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                 }
 169
 170                 if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 171                         fire_user_return_notifiers();
 172
 173                 /* Disable IRQs and retry */
 174                 local_irq_disable();
 175
 176                 cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);
 177
 178                 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 179                         break;
 180
 181         }
 182 }
 183
 184 /* Called with IRQs disabled. */
 185 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 186 {
 187         struct thread_info *ti = pt_regs_to_thread_info(regs);
 188         u32 cached_flags;
 189
 190         if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
 191                 local_irq_disable();
 192
 193         lockdep_sys_exit();
 194
 195         cached_flags = READ_ONCE(ti->flags);
 196
 197         if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 198                 exit_to_usermode_loop(regs, cached_flags);
 199
 200 #ifdef CONFIG_COMPAT
 201         /*
 202          * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 203          * returning to user mode.  We need to clear it *after* signal
 204          * handling, because syscall restart has a fixup for compat
 205          * syscalls.  The fixup is exercised by the ptrace_syscall_32
 206          * selftest.
 207          *
 208          * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
 209          * special case only applies after poking regs and before the
 210          * very next return to user mode.
 211          */
 212         ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
 213 #endif
 214
 215         user_enter_irqoff();
 216 }
 217
 218 #define SYSCALL_EXIT_WORK_FLAGS                         \
 219         (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |      \
 220          _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
 221
 222 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
 223 {
 224         bool step;
 225
 226         audit_syscall_exit(regs);
 227
 228         if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
 229                 trace_sys_exit(regs, regs->ax);
 230
 231         /*
 232          * If TIF_SYSCALL_EMU is set, we only get here because of
 233          * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
 234          * We already reported this syscall instruction in
 235          * syscall_trace_enter().
 236          */
 237         step = unlikely(
 238                 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
 239                 == _TIF_SINGLESTEP);
 240         if (step || cached_flags & _TIF_SYSCALL_TRACE)
 241                 tracehook_report_syscall_exit(regs, step);
 242 }
 243
 244 /*
 245  * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
 246  * state such that we can immediately switch to user mode.
 247  */
 248 __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 249 {
 250         struct thread_info *ti = pt_regs_to_thread_info(regs);
 251         u32 cached_flags = READ_ONCE(ti->flags);
 252
 253         CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
 254
 255         if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
 256             WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 257                 local_irq_enable();
 258
 259         /*
 260          * First do one-time work.  If these work items are enabled, we
 261          * want to run them exactly once per syscall exit with IRQs on.
 262          */
 263         if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
 264                 syscall_slow_exit_work(regs, cached_flags);
 265
 266         local_irq_disable();
 267         prepare_exit_to_usermode(regs);
 268 }
 269
 270 #ifdef CONFIG_X86_64
 271 __visible void do_syscall_64(struct pt_regs *regs)
 272 {
 273         struct thread_info *ti = pt_regs_to_thread_info(regs);
 274         unsigned long nr = regs->orig_ax;
 275
 276         enter_from_user_mode();
 277         local_irq_enable();
 278
 279         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
 280                 nr = syscall_trace_enter(regs);
 281
 282         /*
 283          * NB: Native and x32 syscalls are dispatched from the same
 284          * table.  The only functional difference is the x32 bit in
 285          * regs->orig_ax, which changes the behavior of some syscalls.
 286          */
 287         if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
 288                 regs->ax = sys_call_table[nr & __SYSCALL_MASK](
 289                         regs->di, regs->si, regs->dx,
 290                         regs->r10, regs->r8, regs->r9);
 291         }
 292
 293         syscall_return_slowpath(regs);
 294 }
 295 #endif
 296
 297 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 298 /*
 299  * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
 300  * all entry and exit work and returns with IRQs off.  This function is
 301  * extremely hot in workloads that use it, and it's usually called from
 302  * do_fast_syscall_32, so forcibly inline it to improve performance.
 303  */
 304 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 305 {
 306         struct thread_info *ti = pt_regs_to_thread_info(regs);
 307         unsigned int nr = (unsigned int)regs->orig_ax;
 308
 309 #ifdef CONFIG_IA32_EMULATION
 310         ti->status |= TS_COMPAT;
 311 #endif
 312
 313         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
 314                 /*
 315                  * Subtlety here: if ptrace pokes something larger than
 316                  * 2^32-1 into orig_ax, this truncates it.  This may or
 317                  * may not be necessary, but it matches the old asm
 318                  * behavior.
 319                  */
 320                 nr = syscall_trace_enter(regs);
 321         }
 322
 323         if (likely(nr < IA32_NR_syscalls)) {
 324                 /*
 325                  * It's possible that a 32-bit syscall implementation
 326                  * takes a 64-bit parameter but nonetheless assumes that
 327                  * the high bits are zero.  Make sure we zero-extend all
 328                  * of the args.
 329                  */
 330                 regs->ax = ia32_sys_call_table[nr](
 331                         (unsigned int)regs->bx, (unsigned int)regs->cx,
 332                         (unsigned int)regs->dx, (unsigned int)regs->si,
 333                         (unsigned int)regs->di, (unsigned int)regs->bp);
 334         }
 335
 336         syscall_return_slowpath(regs);
 337 }
 338
 339 /* Handles int $0x80 */
 340 __visible void do_int80_syscall_32(struct pt_regs *regs)
 341 {
 342         enter_from_user_mode();
 343         local_irq_enable();
 344         do_syscall_32_irqs_on(regs);
 345 }
 346
 347 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
 348 __visible long do_fast_syscall_32(struct pt_regs *regs)
 349 {
 350         /*
 351          * Called using the internal vDSO SYSENTER/SYSCALL32 calling
 352          * convention.  Adjust regs so it looks like we entered using int80.
 353          */
 354
 355         unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
 356                 vdso_image_32.sym_int80_landing_pad;
 357
 358         /*
 359          * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
 360          * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
 361          * Fix it up.
 362          */
 363         regs->ip = landing_pad;
 364
 365         enter_from_user_mode();
 366
 367         local_irq_enable();
 368
 369         /* Fetch EBP from where the vDSO stashed it. */
 370         if (
 371 #ifdef CONFIG_X86_64
 372                 /*
 373                  * Micro-optimization: the pointer we're following is explicitly
 374                  * 32 bits, so it can't be out of range.
 375                  */
 376                 __get_user(*(u32 *)&regs->bp,
 377                             (u32 __user __force *)(unsigned long)(u32)regs->sp)
 378 #else
 379                 get_user(*(u32 *)&regs->bp,
 380                          (u32 __user __force *)(unsigned long)(u32)regs->sp)
 381 #endif
 382                 ) {
 383
 384                 /* User code screwed up. */
 385                 local_irq_disable();
 386                 regs->ax = -EFAULT;
 387                 prepare_exit_to_usermode(regs);
 388                 return 0;       /* Keep it simple: use IRET. */
 389         }
 390
 391         /* Now this is just like a normal syscall. */
 392         do_syscall_32_irqs_on(regs);
 393
 394 #ifdef CONFIG_X86_64
 395         /*
 396          * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
 397          * SYSRETL is available on all 64-bit CPUs, so we don't need to
 398          * bother with SYSEXIT.
 399          *
 400          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 401          * because the ECX fixup above will ensure that this is essentially
 402          * never the case.
 403          */
 404         return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
 405                 regs->ip == landing_pad &&
 406                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
 407 #else
 408         /*
 409          * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
 410          *
 411          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 412          * because the ECX fixup above will ensure that this is essentially
 413          * never the case.
 414          *
 415          * We don't allow syscalls at all from VM86 mode, but we still
 416          * need to check VM, because we might be returning from sys_vm86.
 417          */
 418         return static_cpu_has(X86_FEATURE_SEP) &&
 419                 regs->cs == __USER_CS && regs->ss == __USER_DS &&
 420                 regs->ip == landing_pad &&
 421                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
 422 #endif
 423 }
 424 #endif