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kumquat-buildroot/boot/grub2/0038-efi-Use-grub_is_lockdown-instead-of-hardcoding-a-dis.patch
Stefan Sørensen 1bad507220 boot/grub2: Backport 2021/03/02 securify fixes 
Details: https://lists.gnu.org/archive/html/grub-devel/2021-03/msg00007.html

As detailed in commit 7e64a050fb, it is
difficult to utilize the upstream patches directly, so a number of
patches include changes to generated files so that we don't need invoke
the gentpl.py script.

In addition to the security fixes, these required patches has been
backported:

  f76a27996 efi: Make shim_lock GUID and protocol type public
  04ae030d0 efi: Return grub_efi_status_t from grub_efi_get_variable()
  ac5c93675 efi: Add a function to read EFI variables with attributes
  d7e54b2e5 efi: Add secure boot detection

The following security issues are fixed:

CVE-2020-14372 grub2: The acpi command allows privileged user to load crafted
               ACPI tables when Secure Boot is enabled
CWE-184
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

GRUB2 enables the use of the command acpi even when Secure Boot is signaled by
the firmware. An attacker with local root privileges to can drop a small SSDT
in /boot/efi and modify grub.cfg to instruct grub to load said SSDT. The SSDT
then gets run by the kernel and it overwrites the kernel lock down configuration
enabling the attacker to load unsigned kernel modules and kexec unsigned code.

Reported-by: Máté Kukri

*******************************************************************************

CVE-2020-25632 grub2: Use-after-free in rmmod command
CWE-416
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

The rmmod implementation for GRUB2 is flawed, allowing an attacker to unload
a module used as dependency without checking if any other dependent module is
still loaded. This leads to an use-after-free scenario possibly allowing an
attacker to execute arbitrary code and by-pass Secure Boot protections.

Reported-by: Chris Coulson (Canonical)

*******************************************************************************

CVE-2020-25647 grub2: Out-of-bound write in grub_usb_device_initialize()
CWE-787
6.9/CVSS:3.1/AV:P/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

grub_usb_device_initialize() is called to handle USB device initialization. It
reads out the descriptors it needs from the USB device and uses that data to
fill in some USB data structures. grub_usb_device_initialize() performs very
little bounds checking and simply assumes the USB device provides sane values.
This behavior can trigger memory corruption. If properly exploited, this would
lead to arbitrary code execution allowing the attacker to by-pass Secure Boot
mechanism.

Reported-by: Joseph Tartaro (IOActive) and Ilja van Sprundel (IOActive)

*******************************************************************************

CVE-2020-27749 grub2: Stack buffer overflow in grub_parser_split_cmdline
CWE-121
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

grub_parser_split_cmdline() expands variable names present in the supplied
command line in to their corresponding variable contents and uses a 1kB stack
buffer for temporary storage without sufficient bounds checking. If the
function is called with a command line that references a variable with a
sufficiently large payload, it is possible to overflow the stack buffer,
corrupt the stack frame and control execution. An attacker may use this to
circumvent Secure Boot protections.

Reported-by: Chris Coulson (Canonical)

*******************************************************************************

CVE-2020-27779 grub2: The cutmem command allows privileged user to remove
               memory regions when Secure Boot is enabled
CWE-285
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

The GRUB2's cutmem command does not honor Secure Boot locking. This allows an
privileged attacker to remove address ranges from memory creating an
opportunity to circumvent Secure Boot protections after proper triage about
grub's memory layout.

Reported-by: Teddy Reed

*******************************************************************************

CVE-2021-3418 - grub2: GRUB 2.05 reintroduced CVE-2020-15705
CWE-281
6.4/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

The GRUB2 upstream reintroduced the CVE-2020-15705. This refers to a distro
specific flaw which made upstream in the mentioned version.

If certificates that signed GRUB2 are installed into db, GRUB2 can be booted
directly. It will then boot any kernel without signature validation. The booted
kernel will think it was booted in Secure Boot mode and will implement lock
down, yet it could have been tampered.

This flaw only affects upstream and distributions using the shim_lock verifier.

Reported-by: Dimitri John Ledkov (Canonical)

*******************************************************************************

CVE-2021-20225 grub2: Heap out-of-bounds write in short form option parser
CWE-787
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

The option parser in GRUB2 allows an attacker to write past the end of
a heap-allocated buffer by calling certain commands with a large number
of specific short forms of options.

Reported-by: Daniel Axtens (IBM)

*******************************************************************************

CVE-2021-20233 grub2: Heap out-of-bound write due to mis-calculation of
               space required for quoting
CWE-787
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

There's a flaw on GRUB2 menu rendering code setparam_prefix() in the menu
rendering code performs a length calculation on the assumption that expressing
a quoted single quote will require 3 characters, while it actually requires
4 characters. This allow an attacker to corrupt memory by one byte for each
quote in the input.

Reported-by: Daniel Axtens (IBM)

*******************************************************************************

Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
2021-03-14 08:24:24 +01:00

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From 8f73052885892bc0dbc01e297f79d7cf4925e491 Mon Sep 17 00:00:00 2001
From: Javier Martinez Canillas <javierm@redhat.com>
Date: Mon, 28 Sep 2020 20:08:33 +0200
Subject: [PATCH] efi: Use grub_is_lockdown() instead of hardcoding a disabled
modules list
Now the GRUB can check if it has been locked down and this can be used to
prevent executing commands that can be utilized to circumvent the UEFI
Secure Boot mechanisms. So, instead of hardcoding a list of modules that
have to be disabled, prevent the usage of commands that can be dangerous.
This not only allows the commands to be disabled on other platforms, but
also properly separate the concerns. Since the shim_lock verifier logic
should be only about preventing to run untrusted binaries and not about
defining these kind of policies.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
---
docs/grub.texi | 15 +++++++++------
grub-core/commands/i386/wrmsr.c | 5 +++--
grub-core/commands/iorw.c | 19 ++++++++++---------
grub-core/commands/memrw.c | 19 ++++++++++---------
grub-core/kern/efi/sb.c | 41 -----------------------------------------
5 files changed, 32 insertions(+), 67 deletions(-)
diff --git a/docs/grub.texi b/docs/grub.texi
index bdbb329..bbe60a4 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -5256,6 +5256,9 @@ only applies to the particular cpu/core/thread that runs the command.
Also, if you specify a reserved or unimplemented MSR address, it will
cause a general protection exception (which is not currently being handled)
and the system will reboot.
+
+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
+ This is done to prevent subverting various security mechanisms.
@end deffn
@node xen_hypervisor
@@ -5752,12 +5755,12 @@ boot and the shim. This functionality is provided by the shim_lock verifier. It
is built into the @file{core.img} and is registered if the UEFI secure boot is
enabled.
-All modules not stored in the @file{core.img} and the ACPI tables for the
-@command{acpi} command have to be signed, e.g. using PGP. Additionally, the
-@command{iorw}, the @command{memrw} and the @command{wrmsr} commands are
-prohibited if the UEFI secure boot is enabled. This is done due to
-security reasons. All above mentioned requirements are enforced by the
-shim_lock verifier logic.
+All GRUB modules not stored in the @file{core.img}, OS kernels, ACPI tables,
+Device Trees, etc. have to be signed, e.g, using PGP. Additionally, the commands
+that can be used to subvert the UEFI secure boot mechanism, such as @command{iorw}
+and @command{memrw} will not be available when the UEFI secure boot is enabled.
+This is done for security reasons and are enforced by the GRUB Lockdown mechanism
+(@pxref{Lockdown}).
@node Measured Boot
@section Measuring boot components
diff --git a/grub-core/commands/i386/wrmsr.c b/grub-core/commands/i386/wrmsr.c
index 9c5e510..56a29c2 100644
--- a/grub-core/commands/i386/wrmsr.c
+++ b/grub-core/commands/i386/wrmsr.c
@@ -24,6 +24,7 @@
#include <grub/env.h>
#include <grub/command.h>
#include <grub/extcmd.h>
+#include <grub/lockdown.h>
#include <grub/i18n.h>
#include <grub/i386/cpuid.h>
#include <grub/i386/wrmsr.h>
@@ -83,8 +84,8 @@ grub_cmd_msr_write (grub_command_t cmd __attribute__ ((unused)), int argc, char
GRUB_MOD_INIT(wrmsr)
{
- cmd_write = grub_register_command ("wrmsr", grub_cmd_msr_write, N_("ADDR VALUE"),
- N_("Write a value to a CPU model specific register."));
+ cmd_write = grub_register_command_lockdown ("wrmsr", grub_cmd_msr_write, N_("ADDR VALUE"),
+ N_("Write a value to a CPU model specific register."));
}
GRUB_MOD_FINI(wrmsr)
diff --git a/grub-core/commands/iorw.c b/grub-core/commands/iorw.c
index a0c164e..584baec 100644
--- a/grub-core/commands/iorw.c
+++ b/grub-core/commands/iorw.c
@@ -23,6 +23,7 @@
#include <grub/env.h>
#include <grub/cpu/io.h>
#include <grub/i18n.h>
+#include <grub/lockdown.h>
GRUB_MOD_LICENSE ("GPLv3+");
@@ -131,17 +132,17 @@ GRUB_MOD_INIT(memrw)
N_("PORT"), N_("Read 32-bit value from PORT."),
options);
cmd_write_byte =
- grub_register_command ("outb", grub_cmd_write,
- N_("PORT VALUE [MASK]"),
- N_("Write 8-bit VALUE to PORT."));
+ grub_register_command_lockdown ("outb", grub_cmd_write,
+ N_("PORT VALUE [MASK]"),
+ N_("Write 8-bit VALUE to PORT."));
cmd_write_word =
- grub_register_command ("outw", grub_cmd_write,
- N_("PORT VALUE [MASK]"),
- N_("Write 16-bit VALUE to PORT."));
+ grub_register_command_lockdown ("outw", grub_cmd_write,
+ N_("PORT VALUE [MASK]"),
+ N_("Write 16-bit VALUE to PORT."));
cmd_write_dword =
- grub_register_command ("outl", grub_cmd_write,
- N_("ADDR VALUE [MASK]"),
- N_("Write 32-bit VALUE to PORT."));
+ grub_register_command_lockdown ("outl", grub_cmd_write,
+ N_("ADDR VALUE [MASK]"),
+ N_("Write 32-bit VALUE to PORT."));
}
GRUB_MOD_FINI(memrw)
diff --git a/grub-core/commands/memrw.c b/grub-core/commands/memrw.c
index 98769ea..d401a6d 100644
--- a/grub-core/commands/memrw.c
+++ b/grub-core/commands/memrw.c
@@ -22,6 +22,7 @@
#include <grub/extcmd.h>
#include <grub/env.h>
#include <grub/i18n.h>
+#include <grub/lockdown.h>
GRUB_MOD_LICENSE ("GPLv3+");
@@ -133,17 +134,17 @@ GRUB_MOD_INIT(memrw)
N_("ADDR"), N_("Read 32-bit value from ADDR."),
options);
cmd_write_byte =
- grub_register_command ("write_byte", grub_cmd_write,
- N_("ADDR VALUE [MASK]"),
- N_("Write 8-bit VALUE to ADDR."));
+ grub_register_command_lockdown ("write_byte", grub_cmd_write,
+ N_("ADDR VALUE [MASK]"),
+ N_("Write 8-bit VALUE to ADDR."));
cmd_write_word =
- grub_register_command ("write_word", grub_cmd_write,
- N_("ADDR VALUE [MASK]"),
- N_("Write 16-bit VALUE to ADDR."));
+ grub_register_command_lockdown ("write_word", grub_cmd_write,
+ N_("ADDR VALUE [MASK]"),
+ N_("Write 16-bit VALUE to ADDR."));
cmd_write_dword =
- grub_register_command ("write_dword", grub_cmd_write,
- N_("ADDR VALUE [MASK]"),
- N_("Write 32-bit VALUE to ADDR."));
+ grub_register_command_lockdown ("write_dword", grub_cmd_write,
+ N_("ADDR VALUE [MASK]"),
+ N_("Write 32-bit VALUE to ADDR."));
}
GRUB_MOD_FINI(memrw)
diff --git a/grub-core/kern/efi/sb.c b/grub-core/kern/efi/sb.c
index ce3b7f6..5d7210a 100644
--- a/grub-core/kern/efi/sb.c
+++ b/grub-core/kern/efi/sb.c
@@ -30,9 +30,6 @@
static grub_efi_guid_t shim_lock_guid = GRUB_EFI_SHIM_LOCK_GUID;
-/* List of modules which cannot be loaded if UEFI secure boot mode is enabled. */
-static const char * const disabled_mods[] = {"iorw", "memrw", NULL};
-
/*
* Determine whether we're in secure boot mode.
*
@@ -121,53 +118,15 @@ shim_lock_verifier_init (grub_file_t io __attribute__ ((unused)),
void **context __attribute__ ((unused)),
enum grub_verify_flags *flags)
{
- const char *b, *e;
- int i;
-
*flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
switch (type & GRUB_FILE_TYPE_MASK)
{
- case GRUB_FILE_TYPE_GRUB_MODULE:
- /* Establish GRUB module name. */
- b = grub_strrchr (io->name, '/');
- e = grub_strrchr (io->name, '.');
-
- b = b ? (b + 1) : io->name;
- e = e ? e : io->name + grub_strlen (io->name);
- e = (e > b) ? e : io->name + grub_strlen (io->name);
-
- for (i = 0; disabled_mods[i]; i++)
- if (!grub_strncmp (b, disabled_mods[i], grub_strlen (b) - grub_strlen (e)))
- {
- grub_error (GRUB_ERR_ACCESS_DENIED,
- N_("module cannot be loaded in UEFI secure boot mode: %s"),
- io->name);
- return GRUB_ERR_ACCESS_DENIED;
- }
-
- /* Fall through. */
-
- case GRUB_FILE_TYPE_ACPI_TABLE:
- case GRUB_FILE_TYPE_DEVICE_TREE_IMAGE:
- *flags = GRUB_VERIFY_FLAGS_DEFER_AUTH;
-
- return GRUB_ERR_NONE;
-
case GRUB_FILE_TYPE_LINUX_KERNEL:
case GRUB_FILE_TYPE_MULTIBOOT_KERNEL:
case GRUB_FILE_TYPE_BSD_KERNEL:
case GRUB_FILE_TYPE_XNU_KERNEL:
case GRUB_FILE_TYPE_PLAN9_KERNEL:
- for (i = 0; disabled_mods[i]; i++)
- if (grub_dl_get (disabled_mods[i]))
- {
- grub_error (GRUB_ERR_ACCESS_DENIED,
- N_("cannot boot due to dangerous module in memory: %s"),
- disabled_mods[i]);
- return GRUB_ERR_ACCESS_DENIED;
- }
-
*flags = GRUB_VERIFY_FLAGS_SINGLE_CHUNK;
/* Fall through. */
--
2.14.2
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