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Subject: [PATCH 12/24] ACPI: Limit access to custom_method when the kernel
 is locked down
From:   David Howells <dhowells@redhat.com>
To:     torvalds@linux-foundation.org
Cc:     linux-man@vger.kernel.org, linux-api@vger.kernel.org,
        jmorris@namei.org, linux-kernel@vger.kernel.org,
        dhowells@redhat.com, linux-security-module@vger.kernel.org
Date:   Wed, 11 Apr 2018 17:25:57 +0100
Message-ID: <152346395768.4030.17020230875159368659.stgit@warthog.procyon.org.uk>
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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@srcf.ucam.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
cc: linux-acpi@vger.kernel.org
---

 drivers/acpi/custom_method.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index e967c1173ba3..a07fbe999eb6 100644
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -29,6 +29,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
 	struct acpi_table_header table;
 	acpi_status status;
 
+	if (kernel_is_locked_down("ACPI custom methods"))
+		return -EPERM;
+
 	if (!(*ppos)) {
 		/* parse the table header to get the table length */
 		if (count <= sizeof(struct acpi_table_header))