linux-kernel - [PATCH 15/24] asus-wmi: Restrict debugfs interface when the kernel is locked down

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Message-ID: <149142340198.5101.8171352010918423590.stgit@warthog.procyon.org.uk>
Date:   Wed, 05 Apr 2017 21:16:42 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     matthew.garrett@...ula.com, linux-efi@...r.kernel.org,
        gnomes@...rguk.ukuu.org.uk, gregkh@...uxfoundation.org,
        acpi4asus-user@...ts.sourceforge.net,
        platform-driver-x86@...r.kernel.org, dhowells@...hat.com,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org
Subject: [PATCH 15/24] 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 8fe5890bf539..feef25076813 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -1900,6 +1900,9 @@ static int show_dsts(struct seq_file *m, void *data)
 	int err;
 	u32 retval = -1;
 
+	if (kernel_is_locked_down())
+		return -EPERM;
+
 	err = asus_wmi_get_devstate(asus, asus->debug.dev_id, &retval);
 
 	if (err < 0)
@@ -1916,6 +1919,9 @@ static int show_devs(struct seq_file *m, void *data)
 	int err;
 	u32 retval = -1;
 
+	if (kernel_is_locked_down())
+		return -EPERM;
+
 	err = asus_wmi_set_devstate(asus->debug.dev_id, asus->debug.ctrl_param,
 				    &retval);
 
@@ -1940,6 +1946,9 @@ static int show_call(struct seq_file *m, void *data)
 	union acpi_object *obj;
 	acpi_status status;
 
+	if (kernel_is_locked_down())
+		return -EPERM;
+
 	status = wmi_evaluate_method(ASUS_WMI_MGMT_GUID,
 				     1, asus->debug.method_id,
 				     &input, &output);