c++ - How do you read directly from physical memory?

Question

In C or C++ (windows), how do you read RAM by giving a physical (not virtual) address? That means without going trough virtual memory system (mmu tables), and being specific to one process.

I already know the API ReadProcessMemory, which reads from ram (used by most trainers) but it is only for a specific process.

I searched on MSDN and found that DevicePhysicalMemory seems to give such possibility, but I found no practical example and this feature seems to have been turned off by Windows service packs (to fix some vulnerability).

I know it is possible to do because WinHex does it (if you choose "tools" > "open ram" > "physical memory"). It will then display RAM content from 0x00000000 to your_ram_size just like when you open a traditional file. It requires administrator rights, but there is no driver to install (which means WinHex does it from user mode).

EDIT : added information about os.

Answer 1

You would have to write a kernel mode driver and use memory manager functions to map physical memory range to your kernel driver's system space then export functionality to a user API or driver.

After windows 98 it is not possible in most cases to access physical memory from user mode. As others have put it this is so any old program cant just destroy people's computers. You would have to write a kernel driver, which can only be installed if it is signed and first loaded into the window's store. This alone is not a simple process like linking a DLL.

In summary MmAllocateContiguousMemory() is a windows kernel mode function which maps contiguous physical memory to system memory and is a part of ntoskrnl.exe.

Also you can not call these API's from user mode applications. Only driver's can use them. User mode applications CANNOT access physical memory with out the help of a driver. The driver can either handle request's from the user API or use IOCTLs and map it's resources to the API's virtual memory. Either way you will need the help of a driver which has to be installed by plug n play manager. PnP has to choose to install the driver on it's own either by hardware activation i.e. hot plug or some other method like a bus driver that is always on.

Further windows randomly assign's virtual address so that it is not easily possible to discern any pattern or work out it's physical location.