linux-kernel - [PATCH 5.7 213/265] ACPI: configfs: Disallow loading ACPI tables when locked down

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Date:   Mon, 29 Jun 2020 11:17:26 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH 5.7 213/265] ACPI: configfs: Disallow loading ACPI tables when locked down

From: "Jason A. Donenfeld" <Jason@...c4.com>

commit 75b0cea7bf307f362057cc778efe89af4c615354 upstream.

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@...r.kernel.org> # 5.4+
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/acpi/acpi_configfs.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/acpi_configfs.c b/drivers/acpi/acpi_configfs.c
index ece8c1a921cc1..88c8af455ea3f 100644
--- a/drivers/acpi/acpi_configfs.c
+++ b/drivers/acpi/acpi_configfs.c
@@ -11,6 +11,7 @@
 #include <linux/module.h>
 #include <linux/configfs.h>
 #include <linux/acpi.h>
+#include <linux/security.h>
 
 #include "acpica/accommon.h"
 #include "acpica/actables.h"
@@ -28,7 +29,10 @@ static ssize_t acpi_table_aml_write(struct config_item *cfg,
 {
 	const struct acpi_table_header *header = data;
 	struct acpi_table *table;
-	int ret;
+	int ret = security_locked_down(LOCKDOWN_ACPI_TABLES);
+
+	if (ret)
+		return ret;
 
 	table = container_of(cfg, struct acpi_table, cfg);
 
-- 
2.25.1