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Date: Thu, 30 Jul 2020 13:48:41 +0200
From: "Jason A. Donenfeld" <>
Subject: UEFI SecureBoot bypass fixes rolled out to kernels below radar


I thought I should mention that yesterday's UEFI SecureBoot bypass
headlines neglected to mention the bugs I found over a month ago (with
the exception of Debian's announcement, which got some details wrong
initially but those have since been rectified).

It appears that Linux vendors are now releasing fixes for:

- CVE-2019-20908

- CVE-2020-15780

In the Red Hat Enterprise Linux 8 kernel sources, diffing yesterday's
release with the one from a few weeks prior, we see a patch for both of
these, which I've put at the bottom of this email.

It seems like mention of these was left out from the advisories that
were making news yesterday from Microsoft/Red Hat/etc, presumably
because there's no shiny logo and press release route with these
exploits, but rather just shoddy exploits and posted them here,
alongside patches on LKML.

But anyway, PSA: if you're scrambling to get your systems updated for
this, be sure to update your kernel in addition to GRUB2. This is more
than just a bootloader situation. And I'm sure we'll have plenty more
SecureBoot bypasses coming up too.


RHEL8 patch, which shipped yesterday:

diff -ru linux-4.18.0-193.13.2.el8_2/drivers/acpi/acpi_configfs.c linux-4.18.0-193.14.3.el8_2/drivers/acpi/acpi_configfs.c
--- linux-4.18.0-193.13.2.el8_2/drivers/acpi/acpi_configfs.c	2020-07-14 00:38:37.000000000 +0200
+++ linux-4.18.0-193.14.3.el8_2/drivers/acpi/acpi_configfs.c	2020-07-20 16:02:22.000000000 +0200
@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/configfs.h>
 #include <linux/acpi.h>
+#include <linux/kernel.h>

 #include "acpica/accommon.h"
 #include "acpica/actables.h"
@@ -31,7 +32,10 @@
 	const struct acpi_table_header *header = data;
 	struct acpi_table *table;
-	int ret;
+	int ret = kernel_is_locked_down("Modifying ACPI tables");
+	if (ret)
+		return ret;

 	table = container_of(cfg, struct acpi_table, cfg);

diff -ru linux-4.18.0-193.13.2.el8_2/drivers/firmware/efi/efi.c linux-4.18.0-193.14.3.el8_2/drivers/firmware/efi/efi.c
--- linux-4.18.0-193.13.2.el8_2/drivers/firmware/efi/efi.c	2020-07-14 00:38:37.000000000 +0200
+++ linux-4.18.0-193.14.3.el8_2/drivers/firmware/efi/efi.c	2020-07-20 16:02:22.000000000 +0200
@@ -31,6 +31,7 @@
 #include <linux/acpi.h>
 #include <linux/ucs2_string.h>
 #include <linux/memblock.h>
+#include <linux/kernel.h>

 #include <asm/early_ioremap.h>

@@ -245,6 +246,11 @@
 static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
 static int __init efivar_ssdt_setup(char *str)
+	int ret = kernel_is_locked_down("Modifying ACPI tables");
+	if (ret)
+		return ret;
 	if (strlen(str) < sizeof(efivar_ssdt))
 		memcpy(efivar_ssdt, str, strlen(str));

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