[PATCH v5 2/5] ima: prevent kexec_load syscall based on runtime secureboot flag

[Nayna Jain]

From: Nayna Jain <na...@linux.ibm.com>

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 <na...@linux.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