ima: prevent kexec_load syscall based on runtime secureboot flag

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.

[zohar@linux.ibm.com: add missing mesage on kexec_load failure]
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Peter Jones <pjones@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 13 insertions, 6 deletions

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 1b88d58e1325..df0b2ee49fa2 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -505,20 +505,26 @@ 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) {
+                if (IS_ENABLED(CONFIG_KEXEC_VERIFY_SIG)
+                    && arch_ima_get_secureboot()) {
+                        pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
+                        return -EACCES;
+                }
+
+                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 +532,8 @@ 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 */
                 }