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 static bool write_ok_or_segv(unsigned long ptr, size_t size)
 149 {
 150         /*
 151          * XXX: if access_ok, get_user, and put_user handled
 152          * sig_on_uaccess_error, this could go away.
 153          */
 154
 155         if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
 156                 siginfo_t info;
 157                 struct thread_struct *thread = &current->thread;
 158
 159                 thread->error_code      = 6;  /* user fault, no page, write */
 160                 thread->cr2             = ptr;
 161                 thread->trap_nr         = X86_TRAP_PF;
 162
 163                 memset(&info, 0, sizeof(info));
 164                 info.si_signo           = SIGSEGV;
 165                 info.si_errno           = 0;
 166                 info.si_code            = SEGV_MAPERR;
 167                 info.si_addr            = (void __user *)ptr;
 168
 169                 force_sig_info(SIGSEGV, &info, current);
 170                 return false;
 171         } else {
 172                 return true;
 173         }
 174 }
 175
 176 bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 177 {
 178         struct task_struct *tsk;
 179         unsigned long caller;
 180         int vsyscall_nr, syscall_nr, tmp;
 181         int prev_sig_on_uaccess_error;
 182         long ret;
 183
 184         /*
 185          * No point in checking CS -- the only way to get here is a user mode
 186          * trap to a high address, which means that we're in 64-bit user code.
 187          */
 188
 189         WARN_ON_ONCE(address != regs->ip);
 190
 191         if (vsyscall_mode == NONE) {
 192                 warn_bad_vsyscall(KERN_INFO, regs,
 193                                   "vsyscall attempted with vsyscall=none");
 194                 return false;
 195         }
 196
 197         vsyscall_nr = addr_to_vsyscall_nr(address);
 198
 199         trace_emulate_vsyscall(vsyscall_nr);
 200
 201         if (vsyscall_nr < 0) {
 202                 warn_bad_vsyscall(KERN_WARNING, regs,
 203                                   "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
 204                 goto sigsegv;
 205         }
 206
 207         if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
 208                 warn_bad_vsyscall(KERN_WARNING, regs,
 209                                   "vsyscall with bad stack (exploit attempt?)");
 210                 goto sigsegv;
 211         }
 212
 213         tsk = current;
 214
 215         /*
 216          * Check for access_ok violations and find the syscall nr.
 217          *
 218          * NULL is a valid user pointer (in the access_ok sense) on 32-bit and
 219          * 64-bit, so we don't need to special-case it here.  For all the
 220          * vsyscalls, NULL means "don't write anything" not "write it at
 221          * address 0".
 222          */
 223         switch (vsyscall_nr) {
 224         case 0:
 225                 if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
 226                     !write_ok_or_segv(regs->si, sizeof(struct timezone))) {
 227                         ret = -EFAULT;
 228                         goto check_fault;
 229                 }
 230
 231                 syscall_nr = __NR_gettimeofday;
 232                 break;
 233
 234         case 1:
 235                 if (!write_ok_or_segv(regs->di, sizeof(time_t))) {
 236                         ret = -EFAULT;
 237                         goto check_fault;
 238                 }
 239
 240                 syscall_nr = __NR_time;
 241                 break;
 242
 243         case 2:
 244                 if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
 245                     !write_ok_or_segv(regs->si, sizeof(unsigned))) {
 246                         ret = -EFAULT;
 247                         goto check_fault;
 248                 }
 249
 250                 syscall_nr = __NR_getcpu;
 251                 break;
 252         }
 253
 254         /*
 255          * Handle seccomp.  regs->ip must be the original value.
 256          * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt.
 257          *
 258          * We could optimize the seccomp disabled case, but performance
 259          * here doesn't matter.
 260          */
 261         regs->orig_ax = syscall_nr;
 262         regs->ax = -ENOSYS;
 263         tmp = secure_computing(syscall_nr);
 264         if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
 265                 warn_bad_vsyscall(KERN_DEBUG, regs,
 266                                   "seccomp tried to change syscall nr or ip");
 267                 do_exit(SIGSYS);
 268         }
 269         if (tmp)
 270                 goto do_ret;  /* skip requested */
 271
 272         /*
 273          * With a real vsyscall, page faults cause SIGSEGV.  We want to
 274          * preserve that behavior to make writing exploits harder.
 275          */
 276         prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
 277         current_thread_info()->sig_on_uaccess_error = 1;
 278
 279         ret = -EFAULT;
 280         switch (vsyscall_nr) {
 281         case 0:
 282                 ret = sys_gettimeofday(
 283                         (struct timeval __user *)regs->di,
 284                         (struct timezone __user *)regs->si);
 285                 break;
 286
 287         case 1:
 288                 ret = sys_time((time_t __user *)regs->di);
 289                 break;
 290
 291         case 2:
 292                 ret = sys_getcpu((unsigned __user *)regs->di,
 293                                  (unsigned __user *)regs->si,
 294                                  NULL);
 295                 break;
 296         }
 297
 298         current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;
 299
 300 check_fault:
 301         if (ret == -EFAULT) {
 302                 /* Bad news -- userspace fed a bad pointer to a vsyscall. */
 303                 warn_bad_vsyscall(KERN_INFO, regs,
 304                                   "vsyscall fault (exploit attempt?)");
 305
 306                 /*
 307                  * If we failed to generate a signal for any reason,
 308                  * generate one here.  (This should be impossible.)
 309                  */
 310                 if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
 311                                  !sigismember(&tsk->pending.signal, SIGSEGV)))
 312                         goto sigsegv;
 313
 314                 return true;  /* Don't emulate the ret. */
 315         }
 316
 317         regs->ax = ret;
 318
 319 do_ret:
 320         /* Emulate a ret instruction. */
 321         regs->ip = caller;
 322         regs->sp += 8;
 323         return true;
 324
 325 sigsegv:
 326         force_sig(SIGSEGV, current);
 327         return true;
 328 }
 329
 330 /*
 331  * Assume __initcall executes before all user space. Hopefully kmod
 332  * doesn't violate that. We'll find out if it does.
 333  */
 334 static void vsyscall_set_cpu(int cpu)
 335 {
 336         unsigned long d;
 337         unsigned long node = 0;
 338 #ifdef CONFIG_NUMA
 339         node = cpu_to_node(cpu);
 340 #endif
 341         if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
 342                 write_rdtscp_aux((node << 12) | cpu);
 343
 344         /*
 345          * Store cpu number in limit so that it can be loaded quickly
 346          * in user space in vgetcpu. (12 bits for the CPU and 8 bits for the node)
 347          */
 348         d = 0x0f40000000000ULL;
 349         d |= cpu;
 350         d |= (node & 0xf) << 12;
 351         d |= (node >> 4) << 48;
 352
 353         write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
 354 }
 355
 356 static void cpu_vsyscall_init(void *arg)
 357 {
 358         /* preemption should be already off */
 359         vsyscall_set_cpu(raw_smp_processor_id());
 360 }
 361
 362 static int
 363 cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
 364 {
 365         long cpu = (long)arg;
 366
 367         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
 368                 smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);
 369
 370         return NOTIFY_DONE;
 371 }
 372
 373 void __init map_vsyscall(void)
 374 {
 375         extern char __vsyscall_page;
 376         unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
 377         extern char __vvar_page;
 378         unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);
 379
 380         __set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_vsyscall,
 381                      vsyscall_mode == NATIVE
 382                      ? PAGE_KERNEL_VSYSCALL
 383                      : PAGE_KERNEL_VVAR);
 384         BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_FIRST_PAGE) !=
 385                      (unsigned long)VSYSCALL_START);
 386
 387         __set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
 388         BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) !=
 389                      (unsigned long)VVAR_ADDRESS);
 390 }
 391
 392 static int __init vsyscall_init(void)
 393 {
 394         BUG_ON(VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE));
 395
 396         on_each_cpu(cpu_vsyscall_init, NULL, 1);
 397         /* notifier priority > KVM */
 398         hotcpu_notifier(cpu_vsyscall_notifier, 30);
 399
 400         return 0;
 401 }
 402 __initcall(vsyscall_init);