From: Linn Crosetto <linn@hpe.com>
Date: Mon, 18 Feb 2019 12:45:00 +0000 (+0000)
Subject: acpi: Disable ACPI table override if the kernel is locked down
X-Git-Tag: archive/raspbian/5.2.17-1+rpi1^2~44
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=c8fefbf41a90a24cf42b3465a35f8e6f0e8b8d06;p=linux.git

acpi: Disable ACPI table override if the kernel is locked down

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@hpe.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
cc: linux-acpi@vger.kernel.org

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0017-acpi-Disable-ACPI-table-override-if-the-kernel-is-lo.patch
---

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index de974322a19..7445f3960f3 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -577,6 +577,11 @@ 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);