arch/s390/kernel/ftrace.c

   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): Heiko Carstens <[email protected]>,
   8  *              Martin Schwidefsky <[email protected]>
   9  */
  10
  11 #include <linux/moduleloader.h>
  12 #include <linux/hardirq.h>
  13 #include <linux/uaccess.h>
  14 #include <linux/ftrace.h>
  15 #include <linux/kernel.h>
  16 #include <linux/types.h>
  17 #include <linux/kprobes.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 asm(
  54         "       .align 16\n"
  55         "ftrace_shared_hotpatch_trampoline_br:\n"
  56         "       lmg     %r0,%r1,2(%r1)\n"
  57         "       br      %r1\n"
  58         "ftrace_shared_hotpatch_trampoline_br_end:\n"
  59 );
  60
  61 #ifdef CONFIG_EXPOLINE
  62 asm(
  63         "       .align 16\n"
  64         "ftrace_shared_hotpatch_trampoline_ex:\n"
  65         "       lmg     %r0,%r1,2(%r1)\n"
  66         "       ex      %r0," __stringify(__LC_BR_R1) "(%r0)\n"
  67         "       j       .\n"
  68         "ftrace_shared_hotpatch_trampoline_ex_end:\n"
  69 );
  70
  71 asm(
  72         "       .align 16\n"
  73         "ftrace_shared_hotpatch_trampoline_exrl:\n"
  74         "       lmg     %r0,%r1,2(%r1)\n"
  75         "       .insn   ril,0xc60000000000,%r0,0f\n" /* exrl */
  76         "       j       .\n"
  77         "0:     br      %r1\n"
  78         "ftrace_shared_hotpatch_trampoline_exrl_end:\n"
  79 );
  80 #endif /* CONFIG_EXPOLINE */
  81
  82 #ifdef CONFIG_MODULES
  83 static char *ftrace_plt;
  84 #endif /* CONFIG_MODULES */
  85
  86 static const char *ftrace_shared_hotpatch_trampoline(const char **end)
  87 {
  88         const char *tstart, *tend;
  89
  90         tstart = ftrace_shared_hotpatch_trampoline_br;
  91         tend = ftrace_shared_hotpatch_trampoline_br_end;
  92 #ifdef CONFIG_EXPOLINE
  93         if (!nospec_disable) {
  94                 tstart = ftrace_shared_hotpatch_trampoline_ex;
  95                 tend = ftrace_shared_hotpatch_trampoline_ex_end;
  96                 if (test_facility(35)) { /* exrl */
  97                         tstart = ftrace_shared_hotpatch_trampoline_exrl;
  98                         tend = ftrace_shared_hotpatch_trampoline_exrl_end;
  99                 }
 100         }
 101 #endif /* CONFIG_EXPOLINE */
 102         if (end)
 103                 *end = tend;
 104         return tstart;
 105 }
 106
 107 bool ftrace_need_init_nop(void)
 108 {
 109         return true;
 110 }
 111
 112 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 113 {
 114         static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
 115                 __ftrace_hotpatch_trampolines_start;
 116         static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 };
 117         static struct ftrace_hotpatch_trampoline *trampoline;
 118         struct ftrace_hotpatch_trampoline **next_trampoline;
 119         struct ftrace_hotpatch_trampoline *trampolines_end;
 120         struct ftrace_hotpatch_trampoline tmp;
 121         struct ftrace_insn *insn;
 122         const char *shared;
 123         s32 disp;
 124
 125         BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
 126                      SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);
 127
 128         next_trampoline = &next_vmlinux_trampoline;
 129         trampolines_end = __ftrace_hotpatch_trampolines_end;
 130         shared = ftrace_shared_hotpatch_trampoline(NULL);
 131 #ifdef CONFIG_MODULES
 132         if (mod) {
 133                 next_trampoline = &mod->arch.next_trampoline;
 134                 trampolines_end = mod->arch.trampolines_end;
 135                 shared = ftrace_plt;
 136         }
 137 #endif
 138
 139         if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
 140                 return -ENOMEM;
 141         trampoline = (*next_trampoline)++;
 142
 143         /* Check for the compiler-generated fentry nop (brcl 0, .). */
 144         if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig))))
 145                 return -EINVAL;
 146
 147         /* Generate the trampoline. */
 148         tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
 149         tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
 150         tmp.interceptor = FTRACE_ADDR;
 151         tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
 152         s390_kernel_write(trampoline, &tmp, sizeof(tmp));
 153
 154         /* Generate a jump to the trampoline. */
 155         disp = ((char *)trampoline - (char *)rec->ip) / 2;
 156         insn = (struct ftrace_insn *)rec->ip;
 157         s390_kernel_write(&insn->disp, &disp, sizeof(disp));
 158
 159         return 0;
 160 }
 161
 162 static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec)
 163 {
 164         struct ftrace_hotpatch_trampoline *trampoline;
 165         struct ftrace_insn insn;
 166         s64 disp;
 167         u16 opc;
 168
 169         if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn)))
 170                 return ERR_PTR(-EFAULT);
 171         disp = (s64)insn.disp * 2;
 172         trampoline = (void *)(rec->ip + disp);
 173         if (get_kernel_nofault(opc, &trampoline->brasl_opc))
 174                 return ERR_PTR(-EFAULT);
 175         if (opc != 0xc015)
 176                 return ERR_PTR(-EINVAL);
 177         return trampoline;
 178 }
 179
 180 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 181                        unsigned long addr)
 182 {
 183         struct ftrace_hotpatch_trampoline *trampoline;
 184         u64 old;
 185
 186         trampoline = ftrace_get_trampoline(rec);
 187         if (IS_ERR(trampoline))
 188                 return PTR_ERR(trampoline);
 189         if (get_kernel_nofault(old, &trampoline->interceptor))
 190                 return -EFAULT;
 191         if (old != old_addr)
 192                 return -EINVAL;
 193         s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
 194         return 0;
 195 }
 196
 197 static void brcl_disable(void *brcl)
 198 {
 199         u8 op = 0x04; /* set mask field to zero */
 200
 201         s390_kernel_write((char *)brcl + 1, &op, sizeof(op));
 202 }
 203
 204 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 205                     unsigned long addr)
 206 {
 207         brcl_disable((void *)rec->ip);
 208         return 0;
 209 }
 210
 211 static void brcl_enable(void *brcl)
 212 {
 213         u8 op = 0xf4; /* set mask field to all ones */
 214
 215         s390_kernel_write((char *)brcl + 1, &op, sizeof(op));
 216 }
 217
 218 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 219 {
 220         struct ftrace_hotpatch_trampoline *trampoline;
 221
 222         trampoline = ftrace_get_trampoline(rec);
 223         if (IS_ERR(trampoline))
 224                 return PTR_ERR(trampoline);
 225         s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
 226         brcl_enable((void *)rec->ip);
 227         return 0;
 228 }
 229
 230 int ftrace_update_ftrace_func(ftrace_func_t func)
 231 {
 232         ftrace_func = func;
 233         return 0;
 234 }
 235
 236 void arch_ftrace_update_code(int command)
 237 {
 238         ftrace_modify_all_code(command);
 239 }
 240
 241 int ftrace_arch_code_modify_post_process(void)
 242 {
 243         /*
 244          * Flush any pre-fetched instructions on all
 245          * CPUs to make the new code visible.
 246          */
 247         text_poke_sync_lock();
 248         return 0;
 249 }
 250
 251 #ifdef CONFIG_MODULES
 252
 253 static int __init ftrace_plt_init(void)
 254 {
 255         const char *start, *end;
 256
 257         ftrace_plt = module_alloc(PAGE_SIZE);
 258         if (!ftrace_plt)
 259                 panic("cannot allocate ftrace plt\n");
 260
 261         start = ftrace_shared_hotpatch_trampoline(&end);
 262         memcpy(ftrace_plt, start, end - start);
 263         set_memory_ro((unsigned long)ftrace_plt, 1);
 264         return 0;
 265 }
 266 device_initcall(ftrace_plt_init);
 267
 268 #endif /* CONFIG_MODULES */
 269
 270 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 271 /*
 272  * Hook the return address and push it in the stack of return addresses
 273  * in current thread info.
 274  */
 275 unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
 276                                     unsigned long ip)
 277 {
 278         if (unlikely(ftrace_graph_is_dead()))
 279                 goto out;
 280         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 281                 goto out;
 282         ip -= MCOUNT_INSN_SIZE;
 283         if (!function_graph_enter(ra, ip, 0, (void *) sp))
 284                 ra = (unsigned long) return_to_handler;
 285 out:
 286         return ra;
 287 }
 288 NOKPROBE_SYMBOL(prepare_ftrace_return);
 289
 290 /*
 291  * Patch the kernel code at ftrace_graph_caller location. The instruction
 292  * there is branch relative on condition. To enable the ftrace graph code
 293  * block, we simply patch the mask field of the instruction to zero and
 294  * turn the instruction into a nop.
 295  * To disable the ftrace graph code the mask field will be patched to
 296  * all ones, which turns the instruction into an unconditional branch.
 297  */
 298 int ftrace_enable_ftrace_graph_caller(void)
 299 {
 300         brcl_disable(ftrace_graph_caller);
 301         text_poke_sync_lock();
 302         return 0;
 303 }
 304
 305 int ftrace_disable_ftrace_graph_caller(void)
 306 {
 307         brcl_enable(ftrace_graph_caller);
 308         text_poke_sync_lock();
 309         return 0;
 310 }
 311
 312 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 313
 314 #ifdef CONFIG_KPROBES_ON_FTRACE
 315 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 316                 struct ftrace_ops *ops, struct ftrace_regs *fregs)
 317 {
 318         struct kprobe_ctlblk *kcb;
 319         struct pt_regs *regs;
 320         struct kprobe *p;
 321         int bit;
 322
 323         bit = ftrace_test_recursion_trylock(ip, parent_ip);
 324         if (bit < 0)
 325                 return;
 326
 327         regs = ftrace_get_regs(fregs);
 328         p = get_kprobe((kprobe_opcode_t *)ip);
 329         if (!regs || unlikely(!p) || kprobe_disabled(p))
 330                 goto out;
 331
 332         if (kprobe_running()) {
 333                 kprobes_inc_nmissed_count(p);
 334                 goto out;
 335         }
 336
 337         __this_cpu_write(current_kprobe, p);
 338
 339         kcb = get_kprobe_ctlblk();
 340         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 341
 342         instruction_pointer_set(regs, ip);
 343
 344         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 345
 346                 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
 347
 348                 if (unlikely(p->post_handler)) {
 349                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 350                         p->post_handler(p, regs, 0);
 351                 }
 352         }
 353         __this_cpu_write(current_kprobe, NULL);
 354 out:
 355         ftrace_test_recursion_unlock(bit);
 356 }
 357 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 358
 359 int arch_prepare_kprobe_ftrace(struct kprobe *p)
 360 {
 361         p->ainsn.insn = NULL;
 362         return 0;
 363 }
 364 #endif