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  * Returns the syscall nr to run (which should match regs->orig_ax) or -1
  68  * to skip the syscall.
  69  */
  70 static long syscall_trace_enter(struct pt_regs *regs)
  71 {
  72         u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
  73
  74         struct thread_info *ti = pt_regs_to_thread_info(regs);
  75         unsigned long ret = 0;
  76         bool emulated = false;
  77         u32 work;
  78
  79         if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
  80                 BUG_ON(regs != task_pt_regs(current));
  81
  82         work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
  83
  84         if (unlikely(work & _TIF_SYSCALL_EMU))
  85                 emulated = true;
  86
  87         if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
  88             tracehook_report_syscall_entry(regs))
  89                 return -1L;
  90
  91         if (emulated)
  92                 return -1L;
  93
  94 #ifdef CONFIG_SECCOMP
  95         /*
  96          * Do seccomp after ptrace, to catch any tracer changes.
  97          */
  98         if (work & _TIF_SECCOMP) {
  99                 struct seccomp_data sd;
 100
 101                 sd.arch = arch;
 102                 sd.nr = regs->orig_ax;
 103                 sd.instruction_pointer = regs->ip;
 104 #ifdef CONFIG_X86_64
 105                 if (arch == AUDIT_ARCH_X86_64) {
 106                         sd.args[0] = regs->di;
 107                         sd.args[1] = regs->si;
 108                         sd.args[2] = regs->dx;
 109                         sd.args[3] = regs->r10;
 110                         sd.args[4] = regs->r8;
 111                         sd.args[5] = regs->r9;
 112                 } else
 113 #endif
 114                 {
 115                         sd.args[0] = regs->bx;
 116                         sd.args[1] = regs->cx;
 117                         sd.args[2] = regs->dx;
 118                         sd.args[3] = regs->si;
 119                         sd.args[4] = regs->di;
 120                         sd.args[5] = regs->bp;
 121                 }
 122
 123                 ret = __secure_computing(&sd);
 124                 if (ret == -1)
 125                         return ret;
 126         }
 127 #endif
 128
 129         if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 130                 trace_sys_enter(regs, regs->orig_ax);
 131
 132         do_audit_syscall_entry(regs, arch);
 133
 134         return ret ?: regs->orig_ax;
 135 }
 136
 137 #define EXIT_TO_USERMODE_LOOP_FLAGS                             \
 138         (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |   \
 139          _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
 140
 141 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 142 {
 143         /*
 144          * In order to return to user mode, we need to have IRQs off with
 145          * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
 146          * _TIF_UPROBE, or _TIF_NEED_RESCHED set.  Several of these flags
 147          * can be set at any time on preemptable kernels if we have IRQs on,
 148          * so we need to loop.  Disabling preemption wouldn't help: doing the
 149          * work to clear some of the flags can sleep.
 150          */
 151         while (true) {
 152                 /* We have work to do. */
 153                 local_irq_enable();
 154
 155                 if (cached_flags & _TIF_NEED_RESCHED)
 156                         schedule();
 157
 158                 if (cached_flags & _TIF_UPROBE)
 159                         uprobe_notify_resume(regs);
 160
 161                 /* deal with pending signal delivery */
 162                 if (cached_flags & _TIF_SIGPENDING)
 163                         do_signal(regs);
 164
 165                 if (cached_flags & _TIF_NOTIFY_RESUME) {
 166                         clear_thread_flag(TIF_NOTIFY_RESUME);
 167                         tracehook_notify_resume(regs);
 168                         rseq_handle_notify_resume(regs);
 169                 }
 170
 171                 if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 172                         fire_user_return_notifiers();
 173
 174                 /* Disable IRQs and retry */
 175                 local_irq_disable();
 176
 177                 cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);
 178
 179                 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 180                         break;
 181
 182         }
 183 }
 184
 185 /* Called with IRQs disabled. */
 186 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 187 {
 188         struct thread_info *ti = pt_regs_to_thread_info(regs);
 189         u32 cached_flags;
 190
 191         if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
 192                 local_irq_disable();
 193
 194         lockdep_sys_exit();
 195
 196         cached_flags = READ_ONCE(ti->flags);
 197
 198         if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 199                 exit_to_usermode_loop(regs, cached_flags);
 200
 201 #ifdef CONFIG_COMPAT
 202         /*
 203          * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 204          * returning to user mode.  We need to clear it *after* signal
 205          * handling, because syscall restart has a fixup for compat
 206          * syscalls.  The fixup is exercised by the ptrace_syscall_32
 207          * selftest.
 208          *
 209          * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
 210          * special case only applies after poking regs and before the
 211          * very next return to user mode.
 212          */
 213         ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
 214 #endif
 215
 216         user_enter_irqoff();
 217 }
 218
 219 #define SYSCALL_EXIT_WORK_FLAGS                         \
 220         (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |      \
 221          _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
 222
 223 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
 224 {
 225         bool step;
 226
 227         audit_syscall_exit(regs);
 228
 229         if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
 230                 trace_sys_exit(regs, regs->ax);
 231
 232         /*
 233          * If TIF_SYSCALL_EMU is set, we only get here because of
 234          * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
 235          * We already reported this syscall instruction in
 236          * syscall_trace_enter().
 237          */
 238         step = unlikely(
 239                 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
 240                 == _TIF_SINGLESTEP);
 241         if (step || cached_flags & _TIF_SYSCALL_TRACE)
 242                 tracehook_report_syscall_exit(regs, step);
 243 }
 244
 245 /*
 246  * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
 247  * state such that we can immediately switch to user mode.
 248  */
 249 __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 250 {
 251         struct thread_info *ti = pt_regs_to_thread_info(regs);
 252         u32 cached_flags = READ_ONCE(ti->flags);
 253
 254         CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
 255
 256         if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
 257             WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 258                 local_irq_enable();
 259
 260         /*
 261          * First do one-time work.  If these work items are enabled, we
 262          * want to run them exactly once per syscall exit with IRQs on.
 263          */
 264         if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
 265                 syscall_slow_exit_work(regs, cached_flags);
 266
 267         local_irq_disable();
 268         prepare_exit_to_usermode(regs);
 269 }
 270
 271 #ifdef CONFIG_X86_64
 272 __visible void do_syscall_64(struct pt_regs *regs)
 273 {
 274         struct thread_info *ti = pt_regs_to_thread_info(regs);
 275         unsigned long nr = regs->orig_ax;
 276
 277         enter_from_user_mode();
 278         local_irq_enable();
 279
 280         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
 281                 nr = syscall_trace_enter(regs);
 282
 283         /*
 284          * NB: Native and x32 syscalls are dispatched from the same
 285          * table.  The only functional difference is the x32 bit in
 286          * regs->orig_ax, which changes the behavior of some syscalls.
 287          */
 288         if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
 289                 regs->ax = sys_call_table[nr & __SYSCALL_MASK](
 290                         regs->di, regs->si, regs->dx,
 291                         regs->r10, regs->r8, regs->r9);
 292         }
 293
 294         syscall_return_slowpath(regs);
 295 }
 296 #endif
 297
 298 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 299 /*
 300  * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
 301  * all entry and exit work and returns with IRQs off.  This function is
 302  * extremely hot in workloads that use it, and it's usually called from
 303  * do_fast_syscall_32, so forcibly inline it to improve performance.
 304  */
 305 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 306 {
 307         struct thread_info *ti = pt_regs_to_thread_info(regs);
 308         unsigned int nr = (unsigned int)regs->orig_ax;
 309
 310 #ifdef CONFIG_IA32_EMULATION
 311         ti->status |= TS_COMPAT;
 312 #endif
 313
 314         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
 315                 /*
 316                  * Subtlety here: if ptrace pokes something larger than
 317                  * 2^32-1 into orig_ax, this truncates it.  This may or
 318                  * may not be necessary, but it matches the old asm
 319                  * behavior.
 320                  */
 321                 nr = syscall_trace_enter(regs);
 322         }
 323
 324         if (likely(nr < IA32_NR_syscalls)) {
 325                 /*
 326                  * It's possible that a 32-bit syscall implementation
 327                  * takes a 64-bit parameter but nonetheless assumes that
 328                  * the high bits are zero.  Make sure we zero-extend all
 329                  * of the args.
 330                  */
 331                 regs->ax = ia32_sys_call_table[nr](
 332                         (unsigned int)regs->bx, (unsigned int)regs->cx,
 333                         (unsigned int)regs->dx, (unsigned int)regs->si,
 334                         (unsigned int)regs->di, (unsigned int)regs->bp);
 335         }
 336
 337         syscall_return_slowpath(regs);
 338 }
 339
 340 /* Handles int $0x80 */
 341 __visible void do_int80_syscall_32(struct pt_regs *regs)
 342 {
 343         enter_from_user_mode();
 344         local_irq_enable();
 345         do_syscall_32_irqs_on(regs);
 346 }
 347
 348 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
 349 __visible long do_fast_syscall_32(struct pt_regs *regs)
 350 {
 351         /*
 352          * Called using the internal vDSO SYSENTER/SYSCALL32 calling
 353          * convention.  Adjust regs so it looks like we entered using int80.
 354          */
 355
 356         unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
 357                 vdso_image_32.sym_int80_landing_pad;
 358
 359         /*
 360          * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
 361          * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
 362          * Fix it up.
 363          */
 364         regs->ip = landing_pad;
 365
 366         enter_from_user_mode();
 367
 368         local_irq_enable();
 369
 370         /* Fetch EBP from where the vDSO stashed it. */
 371         if (
 372 #ifdef CONFIG_X86_64
 373                 /*
 374                  * Micro-optimization: the pointer we're following is explicitly
 375                  * 32 bits, so it can't be out of range.
 376                  */
 377                 __get_user(*(u32 *)&regs->bp,
 378                             (u32 __user __force *)(unsigned long)(u32)regs->sp)
 379 #else
 380                 get_user(*(u32 *)&regs->bp,
 381                          (u32 __user __force *)(unsigned long)(u32)regs->sp)
 382 #endif
 383                 ) {
 384
 385                 /* User code screwed up. */
 386                 local_irq_disable();
 387                 regs->ax = -EFAULT;
 388                 prepare_exit_to_usermode(regs);
 389                 return 0;       /* Keep it simple: use IRET. */
 390         }
 391
 392         /* Now this is just like a normal syscall. */
 393         do_syscall_32_irqs_on(regs);
 394
 395 #ifdef CONFIG_X86_64
 396         /*
 397          * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
 398          * SYSRETL is available on all 64-bit CPUs, so we don't need to
 399          * bother with SYSEXIT.
 400          *
 401          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 402          * because the ECX fixup above will ensure that this is essentially
 403          * never the case.
 404          */
 405         return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
 406                 regs->ip == landing_pad &&
 407                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
 408 #else
 409         /*
 410          * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
 411          *
 412          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 413          * because the ECX fixup above will ensure that this is essentially
 414          * never the case.
 415          *
 416          * We don't allow syscalls at all from VM86 mode, but we still
 417          * need to check VM, because we might be returning from sys_vm86.
 418          */
 419         return static_cpu_has(X86_FEATURE_SEP) &&
 420                 regs->cs == __USER_CS && regs->ss == __USER_DS &&
 421                 regs->ip == landing_pad &&
 422                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
 423 #endif
 424 }
 425 #endif