[PATCH v3 4/6] arm: stm32mp1: Implement ECDSA signature verification

[Patrick DELAUNAY]

Hi,

On 3/30/21 8:32 PM, Alexandru Gagniuc wrote:
> The STM32MP ROM provides several service. One of them is the ability
> to verify ecdsa256 signatures. Hook the ROM API into the ECDSA uclass.
>
> Signed-off-by: Alexandru Gagniuc<mr.nuke.me at gmail.com>
> ---
>   arch/arm/mach-stm32mp/Kconfig        |   9 +++
>   arch/arm/mach-stm32mp/Makefile       |   1 +
>   arch/arm/mach-stm32mp/ecdsa_romapi.c | 106 +++++++++++++++++++++++++++
>   3 files changed, 116 insertions(+)
>   create mode 100644 arch/arm/mach-stm32mp/ecdsa_romapi.c
>
> diff --git a/arch/arm/mach-stm32mp/Kconfig b/arch/arm/mach-stm32mp/Kconfig
> index 079d66a80c..92c4c5a7b0 100644
> --- a/arch/arm/mach-stm32mp/Kconfig
> +++ b/arch/arm/mach-stm32mp/Kconfig
> @@ -121,6 +121,15 @@ config STM32_ETZPC
>   	help
>   	  Say y to enable STM32 Extended TrustZone Protection
>   
> +config STM32_ECDSA_VERIFY
> +	bool "STM32 ECDSA verification via the ROM API"
> +	depends on SPL_ECDSA_VERIFY
> +	default y
> +	help
> +	  Say y to enable the uclass driver for ECDSA verification using the
> +	  ROM API provided on STM32MP.
> +	  The ROM API is only available during SPL for now.
> +
>   config CMD_STM32KEY
>   	bool "command stm32key to fuse public key hash"
>   	default y
> diff --git a/arch/arm/mach-stm32mp/Makefile b/arch/arm/mach-stm32mp/Makefile
> index aa39867080..0942092d8e 100644
> --- a/arch/arm/mach-stm32mp/Makefile
> +++ b/arch/arm/mach-stm32mp/Makefile
> @@ -10,6 +10,7 @@ obj-y += bsec.o
>   
>   ifdef CONFIG_SPL_BUILD
>   obj-y += spl.o
> +obj-$(CONFIG_STM32_ECDSA_VERIFY) += ecdsa_romapi.o
>   else
>   obj-y += cmd_stm32prog/
>   obj-$(CONFIG_CMD_STM32KEY) += cmd_stm32key.o
> diff --git a/arch/arm/mach-stm32mp/ecdsa_romapi.c b/arch/arm/mach-stm32mp/ecdsa_romapi.c
> new file mode 100644
> index 0000000000..ca32925a12
> --- /dev/null
> +++ b/arch/arm/mach-stm32mp/ecdsa_romapi.c
> @@ -0,0 +1,106 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * STM32MP ECDSA verification via the ROM API
> + *
> + * Implements ECDSA signature verification via the STM32MP ROM.
> + */

#define LOG_CATEGORY UCLASS_ECDSA

to allow filtering with log command

> +#include <asm/system.h>
> +#include <dm/device.h>
> +#include <linux/types.h>
> +#include <u-boot/ecdsa.h>
> +#include <crypto/ecdsa-uclass.h>
> +#include <linux/libfdt.h>
> +#include <dm/platdata.h>
> +
> +#define ROM_API_SUCCESS				0x77
> +#define ROM_API_ECDSA_ALGO_PRIME_256V1		1
> +#define ROM_API_ECDSA_ALGO_BRAINPOOL_256	2
> +
> +#define ROM_API_OFFSET_ECDSA_CHECK_KEY		0x5c
> +#define ROM_API_OFFSET_ECDSA_VERIFY		0x60
> +
> +struct ecdsa_rom_api {
> +	uint32_t (*ecdsa_check_key)(const void *pubkey_in, void *pubkey_out);
> +	uint32_t (*ecdsa_verify_signature)(const void *hash, const void *pubkey,
> +					   const void *signature,
> +				    uint32_t ecc_algo);
> +};
> +
> +/*
> + * Without forcing the ".data" section, this would get saved in ".bss". BSS
> + * will be cleared soon after, so it's not suitable.
> + */
> +static uintptr_t rom_api_loc __section(".data");
> +
> +/*
> + * The ROM gives us the API location in r0 when starting. This is only available
> + * during SPL, as there isn't (yet) a mechanism to pass this on to u-boot.
> + */
> +void save_boot_params(unsigned long r0, unsigned long r1, unsigned long r2,
> +		      unsigned long r3)
> +{
> +	rom_api_loc = r0;
> +	save_boot_params_ret();
> +}
> +
> +static void stm32mp_rom_get_ecdsa_functions(struct ecdsa_rom_api *rom)
> +{
> +	uintptr_t verify_ptr = rom_api_loc + ROM_API_OFFSET_ECDSA_VERIFY;
> +	uintptr_t check_key_ptr = rom_api_loc + ROM_API_OFFSET_ECDSA_CHECK_KEY;
> +
> +	rom->ecdsa_verify_signature = *(void **)verify_ptr;
> +	rom->ecdsa_check_key = *(void **)check_key_ptr;


the check key API (rom->ecdsa_check_key at offset 
ROM_API_OFFSET_ECDSA_CHECK_KEY)

is never used...

   

Do you plan to use it in futures patches ?

if no, you can remove it.

PS: this API is no more used in recent TF-A downstrean version based on 
auth-framework


> +}
> +
> +static int ecdsa_key_algo(const char *curve_name)
> +{
> +	if (!strcmp(curve_name, "prime256v1"))
> +		return ROM_API_ECDSA_ALGO_PRIME_256V1;
> +	else if (!strcmp(curve_name, "brainpool256"))
> +		return ROM_API_ECDSA_ALGO_BRAINPOOL_256;
> +	else
> +		return -ENOPROTOOPT;
> +}
> +
> +static int romapi_ecdsa_verify(struct udevice *dev,
> +			       const struct ecdsa_public_key *pubkey,
> +			       const void *hash, size_t hash_len,
> +			       const void *signature, size_t sig_len)
> +{
> +	struct ecdsa_rom_api rom;
> +	uint8_t raw_key[64];
> +	uint32_t rom_ret;
> +	int algo;
> +
> +	/* The ROM API can only handle 256-bit ECDSA keys. */
> +	if (sig_len != 64 || hash_len != 32 || pubkey->size_bits != 256)
> +		return -EINVAL;
> +
> +	algo = ecdsa_key_algo(pubkey->curve_name);
> +	if (algo < 0)
> +		return algo;
> +
> +	/* The ROM API wants the (X, Y) coordinates concatenated. */
> +	memcpy(raw_key, pubkey->x, 32);
> +	memcpy(raw_key + 32, pubkey->y, 32);
> +
> +	stm32mp_rom_get_ecdsa_functions(&rom);
> +	rom_ret = rom.ecdsa_verify_signature(hash, raw_key, signature, algo);
> +
> +	return rom_ret == ROM_API_SUCCESS ? 0 : -EPERM;
> +}
> +
> +static const struct ecdsa_ops rom_api_ops = {
> +	.verify = romapi_ecdsa_verify,
> +};
> +
> +U_BOOT_DRIVER(stm32mp_rom_api_ecdsa) = {
> +	.name	= "stm32mp_rom_api_ecdsa",
> +	.id	= UCLASS_ECDSA,
> +	.ops	= &rom_api_ops,
> +	.flags	= DM_FLAG_PRE_RELOC,
> +};
> +
> +U_BOOT_DRVINFO(stm32mp_rom_api_ecdsa) = {
> +	.name = "stm32mp_rom_api_ecdsa",
> +};


Regards


Patrick