1/**
2 * @file backtrace.c
3 *
4 * @remark Copyright 2002 OProfile authors
5 * @remark Read the file COPYING
6 *
7 * @author John Levon
8 * @author David Smith
9 */
10
11#include <linux/oprofile.h>
12#include <linux/sched.h>
13#include <linux/mm.h>
14#include <asm/ptrace.h>
15#include <asm/uaccess.h>
16
17struct frame_head {
18	struct frame_head * ebp;
19	unsigned long ret;
20} __attribute__((packed));
21
22static struct frame_head *
23dump_kernel_backtrace(struct frame_head * head)
24{
25	oprofile_add_trace(head->ret);
26
27	/* frame pointers should strictly progress back up the stack
28	 * (towards higher addresses) */
29	if (head >= head->ebp)
30		return NULL;
31
32	return head->ebp;
33}
34
35static struct frame_head *
36dump_user_backtrace(struct frame_head * head)
37{
38	struct frame_head bufhead[2];
39
40	/* Also check accessibility of one struct frame_head beyond */
41	if (!access_ok(VERIFY_READ, head, sizeof(bufhead)))
42		return NULL;
43	if (__copy_from_user_inatomic(bufhead, head, sizeof(bufhead)))
44		return NULL;
45
46	oprofile_add_trace(bufhead[0].ret);
47
48	/* frame pointers should strictly progress back up the stack
49	 * (towards higher addresses) */
50	if (head >= bufhead[0].ebp)
51		return NULL;
52
53	return bufhead[0].ebp;
54}
55
56/*
57 * |             | /\ Higher addresses
58 * |             |
59 * --------------- stack base (address of current_thread_info)
60 * | thread info |
61 * .             .
62 * |    stack    |
63 * --------------- saved regs->ebp value if valid (frame_head address)
64 * .             .
65 * --------------- saved regs->rsp value if x86_64
66 * |             |
67 * --------------- struct pt_regs * stored on stack if 32-bit
68 * |             |
69 * .             .
70 * |             |
71 * --------------- %esp
72 * |             |
73 * |             | \/ Lower addresses
74 *
75 * Thus, regs (or regs->rsp for x86_64) <-> stack base restricts the
76 * valid(ish) ebp values. Note: (1) for x86_64, NMI and several other
77 * exceptions use special stacks, maintained by the interrupt stack table
78 * (IST). These stacks are set up in trap_init() in
79 * arch/x86_64/kernel/traps.c. Thus, for x86_64, regs now does not point
80 * to the kernel stack; instead, it points to some location on the NMI
81 * stack. On the other hand, regs->rsp is the stack pointer saved when the
82 * NMI occurred. (2) For 32-bit, regs->esp is not valid because the
83 * processor does not save %esp on the kernel stack when interrupts occur
84 * in the kernel mode.
85 */
86#ifdef CONFIG_FRAME_POINTER
87static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
88{
89	unsigned long headaddr = (unsigned long)head;
90#ifdef CONFIG_X86_64
91	unsigned long stack = (unsigned long)regs->rsp;
92#else
93	unsigned long stack = (unsigned long)regs;
94#endif
95	unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
96
97	return headaddr > stack && headaddr < stack_base;
98}
99#else
100/* without fp, it's just junk */
101static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
102{
103	return 0;
104}
105#endif
106
107
108void
109x86_backtrace(struct pt_regs * const regs, unsigned int depth)
110{
111	struct frame_head *head;
112
113#ifdef CONFIG_X86_64
114	head = (struct frame_head *)regs->rbp;
115#else
116	head = (struct frame_head *)regs->ebp;
117#endif
118
119	if (!user_mode_vm(regs)) {
120		while (depth-- && valid_kernel_stack(head, regs))
121			head = dump_kernel_backtrace(head);
122		return;
123	}
124
125	while (depth-- && head)
126		head = dump_user_backtrace(head);
127}
128