1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * This code tests that the current task stack is properly erased (filled
4 * with STACKLEAK_POISON).
5 *
6 * Authors:
7 * Alexander Popov <alex.popov@linux.com>
8 * Tycho Andersen <tycho@tycho.ws>
9 */
10
11 #include "lkdtm.h"
12 #include <linux/stackleak.h>
13
lkdtm_STACKLEAK_ERASING(void)14 void lkdtm_STACKLEAK_ERASING(void)
15 {
16 unsigned long *sp, left, found, i;
17 const unsigned long check_depth =
18 STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
19 bool test_failed = false;
20
21 /*
22 * For the details about the alignment of the poison values, see
23 * the comment in stackleak_track_stack().
24 */
25 sp = PTR_ALIGN(&i, sizeof(unsigned long));
26
27 left = ((unsigned long)sp & (THREAD_SIZE - 1)) / sizeof(unsigned long);
28 sp--;
29
30 /*
31 * One 'long int' at the bottom of the thread stack is reserved
32 * and not poisoned.
33 */
34 if (left > 1) {
35 left--;
36 } else {
37 pr_err("FAIL: not enough stack space for the test\n");
38 test_failed = true;
39 goto end;
40 }
41
42 pr_info("checking unused part of the thread stack (%lu bytes)...\n",
43 left * sizeof(unsigned long));
44
45 /*
46 * Search for 'check_depth' poison values in a row (just like
47 * stackleak_erase() does).
48 */
49 for (i = 0, found = 0; i < left && found <= check_depth; i++) {
50 if (*(sp - i) == STACKLEAK_POISON)
51 found++;
52 else
53 found = 0;
54 }
55
56 if (found <= check_depth) {
57 pr_err("FAIL: the erased part is not found (checked %lu bytes)\n",
58 i * sizeof(unsigned long));
59 test_failed = true;
60 goto end;
61 }
62
63 pr_info("the erased part begins after %lu not poisoned bytes\n",
64 (i - found) * sizeof(unsigned long));
65
66 /* The rest of thread stack should be erased */
67 for (; i < left; i++) {
68 if (*(sp - i) != STACKLEAK_POISON) {
69 pr_err("FAIL: bad value number %lu in the erased part: 0x%lx\n",
70 i, *(sp - i));
71 test_failed = true;
72 }
73 }
74
75 end:
76 if (test_failed) {
77 pr_err("FAIL: the thread stack is NOT properly erased\n");
78 dump_stack();
79 } else {
80 pr_info("OK: the rest of the thread stack is properly erased\n");
81 }
82 }
83
