Pileus Git - ~andy/linux/blob - arch/x86/kernel/vsyscall_64.c

   1 /*
   2  *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
   3  *  Copyright 2003 Andi Kleen, SuSE Labs.
   4  *
   5  *  [ NOTE: this mechanism is now deprecated in favor of the vDSO. ]
   6  *
   7  *  Thanks to hpa@transmeta.com for some useful hint.
   8  *  Special thanks to Ingo Molnar for his early experience with
   9  *  a different vsyscall implementation for Linux/IA32 and for the name.
  10  *
  11  *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
  12  *  at virtual address -10Mbyte+1024bytes etc... There are at max 4
  13  *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
  14  *  jumping out of line if necessary. We cannot add more with this
  15  *  mechanism because older kernels won't return -ENOSYS.
  16  *
  17  *  Note: the concept clashes with user mode linux.  UML users should
  18  *  use the vDSO.
  19  */
  20
  21 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  22
  23 #include <linux/time.h>
  24 #include <linux/init.h>
  25 #include <linux/kernel.h>
  26 #include <linux/timer.h>
  27 #include <linux/seqlock.h>
  28 #include <linux/jiffies.h>
  29 #include <linux/sysctl.h>
  30 #include <linux/topology.h>
  31 #include <linux/timekeeper_internal.h>
  32 #include <linux/getcpu.h>
  33 #include <linux/cpu.h>
  34 #include <linux/smp.h>
  35 #include <linux/notifier.h>
  36 #include <linux/syscalls.h>
  37 #include <linux/ratelimit.h>
  38
  39 #include <asm/vsyscall.h>
  40 #include <asm/pgtable.h>
  41 #include <asm/compat.h>
  42 #include <asm/page.h>
  43 #include <asm/unistd.h>
  44 #include <asm/fixmap.h>
  45 #include <asm/errno.h>
  46 #include <asm/io.h>
  47 #include <asm/segment.h>
  48 #include <asm/desc.h>
  49 #include <asm/topology.h>
  50 #include <asm/vgtod.h>
  51 #include <asm/traps.h>
  52
  53 #define CREATE_TRACE_POINTS
  54 #include "vsyscall_trace.h"
  55
  56 DEFINE_VVAR(int, vgetcpu_mode);
  57 DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data);
  58
  59 static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
  60
  61 static int __init vsyscall_setup(char *str)
  62 {
  63         if (str) {
  64                 if (!strcmp("emulate", str))
  65                         vsyscall_mode = EMULATE;
  66                 else if (!strcmp("native", str))
  67                         vsyscall_mode = NATIVE;
  68                 else if (!strcmp("none", str))
  69                         vsyscall_mode = NONE;
  70                 else
  71                         return -EINVAL;
  72
  73                 return 0;
  74         }
  75
  76         return -EINVAL;
  77 }
  78 early_param("vsyscall", vsyscall_setup);
  79
  80 void update_vsyscall_tz(void)
  81 {
  82         vsyscall_gtod_data.sys_tz = sys_tz;
  83 }
  84
  85 void update_vsyscall(struct timekeeper *tk)
  86 {
  87         struct vsyscall_gtod_data *vdata = &vsyscall_gtod_data;
  88
  89         write_seqcount_begin(&vdata->seq);
  90
  91         /* copy vsyscall data */
  92         vdata->clock.vclock_mode        = tk->clock->archdata.vclock_mode;
  93         vdata->clock.cycle_last         = tk->clock->cycle_last;
  94         vdata->clock.mask               = tk->clock->mask;
  95         vdata->clock.mult               = tk->mult;
  96         vdata->clock.shift              = tk->shift;
  97
  98         vdata->wall_time_sec            = tk->xtime_sec;
  99         vdata->wall_time_snsec          = tk->xtime_nsec;
 100
 101         vdata->monotonic_time_sec       = tk->xtime_sec
 102                                         + tk->wall_to_monotonic.tv_sec;
 103         vdata->monotonic_time_snsec     = tk->xtime_nsec
 104                                         + (tk->wall_to_monotonic.tv_nsec
 105                                                 << tk->shift);
 106         while (vdata->monotonic_time_snsec >=
 107                                         (((u64)NSEC_PER_SEC) << tk->shift)) {
 108                 vdata->monotonic_time_snsec -=
 109                                         ((u64)NSEC_PER_SEC) << tk->shift;
 110                 vdata->monotonic_time_sec++;
 111         }
 112
 113         vdata->wall_time_coarse.tv_sec  = tk->xtime_sec;
 114         vdata->wall_time_coarse.tv_nsec = (long)(tk->xtime_nsec >> tk->shift);
 115
 116         vdata->monotonic_time_coarse    = timespec_add(vdata->wall_time_coarse,
 117                                                         tk->wall_to_monotonic);
 118
 119         write_seqcount_end(&vdata->seq);
 120 }
 121
 122 static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
 123                               const char *message)
 124 {
 125         if (!show_unhandled_signals)
 126                 return;
 127
 128         pr_notice_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
 129                               level, current->comm, task_pid_nr(current),
 130                               message, regs->ip, regs->cs,
 131                               regs->sp, regs->ax, regs->si, regs->di);
 132 }
 133
 134 static int addr_to_vsyscall_nr(unsigned long addr)
 135 {
 136         int nr;
 137
 138         if ((addr & ~0xC00UL) != VSYSCALL_START)
 139                 return -EINVAL;
 140
 141         nr = (addr & 0xC00UL) >> 10;
 142         if (nr >= 3)
 143                 return -EINVAL;
 144
 145         return nr;
 146 }
 147
 148 #ifdef CONFIG_SECCOMP
 149 static int vsyscall_seccomp(struct task_struct *tsk, int syscall_nr)
 150 {
 151         if (!seccomp_mode(&tsk->seccomp))
 152                 return 0;
 153         task_pt_regs(tsk)->orig_ax = syscall_nr;
 154         task_pt_regs(tsk)->ax = syscall_nr;
 155         return __secure_computing(syscall_nr);
 156 }
 157 #else
 158 #define vsyscall_seccomp(_tsk, _nr) 0
 159 #endif
 160
 161 static bool write_ok_or_segv(unsigned long ptr, size_t size)
 162 {
 163         /*
 164          * XXX: if access_ok, get_user, and put_user handled
 165          * sig_on_uaccess_error, this could go away.
 166          */
 167
 168         if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
 169                 siginfo_t info;
 170                 struct thread_struct *thread = &current->thread;
 171
 172                 thread->error_code      = 6;  /* user fault, no page, write */
 173                 thread->cr2             = ptr;
 174                 thread->trap_nr         = X86_TRAP_PF;
 175
 176                 memset(&info, 0, sizeof(info));
 177                 info.si_signo           = SIGSEGV;
 178                 info.si_errno           = 0;
 179                 info.si_code            = SEGV_MAPERR;
 180                 info.si_addr            = (void __user *)ptr;
 181
 182                 force_sig_info(SIGSEGV, &info, current);
 183                 return false;
 184         } else {
 185                 return true;
 186         }
 187 }
 188
 189 bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 190 {
 191         struct task_struct *tsk;
 192         unsigned long caller;
 193         int vsyscall_nr;
 194         int prev_sig_on_uaccess_error;
 195         long ret;
 196         int skip;
 197
 198         /*
 199          * No point in checking CS -- the only way to get here is a user mode
 200          * trap to a high address, which means that we're in 64-bit user code.
 201          */
 202
 203         WARN_ON_ONCE(address != regs->ip);
 204
 205         if (vsyscall_mode == NONE) {
 206                 warn_bad_vsyscall(KERN_INFO, regs,
 207                                   "vsyscall attempted with vsyscall=none");
 208                 return false;
 209         }
 210
 211         vsyscall_nr = addr_to_vsyscall_nr(address);
 212
 213         trace_emulate_vsyscall(vsyscall_nr);
 214
 215         if (vsyscall_nr < 0) {
 216                 warn_bad_vsyscall(KERN_WARNING, regs,
 217                                   "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
 218                 goto sigsegv;
 219         }
 220
 221         if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
 222                 warn_bad_vsyscall(KERN_WARNING, regs,
 223                                   "vsyscall with bad stack (exploit attempt?)");
 224                 goto sigsegv;
 225         }
 226
 227         tsk = current;
 228         /*
 229          * With a real vsyscall, page faults cause SIGSEGV.  We want to
 230          * preserve that behavior to make writing exploits harder.
 231          */
 232         prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
 233         current_thread_info()->sig_on_uaccess_error = 1;
 234
 235         /*
 236          * NULL is a valid user pointer (in the access_ok sense) on 32-bit and
 237          * 64-bit, so we don't need to special-case it here.  For all the
 238          * vsyscalls, NULL means "don't write anything" not "write it at
 239          * address 0".
 240          */
 241         ret = -EFAULT;
 242         skip = 0;
 243         switch (vsyscall_nr) {
 244         case 0:
 245                 skip = vsyscall_seccomp(tsk, __NR_gettimeofday);
 246                 if (skip)
 247                         break;
 248
 249                 if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
 250                     !write_ok_or_segv(regs->si, sizeof(struct timezone)))
 251                         break;
 252
 253                 ret = sys_gettimeofday(
 254                         (struct timeval __user *)regs->di,
 255                         (struct timezone __user *)regs->si);
 256                 break;
 257
 258         case 1:
 259                 skip = vsyscall_seccomp(tsk, __NR_time);
 260                 if (skip)
 261                         break;
 262
 263                 if (!write_ok_or_segv(regs->di, sizeof(time_t)))
 264                         break;
 265
 266                 ret = sys_time((time_t __user *)regs->di);
 267                 break;
 268
 269         case 2:
 270                 skip = vsyscall_seccomp(tsk, __NR_getcpu);
 271                 if (skip)
 272                         break;
 273
 274                 if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
 275                     !write_ok_or_segv(regs->si, sizeof(unsigned)))
 276                         break;
 277
 278                 ret = sys_getcpu((unsigned __user *)regs->di,
 279                                  (unsigned __user *)regs->si,
 280                                  NULL);
 281                 break;
 282         }
 283
 284         current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;
 285
 286         if (skip) {
 287                 if ((long)regs->ax <= 0L) /* seccomp errno emulation */
 288                         goto do_ret;
 289                 goto done; /* seccomp trace/trap */
 290         }
 291
 292         if (ret == -EFAULT) {
 293                 /* Bad news -- userspace fed a bad pointer to a vsyscall. */
 294                 warn_bad_vsyscall(KERN_INFO, regs,
 295                                   "vsyscall fault (exploit attempt?)");
 296
 297                 /*
 298                  * If we failed to generate a signal for any reason,
 299                  * generate one here.  (This should be impossible.)
 300                  */
 301                 if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
 302                                  !sigismember(&tsk->pending.signal, SIGSEGV)))
 303                         goto sigsegv;
 304
 305                 return true;  /* Don't emulate the ret. */
 306         }
 307
 308         regs->ax = ret;
 309
 310 do_ret:
 311         /* Emulate a ret instruction. */
 312         regs->ip = caller;
 313         regs->sp += 8;
 314 done:
 315         return true;
 316
 317 sigsegv:
 318         force_sig(SIGSEGV, current);
 319         return true;
 320 }
 321
 322 /*
 323  * Assume __initcall executes before all user space. Hopefully kmod
 324  * doesn't violate that. We'll find out if it does.
 325  */
 326 static void __cpuinit vsyscall_set_cpu(int cpu)
 327 {
 328         unsigned long d;
 329         unsigned long node = 0;
 330 #ifdef CONFIG_NUMA
 331         node = cpu_to_node(cpu);
 332 #endif
 333         if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
 334                 write_rdtscp_aux((node << 12) | cpu);
 335
 336         /*
 337          * Store cpu number in limit so that it can be loaded quickly
 338          * in user space in vgetcpu. (12 bits for the CPU and 8 bits for the node)
 339          */
 340         d = 0x0f40000000000ULL;
 341         d |= cpu;
 342         d |= (node & 0xf) << 12;
 343         d |= (node >> 4) << 48;
 344
 345         write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
 346 }
 347
 348 static void __cpuinit cpu_vsyscall_init(void *arg)
 349 {
 350         /* preemption should be already off */
 351         vsyscall_set_cpu(raw_smp_processor_id());
 352 }
 353
 354 static int __cpuinit
 355 cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
 356 {
 357         long cpu = (long)arg;
 358
 359         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
 360                 smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);
 361
 362         return NOTIFY_DONE;
 363 }
 364
 365 void __init map_vsyscall(void)
 366 {
 367         extern char __vsyscall_page;
 368         unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
 369         extern char __vvar_page;
 370         unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);
 371
 372         __set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_vsyscall,
 373                      vsyscall_mode == NATIVE
 374                      ? PAGE_KERNEL_VSYSCALL
 375                      : PAGE_KERNEL_VVAR);
 376         BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_FIRST_PAGE) !=
 377                      (unsigned long)VSYSCALL_START);
 378
 379         __set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
 380         BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) !=
 381                      (unsigned long)VVAR_ADDRESS);
 382 }
 383
 384 static int __init vsyscall_init(void)
 385 {
 386         BUG_ON(VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE));
 387
 388         on_each_cpu(cpu_vsyscall_init, NULL, 1);
 389         /* notifier priority > KVM */
 390         hotcpu_notifier(cpu_vsyscall_notifier, 30);
 391
 392         return 0;
 393 }
 394 __initcall(vsyscall_init);