ptrace.c revision 13b54a50525a9685065684e1e11258d27dd27bdf 
1/*
2 * Copyright (C) 2004-2006 Atmel Corporation
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 version 2 as
6 * published by the Free Software Foundation.
7 */
8#undef DEBUG
9#include <linux/kernel.h>
10#include <linux/sched.h>
11#include <linux/mm.h>
12#include <linux/ptrace.h>
13#include <linux/errno.h>
14#include <linux/user.h>
15#include <linux/security.h>
16#include <linux/unistd.h>
17#include <linux/notifier.h>
18
19#include <asm/traps.h>
20#include <asm/uaccess.h>
21#include <asm/ocd.h>
22#include <asm/mmu_context.h>
23#include <linux/kdebug.h>
24
25static struct pt_regs *get_user_regs(struct task_struct *tsk)
26{
27	return (struct pt_regs *)((unsigned long)task_stack_page(tsk) +
28				  THREAD_SIZE - sizeof(struct pt_regs));
29}
30
31static void ptrace_single_step(struct task_struct *tsk)
32{
33	pr_debug("ptrace_single_step: pid=%u, PC=0x%08lx, SR=0x%08lx\n",
34		 tsk->pid, task_pt_regs(tsk)->pc, task_pt_regs(tsk)->sr);
35
36	/*
37	 * We can't schedule in Debug mode, so when TIF_BREAKPOINT is
38	 * set, the system call or exception handler will do a
39	 * breakpoint to enter monitor mode before returning to
40	 * userspace.
41	 *
42	 * The monitor code will then notice that TIF_SINGLE_STEP is
43	 * set and return to userspace with single stepping enabled.
44	 * The CPU will then enter monitor mode again after exactly
45	 * one instruction has been executed, and the monitor code
46	 * will then send a SIGTRAP to the process.
47	 */
48	set_tsk_thread_flag(tsk, TIF_BREAKPOINT);
49	set_tsk_thread_flag(tsk, TIF_SINGLE_STEP);
50}
51
52/*
53 * Called by kernel/ptrace.c when detaching
54 *
55 * Make sure any single step bits, etc. are not set
56 */
57void ptrace_disable(struct task_struct *child)
58{
59	clear_tsk_thread_flag(child, TIF_SINGLE_STEP);
60	clear_tsk_thread_flag(child, TIF_BREAKPOINT);
61	ocd_disable(child);
62}
63
64/*
65 * Read the word at offset "offset" into the task's "struct user". We
66 * actually access the pt_regs struct stored on the kernel stack.
67 */
68static int ptrace_read_user(struct task_struct *tsk, unsigned long offset,
69			    unsigned long __user *data)
70{
71	unsigned long *regs;
72	unsigned long value;
73
74	if (offset & 3 || offset >= sizeof(struct user)) {
75		printk("ptrace_read_user: invalid offset 0x%08lx\n", offset);
76		return -EIO;
77	}
78
79	regs = (unsigned long *)get_user_regs(tsk);
80
81	value = 0;
82	if (offset < sizeof(struct pt_regs))
83		value = regs[offset / sizeof(regs[0])];
84
85	pr_debug("ptrace_read_user(%s[%u], %#lx, %p) -> %#lx\n",
86		 tsk->comm, tsk->pid, offset, data, value);
87
88	return put_user(value, data);
89}
90
91/*
92 * Write the word "value" to offset "offset" into the task's "struct
93 * user". We actually access the pt_regs struct stored on the kernel
94 * stack.
95 */
96static int ptrace_write_user(struct task_struct *tsk, unsigned long offset,
97			     unsigned long value)
98{
99	unsigned long *regs;
100
101	pr_debug("ptrace_write_user(%s[%u], %#lx, %#lx)\n",
102			tsk->comm, tsk->pid, offset, value);
103
104	if (offset & 3 || offset >= sizeof(struct user)) {
105		pr_debug("  invalid offset 0x%08lx\n", offset);
106		return -EIO;
107	}
108
109	if (offset >= sizeof(struct pt_regs))
110		return 0;
111
112	regs = (unsigned long *)get_user_regs(tsk);
113	regs[offset / sizeof(regs[0])] = value;
114
115	return 0;
116}
117
118static int ptrace_getregs(struct task_struct *tsk, void __user *uregs)
119{
120	struct pt_regs *regs = get_user_regs(tsk);
121
122	return copy_to_user(uregs, regs, sizeof(*regs)) ? -EFAULT : 0;
123}
124
125static int ptrace_setregs(struct task_struct *tsk, const void __user *uregs)
126{
127	struct pt_regs newregs;
128	int ret;
129
130	ret = -EFAULT;
131	if (copy_from_user(&newregs, uregs, sizeof(newregs)) == 0) {
132		struct pt_regs *regs = get_user_regs(tsk);
133
134		ret = -EINVAL;
135		if (valid_user_regs(&newregs)) {
136			*regs = newregs;
137			ret = 0;
138		}
139	}
140
141	return ret;
142}
143
144long arch_ptrace(struct task_struct *child, long request, long addr, long data)
145{
146	int ret;
147
148	switch (request) {
149	/* Read the word at location addr in the child process */
150	case PTRACE_PEEKTEXT:
151	case PTRACE_PEEKDATA:
152		ret = generic_ptrace_peekdata(child, addr, data);
153		break;
154
155	case PTRACE_PEEKUSR:
156		ret = ptrace_read_user(child, addr,
157				       (unsigned long __user *)data);
158		break;
159
160	/* Write the word in data at location addr */
161	case PTRACE_POKETEXT:
162	case PTRACE_POKEDATA:
163		ret = generic_ptrace_pokedata(child, addr, data);
164		break;
165
166	case PTRACE_POKEUSR:
167		ret = ptrace_write_user(child, addr, data);
168		break;
169
170	/* continue and stop at next (return from) syscall */
171	case PTRACE_SYSCALL:
172	/* restart after signal */
173	case PTRACE_CONT:
174		ret = -EIO;
175		if (!valid_signal(data))
176			break;
177		if (request == PTRACE_SYSCALL)
178			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
179		else
180			clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
181		child->exit_code = data;
182		/* XXX: Are we sure no breakpoints are active here? */
183		wake_up_process(child);
184		ret = 0;
185		break;
186
187	/*
188	 * Make the child exit. Best I can do is send it a
189	 * SIGKILL. Perhaps it should be put in the status that it
190	 * wants to exit.
191	 */
192	case PTRACE_KILL:
193		ret = 0;
194		if (child->exit_state == EXIT_ZOMBIE)
195			break;
196		child->exit_code = SIGKILL;
197		wake_up_process(child);
198		break;
199
200	/*
201	 * execute single instruction.
202	 */
203	case PTRACE_SINGLESTEP:
204		ret = -EIO;
205		if (!valid_signal(data))
206			break;
207		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
208		ptrace_single_step(child);
209		child->exit_code = data;
210		wake_up_process(child);
211		ret = 0;
212		break;
213
214	case PTRACE_GETREGS:
215		ret = ptrace_getregs(child, (void __user *)data);
216		break;
217
218	case PTRACE_SETREGS:
219		ret = ptrace_setregs(child, (const void __user *)data);
220		break;
221
222	default:
223		ret = ptrace_request(child, request, addr, data);
224		break;
225	}
226
227	return ret;
228}
229
230asmlinkage void syscall_trace(void)
231{
232	if (!test_thread_flag(TIF_SYSCALL_TRACE))
233		return;
234	if (!(current->ptrace & PT_PTRACED))
235		return;
236
237	/* The 0x80 provides a way for the tracing parent to
238	 * distinguish between a syscall stop and SIGTRAP delivery */
239	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
240				 ? 0x80 : 0));
241
242	/*
243	 * this isn't the same as continuing with a signal, but it
244	 * will do for normal use.  strace only continues with a
245	 * signal if the stopping signal is not SIGTRAP.  -brl
246	 */
247	if (current->exit_code) {
248		pr_debug("syscall_trace: sending signal %d to PID %u\n",
249			 current->exit_code, current->pid);
250		send_sig(current->exit_code, current, 1);
251		current->exit_code = 0;
252	}
253}
254
255/*
256 * debug_trampoline() is an assembly stub which will store all user
257 * registers on the stack and execute a breakpoint instruction.
258 *
259 * If we single-step into an exception handler which runs with
260 * interrupts disabled the whole time so it doesn't have to check for
261 * pending work, its return address will be modified so that it ends
262 * up returning to debug_trampoline.
263 *
264 * If the exception handler decides to store the user context and
265 * enable interrupts after all, it will restore the original return
266 * address and status register value. Before it returns, it will
267 * notice that TIF_BREAKPOINT is set and execute a breakpoint
268 * instruction.
269 */
270extern void debug_trampoline(void);
271
272asmlinkage struct pt_regs *do_debug(struct pt_regs *regs)
273{
274	struct thread_info	*ti;
275	unsigned long		trampoline_addr;
276	u32			status;
277	u32			ctrl;
278	int			code;
279
280	status = ocd_read(DS);
281	ti = current_thread_info();
282	code = TRAP_BRKPT;
283
284	pr_debug("do_debug: status=0x%08x PC=0x%08lx SR=0x%08lx tif=0x%08lx\n",
285			status, regs->pc, regs->sr, ti->flags);
286
287	if (!user_mode(regs)) {
288		unsigned long	die_val = DIE_BREAKPOINT;
289
290		if (status & (1 << OCD_DS_SSS_BIT))
291			die_val = DIE_SSTEP;
292
293		if (notify_die(die_val, "ptrace", regs, 0, 0, SIGTRAP)
294				== NOTIFY_STOP)
295			return regs;
296
297		if ((status & (1 << OCD_DS_SWB_BIT))
298				&& test_and_clear_ti_thread_flag(
299					ti, TIF_BREAKPOINT)) {
300			/*
301			 * Explicit breakpoint from trampoline or
302			 * exception/syscall/interrupt handler.
303			 *
304			 * The real saved regs are on the stack right
305			 * after the ones we saved on entry.
306			 */
307			regs++;
308			pr_debug("  -> TIF_BREAKPOINT done, adjusted regs:"
309					"PC=0x%08lx SR=0x%08lx\n",
310					regs->pc, regs->sr);
311			BUG_ON(!user_mode(regs));
312
313			if (test_thread_flag(TIF_SINGLE_STEP)) {
314				pr_debug("Going to do single step...\n");
315				return regs;
316			}
317
318			/*
319			 * No TIF_SINGLE_STEP means we're done
320			 * stepping over a syscall. Do the trap now.
321			 */
322			code = TRAP_TRACE;
323		} else if ((status & (1 << OCD_DS_SSS_BIT))
324				&& test_ti_thread_flag(ti, TIF_SINGLE_STEP)) {
325
326			pr_debug("Stepped into something, "
327					"setting TIF_BREAKPOINT...\n");
328			set_ti_thread_flag(ti, TIF_BREAKPOINT);
329
330			/*
331			 * We stepped into an exception, interrupt or
332			 * syscall handler. Some exception handlers
333			 * don't check for pending work, so we need to
334			 * set up a trampoline just in case.
335			 *
336			 * The exception entry code will undo the
337			 * trampoline stuff if it does a full context
338			 * save (which also means that it'll check for
339			 * pending work later.)
340			 */
341			if ((regs->sr & MODE_MASK) == MODE_EXCEPTION) {
342				trampoline_addr
343					= (unsigned long)&debug_trampoline;
344
345				pr_debug("Setting up trampoline...\n");
346				ti->rar_saved = sysreg_read(RAR_EX);
347				ti->rsr_saved = sysreg_read(RSR_EX);
348				sysreg_write(RAR_EX, trampoline_addr);
349				sysreg_write(RSR_EX, (MODE_EXCEPTION
350							| SR_EM | SR_GM));
351				BUG_ON(ti->rsr_saved & MODE_MASK);
352			}
353
354			/*
355			 * If we stepped into a system call, we
356			 * shouldn't do a single step after we return
357			 * since the return address is right after the
358			 * "scall" instruction we were told to step
359			 * over.
360			 */
361			if ((regs->sr & MODE_MASK) == MODE_SUPERVISOR) {
362				pr_debug("Supervisor; no single step\n");
363				clear_ti_thread_flag(ti, TIF_SINGLE_STEP);
364			}
365
366			ctrl = ocd_read(DC);
367			ctrl &= ~(1 << OCD_DC_SS_BIT);
368			ocd_write(DC, ctrl);
369
370			return regs;
371		} else {
372			printk(KERN_ERR "Unexpected OCD_DS value: 0x%08x\n",
373					status);
374			printk(KERN_ERR "Thread flags: 0x%08lx\n", ti->flags);
375			die("Unhandled debug trap in kernel mode",
376					regs, SIGTRAP);
377		}
378	} else if (status & (1 << OCD_DS_SSS_BIT)) {
379		/* Single step in user mode */
380		code = TRAP_TRACE;
381
382		ctrl = ocd_read(DC);
383		ctrl &= ~(1 << OCD_DC_SS_BIT);
384		ocd_write(DC, ctrl);
385	}
386
387	pr_debug("Sending SIGTRAP: code=%d PC=0x%08lx SR=0x%08lx\n",
388			code, regs->pc, regs->sr);
389
390	clear_thread_flag(TIF_SINGLE_STEP);
391	_exception(SIGTRAP, regs, code, instruction_pointer(regs));
392
393	return regs;
394}
395