Re: [PATCH V40 16/29] acpi: Disable ACPI table override if the kernel is locked down

[Rafael J. Wysocki]

On Tuesday, August 20, 2019 2:17:52 AM CEST Matthew Garrett wrote:
> From: Linn Crosetto 
> 
> >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 lockdown is enabled, 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 
> Signed-off-by: David Howells 
> Signed-off-by: Matthew Garrett 
> Reviewed-by: Kees Cook 
> cc: linux-a...@vger.kernel.org
> Signed-off-by: James Morris 

Acked-by: Rafael J. Wysocki 

> ---
>  drivers/acpi/tables.c | 6 ++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> index de974322a197..b7c29a11c0c1 100644
> --- a/drivers/acpi/tables.c
> +++ b/drivers/acpi/tables.c
> @@ -20,6 +20,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include "internal.h"
>  
>  #ifdef CONFIG_ACPI_CUSTOM_DSDT
> @@ -577,6 +578,11 @@ void __init acpi_table_upgrade(void)
>   if (table_nr == 0)
>   return;
>  
> + if (security_locked_down(LOCKDOWN_ACPI_TABLES)) {
> + 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);
> 

[PATCH V40 16/29] acpi: Disable ACPI table override if the kernel is locked down

[Matthew Garrett]

From: Linn Crosetto 

>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 lockdown is enabled, 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 
Signed-off-by: David Howells 
Signed-off-by: Matthew Garrett 
Reviewed-by: Kees Cook 
cc: linux-a...@vger.kernel.org
Signed-off-by: James Morris 
---
 drivers/acpi/tables.c | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index de974322a197..b7c29a11c0c1 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -20,6 +20,7 @@
 #include 
 #include 
 #include 
+#include 
 #include "internal.h"
 
 #ifdef CONFIG_ACPI_CUSTOM_DSDT
@@ -577,6 +578,11 @@ void __init acpi_table_upgrade(void)
if (table_nr == 0)
return;
 
+   if (security_locked_down(LOCKDOWN_ACPI_TABLES)) {
+   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);
-- 
2.23.0.rc1.153.gdeed80330f-goog