arch/x86/entry/common.c

   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 inline void enter_from_user_mode(void)
  44 {
  45         CT_WARN_ON(ct_state() != CONTEXT_USER);
  46         user_exit_irqoff();
  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_irqoff();
 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 *)&regs->bp,
 439                             (u32 __user __force *)(unsigned long)(u32)regs->sp)
 440 #else
 441                 get_user(*(u32 *)&regs->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