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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>
106 lines
4.1 KiB
Diff
106 lines
4.1 KiB
Diff
From 468a5699b249fe6816b4e7e86c5dc9d325c9b09e Mon Sep 17 00:00:00 2001
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From: Javier Martinez Canillas <javierm@redhat.com>
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Date: Wed, 24 Feb 2021 09:00:05 +0100
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Subject: [PATCH] commands: Restrict commands that can load BIOS or DT blobs
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when locked down
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There are some more commands that should be restricted when the GRUB is
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locked down. Following is the list of commands and reasons to restrict:
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* fakebios: creates BIOS-like structures for backward compatibility with
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existing OSes. This should not be allowed when locked down.
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* loadbios: reads a BIOS dump from storage and loads it. This action
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should not be allowed when locked down.
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* devicetree: loads a Device Tree blob and passes it to the OS. It replaces
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any Device Tree provided by the firmware. This also should
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not be allowed when locked down.
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Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
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---
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docs/grub.texi | 3 +++
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grub-core/commands/efi/loadbios.c | 16 ++++++++--------
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grub-core/loader/arm/linux.c | 6 +++---
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grub-core/loader/efi/fdt.c | 4 ++--
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4 files changed, 16 insertions(+), 13 deletions(-)
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diff --git a/docs/grub.texi b/docs/grub.texi
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index f2fe149..79f58c5 100644
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--- a/docs/grub.texi
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+++ b/docs/grub.texi
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@@ -4235,6 +4235,9 @@ hour, minute, and second unchanged.
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Load a device tree blob (.dtb) from a filesystem, for later use by a Linux
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kernel. Does not perform merging with any device tree supplied by firmware,
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but rather replaces it completely.
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+
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+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
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+ This is done to prevent subverting various security mechanisms.
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@ref{GNU/Linux}.
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@end deffn
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diff --git a/grub-core/commands/efi/loadbios.c b/grub-core/commands/efi/loadbios.c
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index d41d521..5c7725f 100644
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--- a/grub-core/commands/efi/loadbios.c
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+++ b/grub-core/commands/efi/loadbios.c
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@@ -205,14 +205,14 @@ static grub_command_t cmd_fakebios, cmd_loadbios;
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GRUB_MOD_INIT(loadbios)
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{
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- cmd_fakebios = grub_register_command ("fakebios", grub_cmd_fakebios,
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- 0, N_("Create BIOS-like structures for"
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- " backward compatibility with"
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- " existing OS."));
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-
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- cmd_loadbios = grub_register_command ("loadbios", grub_cmd_loadbios,
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- N_("BIOS_DUMP [INT10_DUMP]"),
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- N_("Load BIOS dump."));
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+ cmd_fakebios = grub_register_command_lockdown ("fakebios", grub_cmd_fakebios,
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+ 0, N_("Create BIOS-like structures for"
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+ " backward compatibility with"
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+ " existing OS."));
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+
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+ cmd_loadbios = grub_register_command_lockdown ("loadbios", grub_cmd_loadbios,
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+ N_("BIOS_DUMP [INT10_DUMP]"),
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+ N_("Load BIOS dump."));
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}
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GRUB_MOD_FINI(loadbios)
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diff --git a/grub-core/loader/arm/linux.c b/grub-core/loader/arm/linux.c
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index d70c174..ed23dc7 100644
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--- a/grub-core/loader/arm/linux.c
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+++ b/grub-core/loader/arm/linux.c
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@@ -493,9 +493,9 @@ GRUB_MOD_INIT (linux)
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0, N_("Load Linux."));
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cmd_initrd = grub_register_command ("initrd", grub_cmd_initrd,
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0, N_("Load initrd."));
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- cmd_devicetree = grub_register_command ("devicetree", grub_cmd_devicetree,
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- /* TRANSLATORS: DTB stands for device tree blob. */
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- 0, N_("Load DTB file."));
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+ cmd_devicetree = grub_register_command_lockdown ("devicetree", grub_cmd_devicetree,
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+ /* TRANSLATORS: DTB stands for device tree blob. */
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+ 0, N_("Load DTB file."));
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my_mod = mod;
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current_fdt = (const void *) grub_arm_firmware_get_boot_data ();
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machine_type = grub_arm_firmware_get_machine_type ();
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diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
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index ee9c559..003d07c 100644
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--- a/grub-core/loader/efi/fdt.c
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+++ b/grub-core/loader/efi/fdt.c
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@@ -165,8 +165,8 @@ static grub_command_t cmd_devicetree;
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GRUB_MOD_INIT (fdt)
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{
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cmd_devicetree =
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- grub_register_command ("devicetree", grub_cmd_devicetree, 0,
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- N_("Load DTB file."));
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+ grub_register_command_lockdown ("devicetree", grub_cmd_devicetree, 0,
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+ N_("Load DTB file."));
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}
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GRUB_MOD_FINI (fdt)
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--
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2.14.2
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