zinger: check RW firmware signature

The Zinger RW is now signed with 2048-bit RSA key (using SHA-256 as
digest).
This CL implements the verification mechanism.

note: the RSA key used for signing must be provided as a .pem file.
The path to .pem file must be provided in the PEM environment variable.
By default, it's using the dev key stored in zinger_dev_key.pem.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=samus
BUG=chrome-os-partner:28336
TEST=on Zinger, run with properly signed RW firmware and corrupted
firmware and check the serial traces.

Change-Id: Ia58482458904a3ed72d6b0e95996cae86a0ead83
Reviewed-on: https://chromium-review.googlesource.com/220178
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Alec Berg <alecaberg@chromium.org>

6 files changed, 61 insertions, 25 deletions

diff --git a/board/zinger/board.c b/board/zinger/board.c
index faab419cc4..bf974cef24 100644
--- a/board/zinger/board.c
+++ b/board/zinger/board.c
@@ -7,11 +7,22 @@
 #include "common.h"
 #include "debug.h"
 #include "registers.h"
+#include "rsa.h"
 #include "sha1.h"
+#include "sha256.h"
 #include "task.h"
 #include "usb_pd.h"
 #include "util.h"
 
+/* Insert the RSA public key definition */
+const struct rsa_public_key pkey __attribute__((section(".rsa_pubkey"))) =
+#include "gen_pub_key.h"
+/* The RSA signature is stored at the end of the RW firmware */
+static const void *rw_sig = (void *)CONFIG_FLASH_BASE + CONFIG_FW_RW_OFF
+				 + CONFIG_FW_RW_SIZE - RSANUMBYTES;
+/* Large 768-Byte buffer for RSA computation : could be re-use afterwards... */
+static uint32_t rsa_workbuf[3 * RSANUMWORDS];
+
 extern void pd_rx_handler(void);
 
 /* RW firmware reset vector */
@@ -44,23 +55,17 @@ int is_ro_mode(void)
 
 static int check_rw_valid(void)
 {
-	uint32_t *hash;
-	uint32_t *fw_hash = (uint32_t *)
-		(CONFIG_FLASH_BASE + CONFIG_FLASH_SIZE - 32);
+	int good;
+	uint8_t *hash;
 
 	/* Check if we have a RW firmware flashed */
 	if (*rw_rst == 0xffffffff)
 		return 0;
 
-	hash = (uint32_t *)flash_hash_rw();
-	/* TODO(crosbug.com/p/28336) use secret key to check RW */
-	if (memcmp(hash, fw_hash, SHA1_DIGEST_SIZE) != 0) {
-		/* Firmware doesn't match the recorded hash */
-		debug_printf("SHA-1 %08x %08x %08x %08x %08x\n",
-			hash[0], hash[1], hash[2], hash[3], hash[4]);
-		debug_printf("FW SHA-1 %08x %08x %08x %08x %08x\n",
-			fw_hash[0], fw_hash[1], fw_hash[2],
-			fw_hash[3], fw_hash[4]);
+	hash = flash_hash_rw();
+	good = rsa_verify(&pkey, (void *)rw_sig, (void *)hash, rsa_workbuf);
+	if (!good) {
+		debug_printf("RSA verify FAILED\n");
 		return 0;
 	}
 
diff --git a/board/zinger/board.h b/board/zinger/board.h
index daca59de8f..2b420e496a 100644
--- a/board/zinger/board.h
+++ b/board/zinger/board.h
@@ -24,7 +24,8 @@
 #define CONFIG_USB_PD_CUSTOM_VDM
 #undef CONFIG_USB_PD_RX_COMP_IRQ
 #define CONFIG_HW_CRC
-#define CONFIG_SHA1
+#define CONFIG_RSA
+#define CONFIG_SHA256
 #undef CONFIG_WATCHDOG_HELP
 #undef CONFIG_WATCHDOG_PERIOD_MS
 #define CONFIG_WATCHDOG_PERIOD_MS 2300
diff --git a/board/zinger/build.mk b/board/zinger/build.mk
index 4e9e2f1f6d..885b0c5c0a 100644
--- a/board/zinger/build.mk
+++ b/board/zinger/build.mk
@@ -12,3 +12,6 @@ CHIP_VARIANT:=stm32f03x
 
 board-y=board.o hardware.o runtime.o usb_pd_policy.o
 board-$(CONFIG_DEBUG_PRINTF)+=debug.o
+
+# Add dependency to generate the public key coefficients header
+$(out)/board/$(BOARD)/board.o: $(out)/gen_pub_key.h
diff --git a/board/zinger/dev_key.pem b/board/zinger/dev_key.pem
new file mode 100644
index 0000000000..6912b1f44e
--- /dev/null
+++ b/board/zinger/dev_key.pem
@@ -0,0 +1,27 @@
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----
diff --git a/board/zinger/hardware.c b/board/zinger/hardware.c
index 1b22ec64c4..061f3bdf89 100644
--- a/board/zinger/hardware.c
+++ b/board/zinger/hardware.c
@@ -9,7 +9,8 @@
 #include "common.h"
 #include "cpu.h"
 #include "registers.h"
-#include "sha1.h"
+#include "rsa.h"
+#include "sha256.h"
 #include "task.h"
 #include "timer.h"
 #include "util.h"
@@ -374,11 +375,11 @@ exit_er:
 	return res;
 }
 
-static struct sha1_ctx ctx;
+static struct sha256_ctx ctx;
 uint8_t *flash_hash_rw(void)
 {
-	sha1_init(&ctx);
-	sha1_update(&ctx, (void *)CONFIG_FLASH_BASE + CONFIG_FW_RW_OFF,
-		    CONFIG_FW_RW_SIZE - 32);
-	return sha1_final(&ctx);
+	SHA256_init(&ctx);
+	SHA256_update(&ctx, (void *)CONFIG_FLASH_BASE + CONFIG_FW_RW_OFF,
+		    CONFIG_FW_RW_SIZE - RSANUMBYTES);
+	return SHA256_final(&ctx);
 }
diff --git a/board/zinger/usb_pd_policy.c b/board/zinger/usb_pd_policy.c
index bc2a0ede3b..f54841bb72 100644
--- a/board/zinger/usb_pd_policy.c
+++ b/board/zinger/usb_pd_policy.c
@@ -378,13 +378,12 @@ int pd_custom_vdm(int port, int cnt, uint32_t *payload, uint32_t **rpayload)
 		break;
 	case VDO_CMD_READ_INFO:
 		hash = flash_hash_rw();
-		/* copy hash into response */
-		memcpy(payload + 1, hash, SHA1_DIGEST_SIZE);
+		/* copy the 20 first bytes of the hash into response */
+		memcpy(payload + 1, hash, 5 * sizeof(uint32_t));
 		/* copy other info into response */
-		payload[SHA1_DIGEST_SIZE/4 + 1] = VDO_INFO(
-						USB_PD_HARDWARE_DEVICE_ID,
-						ver_get_numcommits(),
-						!is_ro_mode());
+		payload[6] = VDO_INFO(USB_PD_HARDWARE_DEVICE_ID,
+					ver_get_numcommits(),
+					!is_ro_mode());
 		rsize = 7;
 		break;
 	case VDO_CMD_FLASH_ERASE: