kexec_load: Disable at runtime if the kernel is locked down

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: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Acked-by: Dave Young <dyoung@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
cc: kexec@lists.infradead.org
Signed-off-by: James Morris <jmorris@namei.org>

3 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/security.h b/include/linux/security.h
index e5dd446ef35b..b607a8ac97fe 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -105,6 +105,7 @@ enum lockdown_reason {
         LOCKDOWN_NONE,
         LOCKDOWN_MODULE_SIGNATURE,
         LOCKDOWN_DEV_MEM,
+        LOCKDOWN_KEXEC,
         LOCKDOWN_INTEGRITY_MAX,
         LOCKDOWN_CONFIDENTIALITY_MAX,
 };
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 1b018f1a6e0d..bc933c0db9bf 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -206,6 +206,14 @@ static inline int kexec_load_check(unsigned long nr_segments,
                 return result;
 
         /*
+         * kexec can be used to circumvent module loading restrictions, so
+         * prevent loading in that case
+         */
+        result = security_locked_down(LOCKDOWN_KEXEC);
+        if (result)
+                return result;
+
+        /*
          * Verify we have a legal set of flags
          * This leaves us room for future extensions.
          */
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 240ecaa10a1d..aaf30ad351f9 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -20,6 +20,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
         [LOCKDOWN_NONE] = "none",
         [LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",
         [LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port",
+        [LOCKDOWN_KEXEC] = "kexec of unsigned images",
         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };