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(¤t->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 341