified by the original
kexec_load syscall. Enabling this rule will prevent its
usage.
config IMA_APPRAISE_REQUIRE_MODULE_SIGS
bool "Appraise kernel modules signatures"
depends on IMA_APPRAISE_BUILD_POLICY
default n
help
Enabling this rule will require all kernel modules to be signed
and verified by a public key on the trusted IMA keyring.
Kernel module signatures can only be verified by IMA-appraisal,
via the finit_module syscall. Enabling this rule will prevent
the usage of the init_module syscall.
config IMA_APPRAISE_REQUIRE_POLICY_SIGS
bool "Appraise IMA policy signature"
depends on IMA_APPRAISE_BUILD_POLICY
default n
help
Enabling this rule will require the IMA policy to be signed and
and verified by a key on the trusted IMA keyring.
config IMA_APPRAISE_BOOTPARAM
bool "ima_appraise boot parameter"
depends on IMA_APPRAISE

46
security/integrity/ima/ima_policy.c
View File

@ -49,6 +49,7 @@
int ima_policy_flag;
static int temp_ima_appraise;
static int build_ima_appraise __ro_after_init;
#define MAX_LSM_RULES 6
enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
@ -162,6 +163,25 @@ static struct ima_rule_entry default_appraise_rules[] __ro_after_init = {
#endif
};
static struct ima_rule_entry build_appraise_rules[] __ro_after_init = {
#ifdef CONFIG_IMA_APPRAISE_REQUIRE_MODULE_SIGS
{.action = APPRAISE, .func = MODULE_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
#endif
#ifdef CONFIG_IMA_APPRAISE_REQUIRE_FIRMWARE_SIGS
{.action = APPRAISE, .func = FIRMWARE_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
#endif
#ifdef CONFIG_IMA_APPRAISE_REQUIRE_KEXEC_SIGS
{.action = APPRAISE, .func = KEXEC_KERNEL_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
#endif
#ifdef CONFIG_IMA_APPRAISE_REQUIRE_POLICY_SIGS
{.action = APPRAISE, .func = POLICY_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
#endif
};
static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
{.action = APPRAISE, .func = MODULE_CHECK,
.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
@ -435,7 +455,7 @@ void ima_update_policy_flag(void)
ima_policy_flag |= entry->action;
}
ima_appraise |= temp_ima_appraise;
ima_appraise |= (build_ima_appraise | temp_ima_appraise);
if (!ima_appraise)
ima_policy_flag &= ~IMA_APPRAISE;
}
@ -488,8 +508,8 @@ void __init ima_init_policy(void)
}
/*
* Insert the appraise rules requiring file signatures, prior to
* any other appraise rules.
* Insert the builtin "secure_boot" policy 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);
@ -497,6 +517,26 @@ void __init ima_init_policy(void)
ima_appraise_flag(secure_boot_rules[i].func);
}
/*
* Insert the build time appraise rules requiring file signatures
* for both the initial and custom policies, prior to other appraise
* rules.
*/
for (i = 0; i < ARRAY_SIZE(build_appraise_rules); i++) {
struct ima_rule_entry *entry;
if (!secure_boot_entries)
list_add_tail(&build_appraise_rules[i].list,
&ima_default_rules);
entry = kmemdup(&build_appraise_rules[i], sizeof(*entry),
GFP_KERNEL);
if (entry)
list_add_tail(&entry->list, &ima_policy_rules);
build_ima_appraise |=
ima_appraise_flag(build_appraise_rules[i].func);
}
for (i = 0; i < appraise_entries; i++) {
list_add_tail(&default_appraise_rules[i].list,
&ima_default_rules);