From b01dc9aaedb5a5e91e2ca10748fce65406d657c0 Mon Sep 17 00:00:00 2001
From: Fedora Ninjas <grub2-owner@fedoraproject.org>
Date: Mon, 10 Aug 2020 14:54:34 +0800
Subject: [PATCH 7/7] 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. And is indented with gnu ident.

CVE-2020-15705

Reported-by: Mathieu Trudel-Lapierre <cyphermox@ubuntu.com>
Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
Signed-off-by: Baogen Shang <baogen.shang@windriver.com.cn>
---
 grub-core/loader/arm64/linux.c    | 12 ++++++++----
 grub-core/loader/efi/linux.c      |  1 +
 grub-core/loader/i386/efi/linux.c | 13 ++++++++-----
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index 8791b35..a18c487 100644
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -383,11 +383,15 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
 
   grub_dprintf ("linux", "kernel @ %p\n", kernel_addr);
 
-  rc = grub_linuxefi_secure_validate (kernel_addr, kernel_size);
-  if (rc < 0)
+  if (grub_efi_secure_boot ())
     {
-      grub_error (GRUB_ERR_INVALID_COMMAND, N_("%s has invalid signature"), argv[0]);
-      goto fail;
+      rc = grub_linuxefi_secure_validate (kernel_addr, kernel_size);
+      if (rc <= 0)
+	{
+	  grub_error (GRUB_ERR_INVALID_COMMAND,
+		      N_("%s has invalid signature"), argv[0]);
+	  goto fail;
+	}
     }
 
   pe = (void *)((unsigned long)kernel_addr + lh.hdr_offset);
diff --git a/grub-core/loader/efi/linux.c b/grub-core/loader/efi/linux.c
index e09f824..927d89a 100644
--- a/grub-core/loader/efi/linux.c
+++ b/grub-core/loader/efi/linux.c
@@ -33,6 +33,7 @@ struct grub_efi_shim_lock
 };
 typedef struct grub_efi_shim_lock grub_efi_shim_lock_t;
 
+// Returns 1 on success, -1 on error, 0 when not available
 int
 grub_linuxefi_secure_validate (void *data, grub_uint32_t size)
 {
diff --git a/grub-core/loader/i386/efi/linux.c b/grub-core/loader/i386/efi/linux.c
index e5b2736..e613115 100644
--- a/grub-core/loader/i386/efi/linux.c
+++ b/grub-core/loader/i386/efi/linux.c
@@ -301,12 +301,15 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
       goto fail;
     }
 
-  rc = grub_linuxefi_secure_validate (kernel, filelen);
-  if (rc < 0)
+  if (grub_efi_secure_boot ())
     {
-      grub_error (GRUB_ERR_INVALID_COMMAND, N_("%s has invalid signature"),
-		  argv[0]);
-      goto fail;
+      rc = grub_linuxefi_secure_validate (kernel, filelen);
+      if (rc <= 0)
+	{
+	  grub_error (GRUB_ERR_INVALID_COMMAND,
+		      N_("%s has invalid signature"), argv[0]);
+	  goto fail;
+	}
     }
 
   lh = (struct linux_i386_kernel_header *)kernel;
-- 
1.8.3.1