[PATCH] ima: force signature verification when CONFIG_KEXEC_SIG is configured

[Coiby Xu]

Currently, an unsigned kernel could be kexec'ed when IMA arch specific
policy is configured unless lockdown is enabled. Enforce kernel
signature verification check in the kexec_file_load syscall when IMA
arch specific policy is configured.

Fixes: 99d5cadfde2b ("kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE")
Reported-by: Mimi Zohar <zohar at linux.ibm.com>
Suggested-by: Mimi Zohar <zohar at linux.ibm.com>
Signed-off-by: Coiby Xu <coxu at redhat.com>
---
 include/linux/kexec.h            |  3 +++
 kernel/kexec_file.c              | 11 ++++++++++-
 security/integrity/ima/ima_efi.c |  3 +++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index ce6536f1d269..4b8e8d5bcea9 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -134,6 +134,9 @@ typedef int (kexec_cleanup_t)(void *loader_data);
 #ifdef CONFIG_KEXEC_SIG
 typedef int (kexec_verify_sig_t)(const char *kernel_buf,
 				 unsigned long kernel_len);
+void set_kexec_sig_enforced(void);
+#else
+static inline void set_kexec_sig_enforced(void) {}
 #endif
 
 struct kexec_file_ops {
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 145321a5e798..f9261c07b048 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -29,6 +29,15 @@
 #include <linux/vmalloc.h>
 #include "kexec_internal.h"
 
+#ifdef CONFIG_KEXEC_SIG
+static bool sig_enforce = IS_ENABLED(CONFIG_KEXEC_SIG_FORCE);
+
+void set_kexec_sig_enforced(void)
+{
+	sig_enforce = true;
+}
+#endif
+
 static int kexec_calculate_store_digests(struct kimage *image);
 
 /*
@@ -159,7 +168,7 @@ kimage_validate_signature(struct kimage *image)
 					   image->kernel_buf_len);
 	if (ret) {
 
-		if (IS_ENABLED(CONFIG_KEXEC_SIG_FORCE)) {
+		if (sig_enforce) {
 			pr_notice("Enforced kernel signature verification failed (%d).\n", ret);
 			return ret;
 		}
diff --git a/security/integrity/ima/ima_efi.c b/security/integrity/ima/ima_efi.c
index 71786d01946f..ae3fe4cb8d86 100644
--- a/security/integrity/ima/ima_efi.c
+++ b/security/integrity/ima/ima_efi.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2018 IBM Corporation
  */
 #include <linux/efi.h>
+#include <linux/kexec.h>
 #include <linux/module.h>
 #include <linux/ima.h>
 #include <asm/efi.h>
@@ -67,6 +68,8 @@ const char * const *arch_get_ima_policy(void)
 	if (IS_ENABLED(CONFIG_IMA_ARCH_POLICY) && arch_ima_get_secureboot()) {
 		if (IS_ENABLED(CONFIG_MODULE_SIG))
 			set_module_sig_enforced();
+		if (IS_ENABLED(CONFIG_KEXEC_SIG))
+			set_kexec_sig_enforced();
 		return sb_arch_rules;
 	}
 	return NULL;
-- 
2.35.3