diff mbox series

[V33,15/30] ACPI: Limit access to custom_method when the kernel is locked down

Message ID 20190621011941.186255-16-matthewgarrett@google.com (mailing list archive)
State Not Applicable, archived
Headers show
Series None | expand

Commit Message

Matthew Garrett June 21, 2019, 1:19 a.m. UTC 
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 | 4 ++++
 include/linux/security.h     | 1 +
 security/lockdown/lockdown.c | 1 +
 3 files changed, 6 insertions(+)
diff mbox series

Patch

diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index aa972dc5cb7e..5c684b09a2d1 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"
 
@@ -29,6 +30,9 @@  static ssize_t cm_write(struct file *file, const char __user * user_buf,
 	struct acpi_table_header table;
 	acpi_status status;
 
+	if (security_is_locked_down(LOCKDOWN_ACPI_TABLES))
+		return -EPERM;
+
 	if (!(*ppos)) {
 		/* parse the table header to get the table length */
 		if (count <= sizeof(struct acpi_table_header))
diff --git a/include/linux/security.h b/include/linux/security.h
index 81c0968e485f..88d0f5d0cd87 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 a01301972290..bfc0e088aa85 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",
 };