linux-kernel - [PATCH 18/24] acpi: Disable ACPI table override if the kernel is locked down

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Message-ID: <149141235701.31282.4137641379599225390.stgit@warthog.procyon.org.uk>
Date:   Wed, 05 Apr 2017 18:12:37 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     gnomes@...rguk.ukuu.org.uk, linux-efi@...r.kernel.org,
        Linn Crosetto <linn@....com>, matthew.garrett@...ula.com,
        gregkh@...uxfoundation.org, dhowells@...hat.com,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org
Subject: [PATCH 18/24] 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>
---

 drivers/acpi/tables.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 2604189d6cd1..601096d0d849 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -542,6 +542,11 @@ void __init acpi_table_upgrade(void)
 	if (table_nr == 0)
 		return;
 
+	if (kernel_is_locked_down()) {
+		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);