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