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/nospec.h>
  25 #include <linux/uprobes.h>
  26 #include <linux/livepatch.h>
  27 #include <linux/syscalls.h>
  28
  29 #include <asm/desc.h>
  30 #include <asm/traps.h>
  31 #include <asm/vdso.h>
  32 #include <linux/uaccess.h>
  33 #include <asm/cpufeature.h>
  34
  35 #define CREATE_TRACE_POINTS
  36 #include <trace/events/syscalls.h>
  37
  38 #ifdef CONFIG_CONTEXT_TRACKING
  39 /* Called on entry from user mode with IRQs off. */
  40 __visible inline void enter_from_user_mode(void)
  41 {
  42         CT_WARN_ON(ct_state() != CONTEXT_USER);
  43         user_exit_irqoff();
  44 }
  45 #else
  46 static inline void enter_from_user_mode(void) {}
  47 #endif
  48
  49 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
  50 {
  51 #ifdef CONFIG_X86_64
  52         if (arch == AUDIT_ARCH_X86_64) {
  53                 audit_syscall_entry(regs->orig_ax, regs->di,
  54                                     regs->si, regs->dx, regs->r10);
  55         } else
  56 #endif
  57         {
  58                 audit_syscall_entry(regs->orig_ax, regs->bx,
  59                                     regs->cx, regs->dx, regs->si);
  60         }
  61 }
  62
  63 /*
  64  * Returns the syscall nr to run (which should match regs->orig_ax) or -1
  65  * to skip the syscall.
  66  */
  67 static long syscall_trace_enter(struct pt_regs *regs)
  68 {
  69         u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
  70
  71         struct thread_info *ti = current_thread_info();
  72         unsigned long ret = 0;
  73         bool emulated = false;
  74         u32 work;
  75
  76         if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
  77                 BUG_ON(regs != task_pt_regs(current));
  78
  79         work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
  80
  81         if (unlikely(work & _TIF_SYSCALL_EMU))
  82                 emulated = true;
  83
  84         if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
  85             tracehook_report_syscall_entry(regs))
  86                 return -1L;
  87
  88         if (emulated)
  89                 return -1L;
  90
  91 #ifdef CONFIG_SECCOMP
  92         /*
  93          * Do seccomp after ptrace, to catch any tracer changes.
  94          */
  95         if (work & _TIF_SECCOMP) {
  96                 struct seccomp_data sd;
  97
  98                 sd.arch = arch;
  99                 sd.nr = regs->orig_ax;
 100                 sd.instruction_pointer = regs->ip;
 101 #ifdef CONFIG_X86_64
 102                 if (arch == AUDIT_ARCH_X86_64) {
 103                         sd.args[0] = regs->di;
 104                         sd.args[1] = regs->si;
 105                         sd.args[2] = regs->dx;
 106                         sd.args[3] = regs->r10;
 107                         sd.args[4] = regs->r8;
 108                         sd.args[5] = regs->r9;
 109                 } else
 110 #endif
 111                 {
 112                         sd.args[0] = regs->bx;
 113                         sd.args[1] = regs->cx;
 114                         sd.args[2] = regs->dx;
 115                         sd.args[3] = regs->si;
 116                         sd.args[4] = regs->di;
 117                         sd.args[5] = regs->bp;
 118                 }
 119
 120                 ret = __secure_computing(&sd);
 121                 if (ret == -1)
 122                         return ret;
 123         }
 124 #endif
 125
 126         if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 127                 trace_sys_enter(regs, regs->orig_ax);
 128
 129         do_audit_syscall_entry(regs, arch);
 130
 131         return ret ?: regs->orig_ax;
 132 }
 133
 134 #define EXIT_TO_USERMODE_LOOP_FLAGS                             \
 135         (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |   \
 136          _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
 137
 138 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 139 {
 140         /*
 141          * In order to return to user mode, we need to have IRQs off with
 142          * none of EXIT_TO_USERMODE_LOOP_FLAGS set.  Several of these flags
 143          * can be set at any time on preemptable kernels if we have IRQs on,
 144          * so we need to loop.  Disabling preemption wouldn't help: doing the
 145          * work to clear some of the flags can sleep.
 146          */
 147         while (true) {
 148                 /* We have work to do. */
 149                 local_irq_enable();
 150
 151                 if (cached_flags & _TIF_NEED_RESCHED)
 152                         schedule();
 153
 154                 if (cached_flags & _TIF_UPROBE)
 155                         uprobe_notify_resume(regs);
 156
 157                 if (cached_flags & _TIF_PATCH_PENDING)
 158                         klp_update_patch_state(current);
 159
 160                 /* deal with pending signal delivery */
 161                 if (cached_flags & _TIF_SIGPENDING)
 162                         do_signal(regs);
 163
 164                 if (cached_flags & _TIF_NOTIFY_RESUME) {
 165                         clear_thread_flag(TIF_NOTIFY_RESUME);
 166                         tracehook_notify_resume(regs);
 167                 }
 168
 169                 if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 170                         fire_user_return_notifiers();
 171
 172                 /* Disable IRQs and retry */
 173                 local_irq_disable();
 174
 175                 cached_flags = READ_ONCE(current_thread_info()->flags);
 176
 177                 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 178                         break;
 179         }
 180 }
 181
 182 /* Called with IRQs disabled. */
 183 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 184 {
 185         struct thread_info *ti = current_thread_info();
 186         u32 cached_flags;
 187
 188         addr_limit_user_check();
 189
 190         lockdep_assert_irqs_disabled();
 191         lockdep_sys_exit();
 192
 193         cached_flags = READ_ONCE(ti->flags);
 194
 195         if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 196                 exit_to_usermode_loop(regs, cached_flags);
 197
 198 #ifdef CONFIG_COMPAT
 199         /*
 200          * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 201          * returning to user mode.  We need to clear it *after* signal
 202          * handling, because syscall restart has a fixup for compat
 203          * syscalls.  The fixup is exercised by the ptrace_syscall_32
 204          * selftest.
 205          *
 206          * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
 207          * special case only applies after poking regs and before the
 208          * very next return to user mode.
 209          */
 210         ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
 211 #endif
 212
 213         user_enter_irqoff();
 214 }
 215
 216 #define SYSCALL_EXIT_WORK_FLAGS                         \
 217         (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |      \
 218          _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
 219
 220 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
 221 {
 222         bool step;
 223
 224         audit_syscall_exit(regs);
 225
 226         if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
 227                 trace_sys_exit(regs, regs->ax);
 228
 229         /*
 230          * If TIF_SYSCALL_EMU is set, we only get here because of
 231          * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
 232          * We already reported this syscall instruction in
 233          * syscall_trace_enter().
 234          */
 235         step = unlikely(
 236                 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
 237                 == _TIF_SINGLESTEP);
 238         if (step || cached_flags & _TIF_SYSCALL_TRACE)
 239                 tracehook_report_syscall_exit(regs, step);
 240 }
 241
 242 /*
 243  * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
 244  * state such that we can immediately switch to user mode.
 245  */
 246 __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 247 {
 248         struct thread_info *ti = current_thread_info();
 249         u32 cached_flags = READ_ONCE(ti->flags);
 250
 251         CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
 252
 253         if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
 254             WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 255                 local_irq_enable();
 256
 257         /*
 258          * First do one-time work.  If these work items are enabled, we
 259          * want to run them exactly once per syscall exit with IRQs on.
 260          */
 261         if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
 262                 syscall_slow_exit_work(regs, cached_flags);
 263
 264         local_irq_disable();
 265         prepare_exit_to_usermode(regs);
 266 }
 267
 268 #ifdef CONFIG_X86_64
 269 __visible void do_syscall_64(struct pt_regs *regs)
 270 {
 271         struct thread_info *ti = current_thread_info();
 272         unsigned long nr = regs->orig_ax;
 273
 274         enter_from_user_mode();
 275         local_irq_enable();
 276
 277         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
 278                 nr = syscall_trace_enter(regs);
 279
 280         /*
 281          * NB: Native and x32 syscalls are dispatched from the same
 282          * table.  The only functional difference is the x32 bit in
 283          * regs->orig_ax, which changes the behavior of some syscalls.
 284          */
 285         if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
 286                 nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls);
 287                 regs->ax = sys_call_table[nr](
 288                         regs->di, regs->si, regs->dx,
 289                         regs->r10, regs->r8, regs->r9);
 290         }
 291
 292         syscall_return_slowpath(regs);
 293 }
 294 #endif
 295
 296 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 297 /*
 298  * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
 299  * all entry and exit work and returns with IRQs off.  This function is
 300  * extremely hot in workloads that use it, and it's usually called from
 301  * do_fast_syscall_32, so forcibly inline it to improve performance.
 302  */
 303 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 304 {
 305         struct thread_info *ti = current_thread_info();
 306         unsigned int nr = (unsigned int)regs->orig_ax;
 307
 308 #ifdef CONFIG_IA32_EMULATION
 309         ti->status |= TS_COMPAT;
 310 #endif
 311
 312         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
 313                 /*
 314                  * Subtlety here: if ptrace pokes something larger than
 315                  * 2^32-1 into orig_ax, this truncates it.  This may or
 316                  * may not be necessary, but it matches the old asm
 317                  * behavior.
 318                  */
 319                 nr = syscall_trace_enter(regs);
 320         }
 321
 322         if (likely(nr < IA32_NR_syscalls)) {
 323                 nr = array_index_nospec(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