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
14void 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
75end:
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