linux-kernel - [PATCH V32 19/27] x86/mmiotrace: Lock down the testmmiotrace module

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Date:   Wed,  3 Apr 2019 17:32:41 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        linux-api@...r.kernel.org, luto@...nel.org,
        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 V32 19/27] 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>
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 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
index f6ae6830b341..9e8ad665f354 100644
--- a/arch/x86/mm/testmmiotrace.c
+++ b/arch/x86/mm/testmmiotrace.c
@@ -115,6 +115,9 @@ static int __init init(void)
 {
 	unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
 
+	if (kernel_is_locked_down("MMIO trace testing", LOCKDOWN_INTEGRITY))
+		return -EPERM;
+
 	if (mmio_address == 0) {
 		pr_err("you have to use the module argument mmio_address.\n");
 		pr_err("DO NOT LOAD THIS MODULE UNLESS YOU REALLY KNOW WHAT YOU ARE DOING!\n");
-- 
2.21.0.392.gf8f6787159e-goog