libfdt: Add support for disabling dtb checks

Support ASSUME_VALID_DTB to disable some sanity checks

If we assume that the DTB itself is valid then we can skip some checks and
save code space. Add various conditions to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Message-Id: <20200220214557.176528-4-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt.c

@@ -19,6 +19,9 @@ int32_t fdt_ro_probe_(const void *fdt)
 {
 	uint32_t totalsize = fdt_totalsize(fdt);
 
+	if (can_assume(VALID_DTB))
+		return totalsize;
+
 	if (fdt_magic(fdt) == FDT_MAGIC) {
 		/* Complete tree */
 		if (fdt_version(fdt) < FDT_FIRST_SUPPORTED_VERSION)
@@ -81,21 +84,25 @@ int fdt_check_header(const void *fdt)
 
 	if (fdt_magic(fdt) != FDT_MAGIC)
 		return -FDT_ERR_BADMAGIC;
-	hdrsize = fdt_header_size(fdt);
 	if ((fdt_version(fdt) < FDT_FIRST_SUPPORTED_VERSION)
 	    || (fdt_last_comp_version(fdt) > FDT_LAST_SUPPORTED_VERSION))
 		return -FDT_ERR_BADVERSION;
 	if (fdt_version(fdt) < fdt_last_comp_version(fdt))
 		return -FDT_ERR_BADVERSION;
+	hdrsize = fdt_header_size(fdt);
+	if (!can_assume(VALID_DTB)) {
 
 		if ((fdt_totalsize(fdt) < hdrsize)
 		    || (fdt_totalsize(fdt) > INT_MAX))
 			return -FDT_ERR_TRUNCATED;
 
 		/* Bounds check memrsv block */
-	if (!check_off_(hdrsize, fdt_totalsize(fdt), fdt_off_mem_rsvmap(fdt)))
+		if (!check_off_(hdrsize, fdt_totalsize(fdt),
+				fdt_off_mem_rsvmap(fdt)))
 			return -FDT_ERR_TRUNCATED;
+	}
 
+	if (!can_assume(VALID_DTB)) {
 		/* Bounds check structure block */
 		if (fdt_version(fdt) < 17) {
 			if (!check_off_(hdrsize, fdt_totalsize(fdt),
@@ -110,8 +117,10 @@ int fdt_check_header(const void *fdt)
 
 		/* Bounds check strings block */
 		if (!check_block_(hdrsize, fdt_totalsize(fdt),
-			  fdt_off_dt_strings(fdt), fdt_size_dt_strings(fdt)))
+				  fdt_off_dt_strings(fdt),
+				  fdt_size_dt_strings(fdt)))
 			return -FDT_ERR_TRUNCATED;
+	}
 
 	return 0;
 }
@@ -142,7 +151,7 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
 
 	*nextoffset = -FDT_ERR_TRUNCATED;
 	tagp = fdt_offset_ptr(fdt, offset, FDT_TAGSIZE);
-	if (!tagp)
+	if (!can_assume(VALID_DTB) && !tagp)
 		return FDT_END; /* premature end */
 	tag = fdt32_to_cpu(*tagp);
 	offset += FDT_TAGSIZE;
@@ -154,13 +163,13 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
 		do {
 			p = fdt_offset_ptr(fdt, offset++, 1);
 		} while (p && (*p != '\0'));
-		if (!p)
+		if (!can_assume(VALID_DTB) && !p)
 			return FDT_END; /* premature end */
 		break;
 
 	case FDT_PROP:
 		lenp = fdt_offset_ptr(fdt, offset, sizeof(*lenp));
-		if (!lenp)
+		if (!can_assume(VALID_DTB) && !lenp)
 			return FDT_END; /* premature end */
 		/* skip-name offset, length and value */
 		offset += sizeof(struct fdt_property) - FDT_TAGSIZE

libfdt/fdt_ro.c

@@ -388,7 +388,8 @@ static const struct fdt_property *fdt_get_property_namelen_(const void *fdt,
 	     (offset = fdt_next_property_offset(fdt, offset))) {
 		const struct fdt_property *prop;
 
-		if (!(prop = fdt_get_property_by_offset_(fdt, offset, lenp))) {
+		prop = fdt_get_property_by_offset_(fdt, offset, lenp);
+		if (!can_assume(VALID_DTB) && !prop) {
 			offset = -FDT_ERR_INTERNAL;
 			break;
 		}

libfdt/fdt_rw.c

@@ -24,6 +24,8 @@ static int fdt_blocks_misordered_(const void *fdt,
 
 static int fdt_rw_probe_(void *fdt)
 {
+	if (can_assume(VALID_DTB))
+		return 0;
 	FDT_RO_PROBE(fdt);
 
 	if (fdt_version(fdt) < 17)

libfdt/fdt_sw.c

@@ -12,10 +12,13 @@
 
 static int fdt_sw_probe_(void *fdt)
 {
+	if (!can_assume(VALID_DTB)) {
 		if (fdt_magic(fdt) == FDT_MAGIC)
 			return -FDT_ERR_BADSTATE;
 		else if (fdt_magic(fdt) != FDT_SW_MAGIC)
 			return -FDT_ERR_BADMAGIC;
+	}
+
 	return 0;
 }
 
@@ -38,7 +41,7 @@ static int fdt_sw_probe_memrsv_(void *fdt)
 	if (err)
 		return err;
 
-	if (fdt_off_dt_strings(fdt) != 0)
+	if (!can_assume(VALID_DTB) && fdt_off_dt_strings(fdt) != 0)
 		return -FDT_ERR_BADSTATE;
 	return 0;
 }
@@ -151,7 +154,8 @@ int fdt_resize(void *fdt, void *buf, int bufsize)
 	headsize = fdt_off_dt_struct(fdt) + fdt_size_dt_struct(fdt);
 	tailsize = fdt_size_dt_strings(fdt);
 
-	if ((headsize + tailsize) > fdt_totalsize(fdt))
+	if (!can_assume(VALID_DTB) &&
+	    headsize + tailsize > fdt_totalsize(fdt))
 		return -FDT_ERR_INTERNAL;
 
 	if ((headsize + tailsize) > bufsize)