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_ex:\n"
  64         "       lmg     %r0,%r1,2(%r1)\n"
  65         "       ex      %r0," __stringify(__LC_BR_R1) "(%r0)\n"
  66         "       j       .\n"
  67         "ftrace_shared_hotpatch_trampoline_ex_end:\n"
  68 );
  69
  70 asm(
  71         "       .align 16\n"
  72         "ftrace_shared_hotpatch_trampoline_exrl:\n"
  73         "       lmg     %r0,%r1,2(%r1)\n"
  74         "       .insn   ril,0xc60000000000,%r0,0f\n" /* exrl */
  75         "       j       .\n"
  76         "0:     br      %r1\n"
  77         "ftrace_shared_hotpatch_trampoline_exrl_end:\n"
  78 );
  79 #endif /* CONFIG_EXPOLINE */
  80
  81 #ifdef CONFIG_MODULES
  82 static char *ftrace_plt;
  83 #endif /* CONFIG_MODULES */
  84
  85 static const char *ftrace_shared_hotpatch_trampoline(const char **end)
  86 {
  87         const char *tstart, *tend;
  88
  89         tstart = ftrace_shared_hotpatch_trampoline_br;
  90         tend = ftrace_shared_hotpatch_trampoline_br_end;
  91 #ifdef CONFIG_EXPOLINE
  92         if (!nospec_disable) {
  93                 tstart = ftrace_shared_hotpatch_trampoline_ex;
  94                 tend = ftrace_shared_hotpatch_trampoline_ex_end;
  95                 if (test_facility(35)) { /* exrl */
  96                         tstart = ftrace_shared_hotpatch_trampoline_exrl;
  97                         tend = ftrace_shared_hotpatch_trampoline_exrl_end;
  98                 }
  99         }
 100 #endif /* CONFIG_EXPOLINE */
 101         if (end)
 102                 *end = tend;
 103         return tstart;
 104 }
 105
 106 bool ftrace_need_init_nop(void)
 107 {
 108         return true;
 109 }
 110
 111 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 112 {
 113         static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
 114                 __ftrace_hotpatch_trampolines_start;
 115         static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 };
 116         static struct ftrace_hotpatch_trampoline *trampoline;
 117         struct ftrace_hotpatch_trampoline **next_trampoline;
 118         struct ftrace_hotpatch_trampoline *trampolines_end;
 119         struct ftrace_hotpatch_trampoline tmp;
 120         struct ftrace_insn *insn;
 121         const char *shared;
 122         s32 disp;
 123
 124         BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
 125                      SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);
 126
 127         next_trampoline = &next_vmlinux_trampoline;
 128         trampolines_end = __ftrace_hotpatch_trampolines_end;
 129         shared = ftrace_shared_hotpatch_trampoline(NULL);
 130 #ifdef CONFIG_MODULES
 131         if (mod) {
 132                 next_trampoline = &mod->arch.next_trampoline;
 133                 trampolines_end = mod->arch.trampolines_end;
 134                 shared = ftrace_plt;
 135         }
 136 #endif
 137
 138         if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
 139                 return -ENOMEM;
 140         trampoline = (*next_trampoline)++;
 141
 142         /* Check for the compiler-generated fentry nop (brcl 0, .). */
 143         if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig))))
 144                 return -EINVAL;
 145
 146         /* Generate the trampoline. */
 147         tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
 148         tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
 149         tmp.interceptor = FTRACE_ADDR;
 150         tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
 151         s390_kernel_write(trampoline, &tmp, sizeof(tmp));
 152
 153         /* Generate a jump to the trampoline. */
 154         disp = ((char *)trampoline - (char *)rec->ip) / 2;
 155         insn = (struct ftrace_insn *)rec->ip;
 156         s390_kernel_write(&insn->disp, &disp, sizeof(disp));
 157
 158         return 0;
 159 }
 160
 161 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 162                        unsigned long addr)
 163 {
 164         return 0;
 165 }
 166
 167 static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
 168 {
 169         u16 old;
 170         u8 op;
 171
 172         if (get_kernel_nofault(old, addr))
 173                 return -EFAULT;
 174         if (old != expected)
 175                 return -EINVAL;
 176         /* set mask field to all ones or zeroes */
 177         op = enable ? 0xf4 : 0x04;
 178         s390_kernel_write((char *)addr + 1, &op, sizeof(op));
 179         return 0;
 180 }
 181
 182 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 183                     unsigned long addr)
 184 {
 185         /* Expect brcl 0xf,... */
 186         return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
 187 }
 188
 189 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 190 {
 191         /* Expect brcl 0x0,... */
 192         return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
 193 }
 194
 195 int ftrace_update_ftrace_func(ftrace_func_t func)
 196 {
 197         ftrace_func = func;
 198         return 0;
 199 }
 200
 201 void arch_ftrace_update_code(int command)
 202 {
 203         ftrace_modify_all_code(command);
 204 }
 205
 206 int ftrace_arch_code_modify_post_process(void)
 207 {
 208         /*
 209          * Flush any pre-fetched instructions on all
 210          * CPUs to make the new code visible.
 211          */
 212         text_poke_sync_lock();
 213         return 0;
 214 }
 215
 216 #ifdef CONFIG_MODULES
 217
 218 static int __init ftrace_plt_init(void)
 219 {
 220         const char *start, *end;
 221
 222         ftrace_plt = module_alloc(PAGE_SIZE);
 223         if (!ftrace_plt)
 224                 panic("cannot allocate ftrace plt\n");
 225
 226         start = ftrace_shared_hotpatch_trampoline(&end);
 227         memcpy(ftrace_plt, start, end - start);
 228         set_memory_ro((unsigned long)ftrace_plt, 1);
 229         return 0;
 230 }
 231 device_initcall(ftrace_plt_init);
 232
 233 #endif /* CONFIG_MODULES */
 234
 235 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 236 /*
 237  * Hook the return address and push it in the stack of return addresses
 238  * in current thread info.
 239  */
 240 unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
 241                                     unsigned long ip)
 242 {
 243         if (unlikely(ftrace_graph_is_dead()))
 244                 goto out;
 245         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 246                 goto out;
 247         ip -= MCOUNT_INSN_SIZE;
 248         if (!function_graph_enter(ra, ip, 0, (void *) sp))
 249                 ra = (unsigned long) return_to_handler;
 250 out:
 251         return ra;
 252 }
 253 NOKPROBE_SYMBOL(prepare_ftrace_return);
 254
 255 /*
 256  * Patch the kernel code at ftrace_graph_caller location. The instruction
 257  * there is branch relative on condition. To enable the ftrace graph code
 258  * block, we simply patch the mask field of the instruction to zero and
 259  * turn the instruction into a nop.
 260  * To disable the ftrace graph code the mask field will be patched to
 261  * all ones, which turns the instruction into an unconditional branch.
 262  */
 263 int ftrace_enable_ftrace_graph_caller(void)
 264 {
 265         int rc;
 266
 267         /* Expect brc 0xf,... */
 268         rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa7f4, false);
 269         if (rc)
 270                 return rc;
 271         text_poke_sync_lock();
 272         return 0;
 273 }
 274
 275 int ftrace_disable_ftrace_graph_caller(void)
 276 {
 277         int rc;
 278
 279         /* Expect brc 0x0,... */
 280         rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa704, true);
 281         if (rc)
 282                 return rc;
 283         text_poke_sync_lock();
 284         return 0;
 285 }
 286
 287 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 288
 289 #ifdef CONFIG_KPROBES_ON_FTRACE
 290 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 291                 struct ftrace_ops *ops, struct ftrace_regs *fregs)
 292 {
 293         struct kprobe_ctlblk *kcb;
 294         struct pt_regs *regs;
 295         struct kprobe *p;
 296         int bit;
 297
 298         bit = ftrace_test_recursion_trylock(ip, parent_ip);
 299         if (bit < 0)
 300                 return;
 301
 302         regs = ftrace_get_regs(fregs);
 303         p = get_kprobe((kprobe_opcode_t *)ip);
 304         if (unlikely(!p) || kprobe_disabled(p))
 305                 goto out;
 306
 307         if (kprobe_running()) {
 308                 kprobes_inc_nmissed_count(p);
 309                 goto out;
 310         }
 311
 312         __this_cpu_write(current_kprobe, p);
 313
 314         kcb = get_kprobe_ctlblk();
 315         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 316
 317         instruction_pointer_set(regs, ip);
 318
 319         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 320
 321                 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
 322
 323                 if (unlikely(p->post_handler)) {
 324                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 325                         p->post_handler(p, regs, 0);
 326                 }
 327         }
 328         __this_cpu_write(current_kprobe, NULL);
 329 out:
 330         ftrace_test_recursion_unlock(bit);
 331 }
 332 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 333
 334 int arch_prepare_kprobe_ftrace(struct kprobe *p)
 335 {
 336         p->ainsn.insn = NULL;
 337         return 0;
 338 }
 339 #endif