common.h

#ifndef COMMON_H
#define COMMON_H

#define _POSIX_C_SOURCE 200809L
#include <fcntl.h> // open
#include <stdint.h> // uint64_t
#include <stdlib.h> // size_t
#include <unistd.h> // pread, sysconf
#include <stdio.h> // printf

typedef struct {
  uint64_t pfn : 54;
  unsigned int soft_dirty : 1;
  unsigned int file_page : 1;
  unsigned int swapped : 1;
  unsigned int present : 1;
} PagemapEntry;

//Parse the pagemap entry for the given virtual address.
//
//@param[out] entry      the parsed entry
//@param[in]  pagemap_fd file descriptor to an open /proc/pid/pagemap file
//@param[in]  vaddr      virtual address to get entry for
//@return 0 for success, 1 for failure
int pagemap_get_entry(PagemapEntry *entry, int pagemap_fd, uintptr_t vaddr) {
  size_t nread;
  ssize_t ret;
  uint64_t data;
  uintptr_t vpn;

  vpn = vaddr / sysconf(_SC_PAGE_SIZE);
  nread = 0;
  while (nread < sizeof(data)) {
    ret = pread(pagemap_fd, &data, sizeof(data) - nread,
      vpn * sizeof(data) + nread);
    nread += ret;
    if (ret <= 0) {
      return 1;
    }
  }
  entry->pfn = data & (((uint64_t)1 << 54) - 1);
  entry->soft_dirty = (data >> 54) & 1;
  entry->file_page = (data >> 61) & 1;
  entry->swapped = (data >> 62) & 1;
  entry->present = (data >> 63) & 1;
  return 0;
}

// Convert the given virtual address to physical using /proc/PID/pagemap.
// 
// @param[out] paddr physical address
// @param[in]  pid   process to convert for
// @param[in] vaddr virtual address to get entry for
// @return 0 for success, 1 for failure
int virt_to_phys_user(uintptr_t *paddr, pid_t pid, uintptr_t vaddr) {
  char pagemap_file[BUFSIZ];
  int pagemap_fd;

  snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)pid);
  pagemap_fd = open(pagemap_file, O_RDONLY);
  if (pagemap_fd < 0) {
    return 1;
  }
  PagemapEntry entry;
  if (pagemap_get_entry(&entry, pagemap_fd, vaddr)) {
    return 1;
  }
  close(pagemap_fd);
  *paddr = (entry.pfn * sysconf(_SC_PAGE_SIZE)) + (vaddr % sysconf(_SC_PAGE_SIZE));
  return 0;
}

#endif