1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Based on arch/arm64/kernel/ftrace.c
  4 *
  5 * Copyright (C) 2022 Loongson Technology Corporation Limited
  6 */
  7
  8#include <linux/ftrace.h>
  9#include <linux/kprobes.h>
 10#include <linux/uaccess.h>
 11
 12#include <asm/inst.h>
 13#include <asm/module.h>
 14
 15static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, bool validate)
 16{
 17	u32 replaced;
 18
 19	if (validate) {
 20		if (larch_insn_read((void *)pc, &replaced))
 21			return -EFAULT;
 22
 23		if (replaced != old)
 24			return -EINVAL;
 25	}
 26
 27	if (larch_insn_patch_text((void *)pc, new))
 28		return -EPERM;
 29
 30	return 0;
 31}
 32
 33#ifdef CONFIG_MODULES
 34static bool reachable_by_bl(unsigned long addr, unsigned long pc)
 35{
 36	long offset = (long)addr - (long)pc;
 37
 38	return offset >= -SZ_128M && offset < SZ_128M;
 39}
 40
 41static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
 42{
 43	struct plt_entry *plt = mod->arch.ftrace_trampolines;
 44
 45	if (addr == FTRACE_ADDR)
 46		return &plt[FTRACE_PLT_IDX];
 47	if (addr == FTRACE_REGS_ADDR &&
 48			IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
 49		return &plt[FTRACE_REGS_PLT_IDX];
 50
 51	return NULL;
 52}
 53
 54/*
 55 * Find the address the callsite must branch to in order to reach '*addr'.
 56 *
 57 * Due to the limited range of 'bl' instruction, modules may be placed too far
 58 * away to branch directly and we must use a PLT.
 59 *
 60 * Returns true when '*addr' contains a reachable target address, or has been
 61 * modified to contain a PLT address. Returns false otherwise.
 62 */
 63static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, struct module *mod, unsigned long *addr)
 64{
 65	unsigned long pc = rec->ip + LOONGARCH_INSN_SIZE;
 66	struct plt_entry *plt;
 67
 68	/*
 69	 * If a custom trampoline is unreachable, rely on the ftrace_regs_caller
 70	 * trampoline which knows how to indirectly reach that trampoline through
 71	 * ops->direct_call.
 72	 */
 73	if (*addr != FTRACE_ADDR && *addr != FTRACE_REGS_ADDR && !reachable_by_bl(*addr, pc))
 74		*addr = FTRACE_REGS_ADDR;
 75
 76	/*
 77	 * When the target is within range of the 'bl' instruction, use 'addr'
 78	 * as-is and branch to that directly.
 79	 */
 80	if (reachable_by_bl(*addr, pc))
 81		return true;
 82
 83	/*
 84	 * 'mod' is only set at module load time, but if we end up
 85	 * dealing with an out-of-range condition, we can assume it
 86	 * is due to a module being loaded far away from the kernel.
 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	if (!mod) {
 93		preempt_disable();
 94		mod = __module_text_address(pc);
 95		preempt_enable();
 96	}
 97
 98	if (WARN_ON(!mod))
 99		return false;
100
101	plt = get_ftrace_plt(mod, *addr);
102	if (!plt) {
103		pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);
104		return false;
105	}
106
107	*addr = (unsigned long)plt;
108	return true;
109}
110#else /* !CONFIG_MODULES */
111static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, struct module *mod, unsigned long *addr)
112{
113	return true;
114}
115#endif
116
117#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
118int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr)
119{
120	u32 old, new;
121	unsigned long pc;
122
123	pc = rec->ip + LOONGARCH_INSN_SIZE;
124
125	if (!ftrace_find_callable_addr(rec, NULL, &addr))
126		return -EINVAL;
127
128	if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
129		return -EINVAL;
130
131	new = larch_insn_gen_bl(pc, addr);
132	old = larch_insn_gen_bl(pc, old_addr);
133
134	return ftrace_modify_code(pc, old, new, true);
135}
136#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
137
138int ftrace_update_ftrace_func(ftrace_func_t func)
139{
140	u32 new;
141	unsigned long pc;
142
143	pc = (unsigned long)&ftrace_call;
144	new = larch_insn_gen_bl(pc, (unsigned long)func);
145
146	return ftrace_modify_code(pc, 0, new, false);
147}
148
149/*
150 * The compiler has inserted 2 NOPs before the regular function prologue.
151 * T series registers are available and safe because of LoongArch's psABI.
152 *
153 * At runtime, we can replace nop with bl to enable ftrace call and replace bl
154 * with nop to disable ftrace call. The bl requires us to save the original RA
155 * value, so it saves RA at t0 here.
156 *
157 * Details are:
158 *
159 * | Compiled   |       Disabled         |        Enabled         |
160 * +------------+------------------------+------------------------+
161 * | nop        | move     t0, ra        | move     t0, ra        |
162 * | nop        | nop                    | bl       ftrace_caller |
163 * | func_body  | func_body              | func_body              |
164 *
165 * The RA value will be recovered by ftrace_regs_entry, and restored into RA
166 * before returning to the regular function prologue. When a function is not
167 * being traced, the "move t0, ra" is not harmful.
168 */
169
170int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
171{
172	u32 old, new;
173	unsigned long pc;
174
175	pc = rec->ip;
176	old = larch_insn_gen_nop();
177	new = larch_insn_gen_move(LOONGARCH_GPR_T0, LOONGARCH_GPR_RA);
178
179	return ftrace_modify_code(pc, old, new, true);
180}
181
182int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
183{
184	u32 old, new;
185	unsigned long pc;
186
187	pc = rec->ip + LOONGARCH_INSN_SIZE;
188
189	if (!ftrace_find_callable_addr(rec, NULL, &addr))
190		return -EINVAL;
191
192	old = larch_insn_gen_nop();
193	new = larch_insn_gen_bl(pc, addr);
194
195	return ftrace_modify_code(pc, old, new, true);
196}
197
198int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
199{
200	u32 old, new;
201	unsigned long pc;
202
203	pc = rec->ip + LOONGARCH_INSN_SIZE;
204
205	if (!ftrace_find_callable_addr(rec, NULL, &addr))
206		return -EINVAL;
207
208	new = larch_insn_gen_nop();
209	old = larch_insn_gen_bl(pc, addr);
210
211	return ftrace_modify_code(pc, old, new, true);
212}
213
214void arch_ftrace_update_code(int command)
215{
216	command |= FTRACE_MAY_SLEEP;
217	ftrace_modify_all_code(command);
218}
219
220int __init ftrace_dyn_arch_init(void)
221{
222	return 0;
223}
224
225#ifdef CONFIG_FUNCTION_GRAPH_TRACER
226void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent)
227{
228	unsigned long old;
229	unsigned long return_hooker = (unsigned long)&return_to_handler;
230
231	if (unlikely(atomic_read(&current->tracing_graph_pause)))
232		return;
233
234	old = *parent;
235
236	if (!function_graph_enter(old, self_addr, 0, parent))
237		*parent = return_hooker;
238}
239
240#ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
241void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
242		       struct ftrace_ops *op, struct ftrace_regs *fregs)
243{
244	struct pt_regs *regs = &fregs->regs;
245	unsigned long *parent = (unsigned long *)&regs->regs[1];
246
247	prepare_ftrace_return(ip, (unsigned long *)parent);
248}
249#else
250static int ftrace_modify_graph_caller(bool enable)
251{
252	u32 branch, nop;
253	unsigned long pc, func;
254	extern void ftrace_graph_call(void);
255
256	pc = (unsigned long)&ftrace_graph_call;
257	func = (unsigned long)&ftrace_graph_caller;
258
259	nop = larch_insn_gen_nop();
260	branch = larch_insn_gen_b(pc, func);
261
262	if (enable)
263		return ftrace_modify_code(pc, nop, branch, true);
264	else
265		return ftrace_modify_code(pc, branch, nop, true);
266}
267
268int ftrace_enable_ftrace_graph_caller(void)
269{
270	return ftrace_modify_graph_caller(true);
271}
272
273int ftrace_disable_ftrace_graph_caller(void)
274{
275	return ftrace_modify_graph_caller(false);
276}
277#endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
278#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
279
280#ifdef CONFIG_KPROBES_ON_FTRACE
281/* Ftrace callback handler for kprobes -- called under preepmt disabled */
282void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
283			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
284{
285	int bit;
286	struct pt_regs *regs;
287	struct kprobe *p;
288	struct kprobe_ctlblk *kcb;
289
290	bit = ftrace_test_recursion_trylock(ip, parent_ip);
291	if (bit < 0)
292		return;
293
294	p = get_kprobe((kprobe_opcode_t *)ip);
295	if (unlikely(!p) || kprobe_disabled(p))
296		goto out;
297
298	regs = ftrace_get_regs(fregs);
299	if (!regs)
300		goto out;
301
302	kcb = get_kprobe_ctlblk();
303	if (kprobe_running()) {
304		kprobes_inc_nmissed_count(p);
305	} else {
306		unsigned long orig_ip = instruction_pointer(regs);
307
308		instruction_pointer_set(regs, ip);
309
310		__this_cpu_write(current_kprobe, p);
311		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
312		if (!p->pre_handler || !p->pre_handler(p, regs)) {
313			/*
314			 * Emulate singlestep (and also recover regs->csr_era)
315			 * as if there is a nop
316			 */
317			instruction_pointer_set(regs, (unsigned long)p->addr + MCOUNT_INSN_SIZE);
318			if (unlikely(p->post_handler)) {
319				kcb->kprobe_status = KPROBE_HIT_SSDONE;
320				p->post_handler(p, regs, 0);
321			}
322			instruction_pointer_set(regs, orig_ip);
323		}
324
325		/*
326		 * If pre_handler returns !0, it changes regs->csr_era. We have to
327		 * skip emulating post_handler.
328		 */
329		__this_cpu_write(current_kprobe, NULL);
330	}
331out:
332	ftrace_test_recursion_unlock(bit);
333}
334NOKPROBE_SYMBOL(kprobe_ftrace_handler);
335
336int arch_prepare_kprobe_ftrace(struct kprobe *p)
337{
338	p->ainsn.insn = NULL;
339	return 0;
340}
341#endif /* CONFIG_KPROBES_ON_FTRACE */