Replacements for IsBadReadPtr and IsBadWritePtr

[Blake Miller]

Has anybody already written some? I am thinking variations on data returned from VirtualQuery could do the trick. Oh yeah, because IsBadReadPtr and IsBadWritePtr won't do anything on Windows Vista, according to MS documentation.

[Mike Dimmick]

Raymond Chen: IsBadXxxPtr should really be called CrashProgramRandomly[^]. They've been deactivated as they're a common source of problems.

DoEvents: Generating unexpected recursion since 1991

[Blake Miller]

Yes, I know that. I was asking if anyone had already written replacements or knew of anything else.

[Lost User]

For a read pointer all we need to know is if VirtualQuery can read it. So you could do something like this:

BOOL IsBadReadPointerCheck(char *p, size_t size)
{
	MEMORY_BASIC_INFORMATION mbi;
	for (void *pStop = p + size; p < pStop;p =p+mbi.RegionSize)
	{
		if(!VirtualQuery(p,&mbi,sizeof(mbi)))
		{
			return FALSE;
		}
	}
	return TRUE;
}

For a write pointer we would need to iterate through the entire range and check the bits stored in the Protect member of the MEMORY_BASIC_INFORMATION structure. Something like this:

BOOL IsBadWritePointer(char *p, size_t size)
{
	BOOL bRet = FALSE;
	void *pStop = p+size;
	MEMORY_BASIC_INFORMATION mbi;
	for(p;p < pStop;++p))
	{
		if(VirtualQueryEx(GetCurrentProcess(),(LPVOID)p,&mbi,sizeof(MEMORY_BASIC_INFORMATION)))
		{
			if(!(((mbi.Protect & PAGE_READWRITE) == PAGE_READWRITE) || ((mbi.Protect & PAGE_EXECUTE_READWRITE) == PAGE_EXECUTE_READWRITE)))
			{
				return TRUE;
			}
		}
	}
	return bRet;
}

Lets say that you have a pointer to a member function and you want to validate the member function pointer. You might do something like this:

MEMORY_BASIC_INFORMATION mbi;
if(VirtualQueryEx(GetCurrentProcess(),(LPVOID)pInstructions,&mbi,sizeof(MEMORY_BASIC_INFORMATION)))
{
	if(mbi.Protect & PAGE_EXECUTE_READ && mbi.State & MEM_COMMIT && mbi.AllocationProtect & PAGE_EXECUTE_WRITECOPY && mbi.Type & MEM_IMAGE)
	{
		(*this.*MemberFunction)(val);
		return TRUE;
	}
}

*Disclaimer Edit* I have not had time to test these functions as I am currently too busy. These functions were removed from some experimental code I was working on some time back. Use/Modify them at your own risk. Just by looking over them I can see they need to have additional error handling. Best Wishes, -David Delaune

modified on Friday, May 2, 2008 3:05 PM

[Mike Dimmick]

#define IsBadReadPtr(x) ((x) == NULL)
#define IsBadWritePtr(x) ((x) == NULL)

These functions are that bad. An immediate null pointer check is about as good as it's going to get.

DoEvents: Generating unexpected recursion since 1991