linux-kernel - [PATCH 16/27] acpi: Disable ACPI table override if the kernel is locked down

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Message-Id: <20190228231203.212359-16-matthewgarrett@google.com>
Date:   Thu, 28 Feb 2019 15:11:52 -0800
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
Subject: [PATCH 16/27] acpi: Disable ACPI table override if the kernel is
 locked down

From: Linn Crosetto <linn@....com>

>From the kernel documentation (initrd_table_override.txt):

  If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible
  to override nearly any ACPI table provided by the BIOS with an
  instrumented, modified one.

When securelevel is set, the kernel should disallow any unauthenticated
changes to kernel space.  ACPI tables contain code invoked by the kernel,
so do not allow ACPI tables to be overridden if the kernel is locked down.

Signed-off-by: Linn Crosetto <linn@....com>
Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@...e.com>
cc: linux-acpi@...r.kernel.org
---
 drivers/acpi/tables.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 48eabb6c2d4f..f3b4117cd8f3 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -531,6 +531,11 @@ void __init acpi_table_upgrade(void)
 	if (table_nr == 0)
 		return;
 
+	if (kernel_is_locked_down("ACPI table override")) {
+		pr_notice("kernel is locked down, ignoring table override\n");
+		return;
+	}
+
 	acpi_tables_addr =
 		memblock_find_in_range(0, ACPI_TABLE_UPGRADE_MAX_PHYS,
 				       all_tables_size, PAGE_SIZE);
-- 
2.21.0.352.gf09ad66450-goog