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ACPI: configfs: Disallow loading ACPI tables when locked down (CVE-2020-15780) 

This is not a problem for the Debian built binary packages as we do not
enable CONFIG_ACPI_CONFIGFS. Though this is in place in case at some
point this config option would be (unlikely) enabled or for custom
builds.
This commit is contained in:
Salvatore Bonaccorso 2020-08-29 14:14:51 +02:00
parent 046742d201
commit a91434eeb6
3 changed files with 47 additions and 0 deletions
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2
debian/changelog vendored
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@ -620,6 +620,8 @@ linux (4.19.142-1) UNRELEASED; urgency=medium
4.19.142
* [rt] Refresh "Split IRQ-off and zone->lock while freeing pages from PCP
list #1" for context changes in 4.19.142
* ACPI: configfs: Disallow loading ACPI tables when locked down
(CVE-2020-15780)
-- Salvatore Bonaccorso <carnil@debian.org> Tue, 04 Aug 2020 16:33:40 +0200

44
debian/patches/features/all/lockdown/ACPI-configfs-Disallow-loading-ACPI-tables-when-lock.patch vendored Normal file
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@ -0,0 +1,44 @@
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Mon, 15 Jun 2020 04:43:32 -0600
Subject: ACPI: configfs: Disallow loading ACPI tables when locked down
Origin: https://git.kernel.org/linus/75b0cea7bf307f362057cc778efe89af4c615354
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-15780
Like other vectors already patched, this one here allows the root
user to load ACPI tables, which enables arbitrary physical address
writes, which in turn makes it possible to disable lockdown.
Prevents this by checking the lockdown status before allowing a new
ACPI table to be installed. The link in the trailer shows a PoC of
how this might be used.
Link: https://git.zx2c4.com/american-unsigned-language/tree/american-unsigned-language-2.sh
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
[Salvatore Bonaccorso: Backport to v4.19.y: Use kernel_is_locked_down instead
of security_locked_down]
---
drivers/acpi/acpi_configfs.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/drivers/acpi/acpi_configfs.c
+++ b/drivers/acpi/acpi_configfs.c
@@ -14,6 +14,7 @@
#include <linux/module.h>
#include <linux/configfs.h>
#include <linux/acpi.h>
+#include <linux/security.h>
#include "acpica/accommon.h"
#include "acpica/actables.h"
@@ -33,6 +34,9 @@ static ssize_t acpi_table_aml_write(stru
struct acpi_table *table;
int ret;
+ if (kernel_is_locked_down("Modifying ACPI tables"))
+ return -EPERM;
+
table = container_of(cfg, struct acpi_table, cfg);
if (table->header) {

1
debian/patches/series vendored
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@ -137,6 +137,7 @@ features/all/lockdown/0032-efi-Restrict-efivar_ssdt_load-when-the-kernel-is-loc.
features/all/lockdown/enable-cold-boot-attack-mitigation.patch
features/all/lockdown/mtd-disable-slram-and-phram-when-locked-down.patch
features/all/lockdown/arm64-add-kernel-config-option-to-lock-down-when.patch
features/all/lockdown/ACPI-configfs-Disallow-loading-ACPI-tables-when-lock.patch
# until the "kernel_lockdown.7" manual page exists
features/all/lockdown/lockdown-refer-to-debian-wiki-until-manual-page-exists.patch