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
ftrace_modify_code(unsigned long pc,u32 old,u32 new,bool validate)15 static 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
reachable_by_bl(unsigned long addr,unsigned long pc)34 static 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
get_ftrace_plt(struct module * mod,unsigned long addr)41 static 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 */
ftrace_find_callable_addr(struct dyn_ftrace * rec,struct module * mod,unsigned long * addr)63 static 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 */
ftrace_find_callable_addr(struct dyn_ftrace * rec,struct module * mod,unsigned long * addr)110 static 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
ftrace_modify_call(struct dyn_ftrace * rec,unsigned long old_addr,unsigned long addr)117 int 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
ftrace_update_ftrace_func(ftrace_func_t func)137 int 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
ftrace_init_nop(struct module * mod,struct dyn_ftrace * rec)169 int 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
ftrace_make_call(struct dyn_ftrace * rec,unsigned long addr)181 int 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
ftrace_make_nop(struct module * mod,struct dyn_ftrace * rec,unsigned long addr)197 int 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
arch_ftrace_update_code(int command)213 void arch_ftrace_update_code(int command)
214 {
215 command |= FTRACE_MAY_SLEEP;
216 ftrace_modify_all_code(command);
217 }
218
ftrace_dyn_arch_init(void)219 int __init ftrace_dyn_arch_init(void)
220 {
221 return 0;
222 }
223
224 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
prepare_ftrace_return(unsigned long self_addr,unsigned long * parent)225 void 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(¤t->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
ftrace_graph_func(unsigned long ip,unsigned long parent_ip,struct ftrace_ops * op,struct ftrace_regs * fregs)240 void 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 *)®s->regs[1];
245 unsigned long return_hooker = (unsigned long)&return_to_handler;
246 unsigned long old;
247
248 if (unlikely(atomic_read(¤t->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
ftrace_modify_graph_caller(bool enable)257 static 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
ftrace_enable_ftrace_graph_caller(void)275 int ftrace_enable_ftrace_graph_caller(void)
276 {
277 return ftrace_modify_graph_caller(true);
278 }
279
ftrace_disable_ftrace_graph_caller(void)280 int 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 */
kprobe_ftrace_handler(unsigned long ip,unsigned long parent_ip,struct ftrace_ops * ops,struct ftrace_regs * fregs)289 void 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 }
341 out:
342 ftrace_test_recursion_unlock(bit);
343 }
344 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
345
arch_prepare_kprobe_ftrace(struct kprobe * p)346 int arch_prepare_kprobe_ftrace(struct kprobe *p)
347 {
348 p->ainsn.insn = NULL;
349 return 0;
350 }
351 #endif /* CONFIG_KPROBES_ON_FTRACE */
352