[PATCH 04/27] kexec_load: Disable at runtime if the kernel is locked down

From: Matthew Garrett
Date: Mon Mar 25 2019 - 18:10:13 EST

From: Matthew Garrett <mjg59@xxxxxxxxxxxxx>

The kexec_load() syscall 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_load() in this situation.

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

Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Acked-by: Dave Young <dyoung@xxxxxxxxxx>
cc: kexec@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Matthew Garrett <matthewgarrett@xxxxxxxxxx>
kernel/kexec.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 68559808fdfa..8ea0ce31271f 100644
--- 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.