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