From: Linn Crosetto <linn@hpe.com>
Date: Wed, 5 Apr 2017 16:40:31 +0000 (+0100)
Subject: acpi: Disable ACPI table override if the kernel is locked down
X-Git-Tag: archive/raspbian/4.15.4-1+rpi1~43
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=c3bbe791d8a1b332bd50abc0fd4cb96aa45ecbe4;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>

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0055-acpi-Disable-ACPI-table-override-if-the-kernel-is-lo.patch
---

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 80ce2a7d224..946b717606c 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -526,6 +526,11 @@ 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);