Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 21 Jun 2019 17:03:43 -0700
In-Reply-To: <20190622000358.19895-1-matthewgarrett@google.com>
Message-Id: <20190622000358.19895-15-matthewgarrett@google.com>
Mime-Version: 1.0
References: <20190622000358.19895-1-matthewgarrett@google.com>
Subject: [PATCH V34 14/29] ACPI: Limit access to custom_method when the kernel
 is locked down
From:   Matthew Garrett <matthewgarrett@google.com>
To:     jmorris@namei.org
Cc:     linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        Matthew Garrett <mjg59@google.com>,
        David Howells <dhowells@redhat.com>, linux-acpi@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Matthew Garrett <mjg59@srcf.ucam.org>

custom_method effectively allows arbitrary access to system memory, making
it possible for an attacker to circumvent restrictions on module loading.
Disable it if the kernel is locked down.

Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-acpi@vger.kernel.org
---
 drivers/acpi/custom_method.c | 6 ++++++
 include/linux/security.h     | 1 +
 security/lockdown/lockdown.c | 1 +
 3 files changed, 8 insertions(+)

diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index aa972dc5cb7e..6e56f9f43492 100644
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -8,6 +8,7 @@
 #include <linux/uaccess.h>
 #include <linux/debugfs.h>
 #include <linux/acpi.h>
+#include <linux/security.h>
 
 #include "internal.h"
 
@@ -28,6 +29,11 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
 
 	struct acpi_table_header table;
 	acpi_status status;
+	int ret;
+
+	ret = security_locked_down(LOCKDOWN_ACPI_TABLES);
+	if (ret)
+		return ret;
 
 	if (!(*ppos)) {
 		/* parse the table header to get the table length */
diff --git a/include/linux/security.h b/include/linux/security.h
index 30bc6f058926..cc2b5ee4cadd 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -89,6 +89,7 @@ enum lockdown_reason {
 	LOCKDOWN_PCI_ACCESS,
 	LOCKDOWN_IOPORT,
 	LOCKDOWN_MSR,
+	LOCKDOWN_ACPI_TABLES,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 297a065e6261..1725224f0024 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -25,6 +25,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_PCI_ACCESS] = "direct PCI access",
 	[LOCKDOWN_IOPORT] = "raw io port access",
 	[LOCKDOWN_MSR] = "raw MSR access",
+	[LOCKDOWN_ACPI_TABLES] = "modified ACPI tables",
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
-- 
2.22.0.410.gd8fdbe21b5-goog