[PATCH v4 4/6] arm: stm32mp1: Implement ECDSA signature verification

Alexandru Gagniuc
2021-04-15T20:05:07Z

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>
---
arch/arm/mach-stm32mp/Kconfig | 9 +++
arch/arm/mach-stm32mp/Makefile | 1 +
arch/arm/mach-stm32mp/ecdsa_romapi.c | 102 +++++++++++++++++++++++++++
3 files changed, 112 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 7c25266f33..b47fbbb97b 100644
--- a/arch/arm/mach-stm32mp/Kconfig
+++ b/arch/arm/mach-stm32mp/Kconfig
@@ -172,6 +172,15 @@ 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..a2f63ff879
--- /dev/null
+++ b/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",
+};
--
2.26.3