get-pfn

Warning: You probably do not want this tool! This program grants any user access to the physical addresses mapped into arbitrary executables, which is almost certainly a security vulnerability. This is meant to be used as a utility to grant non-privileged users access to the Linux pagemap files, not a tool for general use.

Building and Installing

The get-pfn tool is installed to /usr/local/bin by default. To build and install, run:

make all && sudo make install

Usage

There are two ways to use this tool: via the command line, or through a C++ wrapper defined in pagemap.hh.

Command Line Usage

To get the physical address for a program's virtual address, run get-pfn:

get-pfn <pid> 0x<virtual address>

For example, to get the physical address for the virtual address 0x400017 in process 457, run:

get-pfn 457 0x400017

The get-pfn tool will output the physical address if it is mapped, or zero if it is not mapped. If you do not provide the virtual address as a command line argument, the tool will run in interactive mode. In interactive mode, the tool expects to receive a virtual address in binary form via standard in. It well then write the physical address out to standard out, again in binary form. This is primarily useful for access via the C++ wrapper.

Using the C++ Wrapper

To look up physical addresses programmatically, use the C++ wrapper to start a get-pfn process in interactive mode. This wrapper sets up a communication channel with the child and hides the communication details behind a simple API. To use the wrapper, just include the <pagemap.hh> include file and build with C++11 or later. The following example shows a simple lookup:

#include <pagemap.hh>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
  int x;
  pagemap map(getpid());
  printf("x is at virtual address %p\n", &x);
  printf("x is at physical address %p\n", map[&x]);
  return 0;
}

You can perform lookups using the lookup member function, which takes a uintptr_t, or using array-style indexing with a uintptr_t. In both cases, the pagemap will return a uintptr_t for the physical address. There is also a template member function that allows you to perform a lookup using at pointer type, with the result returned as a void*. The example above uses this method.