linux-kernel - [PATCH 13/27] asus-wmi: Restrict debugfs interface when the kernel is locked down

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Message-ID: <150842473184.7923.9538070958624850416.stgit@warthog.procyon.org.uk>
Date:   Thu, 19 Oct 2017 15:52:11 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-security-module@...r.kernel.org
Cc:     gnomes@...rguk.ukuu.org.uk, linux-efi@...r.kernel.org,
        matthew.garrett@...ula.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        jforbes@...hat.com
Subject: [PATCH 13/27] asus-wmi: Restrict debugfs interface when the kernel
 is locked down

From: Matthew Garrett <matthew.garrett@...ula.com>

We have no way of validating what all of the Asus WMI methods do on a given
machine - and there's a risk that some will allow hardware state to be
manipulated in such a way that arbitrary code can be executed in the
kernel, circumventing module loading restrictions.  Prevent that if the
kernel is locked down.

Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: acpi4asus-user@...ts.sourceforge.net
cc: platform-driver-x86@...r.kernel.org
---

 drivers/platform/x86/asus-wmi.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
index 48e1541dc8d4..ef5587469337 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -1905,6 +1905,9 @@ static int show_dsts(struct seq_file *m, void *data)
 	int err;
 	u32 retval = -1;
 
+	if (kernel_is_locked_down("Asus WMI"))
+		return -EPERM;
+
 	err = asus_wmi_get_devstate(asus, asus->debug.dev_id, &retval);
 
 	if (err < 0)
@@ -1921,6 +1924,9 @@ static int show_devs(struct seq_file *m, void *data)
 	int err;
 	u32 retval = -1;
 
+	if (kernel_is_locked_down("Asus WMI"))
+		return -EPERM;
+
 	err = asus_wmi_set_devstate(asus->debug.dev_id, asus->debug.ctrl_param,
 				    &retval);
 
@@ -1945,6 +1951,9 @@ static int show_call(struct seq_file *m, void *data)
 	union acpi_object *obj;
 	acpi_status status;
 
+	if (kernel_is_locked_down("Asus WMI"))
+		return -EPERM;
+
 	status = wmi_evaluate_method(ASUS_WMI_MGMT_GUID,
 				     0, asus->debug.method_id,
 				     &input, &output);