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): 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 asm(
  53         "       .align 16\n"
  54         "ftrace_shared_hotpatch_trampoline_br:\n"
  55         "       lmg     %r0,%r1,2(%r1)\n"
  56         "       br      %r1\n"
  57         "ftrace_shared_hotpatch_trampoline_br_end:\n"
  58 );
  59
  60 #ifdef CONFIG_EXPOLINE
  61 asm(
  62         "       .align 16\n"
  63         "ftrace_shared_hotpatch_trampoline_exrl:\n"
  64         "       lmg     %r0,%r1,2(%r1)\n"
  65         "       exrl    %r0,0f\n"
  66         "       j       .\n"
  67         "0:     br      %r1\n"
  68         "ftrace_shared_hotpatch_trampoline_exrl_end:\n"
  69 );
  70 #endif /* CONFIG_EXPOLINE */
  71
  72 #ifdef CONFIG_MODULES
  73 static char *ftrace_plt;
  74 #endif /* CONFIG_MODULES */
  75
  76 static const char *ftrace_shared_hotpatch_trampoline(const char **end)
  77 {
  78         const char *tstart, *tend;
  79
  80         tstart = ftrace_shared_hotpatch_trampoline_br;
  81         tend = ftrace_shared_hotpatch_trampoline_br_end;
  82 #ifdef CONFIG_EXPOLINE
  83         if (!nospec_disable) {
  84                 tstart = ftrace_shared_hotpatch_trampoline_exrl;
  85                 tend = ftrace_shared_hotpatch_trampoline_exrl_end;
  86         }
  87 #endif /* CONFIG_EXPOLINE */
  88         if (end)
  89                 *end = tend;
  90         return tstart;
  91 }
  92
  93 bool ftrace_need_init_nop(void)
  94 {
  95         return true;
  96 }
  97
  98 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
  99 {
 100         static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
 101                 __ftrace_hotpatch_trampolines_start;
 102         static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 };
 103         static struct ftrace_hotpatch_trampoline *trampoline;
 104         struct ftrace_hotpatch_trampoline **next_trampoline;
 105         struct ftrace_hotpatch_trampoline *trampolines_end;
 106         struct ftrace_hotpatch_trampoline tmp;
 107         struct ftrace_insn *insn;
 108         const char *shared;
 109         s32 disp;
 110
 111         BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
 112                      SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);
 113
 114         next_trampoline = &next_vmlinux_trampoline;
 115         trampolines_end = __ftrace_hotpatch_trampolines_end;
 116         shared = ftrace_shared_hotpatch_trampoline(NULL);
 117 #ifdef CONFIG_MODULES
 118         if (mod) {
 119                 next_trampoline = &mod->arch.next_trampoline;
 120                 trampolines_end = mod->arch.trampolines_end;
 121                 shared = ftrace_plt;
 122         }
 123 #endif
 124
 125         if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
 126                 return -ENOMEM;
 127         trampoline = (*next_trampoline)++;
 128
 129         /* Check for the compiler-generated fentry nop (brcl 0, .). */
 130         if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig))))
 131                 return -EINVAL;
 132
 133         /* Generate the trampoline. */
 134         tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
 135         tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
 136         tmp.interceptor = FTRACE_ADDR;
 137         tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
 138         s390_kernel_write(trampoline, &tmp, sizeof(tmp));
 139
 140         /* Generate a jump to the trampoline. */
 141         disp = ((char *)trampoline - (char *)rec->ip) / 2;
 142         insn = (struct ftrace_insn *)rec->ip;
 143         s390_kernel_write(&insn->disp, &disp, sizeof(disp));
 144
 145         return 0;
 146 }
 147
 148 static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec)
 149 {
 150         struct ftrace_hotpatch_trampoline *trampoline;
 151         struct ftrace_insn insn;
 152         s64 disp;
 153         u16 opc;
 154
 155         if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn)))
 156                 return ERR_PTR(-EFAULT);
 157         disp = (s64)insn.disp * 2;
 158         trampoline = (void *)(rec->ip + disp);
 159         if (get_kernel_nofault(opc, &trampoline->brasl_opc))
 160                 return ERR_PTR(-EFAULT);
 161         if (opc != 0xc015)
 162                 return ERR_PTR(-EINVAL);
 163         return trampoline;
 164 }
 165
 166 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 167                        unsigned long addr)
 168 {
 169         struct ftrace_hotpatch_trampoline *trampoline;
 170         u64 old;
 171
 172         trampoline = ftrace_get_trampoline(rec);
 173         if (IS_ERR(trampoline))
 174                 return PTR_ERR(trampoline);
 175         if (get_kernel_nofault(old, &trampoline->interceptor))
 176                 return -EFAULT;
 177         if (old != old_addr)
 178                 return -EINVAL;
 179         s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
 180         return 0;
 181 }
 182
 183 static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
 184 {
 185         u16 old;
 186         u8 op;
 187
 188         if (get_kernel_nofault(old, addr))
 189                 return -EFAULT;
 190         if (old != expected)
 191                 return -EINVAL;
 192         /* set mask field to all ones or zeroes */
 193         op = enable ? 0xf4 : 0x04;
 194         s390_kernel_write((char *)addr + 1, &op, sizeof(op));
 195         return 0;
 196 }
 197
 198 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 199                     unsigned long addr)
 200 {
 201         /* Expect brcl 0xf,... */
 202         return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
 203 }
 204
 205 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 206 {
 207         struct ftrace_hotpatch_trampoline *trampoline;
 208
 209         trampoline = ftrace_get_trampoline(rec);
 210         if (IS_ERR(trampoline))
 211                 return PTR_ERR(trampoline);
 212         s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
 213         /* Expect brcl 0x0,... */
 214         return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
 215 }
 216
 217 int ftrace_update_ftrace_func(ftrace_func_t func)
 218 {
 219         ftrace_func = func;
 220         return 0;
 221 }
 222
 223 void arch_ftrace_update_code(int command)
 224 {
 225         ftrace_modify_all_code(command);
 226 }
 227
 228 void ftrace_arch_code_modify_post_process(void)
 229 {
 230         /*
 231          * Flush any pre-fetched instructions on all
 232          * CPUs to make the new code visible.
 233          */
 234         text_poke_sync_lock();
 235 }
 236
 237 #ifdef CONFIG_MODULES
 238
 239 static int __init ftrace_plt_init(void)
 240 {
 241         const char *start, *end;
 242
 243         ftrace_plt = module_alloc(PAGE_SIZE);
 244         if (!ftrace_plt)
 245                 panic("cannot allocate ftrace plt\n");
 246
 247         start = ftrace_shared_hotpatch_trampoline(&end);
 248         memcpy(ftrace_plt, start, end - start);
 249         set_memory_ro((unsigned long)ftrace_plt, 1);
 250         return 0;
 251 }
 252 device_initcall(ftrace_plt_init);
 253
 254 #endif /* CONFIG_MODULES */
 255
 256 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 257 /*
 258  * Hook the return address and push it in the stack of return addresses
 259  * in current thread info.
 260  */
 261 unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
 262                                     unsigned long ip)
 263 {
 264         if (unlikely(ftrace_graph_is_dead()))
 265                 goto out;
 266         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 267                 goto out;
 268         ip -= MCOUNT_INSN_SIZE;
 269         if (!function_graph_enter(ra, ip, 0, (void *) sp))
 270                 ra = (unsigned long) return_to_handler;
 271 out:
 272         return ra;
 273 }
 274 NOKPROBE_SYMBOL(prepare_ftrace_return);
 275
 276 /*
 277  * Patch the kernel code at ftrace_graph_caller location. The instruction
 278  * there is branch relative on condition. To enable the ftrace graph code
 279  * block, we simply patch the mask field of the instruction to zero and
 280  * turn the instruction into a nop.
 281  * To disable the ftrace graph code the mask field will be patched to
 282  * all ones, which turns the instruction into an unconditional branch.
 283  */
 284 int ftrace_enable_ftrace_graph_caller(void)
 285 {
 286         int rc;
 287
 288         /* Expect brc 0xf,... */
 289         rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa7f4, false);
 290         if (rc)
 291                 return rc;
 292         text_poke_sync_lock();
 293         return 0;
 294 }
 295
 296 int ftrace_disable_ftrace_graph_caller(void)
 297 {
 298         int rc;
 299
 300         /* Expect brc 0x0,... */
 301         rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa704, true);
 302         if (rc)
 303                 return rc;
 304         text_poke_sync_lock();
 305         return 0;
 306 }
 307
 308 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 309
 310 #ifdef CONFIG_KPROBES_ON_FTRACE
 311 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 312                 struct ftrace_ops *ops, struct ftrace_regs *fregs)
 313 {
 314         struct kprobe_ctlblk *kcb;
 315         struct pt_regs *regs;
 316         struct kprobe *p;
 317         int bit;
 318
 319         bit = ftrace_test_recursion_trylock(ip, parent_ip);
 320         if (bit < 0)
 321                 return;
 322
 323         regs = ftrace_get_regs(fregs);
 324         p = get_kprobe((kprobe_opcode_t *)ip);
 325         if (!regs || unlikely(!p) || kprobe_disabled(p))
 326                 goto out;
 327
 328         if (kprobe_running()) {
 329                 kprobes_inc_nmissed_count(p);
 330                 goto out;
 331         }
 332
 333         __this_cpu_write(current_kprobe, p);
 334
 335         kcb = get_kprobe_ctlblk();
 336         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 337
 338         instruction_pointer_set(regs, ip);
 339
 340         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 341
 342                 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
 343
 344                 if (unlikely(p->post_handler)) {
 345                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 346                         p->post_handler(p, regs, 0);
 347                 }
 348         }
 349         __this_cpu_write(current_kprobe, NULL);
 350 out:
 351         ftrace_test_recursion_unlock(bit);
 352 }
 353 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 354
 355 int arch_prepare_kprobe_ftrace(struct kprobe *p)
 356 {
 357         p->ainsn.insn = NULL;
 358         return 0;
 359 }
 360 #endif