annotate /proc/<PID>/maps with [heap]/[stack]/[vdso] markers

This patch makes the /proc/<PID>/maps file easier to parse (both for humans and for applications), by annotating the heap, stack and vdso mappings with [heap], [stack] and [vdso] markers.

It makes it easier/faster to determine at a quick glance whether an application has a secure VM layout, and it also makes it easier for tools to determine whether e.g. the heap or stack is executable or not.

new maps file, on a patched kernel:

 001c4000-001d9000 r-xp 00000000 03:01 19954      /lib/ld-2.3.3.so
 001d9000-001db000 rw-p 00014000 03:01 19954      /lib/ld-2.3.3.so
 001dd000-002fb000 r-xp 00000000 03:01 19960      /lib/tls/libc-2.3.3.so
 002fb000-002fd000 r--p 0011d000 03:01 19960      /lib/tls/libc-2.3.3.so
 002fd000-002ff000 rw-p 0011f000 03:01 19960      /lib/tls/libc-2.3.3.so
 002ff000-00301000 rw-p 002ff000 00:00 0
 08048000-0804c000 r-xp 00000000 03:01 31968      /bin/cat
 0804c000-0804d000 rw-p 00003000 03:01 31968      /bin/cat
 0804d000-0806e000 rw-p 0804d000 00:00 0          [heap]
 b7dbc000-b7dbd000 r--p 009d1000 03:01 83628      /usr/lib/locale/locale-archive
 b7dbd000-b7dc4000 r--p 0097d000 03:01 83628      /usr/lib/locale/locale-archive
 b7dc4000-b7df1000 r--p 0094a000 03:01 83628      /usr/lib/locale/locale-archive
 b7df1000-b7ff1000 r--p 00000000 03:01 83628      /usr/lib/locale/locale-archive

b7ff1000-b7ff2000 rw-p b7ff1000 00:00 0
bffeb000-c0000000 rw-p bffeb000 00:00 0 [stack]
ffffe000-fffff000 ---p 00000000 00:00 0 [vdso]

Tested on x86, but should work on all architectures.

@@ -77,9 +77,18 @@ out:
 	return result;
 }
 
+static void pad_len_spaces(struct seq_file *m, int len)
+{
+	len = 25 + sizeof(void*) * 6 - len;
+	if (len < 1)
+		len = 1;
+	seq_printf(m, "%*c", len, ' ');
+}
+
 static int show_map(struct seq_file *m, void *v)
 {
 	struct vm_area_struct *map = v;
+	struct mm_struct *mm = map->vm_mm;
 	struct file *file = map->vm_file;
 	int flags = map->vm_flags;
 	unsigned long ino = 0;

@@ -102,12 +117,31 @@ static int show_map(struct seq_file *m, 
 			map->vm_pgoff << PAGE_SHIFT,
 			MAJOR(dev), MINOR(dev), ino, &len);
 
+	/*
+	 * Print the dentry name for named mappings, and a
+	 * special [heap] marker for the heap:
+	 */
 	if (map->vm_file) {
-		len = 25 + sizeof(void*) * 6 - len;
-		if (len < 1)
-			len = 1;
-		seq_printf(m, "%*c", len, ' ');
+		pad_len_spaces(m, len);
 		seq_path(m, file->f_vfsmnt, file->f_dentry, "");
+	} else {
+		if (mm) {
+			if (map->vm_start <= mm->start_brk &&
+						map->vm_end >= mm->brk) {
+				pad_len_spaces(m, len);
+				seq_puts(m, "[heap]");
+			} else {
+				if (map->vm_start <= mm->start_stack &&
+					map->vm_end >= mm->start_stack) {
+
+					pad_len_spaces(m, len);
+					seq_puts(m, "[stack]");
+				}
+			}
+		} else {
+			pad_len_spaces(m, len);
+			seq_puts(m, "[vdso]");
+		}
 	}
 	seq_putc(m, '\n');
 	return 0;