1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Dynamic function tracer architecture backend.
4 *
5 * Copyright IBM Corp. 2009,2014
6 *
7 * Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
8 */
9
10 #include <linux/hardirq.h>
11 #include <linux/uaccess.h>
12 #include <linux/ftrace.h>
13 #include <linux/kernel.h>
14 #include <linux/types.h>
15 #include <linux/kmsan-checks.h>
16 #include <linux/kprobes.h>
17 #include <linux/execmem.h>
18 #include <trace/syscall.h>
19 #include <asm/asm-offsets.h>
20 #include <asm/text-patching.h>
21 #include <asm/cacheflush.h>
22 #include <asm/ftrace.lds.h>
23 #include <asm/nospec-branch.h>
24 #include <asm/set_memory.h>
25 #include "entry.h"
26 #include "ftrace.h"
27
28 /*
29 * To generate function prologue either gcc's hotpatch feature (since gcc 4.8)
30 * or a combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags
31 * (since gcc 9 / clang 10) is used.
32 * In both cases the original and also the disabled function prologue contains
33 * only a single six byte instruction and looks like this:
34 * > brcl 0,0 # offset 0
35 * To enable ftrace the code gets patched like above and afterwards looks
36 * like this:
37 * > brasl %r0,ftrace_caller # offset 0
38 *
39 * The instruction will be patched by ftrace_make_call / ftrace_make_nop.
40 * The ftrace function gets called with a non-standard C function call ABI
41 * where r0 contains the return address. It is also expected that the called
42 * function only clobbers r0 and r1, but restores r2-r15.
43 * For module code we can't directly jump to ftrace caller, but need a
44 * trampoline (ftrace_plt), which clobbers also r1.
45 */
46
47 void *ftrace_func __read_mostly = ftrace_stub;
48 struct ftrace_insn {
49 u16 opc;
50 s32 disp;
51 } __packed;
52
53 #ifdef CONFIG_MODULES
54 static char *ftrace_plt;
55 #endif /* CONFIG_MODULES */
56
57 static const char *ftrace_shared_hotpatch_trampoline(const char **end)
58 {
59 const char *tstart, *tend;
60
61 tstart = ftrace_shared_hotpatch_trampoline_br;
62 tend = ftrace_shared_hotpatch_trampoline_br_end;
63 #ifdef CONFIG_EXPOLINE
64 if (!nospec_disable) {
65 tstart = ftrace_shared_hotpatch_trampoline_exrl;
66 tend = ftrace_shared_hotpatch_trampoline_exrl_end;
67 }
68 #endif /* CONFIG_EXPOLINE */
69 if (end)
70 *end = tend;
71 return tstart;
72 }
73
74 bool ftrace_need_init_nop(void)
75 {
76 return true;
77 }
78
79 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
80 {
81 static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
82 __ftrace_hotpatch_trampolines_start;
83 static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 };
84 static struct ftrace_hotpatch_trampoline *trampoline;
85 struct ftrace_hotpatch_trampoline **next_trampoline;
86 struct ftrace_hotpatch_trampoline *trampolines_end;
87 struct ftrace_hotpatch_trampoline tmp;
88 struct ftrace_insn *insn;
89 const char *shared;
90 s32 disp;
91
92 BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
93 SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);
94
95 next_trampoline = &next_vmlinux_trampoline;
96 trampolines_end = __ftrace_hotpatch_trampolines_end;
97 shared = ftrace_shared_hotpatch_trampoline(NULL);
98 #ifdef CONFIG_MODULES
99 if (mod) {
100 next_trampoline = &mod->arch.next_trampoline;
101 trampolines_end = mod->arch.trampolines_end;
102 shared = ftrace_plt;
103 }
104 #endif
105
106 if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
107 return -ENOMEM;
108 trampoline = (*next_trampoline)++;
109
110 /* Check for the compiler-generated fentry nop (brcl 0, .). */
111 if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig))))
112 return -EINVAL;
113
114 /* Generate the trampoline. */
115 tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
116 tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
117 tmp.interceptor = FTRACE_ADDR;
118 tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
119 s390_kernel_write(trampoline, &tmp, sizeof(tmp));
120
121 /* Generate a jump to the trampoline. */
122 disp = ((char *)trampoline - (char *)rec->ip) / 2;
123 insn = (struct ftrace_insn *)rec->ip;
124 s390_kernel_write(&insn->disp, &disp, sizeof(disp));
125
126 return 0;
127 }
128
129 static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec)
130 {
131 struct ftrace_hotpatch_trampoline *trampoline;
132 struct ftrace_insn insn;
133 s64 disp;
134 u16 opc;
135
136 if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn)))
137 return ERR_PTR(-EFAULT);
138 disp = (s64)insn.disp * 2;
139 trampoline = (void *)(rec->ip + disp);
140 if (get_kernel_nofault(opc, &trampoline->brasl_opc))
141 return ERR_PTR(-EFAULT);
142 if (opc != 0xc015)
143 return ERR_PTR(-EINVAL);
144 return trampoline;
145 }
146
147 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
148 unsigned long addr)
149 {
150 struct ftrace_hotpatch_trampoline *trampoline;
151 u64 old;
152
153 trampoline = ftrace_get_trampoline(rec);
154 if (IS_ERR(trampoline))
155 return PTR_ERR(trampoline);
156 if (get_kernel_nofault(old, &trampoline->interceptor))
157 return -EFAULT;
158 if (old != old_addr)
159 return -EINVAL;
160 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
161 return 0;
162 }
163
164 static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
165 {
166 u16 old;
167 u8 op;
168
169 if (get_kernel_nofault(old, addr))
170 return -EFAULT;
171 if (old != expected)
172 return -EINVAL;
173 /* set mask field to all ones or zeroes */
174 op = enable ? 0xf4 : 0x04;
175 s390_kernel_write((char *)addr + 1, &op, sizeof(op));
176 return 0;
177 }
178
179 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
180 unsigned long addr)
181 {
182 /* Expect brcl 0xf,... */
183 return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
184 }
185
186 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
187 {
188 struct ftrace_hotpatch_trampoline *trampoline;
189
190 trampoline = ftrace_get_trampoline(rec);
191 if (IS_ERR(trampoline))
192 return PTR_ERR(trampoline);
193 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
194 /* Expect brcl 0x0,... */
195 return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
196 }
197
198 int ftrace_update_ftrace_func(ftrace_func_t func)
199 {
200 ftrace_func = func;
201 return 0;
202 }
203
204 void arch_ftrace_update_code(int command)
205 {
206 ftrace_modify_all_code(command);
207 }
208
209 void ftrace_arch_code_modify_post_process(void)
210 {
211 /*
212 * Flush any pre-fetched instructions on all
213 * CPUs to make the new code visible.
214 */
215 text_poke_sync_lock();
216 }
217
218 #ifdef CONFIG_MODULES
219
220 static int __init ftrace_plt_init(void)
221 {
222 const char *start, *end;
223
224 ftrace_plt = execmem_alloc(EXECMEM_FTRACE, PAGE_SIZE);
225 if (!ftrace_plt)
226 panic("cannot allocate ftrace plt\n");
227
228 start = ftrace_shared_hotpatch_trampoline(&end);
229 memcpy(ftrace_plt, start, end - start);
230 set_memory_rox((unsigned long)ftrace_plt, 1);
231 return 0;
232 }
233 device_initcall(ftrace_plt_init);
234
235 #endif /* CONFIG_MODULES */
236
237 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
238 /*
239 * Hook the return address and push it in the stack of return addresses
240 * in current thread info.
241 */
242 unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
243 unsigned long ip)
244 {
245 if (unlikely(ftrace_graph_is_dead()))
246 goto out;
247 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
248 goto out;
249 ip -= MCOUNT_INSN_SIZE;
250 if (!function_graph_enter(ra, ip, 0, (void *) sp))
251 ra = (unsigned long) return_to_handler;
252 out:
253 return ra;
254 }
255 NOKPROBE_SYMBOL(prepare_ftrace_return);
256
257 /*
258 * Patch the kernel code at ftrace_graph_caller location. The instruction
259 * there is branch relative on condition. To enable the ftrace graph code
260 * block, we simply patch the mask field of the instruction to zero and
261 * turn the instruction into a nop.
262 * To disable the ftrace graph code the mask field will be patched to
263 * all ones, which turns the instruction into an unconditional branch.
264 */
265 int ftrace_enable_ftrace_graph_caller(void)
266 {
267 int rc;
268
269 /* Expect brc 0xf,... */
270 rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa7f4, false);
271 if (rc)
272 return rc;
273 text_poke_sync_lock();
274 return 0;
275 }
276
277 int ftrace_disable_ftrace_graph_caller(void)
278 {
279 int rc;
280
281 /* Expect brc 0x0,... */
282 rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa704, true);
283 if (rc)
284 return rc;
285 text_poke_sync_lock();
286 return 0;
287 }
288
289 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
290
291 #ifdef CONFIG_KPROBES_ON_FTRACE
292 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
293 struct ftrace_ops *ops, struct ftrace_regs *fregs)
294 {
295 struct kprobe_ctlblk *kcb;
296 struct pt_regs *regs;
297 struct kprobe *p;
298 int bit;
299
300 if (unlikely(kprobe_ftrace_disabled))
301 return;
302
303 bit = ftrace_test_recursion_trylock(ip, parent_ip);
304 if (bit < 0)
305 return;
306
307 kmsan_unpoison_memory(fregs, sizeof(*fregs));
308 regs = ftrace_get_regs(fregs);
309 p = get_kprobe((kprobe_opcode_t *)ip);
310 if (!regs || unlikely(!p) || kprobe_disabled(p))
311 goto out;
312
313 if (kprobe_running()) {
314 kprobes_inc_nmissed_count(p);
315 goto out;
316 }
317
318 __this_cpu_write(current_kprobe, p);
319
320 kcb = get_kprobe_ctlblk();
321 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
322
323 instruction_pointer_set(regs, ip);
324
325 if (!p->pre_handler || !p->pre_handler(p, regs)) {
326
327 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
328
329 if (unlikely(p->post_handler)) {
330 kcb->kprobe_status = KPROBE_HIT_SSDONE;
331 p->post_handler(p, regs, 0);
332 }
333 }
334 __this_cpu_write(current_kprobe, NULL);
335 out:
336 ftrace_test_recursion_unlock(bit);
337 }
338 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
339
340 int arch_prepare_kprobe_ftrace(struct kprobe *p)
341 {
342 p->ainsn.insn = NULL;
343 return 0;
344 }
345 #endif
346
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.