[linux-2.6-block.git] / arch / arm64 / kernel / ftrace.c

/*
 * arch/arm64/kernel/ftrace.c
 *
 * Copyright (C) 2013 Linaro Limited
 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/swab.h>
#include <linux/uaccess.h>

#include <asm/cacheflush.h>
#include <asm/debug-monitors.h>
#include <asm/ftrace.h>
#include <asm/insn.h>

#ifdef CONFIG_DYNAMIC_FTRACE
/*
 * Replace a single instruction, which may be a branch or NOP.
 * If @validate == true, a replaced instruction is checked against 'old'.
 */
static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
			      bool validate)
{
	u32 replaced;

	/*
	 * Note:
	 * We are paranoid about modifying text, as if a bug were to happen, it
	 * could cause us to read or write to someplace that could cause harm.
	 * Carefully read and modify the code with aarch64_insn_*() which uses
	 * probe_kernel_*(), and make sure what we read is what we expected it
	 * to be before modifying it.
	 */
	if (validate) {
		if (aarch64_insn_read((void *)pc, &replaced))
			return -EFAULT;

		if (replaced != old)
			return -EINVAL;
	}
	if (aarch64_insn_patch_text_nosync((void *)pc, new))
		return -EPERM;

	return 0;
}

/*
 * Replace tracer function in ftrace_caller()
 */
int ftrace_update_ftrace_func(ftrace_func_t func)
{
	unsigned long pc;
	u32 new;

	pc = (unsigned long)&ftrace_call;
	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
					  AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, 0, new, false);
}

/*
 * Turn on the call to ftrace_caller() in instrumented function
 */
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned long pc = rec->ip;
	u32 old, new;
	long offset = (long)pc - (long)addr;

	if (offset < -SZ_128M || offset >= SZ_128M) {
#ifdef CONFIG_ARM64_MODULE_PLTS
		struct plt_entry trampoline;
		struct module *mod;

		/*
		 * On kernels that support module PLTs, the offset between the
		 * branch instruction and its target may legally exceed the
		 * range of an ordinary relative 'bl' opcode. In this case, we
		 * need to branch via a trampoline in the module.
		 *
		 * NOTE: __module_text_address() must be called with preemption
		 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
		 * retains its validity throughout the remainder of this code.
		 */
		preempt_disable();
		mod = __module_text_address(pc);
		preempt_enable();

		if (WARN_ON(!mod))
			return -EINVAL;

		/*
		 * There is only one ftrace trampoline per module. For now,
		 * this is not a problem since on arm64, all dynamic ftrace
		 * invocations are routed via ftrace_caller(). This will need
		 * to be revisited if support for multiple ftrace entry points
		 * is added in the future, but for now, the pr_err() below
		 * deals with a theoretical issue only.
		 */
		trampoline = get_plt_entry(addr, mod->arch.ftrace_trampoline);
		if (!plt_entries_equal(mod->arch.ftrace_trampoline,
				       &trampoline)) {
			if (!plt_entries_equal(mod->arch.ftrace_trampoline,
					       &(struct plt_entry){})) {
				pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
				return -EINVAL;
			}

			/* point the trampoline to our ftrace entry point */
			module_disable_ro(mod);
			*mod->arch.ftrace_trampoline = trampoline;
			module_enable_ro(mod, true);

			/* update trampoline before patching in the branch */
			smp_wmb();
		}
		addr = (unsigned long)(void *)mod->arch.ftrace_trampoline;
#else /* CONFIG_ARM64_MODULE_PLTS */
		return -EINVAL;
#endif /* CONFIG_ARM64_MODULE_PLTS */
	}

	old = aarch64_insn_gen_nop();
	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, old, new, true);
}

/*
 * Turn off the call to ftrace_caller() in instrumented function
 */
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
		    unsigned long addr)
{
	unsigned long pc = rec->ip;
	bool validate = true;
	u32 old = 0, new;
	long offset = (long)pc - (long)addr;

	if (offset < -SZ_128M || offset >= SZ_128M) {
#ifdef CONFIG_ARM64_MODULE_PLTS
		u32 replaced;

		/*
		 * 'mod' is only set at module load time, but if we end up
		 * dealing with an out-of-range condition, we can assume it
		 * is due to a module being loaded far away from the kernel.
		 */
		if (!mod) {
			preempt_disable();
			mod = __module_text_address(pc);
			preempt_enable();

			if (WARN_ON(!mod))
				return -EINVAL;
		}

		/*
		 * The instruction we are about to patch may be a branch and
		 * link instruction that was redirected via a PLT entry. In
		 * this case, the normal validation will fail, but we can at
		 * least check that we are dealing with a branch and link
		 * instruction that points into the right module.
		 */
		if (aarch64_insn_read((void *)pc, &replaced))
			return -EFAULT;

		if (!aarch64_insn_is_bl(replaced) ||
		    !within_module(pc + aarch64_get_branch_offset(replaced),
				   mod))
			return -EINVAL;

		validate = false;
#else /* CONFIG_ARM64_MODULE_PLTS */
		return -EINVAL;
#endif /* CONFIG_ARM64_MODULE_PLTS */
	} else {
		old = aarch64_insn_gen_branch_imm(pc, addr,
						  AARCH64_INSN_BRANCH_LINK);
	}

	new = aarch64_insn_gen_nop();

	return ftrace_modify_code(pc, old, new, validate);
}

void arch_ftrace_update_code(int command)
{
	command |= FTRACE_MAY_SLEEP;
	ftrace_modify_all_code(command);
}

int __init ftrace_dyn_arch_init(void)
{
	return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
 * function_graph tracer expects ftrace_return_to_handler() to be called
 * on the way back to parent. For this purpose, this function is called
 * in _mcount() or ftrace_caller() to replace return address (*parent) on
 * the call stack to return_to_handler.
 *
 * Note that @frame_pointer is used only for sanity check later.
 */
void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
			   unsigned long frame_pointer)
{
	unsigned long return_hooker = (unsigned long)&return_to_handler;
	unsigned long old;

	if (unlikely(atomic_read(&current->tracing_graph_pause)))
		return;

	/*
	 * Note:
	 * No protection against faulting at *parent, which may be seen
	 * on other archs. It's unlikely on AArch64.
	 */
	old = *parent;

	if (!function_graph_enter(old, self_addr, frame_pointer, NULL))
		*parent = return_hooker;
}

#ifdef CONFIG_DYNAMIC_FTRACE
/*
 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
 * depending on @enable.
 */
static int ftrace_modify_graph_caller(bool enable)
{
	unsigned long pc = (unsigned long)&ftrace_graph_call;
	u32 branch, nop;

	branch = aarch64_insn_gen_branch_imm(pc,
					     (unsigned long)ftrace_graph_caller,
					     AARCH64_INSN_BRANCH_NOLINK);
	nop = aarch64_insn_gen_nop();

	if (enable)
		return ftrace_modify_code(pc, nop, branch, true);
	else
		return ftrace_modify_code(pc, branch, nop, true);
}

int ftrace_enable_ftrace_graph_caller(void)
{
	return ftrace_modify_graph_caller(true);
}

int ftrace_disable_ftrace_graph_caller(void)
{
	return ftrace_modify_graph_caller(false);
}
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
Commit	Line	Data
819e50e2 AT	1	/*
	2	* arch/arm64/kernel/ftrace.c
	3	*
	4	* Copyright (C) 2013 Linaro Limited
	5	* Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
	6	*
	7	* This program is free software; you can redistribute it and/or modify
	8	* it under the terms of the GNU General Public License version 2 as
	9	* published by the Free Software Foundation.
	10	*/
	11
	12	#include <linux/ftrace.h>
e71a4e1b	13	#include <linux/module.h>
819e50e2 AT	14	#include <linux/swab.h>
	15	#include <linux/uaccess.h>
	16
	17	#include <asm/cacheflush.h>
e71a4e1b	18	#include <asm/debug-monitors.h>
819e50e2 AT	19	#include <asm/ftrace.h>
	20	#include <asm/insn.h>
	21
bd7d38db AT	22	#ifdef CONFIG_DYNAMIC_FTRACE
	23	/*
	24	* Replace a single instruction, which may be a branch or NOP.
	25	* If @validate == true, a replaced instruction is checked against 'old'.
	26	*/
	27	static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
	28	bool validate)
	29	{
	30	u32 replaced;
	31
	32	/*
	33	* Note:
004ab584 LB	34	* We are paranoid about modifying text, as if a bug were to happen, it
	35	* could cause us to read or write to someplace that could cause harm.
	36	* Carefully read and modify the code with aarch64_insn_*() which uses
	37	* probe_kernel_*(), and make sure what we read is what we expected it
	38	* to be before modifying it.
bd7d38db AT	39	*/
	40	if (validate) {
	41	if (aarch64_insn_read((void *)pc, &replaced))
	42	return -EFAULT;
	43
	44	if (replaced != old)
	45	return -EINVAL;
	46	}
	47	if (aarch64_insn_patch_text_nosync((void *)pc, new))
	48	return -EPERM;
	49
	50	return 0;
	51	}
	52
	53	/*
	54	* Replace tracer function in ftrace_caller()
	55	*/
	56	int ftrace_update_ftrace_func(ftrace_func_t func)
	57	{
	58	unsigned long pc;
	59	u32 new;
	60
	61	pc = (unsigned long)&ftrace_call;
9f1ae759 CM	62	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
9f1ae759 CM	63	AARCH64_INSN_BRANCH_LINK);
bd7d38db AT	64
	65	return ftrace_modify_code(pc, 0, new, false);
	66	}
	67
	68	/*
	69	* Turn on the call to ftrace_caller() in instrumented function
	70	*/
	71	int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
	72	{
	73	unsigned long pc = rec->ip;
	74	u32 old, new;
68764420 WD	75	long offset = (long)pc - (long)addr;
	76
	77	if (offset < -SZ_128M \|\| offset >= SZ_128M) {
8486e54d	78	#ifdef CONFIG_ARM64_MODULE_PLTS
be0f272b	79	struct plt_entry trampoline;
e71a4e1b AB	80	struct module *mod;
	81
	82	/*
	83	* On kernels that support module PLTs, the offset between the
	84	* branch instruction and its target may legally exceed the
	85	* range of an ordinary relative 'bl' opcode. In this case, we
	86	* need to branch via a trampoline in the module.
	87	*
	88	* NOTE: __module_text_address() must be called with preemption
	89	* disabled, but we can rely on ftrace_lock to ensure that 'mod'
	90	* retains its validity throughout the remainder of this code.
	91	*/
	92	preempt_disable();
	93	mod = __module_text_address(pc);
	94	preempt_enable();
	95
	96	if (WARN_ON(!mod))
	97	return -EINVAL;
	98
	99	/*
	100	* There is only one ftrace trampoline per module. For now,
	101	* this is not a problem since on arm64, all dynamic ftrace
	102	* invocations are routed via ftrace_caller(). This will need
	103	* to be revisited if support for multiple ftrace entry points
	104	* is added in the future, but for now, the pr_err() below
	105	* deals with a theoretical issue only.
	106	*/
bdb85cd1	107	trampoline = get_plt_entry(addr, mod->arch.ftrace_trampoline);
be0f272b AB	108	if (!plt_entries_equal(mod->arch.ftrace_trampoline,
	109	&trampoline)) {
	110	if (!plt_entries_equal(mod->arch.ftrace_trampoline,
	111	&(struct plt_entry){})) {
e71a4e1b AB	112	pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
	113	return -EINVAL;
	114	}
	115
	116	/* point the trampoline to our ftrace entry point */
	117	module_disable_ro(mod);
be0f272b	118	*mod->arch.ftrace_trampoline = trampoline;
e71a4e1b AB	119	module_enable_ro(mod, true);
	120
	121	/* update trampoline before patching in the branch */
	122	smp_wmb();
	123	}
be0f272b	124	addr = (unsigned long)(void *)mod->arch.ftrace_trampoline;
8486e54d MR	125	#else /* CONFIG_ARM64_MODULE_PLTS */
8486e54d MR	126	return -EINVAL;
68764420	127	#endif /* CONFIG_ARM64_MODULE_PLTS */
8486e54d	128	}
e71a4e1b	129
bd7d38db	130	old = aarch64_insn_gen_nop();
9f1ae759	131	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
bd7d38db AT	132
	133	return ftrace_modify_code(pc, old, new, true);
	134	}
	135
	136	/*
	137	* Turn off the call to ftrace_caller() in instrumented function
	138	*/
	139	int ftrace_make_nop(struct module mod, struct dyn_ftrace rec,
	140	unsigned long addr)
	141	{
	142	unsigned long pc = rec->ip;
f8af0b36 AB	143	bool validate = true;
f8af0b36 AB	144	u32 old = 0, new;
68764420 WD	145	long offset = (long)pc - (long)addr;
	146
	147	if (offset < -SZ_128M \|\| offset >= SZ_128M) {
8486e54d	148	#ifdef CONFIG_ARM64_MODULE_PLTS
f8af0b36 AB	149	u32 replaced;
	150
	151	/*
	152	* 'mod' is only set at module load time, but if we end up
	153	* dealing with an out-of-range condition, we can assume it
	154	* is due to a module being loaded far away from the kernel.
	155	*/
	156	if (!mod) {
	157	preempt_disable();
	158	mod = __module_text_address(pc);
	159	preempt_enable();
	160
	161	if (WARN_ON(!mod))
	162	return -EINVAL;
	163	}
	164
	165	/*
	166	* The instruction we are about to patch may be a branch and
	167	* link instruction that was redirected via a PLT entry. In
	168	* this case, the normal validation will fail, but we can at
	169	* least check that we are dealing with a branch and link
	170	* instruction that points into the right module.
	171	*/
	172	if (aarch64_insn_read((void *)pc, &replaced))
	173	return -EFAULT;
	174
	175	if (!aarch64_insn_is_bl(replaced) \|\|
	176	!within_module(pc + aarch64_get_branch_offset(replaced),
	177	mod))
	178	return -EINVAL;
	179
	180	validate = false;
8486e54d MR	181	#else /* CONFIG_ARM64_MODULE_PLTS */
	182	return -EINVAL;
	183	#endif /* CONFIG_ARM64_MODULE_PLTS */
f8af0b36 AB	184	} else {
	185	old = aarch64_insn_gen_branch_imm(pc, addr,
	186	AARCH64_INSN_BRANCH_LINK);
	187	}
bd7d38db	188
bd7d38db AT	189	new = aarch64_insn_gen_nop();
bd7d38db AT	190
f8af0b36	191	return ftrace_modify_code(pc, old, new, validate);
bd7d38db AT	192	}
bd7d38db AT	193
81a6a146 LB	194	void arch_ftrace_update_code(int command)
81a6a146 LB	195	{
e4c07bf9	196	command \|= FTRACE_MAY_SLEEP;
81a6a146 LB	197	ftrace_modify_all_code(command);
	198	}
	199
bd7d38db AT	200	int __init ftrace_dyn_arch_init(void)
	201	{
	202	return 0;
	203	}
	204	#endif /* CONFIG_DYNAMIC_FTRACE */
	205
819e50e2 AT	206	#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	207	/*
	208	* function_graph tracer expects ftrace_return_to_handler() to be called
	209	* on the way back to parent. For this purpose, this function is called
	210	* in _mcount() or ftrace_caller() to replace return address (*parent) on
	211	* the call stack to return_to_handler.
	212	*
	213	* Note that @frame_pointer is used only for sanity check later.
	214	*/
7dc48bf9	215	void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
819e50e2 AT	216	unsigned long frame_pointer)
	217	{
	218	unsigned long return_hooker = (unsigned long)&return_to_handler;
	219	unsigned long old;
819e50e2 AT	220
	221	if (unlikely(atomic_read(&current->tracing_graph_pause)))
	222	return;
	223
	224	/*
	225	* Note:
	226	* No protection against faulting at *parent, which may be seen
	227	* on other archs. It's unlikely on AArch64.
	228	*/
	229	old = *parent;
819e50e2	230
01e0ab2c	231	if (!function_graph_enter(old, self_addr, frame_pointer, NULL))
79fdee9b	232	*parent = return_hooker;
819e50e2	233	}
bd7d38db AT	234
	235	#ifdef CONFIG_DYNAMIC_FTRACE
	236	/*
	237	* Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
	238	* depending on @enable.
	239	*/
	240	static int ftrace_modify_graph_caller(bool enable)
	241	{
	242	unsigned long pc = (unsigned long)&ftrace_graph_call;
	243	u32 branch, nop;
	244
	245	branch = aarch64_insn_gen_branch_imm(pc,
9f1ae759	246	(unsigned long)ftrace_graph_caller,
d0d62230	247	AARCH64_INSN_BRANCH_NOLINK);
bd7d38db AT	248	nop = aarch64_insn_gen_nop();
	249
	250	if (enable)
	251	return ftrace_modify_code(pc, nop, branch, true);
	252	else
	253	return ftrace_modify_code(pc, branch, nop, true);
	254	}
	255
	256	int ftrace_enable_ftrace_graph_caller(void)
	257	{
	258	return ftrace_modify_graph_caller(true);
	259	}
	260
	261	int ftrace_disable_ftrace_graph_caller(void)
	262	{
	263	return ftrace_modify_graph_caller(false);
	264	}
	265	#endif /* CONFIG_DYNAMIC_FTRACE */
819e50e2	266	#endif /* CONFIG_FUNCTION_GRAPH_TRACER */