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/sched/task_stack.h>
  13 #include <linux/mm.h>
  14 #include <linux/smp.h>
  15 #include <linux/errno.h>
  16 #include <linux/ptrace.h>
  17 #include <linux/tracehook.h>
  18 #include <linux/audit.h>
  19 #include <linux/seccomp.h>
  20 #include <linux/signal.h>
  21 #include <linux/export.h>
  22 #include <linux/context_tracking.h>
  23 #include <linux/user-return-notifier.h>
  24 #include <linux/uprobes.h>
  25
  26 #include <asm/desc.h>
  27 #include <asm/traps.h>
  28 #include <asm/vdso.h>
  29 #include <linux/uaccess.h>
  30 #include <asm/cpufeature.h>
  31
  32 #define CREATE_TRACE_POINTS
  33 #include <trace/events/syscalls.h>
  34
  35 #ifdef CONFIG_CONTEXT_TRACKING
  36 /* Called on entry from user mode with IRQs off. */
  37 __visible inline void enter_from_user_mode(void)
  38 {
  39         CT_WARN_ON(ct_state() != CONTEXT_USER);
  40         user_exit_irqoff();
  41 }
  42 #else
  43 static inline void enter_from_user_mode(void) {}
  44 #endif
  45
  46 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
  47 {
  48 #ifdef CONFIG_X86_64
  49         if (arch == AUDIT_ARCH_X86_64) {
  50                 audit_syscall_entry(regs->orig_ax, regs->di,
  51                                     regs->si, regs->dx, regs->r10);
  52         } else
  53 #endif
  54         {
  55                 audit_syscall_entry(regs->orig_ax, regs->bx,
  56                                     regs->cx, regs->dx, regs->si);
  57         }
  58 }
  59
  60 /*
  61  * Returns the syscall nr to run (which should match regs->orig_ax) or -1
  62  * to skip the syscall.
  63  */
  64 static long syscall_trace_enter(struct pt_regs *regs)
  65 {
  66         u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
  67
  68         struct thread_info *ti = current_thread_info();
  69         unsigned long ret = 0;
  70         bool emulated = false;
  71         u32 work;
  72
  73         if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
  74                 BUG_ON(regs != task_pt_regs(current));
  75
  76         work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
  77
  78         if (unlikely(work & _TIF_SYSCALL_EMU))
  79                 emulated = true;
  80
  81         if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
  82             tracehook_report_syscall_entry(regs))
  83                 return -1L;
  84
  85         if (emulated)
  86                 return -1L;
  87
  88 #ifdef CONFIG_SECCOMP
  89         /*
  90          * Do seccomp after ptrace, to catch any tracer changes.
  91          */
  92         if (work & _TIF_SECCOMP) {
  93                 struct seccomp_data sd;
  94
  95                 sd.arch = arch;
  96                 sd.nr = regs->orig_ax;
  97                 sd.instruction_pointer = regs->ip;
  98 #ifdef CONFIG_X86_64
  99                 if (arch == AUDIT_ARCH_X86_64) {
 100                         sd.args[0] = regs->di;
 101                         sd.args[1] = regs->si;
 102                         sd.args[2] = regs->dx;
 103                         sd.args[3] = regs->r10;
 104                         sd.args[4] = regs->r8;
 105                         sd.args[5] = regs->r9;
 106                 } else
 107 #endif
 108                 {
 109                         sd.args[0] = regs->bx;
 110                         sd.args[1] = regs->cx;
 111                         sd.args[2] = regs->dx;
 112                         sd.args[3] = regs->si;
 113                         sd.args[4] = regs->di;
 114                         sd.args[5] = regs->bp;
 115                 }
 116
 117                 ret = __secure_computing(&sd);
 118                 if (ret == -1)
 119                         return ret;
 120         }
 121 #endif
 122
 123         if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 124                 trace_sys_enter(regs, regs->orig_ax);
 125
 126         do_audit_syscall_entry(regs, arch);
 127
 128         return ret ?: regs->orig_ax;
 129 }
 130
 131 #define EXIT_TO_USERMODE_LOOP_FLAGS                             \
 132         (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |   \
 133          _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
 134
 135 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 136 {
 137         /*
 138          * In order to return to user mode, we need to have IRQs off with
 139          * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
 140          * _TIF_UPROBE, or _TIF_NEED_RESCHED set.  Several of these flags
 141          * can be set at any time on preemptable kernels if we have IRQs on,
 142          * so we need to loop.  Disabling preemption wouldn't help: doing the
 143          * work to clear some of the flags can sleep.
 144          */
 145         while (true) {
 146                 /* We have work to do. */
 147                 local_irq_enable();
 148
 149                 if (cached_flags & _TIF_NEED_RESCHED)
 150                         schedule();
 151
 152                 if (cached_flags & _TIF_UPROBE)
 153                         uprobe_notify_resume(regs);
 154
 155                 /* deal with pending signal delivery */
 156                 if (cached_flags & _TIF_SIGPENDING)
 157                         do_signal(regs);
 158
 159                 if (cached_flags & _TIF_NOTIFY_RESUME) {
 160                         clear_thread_flag(TIF_NOTIFY_RESUME);
 161                         tracehook_notify_resume(regs);
 162                 }
 163
 164                 if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 165                         fire_user_return_notifiers();
 166
 167                 /* Disable IRQs and retry */
 168                 local_irq_disable();
 169
 170                 cached_flags = READ_ONCE(current_thread_info()->flags);
 171
 172                 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 173                         break;
 174         }
 175 }
 176
 177 /* Called with IRQs disabled. */
 178 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 179 {
 180         struct thread_info *ti = current_thread_info();
 181         u32 cached_flags;
 182
 183         if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
 184                 local_irq_disable();
 185
 186         lockdep_sys_exit();
 187
 188         cached_flags = READ_ONCE(ti->flags);
 189
 190         if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 191                 exit_to_usermode_loop(regs, cached_flags);
 192
 193 #ifdef CONFIG_COMPAT
 194         /*
 195          * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 196          * returning to user mode.  We need to clear it *after* signal
 197          * handling, because syscall restart has a fixup for compat
 198          * syscalls.  The fixup is exercised by the ptrace_syscall_32
 199          * selftest.
 200          *
 201          * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
 202          * special case only applies after poking regs and before the
 203          * very next return to user mode.
 204          */
 205         current->thread.status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
 206 #endif
 207
 208         user_enter_irqoff();
 209 }
 210
 211 #define SYSCALL_EXIT_WORK_FLAGS                         \
 212         (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |      \
 213          _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
 214
 215 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
 216 {
 217         bool step;
 218
 219         audit_syscall_exit(regs);
 220
 221         if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
 222                 trace_sys_exit(regs, regs->ax);
 223
 224         /*
 225          * If TIF_SYSCALL_EMU is set, we only get here because of
 226          * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
 227          * We already reported this syscall instruction in
 228          * syscall_trace_enter().
 229          */
 230         step = unlikely(
 231                 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
 232                 == _TIF_SINGLESTEP);
 233         if (step || cached_flags & _TIF_SYSCALL_TRACE)
 234                 tracehook_report_syscall_exit(regs, step);
 235 }
 236
 237 /*
 238  * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
 239  * state such that we can immediately switch to user mode.
 240  */
 241 __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 242 {
 243         struct thread_info *ti = current_thread_info();
 244         u32 cached_flags = READ_ONCE(ti->flags);
 245
 246         CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
 247
 248         if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
 249             WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 250                 local_irq_enable();
 251
 252         /*
 253          * First do one-time work.  If these work items are enabled, we
 254          * want to run them exactly once per syscall exit with IRQs on.
 255          */
 256         if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
 257                 syscall_slow_exit_work(regs, cached_flags);
 258
 259         local_irq_disable();
 260         prepare_exit_to_usermode(regs);
 261 }
 262
 263 #ifdef CONFIG_X86_64
 264 __visible void do_syscall_64(struct pt_regs *regs)
 265 {
 266         struct thread_info *ti = current_thread_info();
 267         unsigned long nr = regs->orig_ax;
 268
 269         enter_from_user_mode();
 270         local_irq_enable();
 271
 272         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
 273                 nr = syscall_trace_enter(regs);
 274
 275         /*
 276          * NB: Native and x32 syscalls are dispatched from the same
 277          * table.  The only functional difference is the x32 bit in
 278          * regs->orig_ax, which changes the behavior of some syscalls.
 279          */
 280         if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
 281                 regs->ax = sys_call_table[nr & __SYSCALL_MASK](
 282                         regs->di, regs->si, regs->dx,
 283                         regs->r10, regs->r8, regs->r9);
 284         }
 285
 286         syscall_return_slowpath(regs);
 287 }
 288 #endif
 289
 290 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 291 /*
 292  * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
 293  * all entry and exit work and returns with IRQs off.  This function is
 294  * extremely hot in workloads that use it, and it's usually called from
 295  * do_fast_syscall_32, so forcibly inline it to improve performance.
 296  */
 297 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 298 {
 299         struct thread_info *ti = current_thread_info();
 300         unsigned int nr = (unsigned int)regs->orig_ax;
 301
 302 #ifdef CONFIG_IA32_EMULATION
 303         current->thread.status |= TS_COMPAT;
 304 #endif
 305
 306         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
 307                 /*
 308                  * Subtlety here: if ptrace pokes something larger than
 309                  * 2^32-1 into orig_ax, this truncates it.  This may or
 310                  * may not be necessary, but it matches the old asm
 311                  * behavior.
 312                  */
 313                 nr = syscall_trace_enter(regs);
 314         }
 315
 316         if (likely(nr < IA32_NR_syscalls)) {
 317                 /*
 318                  * It's possible that a 32-bit syscall implementation
 319                  * takes a 64-bit parameter but nonetheless assumes that
 320                  * the high bits are zero.  Make sure we zero-extend all
 321                  * of the args.
 322                  */
 323                 regs->ax = ia32_sys_call_table[nr](
 324                         (unsigned int)regs->bx, (unsigned int)regs->cx,
 325                         (unsigned int)regs->dx, (unsigned int)regs->si,
 326                         (unsigned int)regs->di, (unsigned int)regs->bp);
 327         }
 328
 329         syscall_return_slowpath(regs);
 330 }
 331
 332 /* Handles int $0x80 */
 333 __visible void do_int80_syscall_32(struct pt_regs *regs)
 334 {
 335         enter_from_user_mode();
 336         local_irq_enable();
 337         do_syscall_32_irqs_on(regs);
 338 }
 339
 340 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
 341 __visible long do_fast_syscall_32(struct pt_regs *regs)
 342 {
 343         /*
 344          * Called using the internal vDSO SYSENTER/SYSCALL32 calling
 345          * convention.  Adjust regs so it looks like we entered using int80.
 346          */
 347
 348         unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
 349                 vdso_image_32.sym_int80_landing_pad;
 350
 351         /*
 352          * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
 353          * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
 354          * Fix it up.
 355          */
 356         regs->ip = landing_pad;
 357
 358         enter_from_user_mode();
 359
 360         local_irq_enable();
 361
 362         /* Fetch EBP from where the vDSO stashed it. */
 363         if (
 364 #ifdef CONFIG_X86_64
 365                 /*
 366                  * Micro-optimization: the pointer we're following is explicitly
 367                  * 32 bits, so it can't be out of range.
 368                  */
 369                 __get_user(*(u32 *)&regs->bp,
 370                             (u32 __user __force *)(unsigned long)(u32)regs->sp)
 371 #else
 372                 get_user(*(u32 *)&regs->bp,
 373                          (u32 __user __force *)(unsigned long)(u32)regs->sp)
 374 #endif
 375                 ) {
 376
 377                 /* User code screwed up. */
 378                 local_irq_disable();
 379                 regs->ax = -EFAULT;
 380                 prepare_exit_to_usermode(regs);
 381                 return 0;       /* Keep it simple: use IRET. */
 382         }
 383
 384         /* Now this is just like a normal syscall. */
 385         do_syscall_32_irqs_on(regs);
 386
 387 #ifdef CONFIG_X86_64
 388         /*
 389          * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
 390          * SYSRETL is available on all 64-bit CPUs, so we don't need to
 391          * bother with SYSEXIT.
 392          *
 393          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 394          * because the ECX fixup above will ensure that this is essentially
 395          * never the case.
 396          */
 397         return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
 398                 regs->ip == landing_pad &&
 399                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
 400 #else
 401         /*
 402          * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
 403          *
 404          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 405          * because the ECX fixup above will ensure that this is essentially
 406          * never the case.
 407          *
 408          * We don't allow syscalls at all from VM86 mode, but we still
 409          * need to check VM, because we might be returning from sys_vm86.
 410          */
 411         return static_cpu_has(X86_FEATURE_SEP) &&
 412                 regs->cs == __USER_CS && regs->ss == __USER_DS &&
 413                 regs->ip == landing_pad &&
 414                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
 415 #endif
 416 }
 417 #endif