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 b2024db225a9dd116cf5d2ba49d62bc79c8e0bf8..2d90d019b48e66fc230c7e66eb979ebba6fdf60d 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1044,6 +1044,18 @@ 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 1027d7b44358d3b5806e8dcd58c65fecdcab9664..9d819a0dbbb14116fab67e943a70dad74a56db88 100644 (file)
--- 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>
 
@@ -244,6 +245,11 @@ 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 045d6d311bde2defc5ebabaf229ff7f71a94f60f..8a565d779d832d271b7e688b94d35495b6934721 100644 (file)
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -614,7 +614,8 @@ 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 8830fa601e45d9a1b1094419cd1ec66f41a25e49..b77d71b36ff27d6ec0b88ceb7e956d9d56d7cd76 100644 (file)
--- 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 381b3f6670d379626d1ee90628d2035342ab1c98..0918390a9016be85132ff9e59d7291129b451469 100644 (file)
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -736,6 +736,7 @@ struct efi_fdt_params {
        u32 mmap_size;
        u32 desc_size;
        u32 desc_ver;
+       u32 secure_boot;
 };
 
 typedef struct {