virt_to_phys_user

kernel_module/user/common.h

@@ -0,0 +1,74 @@
+#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 */
+
+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;
+
+	nread = 0;
+	while (nread < sizeof(data)) {
+		ret = pread(pagemap_fd, &data, sizeof(data),
+				(vaddr / sysconf(_SC_PAGE_SIZE)) * 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