ucode: Fix validation on Intel platforms

The check for the extended signature table was backwards, so we always
ignored it.

We should verify that the extended signature table fits within the total
image size.

Reviewed by:	jrm, kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D57209

sys/x86/x86/ucode.c

@@ -204,7 +204,6 @@ ucode_intel_match(const uint8_t *data, size_t *len)
 	uint64_t platformid;
 	size_t resid;
 	uint32_t data_size, flags, regs[4], sig, total_size;
-	int i;
 
 	do_cpuid(1, regs);
 	sig = regs[0];
@@ -226,19 +225,35 @@ ucode_intel_match(const uint8_t *data, size_t *len)
 		if (total_size == 0)
 			total_size = UCODE_INTEL_DEFAULT_DATA_SIZE +
 			    sizeof(struct ucode_intel_header);
-		if (data_size > total_size + sizeof(struct ucode_intel_header))
+
+		if (total_size > data_size + sizeof(struct ucode_intel_header))
 			table = (const struct ucode_intel_extsig_table *)
 			    ((const uint8_t *)(hdr + 1) + data_size);
 		else
 			table = NULL;
 
-		if (hdr->processor_signature == sig) {
-			if ((hdr->processor_flags & flags) != 0) {
-				*len = data_size;
-				return (hdr + 1);
+		if (hdr->processor_signature == sig &&
+		    (hdr->processor_flags & flags) != 0) {
+			*len = data_size;
+			return (hdr + 1);
+		}
+		if (table != NULL) {
+			size_t extsize;
+
+			extsize = total_size -
+			    (data_size + sizeof(struct ucode_intel_header));
+			if (extsize < sizeof(struct ucode_intel_extsig_table)) {
+				ucode_error = VERIFICATION_FAILED;
+				break;
 			}
-		} else if (table != NULL) {
-			for (i = 0; i < table->signature_count; i++) {
+			extsize -= sizeof(struct ucode_intel_extsig_table);
+			for (uint32_t i = 0; i < table->signature_count; i++) {
+				if (extsize < sizeof(struct ucode_intel_extsig)) {
+					ucode_error = VERIFICATION_FAILED;
+					goto out;
+				}
+				extsize -= sizeof(struct ucode_intel_extsig);
+
 				entry = &table->entries[i];
 				if (entry->processor_signature == sig &&
 				    (entry->processor_flags & flags) != 0) {
@@ -248,6 +263,7 @@ ucode_intel_match(const uint8_t *data, size_t *len)
 			}
 		}
 	}
+out:
 	return (NULL);
 }