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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
47void *ftrace_func __read_mostly = ftrace_stub;
48struct ftrace_insn {
49 u16 opc;
50 s32 disp;
51} __packed;
52
53static const char *ftrace_shared_hotpatch_trampoline(const char **end)
54{
55 const char *tstart, *tend;
56
57 tstart = ftrace_shared_hotpatch_trampoline_br;
58 tend = ftrace_shared_hotpatch_trampoline_br_end;
59#ifdef CONFIG_EXPOLINE
60 if (!nospec_disable) {
61 tstart = ftrace_shared_hotpatch_trampoline_exrl;
62 tend = ftrace_shared_hotpatch_trampoline_exrl_end;
63 }
64#endif /* CONFIG_EXPOLINE */
65 if (end)
66 *end = tend;
67 return tstart;
68}
69
70bool ftrace_need_init_nop(void)
71{
72 return !MACHINE_HAS_SEQ_INSN;
73}
74
75int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
76{
77 static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
78 __ftrace_hotpatch_trampolines_start;
79 static const struct ftrace_insn orig = { .opc = 0xc004, .disp = 0 };
80 static struct ftrace_hotpatch_trampoline *trampoline;
81 struct ftrace_hotpatch_trampoline **next_trampoline;
82 struct ftrace_hotpatch_trampoline *trampolines_end;
83 struct ftrace_hotpatch_trampoline tmp;
84 struct ftrace_insn *insn;
85 struct ftrace_insn old;
86 const char *shared;
87 s32 disp;
88
89 BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
90 SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);
91
92 next_trampoline = &next_vmlinux_trampoline;
93 trampolines_end = __ftrace_hotpatch_trampolines_end;
94 shared = ftrace_shared_hotpatch_trampoline(NULL);
95#ifdef CONFIG_MODULES
96 if (mod) {
97 next_trampoline = &mod->arch.next_trampoline;
98 trampolines_end = mod->arch.trampolines_end;
99 }
100#endif
101
102 if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
103 return -ENOMEM;
104 trampoline = (*next_trampoline)++;
105
106 if (copy_from_kernel_nofault(&old, (void *)rec->ip, sizeof(old)))
107 return -EFAULT;
108 /* Check for the compiler-generated fentry nop (brcl 0, .). */
109 if (WARN_ON_ONCE(memcmp(&orig, &old, sizeof(old))))
110 return -EINVAL;
111
112 /* Generate the trampoline. */
113 tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
114 tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
115 tmp.interceptor = FTRACE_ADDR;
116 tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
117 s390_kernel_write(trampoline, &tmp, sizeof(tmp));
118
119 /* Generate a jump to the trampoline. */
120 disp = ((char *)trampoline - (char *)rec->ip) / 2;
121 insn = (struct ftrace_insn *)rec->ip;
122 s390_kernel_write(&insn->disp, &disp, sizeof(disp));
123
124 return 0;
125}
126
127static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec)
128{
129 struct ftrace_hotpatch_trampoline *trampoline;
130 struct ftrace_insn insn;
131 s64 disp;
132 u16 opc;
133
134 if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn)))
135 return ERR_PTR(-EFAULT);
136 disp = (s64)insn.disp * 2;
137 trampoline = (void *)(rec->ip + disp);
138 if (get_kernel_nofault(opc, &trampoline->brasl_opc))
139 return ERR_PTR(-EFAULT);
140 if (opc != 0xc015)
141 return ERR_PTR(-EINVAL);
142 return trampoline;
143}
144
145static inline struct ftrace_insn
146ftrace_generate_branch_insn(unsigned long ip, unsigned long target)
147{
148 /* brasl r0,target or brcl 0,0 */
149 return (struct ftrace_insn){ .opc = target ? 0xc005 : 0xc004,
150 .disp = target ? (target - ip) / 2 : 0 };
151}
152
153static int ftrace_patch_branch_insn(unsigned long ip, unsigned long old_target,
154 unsigned long target)
155{
156 struct ftrace_insn orig = ftrace_generate_branch_insn(ip, old_target);
157 struct ftrace_insn new = ftrace_generate_branch_insn(ip, target);
158 struct ftrace_insn old;
159
160 if (!IS_ALIGNED(ip, 8))
161 return -EINVAL;
162 if (copy_from_kernel_nofault(&old, (void *)ip, sizeof(old)))
163 return -EFAULT;
164 /* Verify that the to be replaced code matches what we expect. */
165 if (memcmp(&orig, &old, sizeof(old)))
166 return -EINVAL;
167 s390_kernel_write((void *)ip, &new, sizeof(new));
168 return 0;
169}
170
171static int ftrace_modify_trampoline_call(struct dyn_ftrace *rec,
172 unsigned long old_addr,
173 unsigned long addr)
174{
175 struct ftrace_hotpatch_trampoline *trampoline;
176 u64 old;
177
178 trampoline = ftrace_get_trampoline(rec);
179 if (IS_ERR(trampoline))
180 return PTR_ERR(trampoline);
181 if (get_kernel_nofault(old, &trampoline->interceptor))
182 return -EFAULT;
183 if (old != old_addr)
184 return -EINVAL;
185 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
186 return 0;
187}
188
189int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
190 unsigned long addr)
191{
192 if (MACHINE_HAS_SEQ_INSN)
193 return ftrace_patch_branch_insn(rec->ip, old_addr, addr);
194 else
195 return ftrace_modify_trampoline_call(rec, old_addr, addr);
196}
197
198static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
199{
200 u16 old;
201 u8 op;
202
203 if (get_kernel_nofault(old, addr))
204 return -EFAULT;
205 if (old != expected)
206 return -EINVAL;
207 /* set mask field to all ones or zeroes */
208 op = enable ? 0xf4 : 0x04;
209 s390_kernel_write((char *)addr + 1, &op, sizeof(op));
210 return 0;
211}
212
213int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
214 unsigned long addr)
215{
216 /* Expect brcl 0xf,... for the !MACHINE_HAS_SEQ_INSN case */
217 if (MACHINE_HAS_SEQ_INSN)
218 return ftrace_patch_branch_insn(rec->ip, addr, 0);
219 else
220 return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
221}
222
223static int ftrace_make_trampoline_call(struct dyn_ftrace *rec, unsigned long addr)
224{
225 struct ftrace_hotpatch_trampoline *trampoline;
226
227 trampoline = ftrace_get_trampoline(rec);
228 if (IS_ERR(trampoline))
229 return PTR_ERR(trampoline);
230 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
231 /* Expect brcl 0x0,... */
232 return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
233}
234
235int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
236{
237 if (MACHINE_HAS_SEQ_INSN)
238 return ftrace_patch_branch_insn(rec->ip, 0, addr);
239 else
240 return ftrace_make_trampoline_call(rec, addr);
241}
242
243int ftrace_update_ftrace_func(ftrace_func_t func)
244{
245 ftrace_func = func;
246 return 0;
247}
248
249void arch_ftrace_update_code(int command)
250{
251 ftrace_modify_all_code(command);
252}
253
254void ftrace_arch_code_modify_post_process(void)
255{
256 /*
257 * Flush any pre-fetched instructions on all
258 * CPUs to make the new code visible.
259 */
260 text_poke_sync_lock();
261}
262
263#ifdef CONFIG_FUNCTION_GRAPH_TRACER
264/*
265 * Hook the return address and push it in the stack of return addresses
266 * in current thread info.
267 */
268unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
269 unsigned long ip)
270{
271 if (unlikely(ftrace_graph_is_dead()))
272 goto out;
273 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
274 goto out;
275 ip -= MCOUNT_INSN_SIZE;
276 if (!function_graph_enter(ra, ip, 0, (void *) sp))
277 ra = (unsigned long) return_to_handler;
278out:
279 return ra;
280}
281NOKPROBE_SYMBOL(prepare_ftrace_return);
282
283/*
284 * Patch the kernel code at ftrace_graph_caller location. The instruction
285 * there is branch relative on condition. To enable the ftrace graph code
286 * block, we simply patch the mask field of the instruction to zero and
287 * turn the instruction into a nop.
288 * To disable the ftrace graph code the mask field will be patched to
289 * all ones, which turns the instruction into an unconditional branch.
290 */
291int ftrace_enable_ftrace_graph_caller(void)
292{
293 /* Expect brc 0xf,... */
294 return ftrace_patch_branch_mask(ftrace_graph_caller, 0xa7f4, false);
295}
296
297int ftrace_disable_ftrace_graph_caller(void)
298{
299 /* Expect brc 0x0,... */
300 return ftrace_patch_branch_mask(ftrace_graph_caller, 0xa704, true);
301}
302
303#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
304
305#ifdef CONFIG_KPROBES_ON_FTRACE
306void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
307 struct ftrace_ops *ops, struct ftrace_regs *fregs)
308{
309 struct kprobe_ctlblk *kcb;
310 struct pt_regs *regs;
311 struct kprobe *p;
312 int bit;
313
314 if (unlikely(kprobe_ftrace_disabled))
315 return;
316
317 bit = ftrace_test_recursion_trylock(ip, parent_ip);
318 if (bit < 0)
319 return;
320
321 kmsan_unpoison_memory(fregs, ftrace_regs_size());
322 regs = ftrace_get_regs(fregs);
323 p = get_kprobe((kprobe_opcode_t *)ip);
324 if (!regs || unlikely(!p) || kprobe_disabled(p))
325 goto out;
326
327 if (kprobe_running()) {
328 kprobes_inc_nmissed_count(p);
329 goto out;
330 }
331
332 __this_cpu_write(current_kprobe, p);
333
334 kcb = get_kprobe_ctlblk();
335 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
336
337 instruction_pointer_set(regs, ip);
338
339 if (!p->pre_handler || !p->pre_handler(p, regs)) {
340
341 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
342
343 if (unlikely(p->post_handler)) {
344 kcb->kprobe_status = KPROBE_HIT_SSDONE;
345 p->post_handler(p, regs, 0);
346 }
347 }
348 __this_cpu_write(current_kprobe, NULL);
349out:
350 ftrace_test_recursion_unlock(bit);
351}
352NOKPROBE_SYMBOL(kprobe_ftrace_handler);
353
354int arch_prepare_kprobe_ftrace(struct kprobe *p)
355{
356 p->ainsn.insn = NULL;
357 return 0;
358}
359#endif
1/*
2 * Dynamic function tracer architecture backend.
3 *
4 * Copyright IBM Corp. 2009
5 *
6 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
7 * 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/kprobes.h>
16#include <trace/syscall.h>
17#include <asm/asm-offsets.h>
18
19#ifdef CONFIG_64BIT
20#define MCOUNT_OFFSET_RET 12
21#else
22#define MCOUNT_OFFSET_RET 22
23#endif
24
25#ifdef CONFIG_DYNAMIC_FTRACE
26
27void ftrace_disable_code(void);
28void ftrace_enable_insn(void);
29
30#ifdef CONFIG_64BIT
31/*
32 * The 64-bit mcount code looks like this:
33 * stg %r14,8(%r15) # offset 0
34 * > larl %r1,<&counter> # offset 6
35 * > brasl %r14,_mcount # offset 12
36 * lg %r14,8(%r15) # offset 18
37 * Total length is 24 bytes. The middle two instructions of the mcount
38 * block get overwritten by ftrace_make_nop / ftrace_make_call.
39 * The 64-bit enabled ftrace code block looks like this:
40 * stg %r14,8(%r15) # offset 0
41 * > lg %r1,__LC_FTRACE_FUNC # offset 6
42 * > lgr %r0,%r0 # offset 12
43 * > basr %r14,%r1 # offset 16
44 * lg %r14,8(%15) # offset 18
45 * The return points of the mcount/ftrace function have the same offset 18.
46 * The 64-bit disable ftrace code block looks like this:
47 * stg %r14,8(%r15) # offset 0
48 * > jg .+18 # offset 6
49 * > lgr %r0,%r0 # offset 12
50 * > basr %r14,%r1 # offset 16
51 * lg %r14,8(%15) # offset 18
52 * The jg instruction branches to offset 24 to skip as many instructions
53 * as possible.
54 */
55asm(
56 " .align 4\n"
57 "ftrace_disable_code:\n"
58 " jg 0f\n"
59 " lgr %r0,%r0\n"
60 " basr %r14,%r1\n"
61 "0:\n"
62 " .align 4\n"
63 "ftrace_enable_insn:\n"
64 " lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
65
66#define FTRACE_INSN_SIZE 6
67
68#else /* CONFIG_64BIT */
69/*
70 * The 31-bit mcount code looks like this:
71 * st %r14,4(%r15) # offset 0
72 * > bras %r1,0f # offset 4
73 * > .long _mcount # offset 8
74 * > .long <&counter> # offset 12
75 * > 0: l %r14,0(%r1) # offset 16
76 * > l %r1,4(%r1) # offset 20
77 * basr %r14,%r14 # offset 24
78 * l %r14,4(%r15) # offset 26
79 * Total length is 30 bytes. The twenty bytes starting from offset 4
80 * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
81 * The 31-bit enabled ftrace code block looks like this:
82 * st %r14,4(%r15) # offset 0
83 * > l %r14,__LC_FTRACE_FUNC # offset 4
84 * > j 0f # offset 8
85 * > .fill 12,1,0x07 # offset 12
86 * 0: basr %r14,%r14 # offset 24
87 * l %r14,4(%r14) # offset 26
88 * The return points of the mcount/ftrace function have the same offset 26.
89 * The 31-bit disabled ftrace code block looks like this:
90 * st %r14,4(%r15) # offset 0
91 * > j .+26 # offset 4
92 * > j 0f # offset 8
93 * > .fill 12,1,0x07 # offset 12
94 * 0: basr %r14,%r14 # offset 24
95 * l %r14,4(%r14) # offset 26
96 * The j instruction branches to offset 30 to skip as many instructions
97 * as possible.
98 */
99asm(
100 " .align 4\n"
101 "ftrace_disable_code:\n"
102 " j 1f\n"
103 " j 0f\n"
104 " .fill 12,1,0x07\n"
105 "0: basr %r14,%r14\n"
106 "1:\n"
107 " .align 4\n"
108 "ftrace_enable_insn:\n"
109 " l %r14,"__stringify(__LC_FTRACE_FUNC)"\n");
110
111#define FTRACE_INSN_SIZE 4
112
113#endif /* CONFIG_64BIT */
114
115
116int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
117 unsigned long addr)
118{
119 if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
120 MCOUNT_INSN_SIZE))
121 return -EPERM;
122 return 0;
123}
124
125int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
126{
127 if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
128 FTRACE_INSN_SIZE))
129 return -EPERM;
130 return 0;
131}
132
133int ftrace_update_ftrace_func(ftrace_func_t func)
134{
135 return 0;
136}
137
138int __init ftrace_dyn_arch_init(void *data)
139{
140 *(unsigned long *) data = 0;
141 return 0;
142}
143
144#endif /* CONFIG_DYNAMIC_FTRACE */
145
146#ifdef CONFIG_FUNCTION_GRAPH_TRACER
147/*
148 * Hook the return address and push it in the stack of return addresses
149 * in current thread info.
150 */
151unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
152 unsigned long ip)
153{
154 struct ftrace_graph_ent trace;
155
156 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
157 goto out;
158 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
159 goto out;
160 trace.func = (ip & PSW_ADDR_INSN) - MCOUNT_OFFSET_RET;
161 /* Only trace if the calling function expects to. */
162 if (!ftrace_graph_entry(&trace)) {
163 current->curr_ret_stack--;
164 goto out;
165 }
166 parent = (unsigned long) return_to_handler;
167out:
168 return parent;
169}
170
171#ifdef CONFIG_DYNAMIC_FTRACE
172/*
173 * Patch the kernel code at ftrace_graph_caller location. The instruction
174 * there is branch relative and save to prepare_ftrace_return. To disable
175 * the call to prepare_ftrace_return we patch the bras offset to point
176 * directly after the instructions. To enable the call we calculate
177 * the original offset to prepare_ftrace_return and put it back.
178 */
179int ftrace_enable_ftrace_graph_caller(void)
180{
181 unsigned short offset;
182
183 offset = ((void *) prepare_ftrace_return -
184 (void *) ftrace_graph_caller) / 2;
185 return probe_kernel_write(ftrace_graph_caller + 2,
186 &offset, sizeof(offset));
187}
188
189int ftrace_disable_ftrace_graph_caller(void)
190{
191 static unsigned short offset = 0x0002;
192
193 return probe_kernel_write(ftrace_graph_caller + 2,
194 &offset, sizeof(offset));
195}
196
197#endif /* CONFIG_DYNAMIC_FTRACE */
198#endif /* CONFIG_FUNCTION_GRAPH_TRACER */