sbverify: Add check for image hash

Add a check to match the calculated image's hash against the one found
in the PKCS7 IndirectDataContext

Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>

Makefile

@@ -5,7 +5,7 @@ CFLAGS = -Wall -Werror -Wextra -ggdb --std=c99
 LDFLAGS = -fwhole-program
 
 sbsign_objs = sbsign.o idc.o image.o
-sbverify_objs = sbverify.o image.o
+sbverify_objs = sbverify.o idc.o image.o
 libs = -lbfd -lcrypto
 
 ccan_objs = lib/ccan/libccan.a

idc.c

@@ -17,6 +17,7 @@
  * USA.
  */
 #include <stdint.h>
+#include <string.h>
 #include <openssl/asn1t.h>
 #include <openssl/evp.h>
 #include <openssl/err.h>
@@ -132,6 +133,17 @@ const char obsolete[] = {
 	0x00, 0x65, 0x00, 0x3e, 0x00, 0x3e, 0x00, 0x3e
 };
 
+const char *sha256_str(const uint8_t *hash)
+{
+	static char s[SHA256_DIGEST_LENGTH * 2 + 1];
+	int i;
+
+	for (i = 0; i < SHA256_DIGEST_LENGTH; i++)
+		snprintf(s + i * 2, 3, "%02x", hash[i]);
+
+	return s;
+}
+
 int IDC_set(PKCS7 *p7, PKCS7_SIGNER_INFO *si, struct image *image)
 {
 	uint8_t *buf, *tmp, sha[SHA256_DIGEST_LENGTH];
@@ -205,4 +217,40 @@ int IDC_set(PKCS7 *p7, PKCS7_SIGNER_INFO *si, struct image *image)
 	return 0;
 }
 
+int IDC_check_hash(struct image *image, PKCS7 *p7)
+{
+	unsigned char sha[SHA256_DIGEST_LENGTH];
+	const unsigned char *buf;
+	ASN1_STRING *str;
+	IDC *idc;
 
+	image_hash_sha256(image, sha);
+
+	/* extract the idc from the signed PKCS7 'other' data */
+	str = p7->d.sign->contents->d.other->value.asn1_string;
+	buf = ASN1_STRING_data(str);
+	idc = d2i_IDC(NULL, &buf, ASN1_STRING_length(str));
+
+	/* check hash algorithm sanity */
+	if (OBJ_cmp(idc->digest->alg->algorithm, OBJ_nid2obj(NID_sha256))) {
+		fprintf(stderr, "Invalid algorithm type\n");
+		return -1;
+	}
+
+	str = idc->digest->digest;
+	if (ASN1_STRING_length(str) != sizeof(sha)) {
+		fprintf(stderr, "Invalid algorithm length\n");
+		return -1;
+	}
+
+	/* check hash against the one we calculated from the image */
+	buf = ASN1_STRING_data(str);
+	if (memcmp(buf, sha, sizeof(sha))) {
+		fprintf(stderr, "Hash doesn't match image\n");
+		fprintf(stderr, " got:       %s\n", sha256_str(buf));
+		fprintf(stderr, " expecting: %s\n", sha256_str(sha));
+		return -1;
+	}
+
+	return 0;
+}

idc.h

@@ -24,6 +24,7 @@
 #include <openssl/pkcs7.h>
 
 int IDC_set(PKCS7 *p7, PKCS7_SIGNER_INFO *si, struct image *image);
+int IDC_check_hash(struct image *image, PKCS7 *p7);
 
 #endif /* IDC_H */
 

sbverify.c

@@ -20,17 +20,25 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#include <ccan/talloc/talloc.h>
+
 #include "image.h"
+#include "idc.h"
 
 #include <openssl/err.h>
 #include <openssl/bio.h>
 #include <openssl/evp.h>
 #include <openssl/pkcs7.h>
 
+enum verify_status {
+	VERIFY_FAIL = 0,
+	VERIFY_OK = 1,
+};
 
 int main(int argc, char **argv)
 {
 	struct cert_table_header *header;
+	enum verify_status status;
 	struct image *image;
 	uint8_t *idcbuf, tmp;
 	const uint8_t *buf;
@@ -38,6 +46,8 @@ int main(int argc, char **argv)
 	BIO *idcbio;
 	PKCS7 *p7;
 
+	status = VERIFY_FAIL;
+
 	if (argc != 2) {
 		fprintf(stderr, "usage: %s <boot-image>\n", argv[0]);
 		return EXIT_FAILURE;
@@ -45,11 +55,12 @@ int main(int argc, char **argv)
 
 	image = image_load(argv[1]);
 	image_pecoff_parse(image);
+	image_find_regions(image);
 
 	if (!image->data_dir_sigtable->addr
 			|| !image->data_dir_sigtable->size) {
 		fprintf(stderr, "No signature table present\n");
-		return EXIT_FAILURE;
+		goto out;
 	}
 
 	header = image->buf + image->data_dir_sigtable->addr;
@@ -59,6 +70,10 @@ int main(int argc, char **argv)
 	buf = (void *)(header + 1);
 	p7 = d2i_PKCS7(NULL, &buf, header->size);
 
+	rc = IDC_check_hash(image, p7);
+	if (rc)
+		goto out;
+
 	idcbuf = p7->d.sign->contents->d.other->value.asn1_string->data;
 
 	/* we don't include the type and length data in the hash */
@@ -81,9 +96,17 @@ int main(int argc, char **argv)
 	if (!rc) {
 		printf("PKCS7 verification failed\n");
 		ERR_print_errors_fp(stderr);
-	} else {
-		printf("Signature verification OK\n");
+		goto out;
 	}
 
-	return rc ? EXIT_SUCCESS : EXIT_FAILURE;
+	status = VERIFY_OK;
+
+out:
+	talloc_free(image);
+	if (status == VERIFY_OK)
+		printf("Signature verification OK\n");
+	else
+		printf("Signature verification failed\n");
+
+	return status == VERIFY_OK ? EXIT_SUCCESS : EXIT_FAILURE;
 }