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 #include <linux/livepatch.h>
  26
  27 #include <asm/desc.h>
  28 #include <asm/traps.h>
  29 #include <asm/vdso.h>
  30 #include <linux/uaccess.h>
  31 #include <asm/cpufeature.h>
  32
  33 #define CREATE_TRACE_POINTS
  34 #include <trace/events/syscalls.h>
  35
  36 #ifdef CONFIG_CONTEXT_TRACKING
  37 /* Called on entry from user mode with IRQs off. */
  38 __visible inline void enter_from_user_mode(void)
  39 {
  40         CT_WARN_ON(ct_state() != CONTEXT_USER);
  41         user_exit_irqoff();
  42 }
  43 #else
  44 static inline void enter_from_user_mode(void) {}
  45 #endif
  46
  47 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
  48 {
  49 #ifdef CONFIG_X86_64
  50         if (arch == AUDIT_ARCH_X86_64) {
  51                 audit_syscall_entry(regs->orig_ax, regs->di,
  52                                     regs->si, regs->dx, regs->r10);
  53         } else
  54 #endif
  55         {
  56                 audit_syscall_entry(regs->orig_ax, regs->bx,
  57                                     regs->cx, regs->dx, regs->si);
  58         }
  59 }
  60
  61 /*
  62  * Returns the syscall nr to run (which should match regs->orig_ax) or -1
  63  * to skip the syscall.
  64  */
  65 static long syscall_trace_enter(struct pt_regs *regs)
  66 {
  67         u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
  68
  69         struct thread_info *ti = current_thread_info();
  70         unsigned long ret = 0;
  71         bool emulated = false;
  72         u32 work;
  73
  74         if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
  75                 BUG_ON(regs != task_pt_regs(current));
  76
  77         work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
  78
  79         if (unlikely(work & _TIF_SYSCALL_EMU))
  80                 emulated = true;
  81
  82         if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
  83             tracehook_report_syscall_entry(regs))
  84                 return -1L;
  85
  86         if (emulated)
  87                 return -1L;
  88
  89 #ifdef CONFIG_SECCOMP
  90         /*
  91          * Do seccomp after ptrace, to catch any tracer changes.
  92          */
  93         if (work & _TIF_SECCOMP) {
  94                 struct seccomp_data sd;
  95
  96                 sd.arch = arch;
  97                 sd.nr = regs->orig_ax;
  98                 sd.instruction_pointer = regs->ip;
  99 #ifdef CONFIG_X86_64
 100                 if (arch == AUDIT_ARCH_X86_64) {
 101                         sd.args[0] = regs->di;
 102                         sd.args[1] = regs->si;
 103                         sd.args[2] = regs->dx;
 104                         sd.args[3] = regs->r10;
 105                         sd.args[4] = regs->r8;
 106                         sd.args[5] = regs->r9;
 107                 } else
 108 #endif
 109                 {
 110                         sd.args[0] = regs->bx;
 111                         sd.args[1] = regs->cx;
 112                         sd.args[2] = regs->dx;
 113                         sd.args[3] = regs->si;
 114                         sd.args[4] = regs->di;
 115                         sd.args[5] = regs->bp;
 116                 }
 117
 118                 ret = __secure_computing(&sd);
 119                 if (ret == -1)
 120                         return ret;
 121         }
 122 #endif
 123
 124         if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 125                 trace_sys_enter(regs, regs->orig_ax);
 126
 127         do_audit_syscall_entry(regs, arch);
 128
 129         return ret ?: regs->orig_ax;
 130 }
 131
 132 #define EXIT_TO_USERMODE_LOOP_FLAGS                             \
 133         (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |   \
 134          _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
 135
 136 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 137 {
 138         /*
 139          * In order to return to user mode, we need to have IRQs off with
 140          * none of EXIT_TO_USERMODE_LOOP_FLAGS 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                 if (cached_flags & _TIF_PATCH_PENDING)
 168                         klp_update_patch_state(current);
 169
 170                 /* Disable IRQs and retry */
 171                 local_irq_disable();
 172
 173                 cached_flags = READ_ONCE(current_thread_info()->flags);
 174
 175                 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 176                         break;
 177         }
 178 }
 179
 180 /* Called with IRQs disabled. */
 181 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 182 {
 183         struct thread_info *ti = current_thread_info();
 184         u32 cached_flags;
 185
 186         if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
 187                 local_irq_disable();
 188
 189         lockdep_sys_exit();
 190
 191         cached_flags = READ_ONCE(ti->flags);
 192
 193         if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 194                 exit_to_usermode_loop(regs, cached_flags);
 195
 196 #ifdef CONFIG_COMPAT
 197         /*
 198          * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 199          * returning to user mode.  We need to clear it *after* signal
 200          * handling, because syscall restart has a fixup for compat
 201          * syscalls.  The fixup is exercised by the ptrace_syscall_32
 202          * selftest.
 203          *
 204          * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
 205          * special case only applies after poking regs and before the
 206          * very next return to user mode.
 207          */
 208         current->thread.status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
 209 #endif
 210
 211         user_enter_irqoff();
 212 }
 213
 214 #define SYSCALL_EXIT_WORK_FLAGS                         \
 215         (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |      \
 216          _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
 217
 218 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
 219 {
 220         bool step;
 221
 222         audit_syscall_exit(regs);
 223
 224         if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
 225                 trace_sys_exit(regs, regs->ax);
 226
 227         /*
 228          * If TIF_SYSCALL_EMU is set, we only get here because of
 229          * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
 230          * We already reported this syscall instruction in
 231          * syscall_trace_enter().
 232          */
 233         step = unlikely(
 234                 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
 235                 == _TIF_SINGLESTEP);
 236         if (step || cached_flags & _TIF_SYSCALL_TRACE)
 237                 tracehook_report_syscall_exit(regs, step);
 238 }
 239
 240 /*
 241  * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
 242  * state such that we can immediately switch to user mode.
 243  */
 244 __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 245 {
 246         struct thread_info *ti = current_thread_info();
 247         u32 cached_flags = READ_ONCE(ti->flags);
 248
 249         CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
 250
 251         if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
 252             WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 253                 local_irq_enable();
 254
 255         /*
 256          * First do one-time work.  If these work items are enabled, we
 257          * want to run them exactly once per syscall exit with IRQs on.
 258          */
 259         if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
 260                 syscall_slow_exit_work(regs, cached_flags);
 261
 262         local_irq_disable();
 263         prepare_exit_to_usermode(regs);
 264 }
 265
 266 #ifdef CONFIG_X86_64
 267 __visible void do_syscall_64(struct pt_regs *regs)
 268 {
 269         struct thread_info *ti = current_thread_info();
 270         unsigned long nr = regs->orig_ax;
 271
 272         enter_from_user_mode();
 273         local_irq_enable();
 274
 275         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
 276                 nr = syscall_trace_enter(regs);
 277
 278         /*
 279          * NB: Native and x32 syscalls are dispatched from the same
 280          * table.  The only functional difference is the x32 bit in
 281          * regs->orig_ax, which changes the behavior of some syscalls.
 282          */
 283         if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
 284                 regs->ax = sys_call_table[nr & __SYSCALL_MASK](
 285                         regs->di, regs->si, regs->dx,
 286                         regs->r10, regs->r8, regs->r9);
 287         }
 288
 289         syscall_return_slowpath(regs);
 290 }
 291 #endif
 292
 293 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 294 /*
 295  * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
 296  * all entry and exit work and returns with IRQs off.  This function is
 297  * extremely hot in workloads that use it, and it's usually called from
 298  * do_fast_syscall_32, so forcibly inline it to improve performance.
 299  */
 300 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 301 {
 302         struct thread_info *ti = current_thread_info();
 303         unsigned int nr = (unsigned int)regs->orig_ax;
 304
 305 #ifdef CONFIG_IA32_EMULATION
 306         current->thread.status |= TS_COMPAT;
 307 #endif
 308
 309         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
 310                 /*
 311                  * Subtlety here: if ptrace pokes something larger than
 312                  * 2^32-1 into orig_ax, this truncates it.  This may or
 313                  * may not be necessary, but it matches the old asm
 314                  * behavior.
 315                  */
 316                 nr = syscall_trace_enter(regs);
 317         }
 318
 319         if (likely(nr < IA32_NR_syscalls)) {
 320                 /*
 321                  * It's possible that a 32-bit syscall implementation
 322                  * takes a 64-bit parameter but nonetheless assumes that
 323                  * the high bits are zero.  Make sure we zero-extend all
 324                  * of the args.
 325                  */
 326                 regs->ax = ia32_sys_call_table[nr](
 327                         (unsigned int)regs->bx, (unsigned int)regs->cx,
 328                         (unsigned int)regs->dx, (unsigned int)regs->si,
 329                         (unsigned int)regs->di, (unsigned int)regs->bp);
 330         }
 331
 332         syscall_return_slowpath(regs);
 333 }
 334
 335 /* Handles int $0x80 */
 336 __visible void do_int80_syscall_32(struct pt_regs *regs)
 337 {
 338         enter_from_user_mode();
 339         local_irq_enable();
 340         do_syscall_32_irqs_on(regs);
 341 }
 342
 343 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
 344 __visible long do_fast_syscall_32(struct pt_regs *regs)
 345 {
 346         /*
 347          * Called using the internal vDSO SYSENTER/SYSCALL32 calling
 348          * convention.  Adjust regs so it looks like we entered using int80.
 349          */
 350
 351         unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
 352                 vdso_image_32.sym_int80_landing_pad;
 353
 354         /*
 355          * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
 356          * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
 357          * Fix it up.
 358          */
 359         regs->ip = landing_pad;
 360
 361         enter_from_user_mode();
 362
 363         local_irq_enable();
 364
 365         /* Fetch EBP from where the vDSO stashed it. */
 366         if (
 367 #ifdef CONFIG_X86_64
 368                 /*
 369                  * Micro-optimization: the pointer we're following is explicitly
 370                  * 32 bits, so it can't be out of range.
 371                  */
 372                 __get_user(*(u32 *)&regs->bp,
 373                             (u32 __user __force *)(unsigned long)(u32)regs->sp)
 374 #else
 375                 get_user(*(u32 *)&regs->bp,
 376                          (u32 __user __force *)(unsigned long)(u32)regs->sp)
 377 #endif
 378                 ) {
 379
 380                 /* User code screwed up. */
 381                 local_irq_disable();
 382                 regs->ax = -EFAULT;
 383                 prepare_exit_to_usermode(regs);
 384                 return 0;       /* Keep it simple: use IRET. */
 385         }
 386
 387         /* Now this is just like a normal syscall. */
 388         do_syscall_32_irqs_on(regs);
 389
 390 #ifdef CONFIG_X86_64
 391         /*
 392          * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
 393          * SYSRETL is available on all 64-bit CPUs, so we don't need to
 394          * bother with SYSEXIT.
 395          *
 396          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 397          * because the ECX fixup above will ensure that this is essentially
 398          * never the case.
 399          */
 400         return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
 401                 regs->ip == landing_pad &&
 402                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
 403 #else
 404         /*
 405          * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
 406          *
 407          * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 408          * because the ECX fixup above will ensure that this is essentially
 409          * never the case.
 410          *
 411          * We don't allow syscalls at all from VM86 mode, but we still
 412          * need to check VM, because we might be returning from sys_vm86.
 413          */
 414         return static_cpu_has(X86_FEATURE_SEP) &&
 415                 regs->cs == __USER_CS && regs->ss == __USER_DS &&
 416                 regs->ip == landing_pad &&
 417                 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
 418 #endif
 419 }
 420 #endif