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From 8a2a8d6021d926f00c5f85dab2d66f4ed8be86a2 Mon Sep 17 00:00:00 2001
From: Colin Watson <cjwatson@ubuntu.com>
Date: Tue, 23 Oct 2012 10:40:49 -0400
Subject: [PATCH] Don't allow insmod when secure boot is enabled.

Hi,

Fedora's patch to forbid insmod in UEFI Secure Boot environments is fine
as far as it goes.  However, the insmod command is not the only way that
modules can be loaded.  In particular, the 'normal' command, which
implements the usual GRUB menu and the fully-featured command prompt,
will implicitly load commands not currently loaded into memory.  This
permits trivial Secure Boot violations by writing commands implementing
whatever you want to do and pointing $prefix at the malicious code.

I'm currently test-building this patch (replacing your current
grub-2.00-no-insmod-on-sb.patch), but this should be more correct.  It
moves the check into grub_dl_load_file.
---
 grub-core/kern/dl.c      | 17 +++++++++++++++++
 grub-core/kern/efi/efi.c | 28 ++++++++++++++++++++++++++++
 include/grub/efi/efi.h   |  1 +
 3 files changed, 46 insertions(+)

diff --git a/grub-core/kern/dl.c b/grub-core/kern/dl.c
index a498682..2578fce 100644
--- a/grub-core/kern/dl.c
+++ b/grub-core/kern/dl.c
@@ -43,6 +43,10 @@
 #include <sys/mman.h>
 #endif
 
+#ifdef GRUB_MACHINE_EFI
+#include <grub/efi/efi.h>
+#endif
+
 
 
 #pragma GCC diagnostic ignored "-Wcast-align"
@@ -721,6 +725,19 @@ grub_dl_load_file (const char *filename)
   void *core = 0;
   grub_dl_t mod = 0;
 
+#ifdef GRUB_MACHINE_EFI
+  if (grub_efi_secure_boot ())
+    {
+#if 0
+      /* This is an error, but grub2-mkconfig still generates a pile of
+       * insmod commands, so emitting it would be mostly just obnoxious. */
+      grub_error (GRUB_ERR_ACCESS_DENIED,
+		  "Secure Boot forbids loading module from %s", filename);
+#endif
+      return 0;
+    }
+#endif
+
   file = grub_file_open (filename);
   if (! file)
     return 0;
diff --git a/grub-core/kern/efi/efi.c b/grub-core/kern/efi/efi.c
index 820968f..ad7aa8d 100644
--- a/grub-core/kern/efi/efi.c
+++ b/grub-core/kern/efi/efi.c
@@ -259,6 +259,34 @@ grub_efi_set_variable(const char *var, const grub_efi_guid_t *guid,
   return grub_error (GRUB_ERR_IO, "could not set EFI variable `%s'", var);
 }
 
+grub_efi_boolean_t
+grub_efi_secure_boot (void)
+{
+  grub_efi_guid_t efi_var_guid = GRUB_EFI_GLOBAL_VARIABLE_GUID;
+  grub_size_t datasize;
+  char *secure_boot = NULL;
+  char *setup_mode = NULL;
+  grub_efi_boolean_t ret = 0;
+
+  secure_boot = grub_efi_get_variable("SecureBoot", &efi_var_guid, &datasize);
+
+  if (datasize != 1 || !secure_boot)
+    goto out;
+
+  setup_mode = grub_efi_get_variable("SetupMode", &efi_var_guid, &datasize);
+
+  if (datasize != 1 || !setup_mode)
+    goto out;
+
+  if (*secure_boot && !*setup_mode)
+    ret = 1;
+
+ out:
+  grub_free (secure_boot);
+  grub_free (setup_mode);
+  return ret;
+}
+
 #pragma GCC diagnostic ignored "-Wcast-align"
 
 /* Search the mods section from the PE32/PE32+ image. This code uses
diff --git a/include/grub/efi/efi.h b/include/grub/efi/efi.h
index 9370fd5..a000c38 100644
--- a/include/grub/efi/efi.h
+++ b/include/grub/efi/efi.h
@@ -72,6 +72,7 @@ EXPORT_FUNC (grub_efi_set_variable) (const char *var,
 				     const grub_efi_guid_t *guid,
 				     void *data,
 				     grub_size_t datasize);
+grub_efi_boolean_t EXPORT_FUNC (grub_efi_secure_boot) (void);
 int
 EXPORT_FUNC (grub_efi_compare_device_paths) (const grub_efi_device_path_t *dp1,
 					     const grub_efi_device_path_t *dp2);
-- 
1.7.12.1