linux-kernel - [PATCH V36 20/29] x86/mmiotrace: Lock down the testmmiotrace module

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Message-Id: <20190718194415.108476-21-matthewgarrett@google.com>
Date:   Thu, 18 Jul 2019 12:44:06 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Matthew Garrett <mjg59@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: [PATCH V36 20/29] x86/mmiotrace: Lock down the testmmiotrace module

From: David Howells <dhowells@...hat.com>

The testmmiotrace module shouldn't be permitted when the kernel is locked
down as it can be used to arbitrarily read and write MMIO space. This is
a runtime check rather than buildtime in order to allow configurations
where the same kernel may be run in both locked down or permissive modes
depending on local policy.

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: David Howells <dhowells@...hat.com
Signed-off-by: Matthew Garrett <mjg59@...gle.com>
Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
cc: Thomas Gleixner <tglx@...utronix.de>
cc: Steven Rostedt <rostedt@...dmis.org>
cc: Ingo Molnar <mingo@...nel.org>
cc: "H. Peter Anvin" <hpa@...or.com>
cc: x86@...nel.org
---
 arch/x86/mm/testmmiotrace.c  | 5 +++++
 include/linux/security.h     | 1 +
 security/lockdown/lockdown.c | 1 +
 3 files changed, 7 insertions(+)

diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
index 0881e1ff1e58..a8bd952e136d 100644
--- a/arch/x86/mm/testmmiotrace.c
+++ b/arch/x86/mm/testmmiotrace.c
@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/io.h>
 #include <linux/mmiotrace.h>
+#include <linux/security.h>
 
 static unsigned long mmio_address;
 module_param_hw(mmio_address, ulong, iomem, 0);
@@ -115,6 +116,10 @@ static void do_test_bulk_ioremapping(void)
 static int __init init(void)
 {
 	unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
+	int ret = security_locked_down(LOCKDOWN_MMIOTRACE);
+
+	if (ret)
+		return ret;
 
 	if (mmio_address == 0) {
 		pr_err("you have to use the module argument mmio_address.\n");
diff --git a/include/linux/security.h b/include/linux/security.h
index 43fa3486522b..3f7b6a4cd65a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -114,6 +114,7 @@ enum lockdown_reason {
 	LOCKDOWN_PCMCIA_CIS,
 	LOCKDOWN_TIOCSSERIAL,
 	LOCKDOWN_MODULE_PARAMETERS,
+	LOCKDOWN_MMIOTRACE,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 5177938cfa0d..37b7d7e50474 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -29,6 +29,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
 	[LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
 	[LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
+	[LOCKDOWN_MMIOTRACE] = "unsafe mmio",
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
-- 
2.22.0.510.g264f2c817a-goog