Question

I am trying to use memory-mapped files as:

hFile = ::CreateFile(State.Path, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE,
                                 0, OPEN_EXISTING,FILE_FLAG_SEQUENTIAL_SCAN, 0);//open the file

if(hFile !=INVALID_HANDLE_VALUE){
hMap= ::CreateFileMapping(hFile, 0, PAGE_READONLY | SEC_COMMIT, 0, 0, 0);//create Mem mapping for the file in virtual memory
if( hMap!=NULL){
base = ::MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, 0);//load the mapped file into the RAM
//start to compare some bytes (values) from mspaint.exe file in Win7
if( *((BYTE *)base + 0x1C3DF0)== 0x05 )
i++; 
if( *((BYTE *)base + 0x25250C)== 0x21 )
i++;
if( *((BYTE *)base + 0x25272A)== 0x97 )
i++;

if(i==3){
// the file is malicious
}

Once the file size be in Gigabytes, the MapViewOfFile function stop working and the application will be crashed! Is there any limitation to use MapViewOfFile ? Any suggestion?

Answer 1

You need to check the return value! The other reason for a crash can be found in the MapViewOfFile remarks section on MSDN:

To guard against EXCEPTION_IN_PAGE_ERROR exceptions, use structured
exception handling to protect any code that writes to or reads from a
memory mapped view of a file other than the page file.

As far as other limitations go; clearly the view has to fit in the virtual memory space of your process and a 32 bit process normally only has 2gb in total. If you are working with gigabyte sized files you need to map smaller views and not the whole file at once…