# \[PATCH V38 28/29\] efi: Restrict efivar\_ssdt\_load when the kernel is locked down

- From: Matthew Garrett \<hidden\>
- Date: 2019-08-08 00:08:43 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2019/08/5681203
- Thread: https://ratatoskr.run/linux-security-module/2019/08/5681185/t.md

```text
efivar_ssdt_load allows the kernel to import arbitrary ACPI code from an
EFI variable, which gives arbitrary code execution in ring 0. Prevent
that when the kernel is locked down.

Signed-off-by: Matthew Garrett <redacted>
Acked-by: Ard Biesheuvel <redacted>
Reviewed-by: Kees Cook <redacted>
Cc: Ard Biesheuvel <redacted>
Cc: <redacted>
---
 drivers/firmware/efi/efi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index ad3b1f4866b3..776f479e5499 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -30,6 +30,7 @@
 #include <linux/acpi.h>
 #include <linux/ucs2_string.h>
 #include <linux/memblock.h>
+#include <linux/security.h>
 
 #include <asm/early_ioremap.h>
 
@@ -242,6 +243,11 @@ static void generic_ops_unregister(void)
 static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
 static int __init efivar_ssdt_setup(char *str)
 {
+	int ret = security_locked_down(LOCKDOWN_ACPI_TABLES);
+
+	if (ret)
+		return ret;
+
 	if (strlen(str) < sizeof(efivar_ssdt))
 		memcpy(efivar_ssdt, str, strlen(str));
 	else
-- 
2.22.0.770.g0f2c4a37fd-goog
```