1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_KSTACK_ERASE_H
3#define _LINUX_KSTACK_ERASE_H
4
5#include <linux/sched.h>
6#include <linux/sched/task_stack.h>
7
8/*
9 * Check that the poison value points to the unused hole in the
10 * virtual memory map for your platform.
11 */
12#define KSTACK_ERASE_POISON -0xBEEF
13#define KSTACK_ERASE_SEARCH_DEPTH 128
14
15#ifdef CONFIG_KSTACK_ERASE
16#include <asm/stacktrace.h>
17#include <linux/linkage.h>
18
19/*
20 * The lowest address on tsk's stack which we can plausibly erase.
21 */
22static __always_inline unsigned long
23stackleak_task_low_bound(const struct task_struct *tsk)
24{
25 /*
26 * The lowest unsigned long on the task stack contains STACK_END_MAGIC,
27 * which we must not corrupt.
28 */
29 return (unsigned long)end_of_stack(tsk) + sizeof(unsigned long);
30}
31
32/*
33 * The address immediately after the highest address on tsk's stack which we
34 * can plausibly erase.
35 */
36static __always_inline unsigned long
37stackleak_task_high_bound(const struct task_struct *tsk)
38{
39 /*
40 * The task's pt_regs lives at the top of the task stack and will be
41 * overwritten by exception entry, so there's no need to erase them.
42 */
43 return (unsigned long)task_pt_regs(tsk);
44}
45
46/*
47 * Find the address immediately above the poisoned region of the stack, where
48 * that region falls between 'low' (inclusive) and 'high' (exclusive).
49 */
50static __always_inline unsigned long
51stackleak_find_top_of_poison(const unsigned long low, const unsigned long high)
52{
53 const unsigned int depth = KSTACK_ERASE_SEARCH_DEPTH / sizeof(unsigned long);
54 unsigned int poison_count = 0;
55 unsigned long poison_high = high;
56 unsigned long sp = high;
57
58 while (sp > low && poison_count < depth) {
59 sp -= sizeof(unsigned long);
60
61 if (*(unsigned long *)sp == KSTACK_ERASE_POISON) {
62 poison_count++;
63 } else {
64 poison_count = 0;
65 poison_high = sp;
66 }
67 }
68
69 return poison_high;
70}
71
72static inline void stackleak_task_init(struct task_struct *t)
73{
74 t->lowest_stack = stackleak_task_low_bound(t);
75# ifdef CONFIG_KSTACK_ERASE_METRICS
76 t->prev_lowest_stack = t->lowest_stack;
77# endif
78}
79
80asmlinkage void noinstr stackleak_erase(void);
81asmlinkage void noinstr stackleak_erase_on_task_stack(void);
82asmlinkage void noinstr stackleak_erase_off_task_stack(void);
83void __no_caller_saved_registers noinstr __sanitizer_cov_stack_depth(void);
84
85#else /* !CONFIG_KSTACK_ERASE */
86static inline void stackleak_task_init(struct task_struct *t) { }
87#endif
88
89#endif
90