memory: Do not allow direct write access to rom_device regions

According to the documentation in memory.h a ROM memory region will be
backed by RAM for reads, but is supposed to go through a callback for
writes. Currently we were not checking for the existence of the rom_device
flag when determining if we could perform a direct write or not.

To correct that add a check to memory_region_is_direct so that if the
memory region has the rom_device flag set we will return false for all
checks where is_write is set.

Signed-off-by: Alexander Duyck <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: Alexander Duyck

include/exec/memory.h

@@ -2351,8 +2351,8 @@ void address_space_write_cached_slow(MemoryRegionCache *cache,
 static inline bool memory_access_is_direct(MemoryRegion *mr, bool is_write)
 {
     if (is_write) {
-        return memory_region_is_ram(mr) &&
-               !mr->readonly && !memory_region_is_ram_device(mr);
+        return memory_region_is_ram(mr) && !mr->readonly &&
+               !mr->rom_device && !memory_region_is_ram_device(mr);
     } else {
         return (memory_region_is_ram(mr) && !memory_region_is_ram_device(mr)) ||
                memory_region_is_romd(mr);