From: Linn Crosetto <linn@hpe.com>
Date: Tue, 30 Aug 2016 17:54:38 +0000 (-0600)
Subject: arm64: add kernel config option to lock down when in Secure Boot mode
X-Git-Tag: archive/raspbian/4.15.4-1+rpi1~34
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=44986bebe6b02cfa3b6be4afec4f30e59dbefc4d;p=linux.git

arm64: add kernel config option to lock down when in Secure Boot mode

Add a kernel configuration option to lock down the kernel, to restrict
userspace's ability to modify the running kernel when UEFI Secure Boot is
enabled. Based on the x86 patch by Matthew Garrett.

Determine the state of Secure Boot in the EFI stub and pass this to the
kernel using the FDT.

Signed-off-by: Linn Crosetto <linn@hpe.com>
[bwh: Forward-ported to 4.10: adjust context]
[Lukas Wunner: Forward-ported to 4.11: drop parts applied upstream]
[bwh: Forward-ported to 4.11 and lockdown patch set:
 - Convert result of efi_get_secureboot() to a boolean
 - Use lockdown API and naming]

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name arm64-add-kernel-config-option-to-lock-down-when.patch
---

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0df64a6a56d..d12af576afa 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1077,6 +1077,18 @@ config EFI
 	  allow the kernel to be booted as an EFI application. This
 	  is only useful on systems that have UEFI firmware.
 
+config EFI_SECURE_BOOT_LOCK_DOWN
+	def_bool n
+	depends on EFI
+	prompt "Lock down the kernel when UEFI Secure Boot is enabled"
+	---help---
+	  UEFI Secure Boot provides a mechanism for ensuring that the firmware
+	  will only load signed bootloaders and kernels.  Certain use cases may
+	  also require that all kernel modules also be signed and that
+	  userspace is prevented from directly changing the running kernel
+	  image.  Say Y here to automatically lock down the kernel when a
+	  system boots with UEFI Secure Boot enabled.
+
 config DMI
 	bool "Enable support for SMBIOS (DMI) tables"
 	depends on EFI
diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
index 80d1a885def..291e63f662a 100644
--- a/drivers/firmware/efi/arm-init.c
+++ b/drivers/firmware/efi/arm-init.c
@@ -21,6 +21,7 @@
 #include <linux/of_fdt.h>
 #include <linux/platform_device.h>
 #include <linux/screen_info.h>
+#include <linux/security.h>
 
 #include <asm/efi.h>
 
@@ -252,6 +253,11 @@ void __init efi_init(void)
 	     "Unexpected EFI_MEMORY_DESCRIPTOR version %ld",
 	      efi.memmap.desc_version);
 
+#ifdef CONFIG_EFI_SECURE_BOOT_LOCK_DOWN
+	if (params.secure_boot > 0)
+		lock_kernel_down();
+#endif
+
 	if (uefi_init() < 0) {
 		efi_memmap_unmap();
 		return;
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index c3eefa126e3..9942fda72d8 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -633,7 +633,8 @@ static __initdata struct params fdt_params[] = {
 	UEFI_PARAM("MemMap Address", "linux,uefi-mmap-start", mmap),
 	UEFI_PARAM("MemMap Size", "linux,uefi-mmap-size", mmap_size),
 	UEFI_PARAM("MemMap Desc. Size", "linux,uefi-mmap-desc-size", desc_size),
-	UEFI_PARAM("MemMap Desc. Version", "linux,uefi-mmap-desc-ver", desc_ver)
+	UEFI_PARAM("MemMap Desc. Version", "linux,uefi-mmap-desc-ver", desc_ver),
+	UEFI_PARAM("Secure Boot Enabled", "linux,uefi-secure-boot", secure_boot)
 };
 
 static __initdata struct params xen_fdt_params[] = {
diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index 8830fa601e4..b77d71b36ff 100644
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -158,6 +158,14 @@ static efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
 			return efi_status;
 		}
 	}
+
+	fdt_val32 = cpu_to_fdt32(efi_get_secureboot(sys_table) !=
+				 efi_secureboot_mode_disabled);
+	status = fdt_setprop(fdt, node, "linux,uefi-secure-boot",
+			     &fdt_val32, sizeof(fdt_val32));
+	if (status)
+		goto fdt_set_fail;
+
 	return EFI_SUCCESS;
 
 fdt_set_fail:
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 429ed06aa6a..71221796dce 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -751,6 +751,7 @@ struct efi_fdt_params {
 	u32 mmap_size;
 	u32 desc_size;
 	u32 desc_ver;
+	u32 secure_boot;
 };
 
 typedef struct {