[PATCH v2 2/6] ima: prevent kexec_load syscall based on runtime secureboot flag

Nayna Jain
2018-09-14T08:00:01Z

When CONFIG_KEXEC_VERIFY_SIG is enabled, the kexec_file_load syscall
requires the kexec'd kernel image to be signed. Distros are concerned
about totally disabling the kexec_load syscall. As a compromise, the
kexec_load syscall will only be disabled when CONFIG_KEXEC_VERIFY_SIG
is configured and the system is booted with secureboot enabled.

This patch disables the kexec_load syscall only for systems booted with
secureboot enabled.

Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
---
security/integrity/ima/ima_main.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index dce0a8a217bb..bdb6e5563d05 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -505,20 +505,24 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
*/
int ima_load_data(enum kernel_load_data_id id)
{
- bool sig_enforce;
+ bool ima_enforce, sig_enforce;

- if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
- return 0;
+ ima_enforce =
+ (ima_appraise & IMA_APPRAISE_ENFORCE) == IMA_APPRAISE_ENFORCE;

switch (id) {
case LOADING_KEXEC_IMAGE:
- if (ima_appraise & IMA_APPRAISE_KEXEC) {
+#ifdef CONFIG_KEXEC_VERIFY_SIG
+ if (arch_ima_get_secureboot())
+ return -EACCES;
+#endif
+ if (ima_enforce && (ima_appraise & IMA_APPRAISE_KEXEC)) {
pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
return -EACCES; /* INTEGRITY_UNKNOWN */
}
break;
case LOADING_FIRMWARE:
- if (ima_appraise & IMA_APPRAISE_FIRMWARE) {
+ if (ima_enforce && (ima_appraise & IMA_APPRAISE_FIRMWARE)) {
pr_err("Prevent firmware sysfs fallback loading.\n");
return -EACCES; /* INTEGRITY_UNKNOWN */
}
@@ -526,7 +530,8 @@ int ima_load_data(enum kernel_load_data_id id)
case LOADING_MODULE:
sig_enforce = is_module_sig_enforced();

- if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES)) {
+ if (ima_enforce && (!sig_enforce
+ && (ima_appraise & IMA_APPRAISE_MODULES))) {
pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
return -EACCES; /* INTEGRITY_UNKNOWN */
}
--
2.13.6