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From: Matthew Garrett <matthewgarrett@google.com>
Date: Wed, 31 Jul 2019 15:16:16 -0700
Subject: efi: Restrict efivar_ssdt_load when the kernel is locked down
Origin: https://patchwork.kernel.org/patch/11069659/
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 <mjg59@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: linux-efi@vger.kernel.org
[bwh: Convert back to the non-LSM lockdown API]
---
--- 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>
@@ -241,6 +242,9 @@ static void generic_ops_unregister(void)
static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
static int __init efivar_ssdt_setup(char *str)
{
+ if (kernel_is_locked_down("ACPI tables"))
+ return -EPERM;
+
if (strlen(str) < sizeof(efivar_ssdt))
memcpy(efivar_ssdt, str, strlen(str));
else
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