diff mbox series

[V34,14/29] ACPI: Limit access to custom_method when the kernel is locked down

Message ID 20190622000358.19895-15-matthewgarrett@google.com (mailing list archive)
State Not Applicable, archived
Headers show
Series None | expand

Commit Message

Matthew Garrett June 22, 2019, 12:03 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 | 6 ++++++
 include/linux/security.h     | 1 +
 security/lockdown/lockdown.c | 1 +
 3 files changed, 8 insertions(+)

Comments

Kees Cook June 22, 2019, 11:59 p.m. UTC | #1
On Fri, Jun 21, 2019 at 05:03:43PM -0700, Matthew Garrett wrote:
> 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>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> 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
>
diff mbox series

Patch

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",
 };