1/*
2 * User-space Probes (UProbes) for powerpc
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * Copyright IBM Corporation, 2007-2012
19 *
20 * Adapted from the x86 port by Ananth N Mavinakayanahalli <ananth@in.ibm.com>
21 */
22#include <linux/kernel.h>
23#include <linux/sched.h>
24#include <linux/ptrace.h>
25#include <linux/uprobes.h>
26#include <linux/uaccess.h>
27#include <linux/kdebug.h>
28
29#include <asm/sstep.h>
30
31#define UPROBE_TRAP_NR	UINT_MAX
32
33/**
34 * is_trap_insn - check if the instruction is a trap variant
35 * @insn: instruction to be checked.
36 * Returns true if @insn is a trap variant.
37 */
38bool is_trap_insn(uprobe_opcode_t *insn)
39{
40	return (is_trap(*insn));
41}
42
43/**
44 * arch_uprobe_analyze_insn
45 * @mm: the probed address space.
46 * @arch_uprobe: the probepoint information.
47 * @addr: vaddr to probe.
48 * Return 0 on success or a -ve number on error.
49 */
50int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
51		struct mm_struct *mm, unsigned long addr)
52{
53	if (addr & 0x03)
54		return -EINVAL;
55
56	return 0;
57}
58
59/*
60 * arch_uprobe_pre_xol - prepare to execute out of line.
61 * @auprobe: the probepoint information.
62 * @regs: reflects the saved user state of current task.
63 */
64int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
65{
66	struct arch_uprobe_task *autask = &current->utask->autask;
67
68	autask->saved_trap_nr = current->thread.trap_nr;
69	current->thread.trap_nr = UPROBE_TRAP_NR;
70	regs->nip = current->utask->xol_vaddr;
71
72	user_enable_single_step(current);
73	return 0;
74}
75
76/**
77 * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
78 * @regs: Reflects the saved state of the task after it has hit a breakpoint
79 * instruction.
80 * Return the address of the breakpoint instruction.
81 */
82unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
83{
84	return instruction_pointer(regs);
85}
86
87/*
88 * If xol insn itself traps and generates a signal (SIGILL/SIGSEGV/etc),
89 * then detect the case where a singlestepped instruction jumps back to its
90 * own address. It is assumed that anything like do_page_fault/do_trap/etc
91 * sets thread.trap_nr != UINT_MAX.
92 *
93 * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
94 * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
95 * UPROBE_TRAP_NR == UINT_MAX set by arch_uprobe_pre_xol().
96 */
97bool arch_uprobe_xol_was_trapped(struct task_struct *t)
98{
99	if (t->thread.trap_nr != UPROBE_TRAP_NR)
100		return true;
101
102	return false;
103}
104
105/*
106 * Called after single-stepping. To avoid the SMP problems that can
107 * occur when we temporarily put back the original opcode to
108 * single-step, we single-stepped a copy of the instruction.
109 *
110 * This function prepares to resume execution after the single-step.
111 */
112int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
113{
114	struct uprobe_task *utask = current->utask;
115
116	WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
117
118	current->thread.trap_nr = utask->autask.saved_trap_nr;
119
120	/*
121	 * On powerpc, except for loads and stores, most instructions
122	 * including ones that alter code flow (branches, calls, returns)
123	 * are emulated in the kernel. We get here only if the emulation
124	 * support doesn't exist and have to fix-up the next instruction
125	 * to be executed.
126	 */
127	regs->nip = utask->vaddr + MAX_UINSN_BYTES;
128
129	user_disable_single_step(current);
130	return 0;
131}
132
133/* callback routine for handling exceptions. */
134int arch_uprobe_exception_notify(struct notifier_block *self,
135				unsigned long val, void *data)
136{
137	struct die_args *args = data;
138	struct pt_regs *regs = args->regs;
139
140	/* regs == NULL is a kernel bug */
141	if (WARN_ON(!regs))
142		return NOTIFY_DONE;
143
144	/* We are only interested in userspace traps */
145	if (!user_mode(regs))
146		return NOTIFY_DONE;
147
148	switch (val) {
149	case DIE_BPT:
150		if (uprobe_pre_sstep_notifier(regs))
151			return NOTIFY_STOP;
152		break;
153	case DIE_SSTEP:
154		if (uprobe_post_sstep_notifier(regs))
155			return NOTIFY_STOP;
156	default:
157		break;
158	}
159	return NOTIFY_DONE;
160}
161
162/*
163 * This function gets called when XOL instruction either gets trapped or
164 * the thread has a fatal signal, so reset the instruction pointer to its
165 * probed address.
166 */
167void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
168{
169	struct uprobe_task *utask = current->utask;
170
171	current->thread.trap_nr = utask->autask.saved_trap_nr;
172	instruction_pointer_set(regs, utask->vaddr);
173
174	user_disable_single_step(current);
175}
176
177/*
178 * See if the instruction can be emulated.
179 * Returns true if instruction was emulated, false otherwise.
180 */
181bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
182{
183	int ret;
184
185	/*
186	 * emulate_step() returns 1 if the insn was successfully emulated.
187	 * For all other cases, we need to single-step in hardware.
188	 */
189	ret = emulate_step(regs, auprobe->insn);
190	if (ret > 0)
191		return true;
192
193	return false;
194}
195
196unsigned long
197arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs)
198{
199	unsigned long orig_ret_vaddr;
200
201	orig_ret_vaddr = regs->link;
202
203	/* Replace the return addr with trampoline addr */
204	regs->link = trampoline_vaddr;
205
206	return orig_ret_vaddr;
207}
208