rwsig: Add support for rwsig image types

usbpd1 futility image type is deprecated and should not be used for
new designs. This adds proper support for rwsig image type.

Key and signatures are added at linker stage step (futility cannot
directly create such signed images). Thanks to VB21 header, rwsig.c
can now tell how many bytes of the RW image need to be
cryptographically verified, and ensure that the rest is blank (0xff).

BRANCH=none
BUG=chromium:690773
TEST=make BOARD=hammer; flash, RW image is verified correctly.
TEST=make runtests -j
TEST=For the rest of the tests:
     Change config option to CONFIG_RWSIG_TYPE_RWSIG
TEST=make BOARD=hammer; flash, hammer still verifies correctly.
TEST=cp build/hammer/ec.RW.bin build/hammer/ec.RW.bin.orig;
     futility sign --type rwsig --prikey build/hammer/key.vbprik2 \
        build/hammer/ec.RW.bin
     diff build/hammer/ec.RW.bin build/hammer/ec.RW.bin.orig
     => Same file
TEST=Add CONFIG_CMD_FLASH, flashwrite 0x1e000, reboot, EC does
     not verify anymore.
TEST=dump_fmap build/hammer/ec.bin shows KEY_RO and SIG_RW at
     correct locations.

Change-Id: I50ec828284c2d1eca67fa8cbddaf6f3b06606c82
Reviewed-on: https://chromium-review.googlesource.com/441546
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

1 files changed, 84 insertions, 8 deletions

diff --git a/common/rwsig.c b/common/rwsig.c
index ee1bd6c9fc..1ad3ed37f9 100644
--- a/common/rwsig.c
+++ b/common/rwsig.c
@@ -15,6 +15,7 @@
 #include "system.h"
 #include "usb_pd.h"
 #include "util.h"
+#include "vb21_struct.h"
 
 /* Console output macros */
 #define CPRINTF(format, args...) cprintf(CC_SYSTEM, format, ## args)
@@ -24,12 +25,44 @@
 static uint32_t * const rw_rst =
 	(uint32_t *)(CONFIG_PROGRAM_MEMORY_BASE + CONFIG_RW_MEM_OFF + 4);
 
+/*
+ * Check that memory between rwdata[start] and rwdata[len-1] is filled
+ * with ones. data, start and len must be aligned on 4-byte boundary.
+ */
+static int check_padding(const uint8_t *data,
+			 unsigned int start, unsigned int len)
+{
+	unsigned int i;
+	const uint32_t *data32 = (const uint32_t *)data;
+
+	if ((start % 4) != 0 || (len % 4) != 0)
+		return 0;
+
+	for (i = start/4; i < len/4; i++) {
+		if (data32[i] != 0xffffffff)
+			return 0;
+	}
+
+	return 1;
+}
+
 void check_rw_signature(void)
 {
 	struct sha256_ctx ctx;
-	int good, res;
+	int res;
+	const struct rsa_public_key *key;
+	const uint8_t *sig;
 	uint8_t *hash;
 	uint32_t *rsa_workbuf;
+	const uint8_t *rwdata = (uint8_t *)CONFIG_PROGRAM_MEMORY_BASE
+					+ CONFIG_RW_MEM_OFF;
+	int good = 0;
+
+	unsigned int rwlen;
+#ifdef CONFIG_RWSIG_TYPE_RWSIG
+	const struct vb21_packed_key *vb21_key;
+	const struct vb21_signature *vb21_sig;
+#endif
 
 	/* Only the Read-Only firmware needs to do the signature check */
 	if (system_get_image_copy() != SYSTEM_IMAGE_RO)
@@ -48,17 +81,60 @@ void check_rw_signature(void)
 		return;
 	}
 
+#ifdef CONFIG_RWSIG_TYPE_USBPD1
+	key = (const struct rsa_public_key *)CONFIG_RO_PUBKEY_ADDR;
+	sig = (const uint8_t *)CONFIG_RW_SIG_ADDR;
+	rwlen = CONFIG_RW_SIZE - CONFIG_RW_SIG_SIZE;
+#elif defined(CONFIG_RWSIG_TYPE_RWSIG)
+	vb21_key = (const struct vb21_packed_key *)CONFIG_RO_PUBKEY_ADDR;
+	vb21_sig = (const struct vb21_signature *)CONFIG_RW_SIG_ADDR;
+
+	if (vb21_key->c.magic != VB21_MAGIC_PACKED_KEY ||
+	    vb21_key->key_size != sizeof(struct rsa_public_key)) {
+		CPRINTS("Invalid key.");
+		goto out;
+	}
+
+	key = (const struct rsa_public_key *)
+		((const uint8_t *)vb21_key + vb21_key->key_offset);
+
+	/*
+	 * TODO(crbug.com/690773): We could verify other parameters such
+	 * as sig_alg/hash_alg actually matches what we build for.
+	 */
+	if (vb21_sig->c.magic != VB21_MAGIC_SIGNATURE ||
+	    vb21_sig->sig_size != RSANUMBYTES ||
+	    vb21_key->sig_alg != vb21_sig->sig_alg ||
+	    vb21_key->hash_alg != vb21_sig->hash_alg ||
+	    /* Sanity check signature offset and data size. */
+	    vb21_sig->sig_offset < sizeof(vb21_sig) ||
+	    (vb21_sig->sig_offset + RSANUMBYTES) > CONFIG_RW_SIG_SIZE ||
+	    vb21_sig->data_size > (CONFIG_RW_SIZE - CONFIG_RW_SIG_SIZE)) {
+		CPRINTS("Invalid signature.");
+		goto out;
+	}
+
+	sig = (const uint8_t *)vb21_sig + vb21_sig->sig_offset;
+	rwlen = vb21_sig->data_size;
+#endif
+
+	/*
+	 * Check that unverified RW region is actually filled with ones.
+	 */
+	good = check_padding(rwdata, rwlen,
+			CONFIG_RW_SIZE - CONFIG_RW_SIG_SIZE);
+	if (!good) {
+		CPRINTS("Invalid padding.");
+		goto out;
+	}
+
 	/* SHA-256 Hash of the RW firmware */
-	/* TODO(crosbug.com/p/44803): Do we have to hash the whole region? */
 	SHA256_init(&ctx);
-	SHA256_update(&ctx, (void *)CONFIG_PROGRAM_MEMORY_BASE
-		      + CONFIG_RW_MEM_OFF,
-		      CONFIG_RW_SIZE - CONFIG_RW_SIG_SIZE);
+	SHA256_update(&ctx, rwdata, rwlen);
 	hash = SHA256_final(&ctx);
 
-	good = rsa_verify((const struct rsa_public_key *)CONFIG_RO_PUBKEY_ADDR,
-			  (const uint8_t *)CONFIG_RW_SIG_ADDR,
-			  hash, rsa_workbuf);
+	good = rsa_verify(key, sig, hash, rsa_workbuf);
+out:
 	if (good) {
 		CPRINTS("RW image verified");
 		/* Jump to the RW firmware */