kexec: Disable at runtime if the kernel is locked down

kexec permits the loading and execution of arbitrary code in ring 0, which
is something that lock-down is meant to prevent. It makes sense to disable
kexec in this situation.

This does not affect kexec_file_load() which can check for a signature on the
image to be booted.

Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0044-kexec-Disable-at-runtime-if-the-kernel-is-locked-dow.patch

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 980936a90ee6ea0a9f83c195277a7c0705a8bbaa..46de8e6b42f4b2ea076d0054352400d281bde48a 100644 (file)
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -193,6 +193,13 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
        if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
                return -EPERM;
 
+       /*
+        * kexec can be used to circumvent module loading restrictions, so
+        * prevent loading in that case
+        */
+       if (kernel_is_locked_down())
+               return -EPERM;
+
        /*
         * Verify we have a legal set of flags
         * This leaves us room for future extensions.