[PATCH] integrity: Do not load MOK and MOKx when secure boot be disabled

The security of Machine Owner Key (MOK) relies on secure boot. When
secure boot is disabled, EFI firmware will not verify binary code. Then
arbitrary efi binary code can modify MOK when rebooting.

This patch prevents MOK/MOKx be loaded when secure boot be disabled.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
 security/integrity/platform_certs/load_uefi.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/security/integrity/platform_certs/load_uefi.c b/security/integrity/platform_certs/load_uefi.c
index f290f78c3f30..08b6d12f99b4 100644
--- a/security/integrity/platform_certs/load_uefi.c
+++ b/security/integrity/platform_certs/load_uefi.c

@@ -6,6 +6,7 @@
 #include <linux/err.h>
 #include <linux/efi.h>
 #include <linux/slab.h>
+#include <linux/ima.h>
 #include <keys/asymmetric-type.h>
 #include <keys/system_keyring.h>
 #include "../integrity.h"

@@ -176,6 +177,10 @@ static int __init load_uefi_certs(void)
 		kfree(dbx);
 	}
 
+	/* the MOK/MOKx can not be trusted when secure boot is disabled */
+	if (!arch_ima_get_secureboot())
+		return 0;
+
 	mokx = get_cert_list(L"MokListXRT", &mok_var, &mokxsize, &status);
 	if (!mokx) {
 		if (status == EFI_NOT_FOUND)

-- 
2.26.2

Hi Joey,

On Sat, 2021-12-18 at 10:09 +0800, Lee, Chun-Yi wrote:

The security of Machine Owner Key (MOK) relies on secure boot. When
secure boot is disabled, EFI firmware will not verify binary code. Then
arbitrary efi binary code can modify MOK when rebooting.

This patch prevents MOK/MOKx be loaded when secure boot be disabled.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>

Sorry for the delay in testing this patch.  I got the booster Friday
and am still suffering from fever spikes, chills, and headaches. The
kexec selftest might need to be updated as well.

thanks,

Mimi

On Sat, 2021-12-18 at 10:09 +0800, Lee, Chun-Yi wrote:

The security of Machine Owner Key (MOK) relies on secure boot. When
secure boot is disabled, EFI firmware will not verify binary code. Then
arbitrary efi binary code can modify MOK when rebooting.

This patch prevents MOK/MOKx be loaded when secure boot be disabled.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>

Thanks, Joey!

This patch is now queued in the next-integrity-testing branch waiting
further review/tags.

Mimi

Hi Mimi,

On Tue, Dec 21, 2021 at 06:28:31PM -0500, Mimi Zohar wrote:

On Sat, 2021-12-18 at 10:09 +0800, Lee, Chun-Yi wrote:

quoted

The security of Machine Owner Key (MOK) relies on secure boot. When
secure boot is disabled, EFI firmware will not verify binary code. Then
arbitrary efi binary code can modify MOK when rebooting.

This patch prevents MOK/MOKx be loaded when secure boot be disabled.

Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>

Thanks, Joey!

This patch is now queued in the next-integrity-testing branch waiting
further review/tags.

Mimi

Thanks for your review!
Joey Lee