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[C++] Error check pointers

 
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iLogic
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PostPosted: Sat Feb 23, 2013 12:42 am    Post subject: [C++] Error check pointers Reply with quote
I'm currently tring to modify the PointerHelper class that I got from SteveAndrew to perform extra checks when building pointers.
I had some trouble with it reading addresses that it shouldn't be reading, which caused it to crash.

This is what I've done to it so far.

Code:
unsigned long long Pointer::BuildOffsets(unsigned long long PtrValue, unsigned long long offset)
{
   MEMORY_BASIC_INFORMATION mbi;
   VirtualQueryEx(GetModuleHandleA(0), (VOID*)(PtrValue + offset), &mbi, sizeof(mbi));

   if((mbi.State == MEM_COMMIT) && (mbi.Protect == PAGE_READWRITE) && ((mbi.Type == MEM_PRIVATE) || (mbi.Type == MEM_MAPPED)))
   {
      if ( !IsBadReadPtr((VOID*)(PtrValue + offset), sizeof(ULONG_PTR)) )
      {
         PtrValue = *(unsigned long long*)(PtrValue + offset);
         return PtrValue;
      }
      else
      {
         return 0;
      }
   }
   return 0;
}

unsigned long long Pointer::GetDynamicAddress()
{
   unsigned long long PtrValue = (unsigned long long)BasePtr;
   
   if(OffsetsList)
   {
      //use all offsets in sequential order to end up with the final pointer
      PointerOffset *CurrentOffset = OffsetsList;
        
      while(CurrentOffset->NextOffset)
      {
         if(!PtrValue) //Don't try to access the pointer if its null
       {
            return 0;
       }

       PtrValue = BuildOffsets(PtrValue, CurrentOffset->Offset);
       CurrentOffset = CurrentOffset->NextOffset;
      }

     if(!PtrValue)
     {
         return 0;
     }

     PtrValue += CurrentOffset->Offset;   

     if(!PtrValue)
     {
         return 0;
     }
      CurrentDynamicAddress = (void*)PtrValue;     
      return PtrValue;
   }

   return 0;
}


Problem is that now it's no longer able to read the pointer that I wanted it to read.

The issue is this, from what I can see:

Code:
VirtualQueryEx(GetModuleHandleA(0), (VOID*)(PtrValue + offset), &mbi, sizeof(mbi));

if((mbi.State == MEM_COMMIT) && (mbi.Protect == PAGE_READWRITE) && ((mbi.Type == MEM_PRIVATE) || (mbi.Type == MEM_MAPPED)))

Any idea what I've done wrong here?


Edit: After some more error checking, it would seem that none of the mbi values are "true".. So, I'm either executing the "VirtualQueryEx" function wrong or the cheat protection have it hooked.
If it is hooked, any suggestions on what I can do to confirm that the address I'm trying to read is indeed readable to avoid crashes?


Edit2: Ok.. I figured out what was wrong...
After some thinking and time spent on msdn I realized that I shouldn't be using VirtualQueryEx. Since I'm doing this within the process I should of used VirtualQuery.


Edit 3:

I got a new issue with this now though. It would seem that VirtualQuery gets stuck in an infinite loop if it reads an invalid memory space.

I've changed it so it looks like this now:
Code:
unsigned long long Pointer::BuildOffsets(unsigned long long PtrValue, unsigned long long offset)
{
   MEMORY_BASIC_INFORMATION mbi;
   if(VirtualQuery((VOID*)(PtrValue + offset), &mbi, sizeof(MEMORY_BASIC_INFORMATION)) != 0)
   {   
      if((mbi.State & MEM_COMMIT) && (mbi.Protect & WRITABLE))
      {
         if ( !IsBadReadPtr((VOID*)(PtrValue + offset), sizeof(ULONG_PTR)) )
         {
            PtrValue = *(unsigned long long*)(PtrValue + offset);
            return PtrValue;
         }
         else
         {
            return 0;
         }
      }
   }
   return 0;
}


Where I've defined "WRITABLE" as:
Code:
#define WRITABLE (PAGE_READWRITE | PAGE_WRITECOPY | PAGE_EXECUTE_READWRITE | PAGE_EXECUTE_WRITECOPY)
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Dark Byte
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PostPosted: Sat Feb 23, 2013 4:45 am    Post subject: Reply with quote
If your memory is unwritable or unreadable nothing will happen to ptrvalue
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iLogic
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Joined: 28 Oct 2012
Posts: 13
PostPosted: Sat Feb 23, 2013 4:52 am    Post subject: Reply with quote
Yeah, but then it should leave the function with a "return 0".
The issue I got now is that it doesn't seem to leave the VirtualQuery function, it starts looping it over and over :/


I'm using this to go through a lot of different pointers, the issue I had before was that some times these pointers would break during certain circumstances, but the code tried to read them anyway causing a crash.

That's why I decided to use VirtualQuery since then I could check the area before I try to add the offsets.

Edit: I've tested it out some more.. turns out it wasn't going in an infinite loop.. It were just going insanely slow...

Any suggestions on how to make it check tons of addresses faster?
By tons of addresses, I mean like reading a span of:
0x2500000 -> 0x3500000
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Dark Byte
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PostPosted: Sat Feb 23, 2013 6:25 am    Post subject: Reply with quote
don't call virtualquery on every address
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