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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: [PATCH 5.4 143/178] ACPI: configfs: Disallow loading ACPI tables when locked down
Date:   Mon, 29 Jun 2020 11:24:48 -0400
Message-Id: <20200629152523.2494198-144-sashal@kernel.org>
In-Reply-To: <20200629152523.2494198-1-sashal@kernel.org>
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From: "Jason A. Donenfeld" <Jason@zx2c4.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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 57d9d574d4dde..01738d8e888e3 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