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>
Acked-by: Dave Young <dyoung@redhat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
Reviewed-by: James Morris <james.l.morris@oracle.com>
cc: kexec@lists.infradead.org
[bwh: Adjust context to apply after commit a210fd32a46b
 "kexec: add call to LSM hook in original kexec_load syscall"]

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0006-kexec-Disable-at-runtime-if-the-kernel-is-locked-dow.patch

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 68559808fdfa119411a3a0f0ee98e49d4ee3cfa3..8ea0ce31271f7de7836f8b7bf29a68bc9837af44 100644 (file)
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -207,6 +207,13 @@ static inline int kexec_load_check(unsigned long nr_segments,
        if (result < 0)
                return result;
 
+       /*
+        * kexec can be used to circumvent module loading restrictions, so
+        * prevent loading in that case
+        */
+       if (kernel_is_locked_down("kexec of unsigned images"))
+               return -EPERM;
+
        /*
         * Verify we have a legal set of flags
         * This leaves us room for future extensions.