[U-Boot] [PATCH v3 2/6] x86: baytrail: secureboot: Add functions for verification of U-Boot

Anatolij Gustschin agust at denx.de
Fri Nov 17 01:14:06 UTC 2017 

From: Markus Valentin <mv at denx.de>

Introduce functions that check the integrity of U-Boot by utilising
the hashes stored in the OEM-data block in Secure Boot Manifest.

The verification functions get called in fsp_init()

Signed-off-by: Markus Valentin <mv at denx.de>
Signed-off-by: Anatolij Gustschin <agust at denx.de>
---
Changes in v3:
 - lower case in hex numbers 
 - fix RAM stage payload hash calculation and add comments
   for associated macros
 - add comments explaining used stage indexes, s/*_ID/*_IDX
 - fixed two spaces in comment
 - s/devicetree/device tree
 - extend the output messages to give more hints when FIT key
   verification fails
 -

Changes in v2:
 - use 'const void *' for fdt property ptr, drop cast
 - s/u-boot/U-Boot/
 - fix function comment style and move comments to header with
   prototypes. Use fsp_ prefix
 - fix multiline comment style
 - s/SB:/Secure Boot/ for non-debug messages

 arch/x86/cpu/baytrail/Makefile                     |   1 +
 arch/x86/cpu/baytrail/secure_boot.c                | 117 +++++++++++++++++++++
 .../include/asm/arch-baytrail/fsp/fsp_configs.h    |  24 +++++
 arch/x86/lib/fsp/fsp_support.c                     |  18 ++++
 4 files changed, 160 insertions(+)
 create mode 100644 arch/x86/cpu/baytrail/secure_boot.c

diff --git a/arch/x86/cpu/baytrail/Makefile b/arch/x86/cpu/baytrail/Makefile
index a0216f3059..dbf9a82c39 100644
--- a/arch/x86/cpu/baytrail/Makefile
+++ b/arch/x86/cpu/baytrail/Makefile
@@ -8,4 +8,5 @@ obj-y += cpu.o
 obj-y += early_uart.o
 obj-y += fsp_configs.o
 obj-y += valleyview.o
+obj-$(CONFIG_BAYTRAIL_SECURE_BOOT) += secure_boot.o
 obj-$(CONFIG_GENERATE_ACPI_TABLE) += acpi.o
diff --git a/arch/x86/cpu/baytrail/secure_boot.c b/arch/x86/cpu/baytrail/secure_boot.c
new file mode 100644
index 0000000000..eaf35c6e24
--- /dev/null
+++ b/arch/x86/cpu/baytrail/secure_boot.c
@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2017 Markus Valentin <mv at denx.de>
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#include <common.h>
+
+#define SB_MANIFEST_BASE		0xfffe0000
+#define SB_MANIFEST_SIZE		0x400
+#define SB_MANIFEST_OEM_DATA_OFFSET	0x58
+#define SB_MANIFEST_OEM_HASH_OFFSET	(SB_MANIFEST_OEM_DATA_OFFSET + 4)
+#define SB_MANIFEST_OEM_HASH_BASE	(SB_MANIFEST_BASE + \
+					 SB_MANIFEST_OEM_HASH_OFFSET)
+#define SB_MANIFEST_END			(SB_MANIFEST_BASE + SB_MANIFEST_SIZE)
+
+#define FIT_KEY_NAME			"dev"
+#define PUB_KEY_MODULUS_SIZE		0x100
+
+/*
+ * U-Boot in RAM stage payload from reset vector to FSP Stage2:
+ * 0xfff0000 to 0xfffc0000
+ */
+#define U_BOOT_STAGE_START		CONFIG_SYS_TEXT_BASE
+#define U_BOOT_STAGE_SIZE		0xc0000
+
+/*
+ * Indexes of 32-byte blocks in the OEM-data area containing sha256 hashes
+ * of RAM stage payload, FSP Stage2 and other OEM specific data. The order
+ * of RAM stage payload and FSP Stage2 blocks is fixed (idx 0 and 1),
+ * do not change it. We do not verify FSP Stage2 here, it will be verified
+ * in FSP (FSP Stage2 idx 1 is not used). So, the first index of OEM specific
+ * data block hash must start from 2.
+ */
+#define SHA256_U_BOOT_STAGE_IDX		0
+#define SHA256_FIT_PUB_KEY_IDX		2
+
+/**
+ * verify_oem_sha256() - oem data block verification
+ *
+ * This function compares a hash which gets retrieved from the oem data block
+ * with the runtime calculated hash of start_address+size. If they match,
+ * this function returns true. If not, it returns false.
+ *
+ * @hash_idx:		index of oem-data block with hash to compare
+ * @start_address:	address where the hash calculation should start
+ * @size:		length of the region for hash calculation
+ *
+ * @retval:		true on success, false on error
+ */
+static bool verify_oem_sha256(unsigned int hash_idx,
+			      const void *start_address,
+			      size_t size)
+{
+	uint8_t value[SHA256_SUM_LEN];
+	int value_len;
+
+	/* Calculate address of hash to compare in the oemdata block */
+	void *hash_to_verify = (void *)SB_MANIFEST_OEM_HASH_BASE +
+			       (SHA256_SUM_LEN * hash_idx);
+#ifdef DEBUG
+	unsigned int i = 0;
+	uint8_t oem_value[SHA256_SUM_LEN];
+
+	memcpy(oem_value, hash_to_verify, SHA256_SUM_LEN);
+	printf("SB: hash to verify:\t");
+	for (i = 0; i < SHA256_SUM_LEN; i++)
+		printf("%02X", oem_value[i]);
+	printf("\n");
+#endif
+
+	/* Calculate the hash of the binary */
+	calculate_hash(start_address, size, "sha256", value, &value_len);
+
+#ifdef DEBUG
+	printf("SB: calculated hash:\t");
+	for (i = 0; i < SHA256_SUM_LEN; i++)
+		printf("%02X", value[i]);
+	printf("\n");
+#endif
+	/* Compare the two hash values */
+	if (memcmp(hash_to_verify, value, SHA256_SUM_LEN))
+		return false;
+	return true;
+}
+
+bool fsp_verify_u_boot_bin(void)
+{
+	return verify_oem_sha256(SHA256_U_BOOT_STAGE_IDX,
+				 (const void *)U_BOOT_STAGE_START,
+				 U_BOOT_STAGE_SIZE);
+}
+
+bool fsp_verify_public_key(void)
+{
+	const void *fit_public_key_modulus;
+	int offset = fdt_node_offset_by_prop_value(gd->fdt_blob, -1,
+						   "key-name-hint",
+						   FIT_KEY_NAME,
+						   4);
+	int ret;
+
+	fit_public_key_modulus =  fdt_getprop(gd->fdt_blob, offset,
+					      "rsa,modulus", NULL);
+	if (!fit_public_key_modulus) {
+		puts("No FIT public key in U-Boot device tree\n");
+		return false;
+	}
+
+	ret = verify_oem_sha256(SHA256_FIT_PUB_KEY_IDX,
+				fit_public_key_modulus,
+				PUB_KEY_MODULUS_SIZE);
+	if (!ret)
+		puts("FIT public key checksum wrong\n");
+
+	return ret;
+}
diff --git a/arch/x86/include/asm/arch-baytrail/fsp/fsp_configs.h b/arch/x86/include/asm/arch-baytrail/fsp/fsp_configs.h
index 1c6c2479f0..2c8c32b9bf 100644
--- a/arch/x86/include/asm/arch-baytrail/fsp/fsp_configs.h
+++ b/arch/x86/include/asm/arch-baytrail/fsp/fsp_configs.h
@@ -103,4 +103,28 @@ struct fspinit_rtbuf {
 #define SCC_MODE_ACPI			0
 #define SCC_MODE_PCI			1
 
+#ifndef __ASSEMBLY__
+/**
+ * fsp_verify_u_boot_bin() - U-Boot binary verification
+ *
+ * This function verifies the integrity for U-Boot, its device tree and the
+ * ucode appended or inserted to the device tree.
+ *
+ * @retval:	true on success, false on error
+ */
+bool fsp_verify_u_boot_bin(void);
+
+/**
+ * fsp_verify_public_key() - integrity of public key for fit image verification
+ *
+ * This function verifies the integrity for the modulus of the public key which
+ * is stored in the U-Boot device tree for fit image verification. It tries to
+ * find the "rsa,modulus" property in the dtb and then verifies it with the
+ * checksum stored in the oem-data block
+ *
+ * @retval:	true on success, false on error
+ */
+bool fsp_verify_public_key(void);
+#endif
+
 #endif /* __FSP_CONFIGS_H__ */
diff --git a/arch/x86/lib/fsp/fsp_support.c b/arch/x86/lib/fsp/fsp_support.c
index d79a6e900a..c7e0a9eff4 100644
--- a/arch/x86/lib/fsp/fsp_support.c
+++ b/arch/x86/lib/fsp/fsp_support.c
@@ -152,6 +152,24 @@ void fsp_init(u32 stack_top, u32 boot_mode, void *nvs_buf)
 	 */
 	printf("FSP: Secure Boot %sabled\n",
 	       fsp_vpd->enable_secure_boot == 1 ? "en" : "dis");
+
+	if (!fsp_verify_u_boot_bin()) {
+		/*
+		 * If our U-Boot binary checksum isn't equal to
+		 * our expected checksum we need to stop booting
+		 */
+		printf("%s Failed to verify U-Boot and dtb\n", SB_PRFX);
+		hang();
+	}
+
+	/*
+	 * Verification of the public key happens with verification of
+	 * the device tree binary (that's where it's stored), this check
+	 * is not necessary, but nice to see it's integer
+	 */
+	if (!fsp_verify_public_key())
+		printf("%s Failed to verify public key for FIT image\n",
+		       SB_PRFX);
 	#endif
 
 	/* Copy default data from Flash */
-- 
2.11.0

More information about the U-Boot mailing list