1 /* 2 * common.c - C code for kernel entry and exit 3 * Copyright (c) 2015 Andrew Lutomirski 4 * GPL v2 5 * 6 * Based on asm and ptrace code by many authors. The code here originated 7 * in ptrace.c and signal.c. 8 */ 9 10 #include <linux/kernel.h> 11 #include <linux/sched.h> 12 #include <linux/mm.h> 13 #include <linux/smp.h> 14 #include <linux/errno.h> 15 #include <linux/ptrace.h> 16 #include <linux/tracehook.h> 17 #include <linux/audit.h> 18 #include <linux/seccomp.h> 19 #include <linux/signal.h> 20 #include <linux/export.h> 21 #include <linux/context_tracking.h> 22 #include <linux/user-return-notifier.h> 23 #include <linux/uprobes.h> 24 25 #include <asm/desc.h> 26 #include <asm/traps.h> 27 #include <asm/vdso.h> 28 #include <asm/uaccess.h> 29 #include <asm/cpufeature.h> 30 31 #define CREATE_TRACE_POINTS 32 #include <trace/events/syscalls.h> 33 34 static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs) 35 { 36 unsigned long top_of_stack = 37 (unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING; 38 return (struct thread_info *)(top_of_stack - THREAD_SIZE); 39 } 40 41 #ifdef CONFIG_CONTEXT_TRACKING 42 /* Called on entry from user mode with IRQs off. */ 43 __visible void enter_from_user_mode(void) 44 { 45 CT_WARN_ON(ct_state() != CONTEXT_USER); 46 user_exit(); 47 } 48 #else 49 static inline void enter_from_user_mode(void) {} 50 #endif 51 52 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) 53 { 54 #ifdef CONFIG_X86_64 55 if (arch == AUDIT_ARCH_X86_64) { 56 audit_syscall_entry(regs->orig_ax, regs->di, 57 regs->si, regs->dx, regs->r10); 58 } else 59 #endif 60 { 61 audit_syscall_entry(regs->orig_ax, regs->bx, 62 regs->cx, regs->dx, regs->si); 63 } 64 } 65 66 /* 67 * We can return 0 to resume the syscall or anything else to go to phase 68 * 2. If we resume the syscall, we need to put something appropriate in 69 * regs->orig_ax. 70 * 71 * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax 72 * are fully functional. 73 * 74 * For phase 2's benefit, our return value is: 75 * 0: resume the syscall 76 * 1: go to phase 2; no seccomp phase 2 needed 77 * anything else: go to phase 2; pass return value to seccomp 78 */ 79 unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch) 80 { 81 struct thread_info *ti = pt_regs_to_thread_info(regs); 82 unsigned long ret = 0; 83 u32 work; 84 85 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 86 BUG_ON(regs != task_pt_regs(current)); 87 88 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; 89 90 #ifdef CONFIG_SECCOMP 91 /* 92 * Do seccomp first -- it should minimize exposure of other 93 * code, and keeping seccomp fast is probably more valuable 94 * than the rest of this. 95 */ 96 if (work & _TIF_SECCOMP) { 97 struct seccomp_data sd; 98 99 sd.arch = arch; 100 sd.nr = regs->orig_ax; 101 sd.instruction_pointer = regs->ip; 102 #ifdef CONFIG_X86_64 103 if (arch == AUDIT_ARCH_X86_64) { 104 sd.args[0] = regs->di; 105 sd.args[1] = regs->si; 106 sd.args[2] = regs->dx; 107 sd.args[3] = regs->r10; 108 sd.args[4] = regs->r8; 109 sd.args[5] = regs->r9; 110 } else 111 #endif 112 { 113 sd.args[0] = regs->bx; 114 sd.args[1] = regs->cx; 115 sd.args[2] = regs->dx; 116 sd.args[3] = regs->si; 117 sd.args[4] = regs->di; 118 sd.args[5] = regs->bp; 119 } 120 121 BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0); 122 BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1); 123 124 ret = seccomp_phase1(&sd); 125 if (ret == SECCOMP_PHASE1_SKIP) { 126 regs->orig_ax = -1; 127 ret = 0; 128 } else if (ret != SECCOMP_PHASE1_OK) { 129 return ret; /* Go directly to phase 2 */ 130 } 131 132 work &= ~_TIF_SECCOMP; 133 } 134 #endif 135 136 /* Do our best to finish without phase 2. */ 137 if (work == 0) 138 return ret; /* seccomp and/or nohz only (ret == 0 here) */ 139 140 #ifdef CONFIG_AUDITSYSCALL 141 if (work == _TIF_SYSCALL_AUDIT) { 142 /* 143 * If there is no more work to be done except auditing, 144 * then audit in phase 1. Phase 2 always audits, so, if 145 * we audit here, then we can't go on to phase 2. 146 */ 147 do_audit_syscall_entry(regs, arch); 148 return 0; 149 } 150 #endif 151 152 return 1; /* Something is enabled that we can't handle in phase 1 */ 153 } 154 155 /* Returns the syscall nr to run (which should match regs->orig_ax). */ 156 long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch, 157 unsigned long phase1_result) 158 { 159 struct thread_info *ti = pt_regs_to_thread_info(regs); 160 long ret = 0; 161 u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; 162 163 if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) 164 BUG_ON(regs != task_pt_regs(current)); 165 166 #ifdef CONFIG_SECCOMP 167 /* 168 * Call seccomp_phase2 before running the other hooks so that 169 * they can see any changes made by a seccomp tracer. 170 */ 171 if (phase1_result > 1 && seccomp_phase2(phase1_result)) { 172 /* seccomp failures shouldn't expose any additional code. */ 173 return -1; 174 } 175 #endif 176 177 if (unlikely(work & _TIF_SYSCALL_EMU)) 178 ret = -1L; 179 180 if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) && 181 tracehook_report_syscall_entry(regs)) 182 ret = -1L; 183 184 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) 185 trace_sys_enter(regs, regs->orig_ax); 186 187 do_audit_syscall_entry(regs, arch); 188 189 return ret ?: regs->orig_ax; 190 } 191 192 long syscall_trace_enter(struct pt_regs *regs) 193 { 194 u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; 195 unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch); 196 197 if (phase1_result == 0) 198 return regs->orig_ax; 199 else 200 return syscall_trace_enter_phase2(regs, arch, phase1_result); 201 } 202 203 #define EXIT_TO_USERMODE_LOOP_FLAGS \ 204 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ 205 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY) 206 207 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) 208 { 209 /* 210 * In order to return to user mode, we need to have IRQs off with 211 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY, 212 * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags 213 * can be set at any time on preemptable kernels if we have IRQs on, 214 * so we need to loop. Disabling preemption wouldn't help: doing the 215 * work to clear some of the flags can sleep. 216 */ 217 while (true) { 218 /* We have work to do. */ 219 local_irq_enable(); 220 221 if (cached_flags & _TIF_NEED_RESCHED) 222 schedule(); 223 224 if (cached_flags & _TIF_UPROBE) 225 uprobe_notify_resume(regs); 226 227 /* deal with pending signal delivery */ 228 if (cached_flags & _TIF_SIGPENDING) 229 do_signal(regs); 230 231 if (cached_flags & _TIF_NOTIFY_RESUME) { 232 clear_thread_flag(TIF_NOTIFY_RESUME); 233 tracehook_notify_resume(regs); 234 } 235 236 if (cached_flags & _TIF_USER_RETURN_NOTIFY) 237 fire_user_return_notifiers(); 238 239 /* Disable IRQs and retry */ 240 local_irq_disable(); 241 242 cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags); 243 244 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 245 break; 246 247 } 248 } 249 250 /* Called with IRQs disabled. */ 251 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) 252 { 253 struct thread_info *ti = pt_regs_to_thread_info(regs); 254 u32 cached_flags; 255 256 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) 257 local_irq_disable(); 258 259 lockdep_sys_exit(); 260 261 cached_flags = READ_ONCE(ti->flags); 262 263 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) 264 exit_to_usermode_loop(regs, cached_flags); 265 266 #ifdef CONFIG_COMPAT 267 /* 268 * Compat syscalls set TS_COMPAT. Make sure we clear it before 269 * returning to user mode. We need to clear it *after* signal 270 * handling, because syscall restart has a fixup for compat 271 * syscalls. The fixup is exercised by the ptrace_syscall_32 272 * selftest. 273 */ 274 ti->status &= ~TS_COMPAT; 275 #endif 276 277 user_enter(); 278 } 279 280 #define SYSCALL_EXIT_WORK_FLAGS \ 281 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ 282 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT) 283 284 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) 285 { 286 bool step; 287 288 audit_syscall_exit(regs); 289 290 if (cached_flags & _TIF_SYSCALL_TRACEPOINT) 291 trace_sys_exit(regs, regs->ax); 292 293 /* 294 * If TIF_SYSCALL_EMU is set, we only get here because of 295 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). 296 * We already reported this syscall instruction in 297 * syscall_trace_enter(). 298 */ 299 step = unlikely( 300 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) 301 == _TIF_SINGLESTEP); 302 if (step || cached_flags & _TIF_SYSCALL_TRACE) 303 tracehook_report_syscall_exit(regs, step); 304 } 305 306 /* 307 * Called with IRQs on and fully valid regs. Returns with IRQs off in a 308 * state such that we can immediately switch to user mode. 309 */ 310 __visible inline void syscall_return_slowpath(struct pt_regs *regs) 311 { 312 struct thread_info *ti = pt_regs_to_thread_info(regs); 313 u32 cached_flags = READ_ONCE(ti->flags); 314 315 CT_WARN_ON(ct_state() != CONTEXT_KERNEL); 316 317 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && 318 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax)) 319 local_irq_enable(); 320 321 /* 322 * First do one-time work. If these work items are enabled, we 323 * want to run them exactly once per syscall exit with IRQs on. 324 */ 325 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS)) 326 syscall_slow_exit_work(regs, cached_flags); 327 328 local_irq_disable(); 329 prepare_exit_to_usermode(regs); 330 } 331 332 #ifdef CONFIG_X86_64 333 __visible void do_syscall_64(struct pt_regs *regs) 334 { 335 struct thread_info *ti = pt_regs_to_thread_info(regs); 336 unsigned long nr = regs->orig_ax; 337 338 enter_from_user_mode(); 339 local_irq_enable(); 340 341 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) 342 nr = syscall_trace_enter(regs); 343 344 /* 345 * NB: Native and x32 syscalls are dispatched from the same 346 * table. The only functional difference is the x32 bit in 347 * regs->orig_ax, which changes the behavior of some syscalls. 348 */ 349 if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) { 350 regs->ax = sys_call_table[nr & __SYSCALL_MASK]( 351 regs->di, regs->si, regs->dx, 352 regs->r10, regs->r8, regs->r9); 353 } 354 355 syscall_return_slowpath(regs); 356 } 357 #endif 358 359 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) 360 /* 361 * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does 362 * all entry and exit work and returns with IRQs off. This function is 363 * extremely hot in workloads that use it, and it's usually called from 364 * do_fast_syscall_32, so forcibly inline it to improve performance. 365 */ 366 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) 367 { 368 struct thread_info *ti = pt_regs_to_thread_info(regs); 369 unsigned int nr = (unsigned int)regs->orig_ax; 370 371 #ifdef CONFIG_IA32_EMULATION 372 ti->status |= TS_COMPAT; 373 #endif 374 375 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) { 376 /* 377 * Subtlety here: if ptrace pokes something larger than 378 * 2^32-1 into orig_ax, this truncates it. This may or 379 * may not be necessary, but it matches the old asm 380 * behavior. 381 */ 382 nr = syscall_trace_enter(regs); 383 } 384 385 if (likely(nr < IA32_NR_syscalls)) { 386 /* 387 * It's possible that a 32-bit syscall implementation 388 * takes a 64-bit parameter but nonetheless assumes that 389 * the high bits are zero. Make sure we zero-extend all 390 * of the args. 391 */ 392 regs->ax = ia32_sys_call_table[nr]( 393 (unsigned int)regs->bx, (unsigned int)regs->cx, 394 (unsigned int)regs->dx, (unsigned int)regs->si, 395 (unsigned int)regs->di, (unsigned int)regs->bp); 396 } 397 398 syscall_return_slowpath(regs); 399 } 400 401 /* Handles int $0x80 */ 402 __visible void do_int80_syscall_32(struct pt_regs *regs) 403 { 404 enter_from_user_mode(); 405 local_irq_enable(); 406 do_syscall_32_irqs_on(regs); 407 } 408 409 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ 410 __visible long do_fast_syscall_32(struct pt_regs *regs) 411 { 412 /* 413 * Called using the internal vDSO SYSENTER/SYSCALL32 calling 414 * convention. Adjust regs so it looks like we entered using int80. 415 */ 416 417 unsigned long landing_pad = (unsigned long)current->mm->context.vdso + 418 vdso_image_32.sym_int80_landing_pad; 419 420 /* 421 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward 422 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction. 423 * Fix it up. 424 */ 425 regs->ip = landing_pad; 426 427 enter_from_user_mode(); 428 429 local_irq_enable(); 430 431 /* Fetch EBP from where the vDSO stashed it. */ 432 if ( 433 #ifdef CONFIG_X86_64 434 /* 435 * Micro-optimization: the pointer we're following is explicitly 436 * 32 bits, so it can't be out of range. 437 */ 438 __get_user(*(u32 *)®s->bp, 439 (u32 __user __force *)(unsigned long)(u32)regs->sp) 440 #else 441 get_user(*(u32 *)®s->bp, 442 (u32 __user __force *)(unsigned long)(u32)regs->sp) 443 #endif 444 ) { 445 446 /* User code screwed up. */ 447 local_irq_disable(); 448 regs->ax = -EFAULT; 449 prepare_exit_to_usermode(regs); 450 return 0; /* Keep it simple: use IRET. */ 451 } 452 453 /* Now this is just like a normal syscall. */ 454 do_syscall_32_irqs_on(regs); 455 456 #ifdef CONFIG_X86_64 457 /* 458 * Opportunistic SYSRETL: if possible, try to return using SYSRETL. 459 * SYSRETL is available on all 64-bit CPUs, so we don't need to 460 * bother with SYSEXIT. 461 * 462 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 463 * because the ECX fixup above will ensure that this is essentially 464 * never the case. 465 */ 466 return regs->cs == __USER32_CS && regs->ss == __USER_DS && 467 regs->ip == landing_pad && 468 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; 469 #else 470 /* 471 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. 472 * 473 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, 474 * because the ECX fixup above will ensure that this is essentially 475 * never the case. 476 * 477 * We don't allow syscalls at all from VM86 mode, but we still 478 * need to check VM, because we might be returning from sys_vm86. 479 */ 480 return static_cpu_has(X86_FEATURE_SEP) && 481 regs->cs == __USER_CS && regs->ss == __USER_DS && 482 regs->ip == landing_pad && 483 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; 484 #endif 485 } 486 #endif 487