grub2/0001-linuxefi-fail-kernel-validation-without-shim-protoco.patch

From 1b4f4b2f5cd9b804a5bb66861b659d05d9a4f35a Mon Sep 17 00:00:00 2001
From: Michael Chang <mchang@suse.com>
Date: Mon, 17 Aug 2020 17:09:01 +0800
Subject: [PATCH 1/2] linuxefi: fail kernel validation without shim protocol.

If certificates that signed grub are installed into db, grub can be
booted directly. It will then boot any kernel without signature
validation. The booted kernel will think it was booted in secureboot
mode and will implement lockdown, yet it could have been tampered.

This version of the patch skips calling verification, when booted
without secureboot.

CVE-2020-15705

Reported-by: Mathieu Trudel-Lapierre <cyphermox@ubuntu.com>
Also-by: Dimitri John Ledkov <xnox@ubuntu.com>
Signed-off-by: Michael Chang <mchang@suse.com>
---
 grub-core/loader/i386/efi/linux.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/grub-core/loader/i386/efi/linux.c b/grub-core/loader/i386/efi/linux.c
index 61b2d5177..8017e8c05 100644
--- a/grub-core/loader/i386/efi/linux.c
+++ b/grub-core/loader/i386/efi/linux.c
@@ -172,6 +172,23 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
       goto fail;
     }
 
+  if (grub_efi_secure_boot())
+    {
+      grub_dl_t mod;
+
+      mod = grub_dl_get ("shim_lock");
+      if (!mod)
+	{
+	  grub_error (GRUB_ERR_ACCESS_DENIED, N_("shim_lock module is not loaded"));
+	  goto fail;
+	}
+      if (!grub_dl_is_persistent (mod))
+	{
+	  grub_error (GRUB_ERR_ACCESS_DENIED, N_("shim_lock protocol is not available"));
+	  goto fail;
+	}
+    }
+
   file = grub_file_open (argv[0], GRUB_FILE_TYPE_LINUX_KERNEL);
   if (! file)
     goto fail;
-- 
2.26.2