[U-Boot] [PATCH 3/5] x86: baytrail: secureboot: Add functions for verification of u-boot

[Lothar Waßmann]

Hi,

On Thu, 11 May 2017 17:14:54 +0200 Anatolij Gustschin wrote:
> 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.
> 
> The verification functions get called in fsp_init()
> 
> Signed-off-by: Markus Valentin <mv at denx.de>
> ---
>  arch/x86/cpu/baytrail/Makefile                     |   1 +
>  arch/x86/cpu/baytrail/secure_boot.c                | 117 +++++++++++++++++++++
>  .../include/asm/arch-baytrail/fsp/fsp_configs.h    |   3 +
>  arch/x86/lib/fsp/fsp_support.c                     |  15 +++
>  4 files changed, 136 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 a0216f3..dbf9a82 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 0000000..37c83db
> --- /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 PUB_KEY_MODULUS_SIZE		0x100
> +#define U_BOOT_STAGE_SIZE		0xDD360
> +#define U_BOOT_OFFSET			0x2CA0
> +
> +#define U_BOOT_STAGE_START		(CONFIG_SYS_TEXT_BASE + U_BOOT_OFFSET)
> +#define U_BOOT_STAGE_END		(U_BOOT_STAGE_START + U_BOOT_STAGE_SIZE)
> +
> +#define SHA256_U_BOOT_STAGE_ID		0
> +#define SHA256_FSP_STAGE2_ID		1
> +#define SHA256_FIT_PUB_KEY_ID		2
> +
> +#define FIT_KEY_NAME			"dev"
> +
> +/**
> + * 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.
> + *
> + * @param hash_id	offset of oem-data block for hash to compare
> + * @param start_address	address where the hash calculation should start
> + * @param size		length of the region for hash calculation
> + * @return true on success, false on error
> + */
> +static bool verify_oem_sha256(unsigned int hash_id,
> +			      void *start_address,
> +			      size_t size)
> +{
> +	uint8_t value[SHA256_SUM_LEN];
>
'unsigned char' here ...

> +	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_id);
> +#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("%X", oem_value[i]);
> +	printf("\n");
> +#endif
> +
> +	/* caluclate the hash of the binary */
> +	calculate_hash(start_address, size, "sha256", (unsigned char *)value,
> +		       &value_len);
>
... would avoid the '(unsigned char *)' cast here.

> +
> +#ifdef DEBUG
> +	printf("SB: calculated hash:\t");
> +	for (i = 0; i < SHA256_SUM_LEN; i++)
> +		printf("%X", value[i]);
> +	printf("\n");
> +#endif
> +	/* compare the two hash  values */
> +	if (memcmp(hash_to_verify, value, SHA256_SUM_LEN))
> +		return false;
> +	return true;
> +}
> +
> +/**
> + * This function verifies the integrity for u-boot, its devicetree and the ucode
> + * appended or inserted to the devicetree.
> + *
> + * @return true on success, false on error
> + */
> +bool verify_u_boot_bin(void)
> +{
> +	return verify_oem_sha256(SHA256_U_BOOT_STAGE_ID,
> +				 (void *)U_BOOT_STAGE_START,
> +				 U_BOOT_STAGE_SIZE);
> +}
> +
> +/**
> + * This function verifies the integrity for the modulus of the public key which
> + * is stored in the u-boot devicetree 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
> + *
> + * @return true on success, false on error
> + */
> +bool verify_public_key(void)
> +{
> +	void *fit_public_key_modulus;
>
'const void *' here ...
> +
> +	int offset = fdt_node_offset_by_prop_value(gd->fdt_blob, -1,
> +						   "key-name-hint",
> +						   FIT_KEY_NAME,
> +						   4);
> +
> +	fit_public_key_modulus =  (void *)fdt_getprop(gd->fdt_blob, offset,
> +						      "rsa,modulus", NULL);
>
... would eliminate the need for the '(void *)' cast here.

> +	if (!fit_public_key_modulus) {
> +		debug("SB: Could not fetch public key from U-Boot Devicetree\n");
> +		return false;
> +	}
> +
> +	return verify_oem_sha256(SHA256_FIT_PUB_KEY_ID,
> +				 fit_public_key_modulus,
> +				 PUB_KEY_MODULUS_SIZE);
> +}


Lothar Waßmann