grub: fix CVE-2020-14372 and CVE-2020-27779

Fix issues with grub in secure boot mode where an attacker could circumvent
secure boot by using acpi and cutmem commands. Also include patches fixing
similar issues.

Most patches are backported directly from grub. One patch
(no-insmod-on-sb.patch) comes from Debian, as the upstream implementation is
too complicated to backport.

CVE-2020-14372 description (from NVD [1]):
A flaw was found in grub2 in versions prior to 2.06, where it incorrectly
enables the usage of the ACPI command when Secure Boot is enabled.
This flaw allows an attacker with privileged access to craft a Secondary
System Description Table (SSDT) containing code to overwrite the Linux
kernel lockdown variable content directly into memory. The table is
further loaded and executed by the kernel, defeating its Secure Boot
lockdown and allowing the attacker to load unsigned code. The highest
threat from this vulnerability is to data confidentiality and integrity,
as well as system availability.

CVE-2020-27779 description (from NVD [2]):
A flaw was found in grub2 in versions prior to 2.06. The cutmem command
does not honor secure boot locking allowing an privileged attacker to
remove address ranges from memory creating an opportunity to circumvent
SecureBoot protections after proper triage about grub's memory layout.
The highest threat from this vulnerability is to data confidentiality
and integrity as well as system availability.

[1] https://nvd.nist.gov/vuln/detail/CVE-2020-14372
[2] https://nvd.nist.gov/vuln/detail/CVE-2020-27779

(From OE-Core rev: da6c0f3cfc920cea57cd409b17303bf735ccd68d)

Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 107 insertions, 0 deletions

diff --git a/meta/recipes-bsp/grub/files/no-insmod-on-sb.patch b/meta/recipes-bsp/grub/files/no-insmod-on-sb.patch
new file mode 100644
index 0000000000..504352b4e3
--- /dev/null
+++ b/meta/recipes-bsp/grub/files/no-insmod-on-sb.patch
@@ -0,0 +1,107 @@
+From b5a6aa7d77439bfeb75f200abffe15c6f685c907 Mon Sep 17 00:00:00 2001
+From: Matthew Garrett <mjg@redhat.com>
+Date: Mon, 13 Jan 2014 12:13:09 +0000
+Subject: Don't permit loading modules on UEFI secure boot
+
+Author: Colin Watson <cjwatson@ubuntu.com>
+Origin: vendor, http://pkgs.fedoraproject.org/cgit/grub2.git/tree/grub-2.00-no-insmod-on-sb.patch
+Forwarded: no
+Last-Update: 2013-12-25
+
+Patch-Name: no-insmod-on-sb.patch
+
+Upstream-Status: Inappropriate [other, https://salsa.debian.org/grub-team/grub/-/blob/debian/2.04-20/debian/patches/no-insmod-on-sb.patch]
+
+Backport of a Debian (and Fedora) patch implementing a way to get secure boot status
+for CVE-2020-14372_4.patch. The upstream solution has too many dependencies to backport.
+Source: https://salsa.debian.org/grub-team/grub/-/blob/debian/2.04-20/debian/patches/no-insmod-on-sb.patch
+
+Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>
+---
+ grub-core/kern/dl.c      | 13 +++++++++++++
+ grub-core/kern/efi/efi.c | 28 ++++++++++++++++++++++++++++
+ include/grub/efi/efi.h   |  1 +
+ 3 files changed, 42 insertions(+)
+
+diff --git a/grub-core/kern/dl.c b/grub-core/kern/dl.c
+index 48eb5e7b6..074dfc3c6 100644
+--- a/grub-core/kern/dl.c
++++ b/grub-core/kern/dl.c
+@@ -38,6 +38,10 @@
+ #define GRUB_MODULES_MACHINE_READONLY
+ #endif
+ 
++#ifdef GRUB_MACHINE_EFI
++#include <grub/efi/efi.h>
++#endif
++
+ 
+ 
+ #pragma GCC diagnostic ignored "-Wcast-align"
+@@ -686,6 +690,15 @@ grub_dl_load_file (const char *filename)
+   void *core = 0;
+   grub_dl_t mod = 0;
+ 
++#ifdef GRUB_MACHINE_EFI
++  if (grub_efi_secure_boot ())
++    {
++      grub_error (GRUB_ERR_ACCESS_DENIED,
++                 "Secure Boot forbids loading module from %s", filename);
++      return 0;
++    }
++#endif
++
+   grub_boot_time ("Loading module %s", filename);
+ 
+   file = grub_file_open (filename, GRUB_FILE_TYPE_GRUB_MODULE);
+diff --git a/grub-core/kern/efi/efi.c b/grub-core/kern/efi/efi.c
+index 6e1ceb905..96204e39b 100644
+--- a/grub-core/kern/efi/efi.c
++++ b/grub-core/kern/efi/efi.c
+@@ -273,6 +273,34 @@ grub_efi_get_variable (const char *var, const grub_efi_guid_t *guid,
+   return NULL;
+ }
+ 
++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 e90e00dc4..a237952b3 100644
+--- a/include/grub/efi/efi.h
++++ b/include/grub/efi/efi.h
+@@ -82,6 +82,7 @@ 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);