1// SPDX-License-Identifier: GPL-2.0
2/*
3 * This code tests that the current task stack is properly erased (filled
4 * with KSTACK_ERASE_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/kstack_erase.h>
13
14#if defined(CONFIG_KSTACK_ERASE)
15/*
16 * Check that stackleak tracks the lowest stack pointer and erases the stack
17 * below this as expected.
18 *
19 * To prevent the lowest stack pointer changing during the test, IRQs are
20 * masked and instrumentation of this function is disabled. We assume that the
21 * compiler will create a fixed-size stack frame for this function.
22 *
23 * Any non-inlined function may make further use of the stack, altering the
24 * lowest stack pointer and/or clobbering poison values. To avoid spurious
25 * failures we must avoid printing until the end of the test or have already
26 * encountered a failure condition.
27 */
28static void noinstr check_stackleak_irqoff(void)
29{
30 const unsigned long task_stack_base = (unsigned long)task_stack_page(current);
31 const unsigned long task_stack_low = stackleak_task_low_bound(current);
32 const unsigned long task_stack_high = stackleak_task_high_bound(current);
33 const unsigned long current_sp = current_stack_pointer;
34 const unsigned long lowest_sp = current->lowest_stack;
35 unsigned long untracked_high;
36 unsigned long poison_high, poison_low;
37 bool test_failed = false;
38
39 /*
40 * Check that the current and lowest recorded stack pointer values fall
41 * within the expected task stack boundaries. These tests should never
42 * fail unless the boundaries are incorrect or we're clobbering the
43 * STACK_END_MAGIC, and in either casee something is seriously wrong.
44 */
45 if (current_sp < task_stack_low || current_sp >= task_stack_high) {
46 instrumentation_begin();
47 pr_err("FAIL: current_stack_pointer (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",
48 current_sp, task_stack_low, task_stack_high - 1);
49 test_failed = true;
50 goto out;
51 }
52 if (lowest_sp < task_stack_low || lowest_sp >= task_stack_high) {
53 instrumentation_begin();
54 pr_err("FAIL: current->lowest_stack (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",
55 lowest_sp, task_stack_low, task_stack_high - 1);
56 test_failed = true;
57 goto out;
58 }
59
60 /*
61 * Depending on what has run prior to this test, the lowest recorded
62 * stack pointer could be above or below the current stack pointer.
63 * Start from the lowest of the two.
64 *
65 * Poison values are naturally-aligned unsigned longs. As the current
66 * stack pointer might not be sufficiently aligned, we must align
67 * downwards to find the lowest known stack pointer value. This is the
68 * high boundary for a portion of the stack which may have been used
69 * without being tracked, and has to be scanned for poison.
70 */
71 untracked_high = min(current_sp, lowest_sp);
72 untracked_high = ALIGN_DOWN(untracked_high, sizeof(unsigned long));
73
74 /*
75 * Find the top of the poison in the same way as the erasing code.
76 */
77 poison_high = stackleak_find_top_of_poison(task_stack_low, untracked_high);
78
79 /*
80 * Check whether the poisoned portion of the stack (if any) consists
81 * entirely of poison. This verifies the entries that
82 * stackleak_find_top_of_poison() should have checked.
83 */
84 poison_low = poison_high;
85 while (poison_low > task_stack_low) {
86 poison_low -= sizeof(unsigned long);
87
88 if (*(unsigned long *)poison_low == KSTACK_ERASE_POISON)
89 continue;
90
91 instrumentation_begin();
92 pr_err("FAIL: non-poison value %lu bytes below poison boundary: 0x%lx\n",
93 poison_high - poison_low, *(unsigned long *)poison_low);
94 test_failed = true;
95 goto out;
96 }
97
98 instrumentation_begin();
99 pr_info("kstack erase stack usage:\n"
100 " high offset: %lu bytes\n"
101 " current: %lu bytes\n"
102 " lowest: %lu bytes\n"
103 " tracked: %lu bytes\n"
104 " untracked: %lu bytes\n"
105 " poisoned: %lu bytes\n"
106 " low offset: %lu bytes\n",
107 task_stack_base + THREAD_SIZE - task_stack_high,
108 task_stack_high - current_sp,
109 task_stack_high - lowest_sp,
110 task_stack_high - untracked_high,
111 untracked_high - poison_high,
112 poison_high - task_stack_low,
113 task_stack_low - task_stack_base);
114
115out:
116 if (test_failed) {
117 pr_err("FAIL: the thread stack is NOT properly erased!\n");
118 } else {
119 pr_info("OK: the rest of the thread stack is properly erased\n");
120 }
121 instrumentation_end();
122}
123
124static void lkdtm_KSTACK_ERASE(void)
125{
126 unsigned long flags;
127
128 local_irq_save(flags);
129 check_stackleak_irqoff();
130 local_irq_restore(flags);
131}
132#else /* defined(CONFIG_KSTACK_ERASE) */
133static void lkdtm_KSTACK_ERASE(void)
134{
135 if (IS_ENABLED(CONFIG_HAVE_ARCH_KSTACK_ERASE)) {
136 pr_err("XFAIL: stackleak is not enabled (CONFIG_KSTACK_ERASE=n)\n");
137 } else {
138 pr_err("XFAIL: stackleak is not supported on this arch (HAVE_ARCH_KSTACK_ERASE=n)\n");
139 }
140}
141#endif /* defined(CONFIG_KSTACK_ERASE) */
142
143static struct crashtype crashtypes[] = {
144 CRASHTYPE(KSTACK_ERASE),
145};
146
147struct crashtype_category stackleak_crashtypes = {
148 .crashtypes = crashtypes,
149 .len = ARRAY_SIZE(crashtypes),
150};
151

source code of linux/drivers/misc/lkdtm/kstack_erase.c