libfdt: Verify alignment of sub-blocks in dtb

A dtb is considered malformed if its structural elements (not things within
property values) are not naturally aligned.  This means that the structure
block must be aligned to a 32-bit boundary, the reserve map must be aligned
to  64-bit boundary and the whole thing must be loaded at a 64-bit aligned
address.  We currently verify that lasat condition in fdt_check_header()
but not the other cases.

Reported-by: Owen Sanzas (Ze Sheng) 盛泽 <zesheng@tamu.edu>
Link: https://github.com/dgibson/dtc/issues/178
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt.c

@@ -110,6 +110,14 @@ int fdt_check_header(const void *fdt)
 		    || (fdt_totalsize(fdt) > INT_MAX))
 			return -FDT_ERR_TRUNCATED;
 
+		/* memrsv block must be 8 byte aligned */
+		if (fdt_off_mem_rsvmap(fdt) % sizeof(uint64_t))
+			return -FDT_ERR_ALIGNMENT;
+
+		/* Structure block must be 4 byte aligned */
+		if (fdt_off_dt_struct(fdt) % FDT_TAGSIZE)
+			return -FDT_ERR_ALIGNMENT;
+
 		/* Bounds check memrsv block */
 		if (!check_off_(hdrsize, fdt_totalsize(fdt),
 				fdt_off_mem_rsvmap(fdt)))