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 #ifdef CONFIG_MODULES
  53 static char *ftrace_plt;
  54 #endif /* CONFIG_MODULES */
  55
  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
  73 bool ftrace_need_init_nop(void)
  74 {
  75         return true;
  76 }
  77
  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
 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
 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
 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
 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
 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
 197 int ftrace_update_ftrace_func(ftrace_func_t func)
 198 {
 199         ftrace_func = func;
 200         return 0;
 201 }
 202
 203 void arch_ftrace_update_code(int command)
 204 {
 205         ftrace_modify_all_code(command);
 206 }
 207
 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
 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  */
 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(&current->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  */
 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
 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
 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         bit = ftrace_test_recursion_trylock(ip, parent_ip);
 300         if (bit < 0)
 301                 return;
 302
 303         regs = ftrace_get_regs(fregs);
 304         p = get_kprobe((kprobe_opcode_t *)ip);
 305         if (!regs || unlikely(!p) || kprobe_disabled(p))
 306                 goto out;
 307
 308         if (kprobe_running()) {
 309                 kprobes_inc_nmissed_count(p);
 310                 goto out;
 311         }
 312
 313         __this_cpu_write(current_kprobe, p);
 314
 315         kcb = get_kprobe_ctlblk();
 316         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 317
 318         instruction_pointer_set(regs, ip);
 319
 320         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 321
 322                 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
 323
 324                 if (unlikely(p->post_handler)) {
 325                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 326                         p->post_handler(p, regs, 0);
 327                 }
 328         }
 329         __this_cpu_write(current_kprobe, NULL);
 330 out:
 331         ftrace_test_recursion_unlock(bit);
 332 }
 333 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 334
 335 int arch_prepare_kprobe_ftrace(struct kprobe *p)
 336 {
 337         p->ainsn.insn = NULL;
 338         return 0;
 339 }
 340 #endif