Initial attempt at guessing engine structure

virt-to-phys.c

@@ -0,0 +1,77 @@
+// XXX: Taken from https://stackoverflow.com/a/45128487
+
+#define _XOPEN_SOURCE 700
+#include <fcntl.h> /* open */
+#include <stdint.h> /* uint64_t  */
+#include <stdio.h> /* printf */
+#include <stdlib.h> /* size_t */
+#include <unistd.h> /* pread, sysconf */
+
+typedef struct {
+    uint64_t pfn : 55;
+    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, ((uint8_t*)&data) + nread, sizeof(data) - nread,
+                vpn * sizeof(data) + nread);
+        nread += ret;
+        if (ret <= 0) {
+            return 1;
+        }
+    }
+    entry->pfn = data & (((uint64_t)1 << 55) - 1);
+    entry->soft_dirty = (data >> 55) & 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[name] name of variable
+ * @param[in] vaddr virtual address to get entry for
+ * @return paddr (physical address) on success, exit on failure
+ */
+int virt_to_phys_user(char* name, uintptr_t vaddr)
+{
+    char pagemap_file[BUFSIZ];
+    int pagemap_fd;
+
+    snprintf(pagemap_file, sizeof(pagemap_file), "/proc/%ju/pagemap", (uintmax_t)getpid());
+    pagemap_fd = open(pagemap_file, O_RDONLY);
+    if (pagemap_fd < 0) {
+        printf("Failed to open pagemap for process!");
+        exit(-1);
+    }
+    PagemapEntry entry;
+    if (pagemap_get_entry(&entry, pagemap_fd, vaddr)) {
+        printf("Failed to get entry for pagemap!");
+        exit(-1);
+    }
+    close(pagemap_fd);
+    
+    uintptr_t paddr = (entry.pfn * sysconf(_SC_PAGE_SIZE)) + (vaddr % sysconf(_SC_PAGE_SIZE));
+    printf("%s: virt @ %p, phys @ %p\n", name, (void *)vaddr, (void*)paddr);
+    return paddr;
+}