arm: stm32mp1: Implement ECDSA signature verification

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@gmail.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

arch/arm/mach-stm32mp/Kconfig

@@ -179,6 +179,15 @@ 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 n

arch/arm/mach-stm32mp/Makefile

@@ -11,6 +11,7 @@ obj-y += bsec.o
 ifdef CONFIG_SPL_BUILD
 obj-y += spl.o
 obj-y += tzc400.o
+obj-$(CONFIG_STM32_ECDSA_VERIFY) += ecdsa_romapi.o
 else
 obj-y += cmd_stm32prog/
 obj-$(CONFIG_CMD_STM32KEY) += cmd_stm32key.o

arch/arm/mach-stm32mp/ecdsa_romapi.c

@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * STM32MP ECDSA verification via the ROM API
+ *
+ * Implements ECDSA signature verification via the STM32MP ROM.
+ */
+#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_VERIFY		0x60
+
+struct ecdsa_rom_api {
+	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;
+
+	rom->ecdsa_verify_signature = *(void **)verify_ptr;
+}
+
+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",
+};