linux-kernel - [PATCH V33 30/30] efi: Restrict efivar_ssdt

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Message-Id: <20190621011941.186255-31-matthewgarrett@google.com>
Date:   Thu, 20 Jun 2019 18:19:41 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org,
        Matthew Garrett <matthewgarrett@...gle.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org
Subject: [PATCH V33 30/30] efi: Restrict efivar_ssdt_load when the kernel is
 locked down

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@...gle.com>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-efi@...r.kernel.org
---
 drivers/firmware/efi/efi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 55b77c576c42..a9ea649e0512 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -31,6 +31,7 @@
 #include <linux/acpi.h>
 #include <linux/ucs2_string.h>
 #include <linux/memblock.h>
+#include <linux/security.h>
 
 #include <asm/early_ioremap.h>
 
@@ -242,6 +243,9 @@ static void generic_ops_unregister(void)
 static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
 static int __init efivar_ssdt_setup(char *str)
 {
+	if (security_is_locked_down(LOCKDOWN_ACPI_TABLES))
+		return -EPERM;
+
 	if (strlen(str) < sizeof(efivar_ssdt))
 		memcpy(efivar_ssdt, str, strlen(str));
 	else
-- 
2.22.0.410.gd8fdbe21b5-goog