ftrace_dyn.c

  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 within a RCU read
 89	 * section, 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		scoped_guard(rcu)
 94			mod = __module_text_address(pc);
 95	}
 96
 97	if (WARN_ON(!mod))
 98		return false;
 99
100	plt = get_ftrace_plt(mod, *addr);
101	if (!plt) {
102		pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);
103		return false;
104	}
105
106	*addr = (unsigned long)plt;
107	return true;
108}
109#else /* !CONFIG_MODULES */
110static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, struct module *mod, unsigned long *addr)
111{
112	return true;
113}
114#endif
115
116#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
117int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr)
118{
119	u32 old, new;
120	unsigned long pc;
121
122	pc = rec->ip + LOONGARCH_INSN_SIZE;
123
124	if (!ftrace_find_callable_addr(rec, NULL, &addr))
125		return -EINVAL;
126
127	if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
128		return -EINVAL;
129
130	new = larch_insn_gen_bl(pc, addr);
131	old = larch_insn_gen_bl(pc, old_addr);
132
133	return ftrace_modify_code(pc, old, new, true);
134}
135#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
136
137int ftrace_update_ftrace_func(ftrace_func_t func)
138{
139	u32 new;
140	unsigned long pc;
141
142	pc = (unsigned long)&ftrace_call;
143	new = larch_insn_gen_bl(pc, (unsigned long)func);
144
145	return ftrace_modify_code(pc, 0, new, false);
146}
147
148/*
149 * The compiler has inserted 2 NOPs before the regular function prologue.
150 * T series registers are available and safe because of LoongArch's psABI.
151 *
152 * At runtime, we can replace nop with bl to enable ftrace call and replace bl
153 * with nop to disable ftrace call. The bl requires us to save the original RA
154 * value, so it saves RA at t0 here.
155 *
156 * Details are:
157 *
158 * | Compiled   |       Disabled         |        Enabled         |
159 * +------------+------------------------+------------------------+
160 * | nop        | move     t0, ra        | move     t0, ra        |
161 * | nop        | nop                    | bl       ftrace_caller |
162 * | func_body  | func_body              | func_body              |
163 *
164 * The RA value will be recovered by ftrace_regs_entry, and restored into RA
165 * before returning to the regular function prologue. When a function is not
166 * being traced, the "move t0, ra" is not harmful.
167 */
168
169int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
170{
171	u32 old, new;
172	unsigned long pc;
173
174	pc = rec->ip;
175	old = larch_insn_gen_nop();
176	new = larch_insn_gen_move(LOONGARCH_GPR_T0, LOONGARCH_GPR_RA);
177
178	return ftrace_modify_code(pc, old, new, true);
179}
180
181int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
182{
183	u32 old, new;
184	unsigned long pc;
185
186	pc = rec->ip + LOONGARCH_INSN_SIZE;
187
188	if (!ftrace_find_callable_addr(rec, NULL, &addr))
189		return -EINVAL;
190
191	old = larch_insn_gen_nop();
192	new = larch_insn_gen_bl(pc, addr);
193
194	return ftrace_modify_code(pc, old, new, true);
195}
196
197int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
198{
199	u32 old, new;
200	unsigned long pc;
201
202	pc = rec->ip + LOONGARCH_INSN_SIZE;
203
204	if (!ftrace_find_callable_addr(rec, NULL, &addr))
205		return -EINVAL;
206
207	new = larch_insn_gen_nop();
208	old = larch_insn_gen_bl(pc, addr);
209
210	return ftrace_modify_code(pc, old, new, true);
211}
212
213void arch_ftrace_update_code(int command)
214{
215	command |= FTRACE_MAY_SLEEP;
216	ftrace_modify_all_code(command);
217}
218
219int __init ftrace_dyn_arch_init(void)
220{
221	return 0;
222}
223
224#ifdef CONFIG_FUNCTION_GRAPH_TRACER
225void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent)
226{
227	unsigned long old;
228	unsigned long return_hooker = (unsigned long)&return_to_handler;
229
230	if (unlikely(atomic_read(&current->tracing_graph_pause)))
231		return;
232
233	old = *parent;
234
235	if (!function_graph_enter(old, self_addr, 0, parent))
236		*parent = return_hooker;
237}
238
239#ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
240void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
241		       struct ftrace_ops *op, struct ftrace_regs *fregs)
242{
243	struct pt_regs *regs = &arch_ftrace_regs(fregs)->regs;
244	unsigned long *parent = (unsigned long *)&regs->regs[1];
245	unsigned long return_hooker = (unsigned long)&return_to_handler;
246	unsigned long old;
247
248	if (unlikely(atomic_read(&current->tracing_graph_pause)))
249		return;
250
251	old = *parent;
252
253	if (!function_graph_enter_regs(old, ip, 0, parent, fregs))
254		*parent = return_hooker;
255}
256#else
257static int ftrace_modify_graph_caller(bool enable)
258{
259	u32 branch, nop;
260	unsigned long pc, func;
261	extern void ftrace_graph_call(void);
262
263	pc = (unsigned long)&ftrace_graph_call;
264	func = (unsigned long)&ftrace_graph_caller;
265
266	nop = larch_insn_gen_nop();
267	branch = larch_insn_gen_b(pc, func);
268
269	if (enable)
270		return ftrace_modify_code(pc, nop, branch, true);
271	else
272		return ftrace_modify_code(pc, branch, nop, true);
273}
274
275int ftrace_enable_ftrace_graph_caller(void)
276{
277	return ftrace_modify_graph_caller(true);
278}
279
280int ftrace_disable_ftrace_graph_caller(void)
281{
282	return ftrace_modify_graph_caller(false);
283}
284#endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
285#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
286
287#ifdef CONFIG_KPROBES_ON_FTRACE
288/* Ftrace callback handler for kprobes -- called under preepmt disabled */
289void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
290			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
291{
292	int bit;
293	struct pt_regs *regs;
294	struct kprobe *p;
295	struct kprobe_ctlblk *kcb;
296
297	if (unlikely(kprobe_ftrace_disabled))
298		return;
299
300	bit = ftrace_test_recursion_trylock(ip, parent_ip);
301	if (bit < 0)
302		return;
303
304	p = get_kprobe((kprobe_opcode_t *)ip);
305	if (unlikely(!p) || kprobe_disabled(p))
306		goto out;
307
308	regs = ftrace_get_regs(fregs);
309	if (!regs)
310		goto out;
311
312	kcb = get_kprobe_ctlblk();
313	if (kprobe_running()) {
314		kprobes_inc_nmissed_count(p);
315	} else {
316		unsigned long orig_ip = instruction_pointer(regs);
317
318		instruction_pointer_set(regs, ip);
319
320		__this_cpu_write(current_kprobe, p);
321		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
322		if (!p->pre_handler || !p->pre_handler(p, regs)) {
323			/*
324			 * Emulate singlestep (and also recover regs->csr_era)
325			 * as if there is a nop
326			 */
327			instruction_pointer_set(regs, (unsigned long)p->addr + MCOUNT_INSN_SIZE);
328			if (unlikely(p->post_handler)) {
329				kcb->kprobe_status = KPROBE_HIT_SSDONE;
330				p->post_handler(p, regs, 0);
331			}
332			instruction_pointer_set(regs, orig_ip);
333		}
334
335		/*
336		 * If pre_handler returns !0, it changes regs->csr_era. We have to
337		 * skip emulating post_handler.
338		 */
339		__this_cpu_write(current_kprobe, NULL);
340	}
341out:
342	ftrace_test_recursion_unlock(bit);
343}
344NOKPROBE_SYMBOL(kprobe_ftrace_handler);
345
346int arch_prepare_kprobe_ftrace(struct kprobe *p)
347{
348	p->ainsn.insn = NULL;
349	return 0;
350}
351#endif /* CONFIG_KPROBES_ON_FTRACE */