efi_capsule: Move signature from DTB to .rodata

The capsule signature is now part of our DTB.  This is problematic when a
user is allowed to change/fixup that DTB from U-Boots command line since he
can overwrite the signature as well.
So Instead of adding the key on the DTB, embed it in the u-boot binary it
self as part of it's .rodata.  This assumes that the U-Boot binary we load
is authenticated by a previous boot stage loader.

Reviewed-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Tested-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Tested-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

4 files changed, 47 insertions, 3 deletions

diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
index 7a469f2272..dacc3b5881 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -214,6 +214,13 @@ config EFI_CAPSULE_AUTHENTICATE
 	  Select this option if you want to enable capsule
 	  authentication
 
+config EFI_CAPSULE_KEY_PATH
+	string "Path to .esl cert for capsule authentication"
+	depends on EFI_CAPSULE_AUTHENTICATE
+	help
+	  Provide the EFI signature list (esl) certificate used for capsule
+	  authentication
+
 config EFI_DEVICE_PATH_TO_TEXT
 	bool "Device path to text protocol"
 	default y
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index fd344cea29..9b369430e2 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -20,11 +20,19 @@ always += helloworld.efi
 targets += helloworld.o
 endif
 
+ifeq ($(CONFIG_EFI_CAPSULE_AUTHENTICATE),y)
+EFI_CAPSULE_KEY_PATH := $(subst $\",,$(CONFIG_EFI_CAPSULE_KEY_PATH))
+ifeq ("$(wildcard $(EFI_CAPSULE_KEY_PATH))","")
+$(error .esl cerificate not found. Configure your CONFIG_EFI_CAPSULE_KEY_PATH)
+endif
+endif
+
 obj-$(CONFIG_CMD_BOOTEFI_HELLO) += helloworld_efi.o
 obj-$(CONFIG_CMD_BOOTEFI_BOOTMGR) += efi_bootmgr.o
 obj-y += efi_boottime.o
 obj-y += efi_helper.o
 obj-$(CONFIG_EFI_HAVE_CAPSULE_SUPPORT) += efi_capsule.o
+obj-$(CONFIG_EFI_CAPSULE_AUTHENTICATE) += efi_capsule_key.o
 obj-$(CONFIG_EFI_CAPSULE_FIRMWARE) += efi_firmware.o
 obj-y += efi_console.o
 obj-y += efi_device_path.o
diff --git a/lib/efi_loader/efi_capsule.c b/lib/efi_loader/efi_capsule.c
index a09c5705f1..f9b0ef591c 100644
--- a/lib/efi_loader/efi_capsule.c
+++ b/lib/efi_loader/efi_capsule.c
@@ -16,6 +16,7 @@
 #include <mapmem.h>
 #include <sort.h>
 
+#include <asm/sections.h>
 #include <crypto/pkcs7.h>
 #include <crypto/pkcs7_parser.h>
 #include <linux/err.h>
@@ -222,12 +223,23 @@ skip:
 const efi_guid_t efi_guid_capsule_root_cert_guid =
 	EFI_FIRMWARE_MANAGEMENT_CAPSULE_ID_GUID;
 
+static int efi_get_public_key_data(void **pkey, efi_uintn_t *pkey_len)
+{
+	const void *blob = __efi_capsule_sig_begin;
+	const int len = __efi_capsule_sig_end - __efi_capsule_sig_begin;
+
+	*pkey = (void *)blob;
+	*pkey_len = len;
+
+	return 0;
+}
+
 efi_status_t efi_capsule_authenticate(const void *capsule, efi_uintn_t capsule_size,
 				      void **image, efi_uintn_t *image_size)
 {
 	u8 *buf;
 	int ret;
-	void *fdt_pkey, *pkey;
+	void *stored_pkey, *pkey;
 	efi_uintn_t pkey_len;
 	uint64_t monotonic_count;
 	struct efi_signature_store *truststore;
@@ -286,7 +298,7 @@ efi_status_t efi_capsule_authenticate(const void *capsule, efi_uintn_t capsule_s
 		goto out;
 	}
 
-	ret = efi_get_public_key_data(&fdt_pkey, &pkey_len);
+	ret = efi_get_public_key_data(&stored_pkey, &pkey_len);
 	if (ret < 0)
 		goto out;
 
@@ -294,7 +306,7 @@ efi_status_t efi_capsule_authenticate(const void *capsule, efi_uintn_t capsule_s
 	if (!pkey)
 		goto out;
 
-	memcpy(pkey, fdt_pkey, pkey_len);
+	memcpy(pkey, stored_pkey, pkey_len);
 	truststore = efi_build_signature_store(pkey, pkey_len);
 	if (!truststore)
 		goto out;
diff --git a/lib/efi_loader/efi_capsule_key.S b/lib/efi_loader/efi_capsule_key.S
new file mode 100644
index 0000000000..58f00b8e4b
--- /dev/null
+++ b/lib/efi_loader/efi_capsule_key.S
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * .esl cert for capsule authentication
+ *
+ * Copyright (c) 2021, Ilias Apalodimas <ilias.apalodimas@linaro.org>
+ */
+
+#include <config.h>
+
+.section .rodata.capsule_key.init,"a"
+.balign 16
+.global __efi_capsule_sig_begin
+__efi_capsule_sig_begin:
+.incbin CONFIG_EFI_CAPSULE_KEY_PATH
+__efi_capsule_sig_end:
+.global __efi_capsule_sig_end
+.balign 16