1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * arch/arm64/kernel/ftrace.c
  4 *
  5 * Copyright (C) 2013 Linaro Limited
  6 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
  7 */
  8
  9#include <linux/ftrace.h>
 10#include <linux/module.h>
 11#include <linux/swab.h>
 12#include <linux/uaccess.h>
 13
 14#include <asm/cacheflush.h>
 15#include <asm/debug-monitors.h>
 16#include <asm/ftrace.h>
 17#include <asm/insn.h>
 18
 19#ifdef CONFIG_DYNAMIC_FTRACE
 20/*
 21 * Replace a single instruction, which may be a branch or NOP.
 22 * If @validate == true, a replaced instruction is checked against 'old'.
 23 */
 24static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
 25			      bool validate)
 26{
 27	u32 replaced;
 28
 29	/*
 30	 * Note:
 31	 * We are paranoid about modifying text, as if a bug were to happen, it
 32	 * could cause us to read or write to someplace that could cause harm.
 33	 * Carefully read and modify the code with aarch64_insn_*() which uses
 34	 * probe_kernel_*(), and make sure what we read is what we expected it
 35	 * to be before modifying it.
 36	 */
 37	if (validate) {
 38		if (aarch64_insn_read((void *)pc, &replaced))
 39			return -EFAULT;
 40
 41		if (replaced != old)
 42			return -EINVAL;
 43	}
 44	if (aarch64_insn_patch_text_nosync((void *)pc, new))
 45		return -EPERM;
 46
 47	return 0;
 48}
 49
 50/*
 51 * Replace tracer function in ftrace_caller()
 52 */
 53int ftrace_update_ftrace_func(ftrace_func_t func)
 54{
 55	unsigned long pc;
 56	u32 new;
 57
 58	pc = (unsigned long)&ftrace_call;
 59	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
 60					  AARCH64_INSN_BRANCH_LINK);
 61
 62	return ftrace_modify_code(pc, 0, new, false);
 63}
 64
 65/*
 66 * Turn on the call to ftrace_caller() in instrumented function
 67 */
 68int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 69{
 70	unsigned long pc = rec->ip;
 71	u32 old, new;
 72	long offset = (long)pc - (long)addr;
 73
 74	if (offset < -SZ_128M || offset >= SZ_128M) {
 75#ifdef CONFIG_ARM64_MODULE_PLTS
 76		struct plt_entry trampoline, *dst;
 77		struct module *mod;
 78
 79		/*
 80		 * On kernels that support module PLTs, the offset between the
 81		 * branch instruction and its target may legally exceed the
 82		 * range of an ordinary relative 'bl' opcode. In this case, we
 83		 * need to branch via a trampoline in the module.
 84		 *
 85		 * NOTE: __module_text_address() must be called with preemption
 86		 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
 87		 * retains its validity throughout the remainder of this code.
 88		 */
 89		preempt_disable();
 90		mod = __module_text_address(pc);
 91		preempt_enable();
 92
 93		if (WARN_ON(!mod))
 94			return -EINVAL;
 95
 96		/*
 97		 * There is only one ftrace trampoline per module. For now,
 98		 * this is not a problem since on arm64, all dynamic ftrace
 99		 * invocations are routed via ftrace_caller(). This will need
100		 * to be revisited if support for multiple ftrace entry points
101		 * is added in the future, but for now, the pr_err() below
102		 * deals with a theoretical issue only.
103		 *
104		 * Note that PLTs are place relative, and plt_entries_equal()
105		 * checks whether they point to the same target. Here, we need
106		 * to check if the actual opcodes are in fact identical,
107		 * regardless of the offset in memory so use memcmp() instead.
108		 */
109		dst = mod->arch.ftrace_trampoline;
110		trampoline = get_plt_entry(addr, dst);
111		if (memcmp(dst, &trampoline, sizeof(trampoline))) {
112			if (plt_entry_is_initialized(dst)) {
113				pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
114				return -EINVAL;
115			}
116
117			/* point the trampoline to our ftrace entry point */
118			module_disable_ro(mod);
119			*dst = trampoline;
120			module_enable_ro(mod, true);
121
122			/*
123			 * Ensure updated trampoline is visible to instruction
124			 * fetch before we patch in the branch. Although the
125			 * architecture doesn't require an IPI in this case,
126			 * Neoverse-N1 erratum #1542419 does require one
127			 * if the TLB maintenance in module_enable_ro() is
128			 * skipped due to rodata_enabled. It doesn't seem worth
129			 * it to make it conditional given that this is
130			 * certainly not a fast-path.
131			 */
132			flush_icache_range((unsigned long)&dst[0],
133					   (unsigned long)&dst[1]);
134		}
135		addr = (unsigned long)dst;
136#else /* CONFIG_ARM64_MODULE_PLTS */
137		return -EINVAL;
138#endif /* CONFIG_ARM64_MODULE_PLTS */
139	}
140
141	old = aarch64_insn_gen_nop();
142	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
143
144	return ftrace_modify_code(pc, old, new, true);
145}
146
147/*
148 * Turn off the call to ftrace_caller() in instrumented function
149 */
150int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
151		    unsigned long addr)
152{
153	unsigned long pc = rec->ip;
154	bool validate = true;
155	u32 old = 0, new;
156	long offset = (long)pc - (long)addr;
157
158	if (offset < -SZ_128M || offset >= SZ_128M) {
159#ifdef CONFIG_ARM64_MODULE_PLTS
160		u32 replaced;
161
162		/*
163		 * 'mod' is only set at module load time, but if we end up
164		 * dealing with an out-of-range condition, we can assume it
165		 * is due to a module being loaded far away from the kernel.
166		 */
167		if (!mod) {
168			preempt_disable();
169			mod = __module_text_address(pc);
170			preempt_enable();
171
172			if (WARN_ON(!mod))
173				return -EINVAL;
174		}
175
176		/*
177		 * The instruction we are about to patch may be a branch and
178		 * link instruction that was redirected via a PLT entry. In
179		 * this case, the normal validation will fail, but we can at
180		 * least check that we are dealing with a branch and link
181		 * instruction that points into the right module.
182		 */
183		if (aarch64_insn_read((void *)pc, &replaced))
184			return -EFAULT;
185
186		if (!aarch64_insn_is_bl(replaced) ||
187		    !within_module(pc + aarch64_get_branch_offset(replaced),
188				   mod))
189			return -EINVAL;
190
191		validate = false;
192#else /* CONFIG_ARM64_MODULE_PLTS */
193		return -EINVAL;
194#endif /* CONFIG_ARM64_MODULE_PLTS */
195	} else {
196		old = aarch64_insn_gen_branch_imm(pc, addr,
197						  AARCH64_INSN_BRANCH_LINK);
198	}
199
200	new = aarch64_insn_gen_nop();
201
202	return ftrace_modify_code(pc, old, new, validate);
203}
204
205void arch_ftrace_update_code(int command)
206{
207	command |= FTRACE_MAY_SLEEP;
208	ftrace_modify_all_code(command);
209}
210
211int __init ftrace_dyn_arch_init(void)
212{
213	return 0;
214}
215#endif /* CONFIG_DYNAMIC_FTRACE */
216
217#ifdef CONFIG_FUNCTION_GRAPH_TRACER
218/*
219 * function_graph tracer expects ftrace_return_to_handler() to be called
220 * on the way back to parent. For this purpose, this function is called
221 * in _mcount() or ftrace_caller() to replace return address (*parent) on
222 * the call stack to return_to_handler.
223 *
224 * Note that @frame_pointer is used only for sanity check later.
225 */
226void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
227			   unsigned long frame_pointer)
228{
229	unsigned long return_hooker = (unsigned long)&return_to_handler;
230	unsigned long old;
231
232	if (unlikely(atomic_read(&current->tracing_graph_pause)))
233		return;
234
235	/*
236	 * Note:
237	 * No protection against faulting at *parent, which may be seen
238	 * on other archs. It's unlikely on AArch64.
239	 */
240	old = *parent;
241
242	if (!function_graph_enter(old, self_addr, frame_pointer, NULL))
243		*parent = return_hooker;
244}
245
246#ifdef CONFIG_DYNAMIC_FTRACE
247/*
248 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
249 * depending on @enable.
250 */
251static int ftrace_modify_graph_caller(bool enable)
252{
253	unsigned long pc = (unsigned long)&ftrace_graph_call;
254	u32 branch, nop;
255
256	branch = aarch64_insn_gen_branch_imm(pc,
257					     (unsigned long)ftrace_graph_caller,
258					     AARCH64_INSN_BRANCH_NOLINK);
259	nop = aarch64_insn_gen_nop();
260
261	if (enable)
262		return ftrace_modify_code(pc, nop, branch, true);
263	else
264		return ftrace_modify_code(pc, branch, nop, true);
265}
266
267int ftrace_enable_ftrace_graph_caller(void)
268{
269	return ftrace_modify_graph_caller(true);
270}
271
272int ftrace_disable_ftrace_graph_caller(void)
273{
274	return ftrace_modify_graph_caller(false);
275}
276#endif /* CONFIG_DYNAMIC_FTRACE */
277#endif /* CONFIG_FUNCTION_GRAPH_TRACER */