linux-kernel - [PATCH V40 28/29] efi: Restrict efivar_ssdt

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Message-Id: <20190820001805.241928-29-matthewgarrett@google.com>
Date:   Mon, 19 Aug 2019 17:18:04 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...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>,
        Kees Cook <keescook@...omium.org>, linux-efi@...r.kernel.org
Subject: [PATCH V40 28/29] 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>
Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-efi@...r.kernel.org
Signed-off-by: James Morris <jmorris@...ei.org>
---
 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 4b7cf7bc0ded..5f98374f77f4 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>
 
@@ -241,6 +242,11 @@ 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
-- 
2.23.0.rc1.153.gdeed80330f-goog