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/traps.h>
  51
  52 #define CREATE_TRACE_POINTS
  53 #include "vsyscall_trace.h"
  54
  55 DEFINE_VVAR(int, vgetcpu_mode);
  56
  57 static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
  58
  59 static int __init vsyscall_setup(char *str)
  60 {
  61         if (str) {
  62                 if (!strcmp("emulate", str))
  63                         vsyscall_mode = EMULATE;
  64                 else if (!strcmp("native", str))
  65                         vsyscall_mode = NATIVE;
  66                 else if (!strcmp("none", str))
  67                         vsyscall_mode = NONE;
  68                 else
  69                         return -EINVAL;
  70
  71                 return 0;
  72         }
  73
  74         return -EINVAL;
  75 }
  76 early_param("vsyscall", vsyscall_setup);
  77
  78 static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
  79                               const char *message)
  80 {
  81         if (!show_unhandled_signals)
  82                 return;
  83
  84         printk_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
  85                            level, current->comm, task_pid_nr(current),
  86                            message, regs->ip, regs->cs,
  87                            regs->sp, regs->ax, regs->si, regs->di);
  88 }
  89
  90 static int addr_to_vsyscall_nr(unsigned long addr)
  91 {
  92         int nr;
  93
  94         if ((addr & ~0xC00UL) != VSYSCALL_ADDR)
  95                 return -EINVAL;
  96
  97         nr = (addr & 0xC00UL) >> 10;
  98         if (nr >= 3)
  99                 return -EINVAL;
 100
 101         return nr;
 102 }
 103
 104 static bool write_ok_or_segv(unsigned long ptr, size_t size)
 105 {
 106         /*
 107          * XXX: if access_ok, get_user, and put_user handled
 108          * sig_on_uaccess_error, this could go away.
 109          */
 110
 111         if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
 112                 siginfo_t info;
 113                 struct thread_struct *thread = &current->thread;
 114
 115                 thread->error_code      = 6;  /* user fault, no page, write */
 116                 thread->cr2             = ptr;
 117                 thread->trap_nr         = X86_TRAP_PF;
 118
 119                 memset(&info, 0, sizeof(info));
 120                 info.si_signo           = SIGSEGV;
 121                 info.si_errno           = 0;
 122                 info.si_code            = SEGV_MAPERR;
 123                 info.si_addr            = (void __user *)ptr;
 124
 125                 force_sig_info(SIGSEGV, &info, current);
 126                 return false;
 127         } else {
 128                 return true;
 129         }
 130 }
 131
 132 bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 133 {
 134         struct task_struct *tsk;
 135         unsigned long caller;
 136         int vsyscall_nr, syscall_nr, tmp;
 137         int prev_sig_on_uaccess_error;
 138         long ret;
 139
 140         /*
 141          * No point in checking CS -- the only way to get here is a user mode
 142          * trap to a high address, which means that we're in 64-bit user code.
 143          */
 144
 145         WARN_ON_ONCE(address != regs->ip);
 146
 147         if (vsyscall_mode == NONE) {
 148                 warn_bad_vsyscall(KERN_INFO, regs,
 149                                   "vsyscall attempted with vsyscall=none");
 150                 return false;
 151         }
 152
 153         vsyscall_nr = addr_to_vsyscall_nr(address);
 154
 155         trace_emulate_vsyscall(vsyscall_nr);
 156
 157         if (vsyscall_nr < 0) {
 158                 warn_bad_vsyscall(KERN_WARNING, regs,
 159                                   "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
 160                 goto sigsegv;
 161         }
 162
 163         if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
 164                 warn_bad_vsyscall(KERN_WARNING, regs,
 165                                   "vsyscall with bad stack (exploit attempt?)");
 166                 goto sigsegv;
 167         }
 168
 169         tsk = current;
 170
 171         /*
 172          * Check for access_ok violations and find the syscall nr.
 173          *
 174          * NULL is a valid user pointer (in the access_ok sense) on 32-bit and
 175          * 64-bit, so we don't need to special-case it here.  For all the
 176          * vsyscalls, NULL means "don't write anything" not "write it at
 177          * address 0".
 178          */
 179         switch (vsyscall_nr) {
 180         case 0:
 181                 if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
 182                     !write_ok_or_segv(regs->si, sizeof(struct timezone))) {
 183                         ret = -EFAULT;
 184                         goto check_fault;
 185                 }
 186
 187                 syscall_nr = __NR_gettimeofday;
 188                 break;
 189
 190         case 1:
 191                 if (!write_ok_or_segv(regs->di, sizeof(time_t))) {
 192                         ret = -EFAULT;
 193                         goto check_fault;
 194                 }
 195
 196                 syscall_nr = __NR_time;
 197                 break;
 198
 199         case 2:
 200                 if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
 201                     !write_ok_or_segv(regs->si, sizeof(unsigned))) {
 202                         ret = -EFAULT;
 203                         goto check_fault;
 204                 }
 205
 206                 syscall_nr = __NR_getcpu;
 207                 break;
 208         }
 209
 210         /*
 211          * Handle seccomp.  regs->ip must be the original value.
 212          * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt.
 213          *
 214          * We could optimize the seccomp disabled case, but performance
 215          * here doesn't matter.
 216          */
 217         regs->orig_ax = syscall_nr;
 218         regs->ax = -ENOSYS;
 219         tmp = secure_computing();
 220         if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
 221                 warn_bad_vsyscall(KERN_DEBUG, regs,
 222                                   "seccomp tried to change syscall nr or ip");
 223                 do_exit(SIGSYS);
 224         }
 225         if (tmp)
 226                 goto do_ret;  /* skip requested */
 227
 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         ret = -EFAULT;
 236         switch (vsyscall_nr) {
 237         case 0:
 238                 ret = sys_gettimeofday(
 239                         (struct timeval __user *)regs->di,
 240                         (struct timezone __user *)regs->si);
 241                 break;
 242
 243         case 1:
 244                 ret = sys_time((time_t __user *)regs->di);
 245                 break;
 246
 247         case 2:
 248                 ret = sys_getcpu((unsigned __user *)regs->di,
 249                                  (unsigned __user *)regs->si,
 250                                  NULL);
 251                 break;
 252         }
 253
 254         current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;
 255
 256 check_fault:
 257         if (ret == -EFAULT) {
 258                 /* Bad news -- userspace fed a bad pointer to a vsyscall. */
 259                 warn_bad_vsyscall(KERN_INFO, regs,
 260                                   "vsyscall fault (exploit attempt?)");
 261
 262                 /*
 263                  * If we failed to generate a signal for any reason,
 264                  * generate one here.  (This should be impossible.)
 265                  */
 266                 if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
 267                                  !sigismember(&tsk->pending.signal, SIGSEGV)))
 268                         goto sigsegv;
 269
 270                 return true;  /* Don't emulate the ret. */
 271         }
 272
 273         regs->ax = ret;
 274
 275 do_ret:
 276         /* Emulate a ret instruction. */
 277         regs->ip = caller;
 278         regs->sp += 8;
 279         return true;
 280
 281 sigsegv:
 282         force_sig(SIGSEGV, current);
 283         return true;
 284 }
 285
 286 /*
 287  * Assume __initcall executes before all user space. Hopefully kmod
 288  * doesn't violate that. We'll find out if it does.
 289  */
 290 static void vsyscall_set_cpu(int cpu)
 291 {
 292         unsigned long d;
 293         unsigned long node = 0;
 294 #ifdef CONFIG_NUMA
 295         node = cpu_to_node(cpu);
 296 #endif
 297         if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
 298                 write_rdtscp_aux((node << 12) | cpu);
 299
 300         /*
 301          * Store cpu number in limit so that it can be loaded quickly
 302          * in user space in vgetcpu. (12 bits for the CPU and 8 bits for the node)
 303          */
 304         d = 0x0f40000000000ULL;
 305         d |= cpu;
 306         d |= (node & 0xf) << 12;
 307         d |= (node >> 4) << 48;
 308
 309         write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
 310 }
 311
 312 static void cpu_vsyscall_init(void *arg)
 313 {
 314         /* preemption should be already off */
 315         vsyscall_set_cpu(raw_smp_processor_id());
 316 }
 317
 318 static int
 319 cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
 320 {
 321         long cpu = (long)arg;
 322
 323         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
 324                 smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);
 325
 326         return NOTIFY_DONE;
 327 }
 328
 329 void __init map_vsyscall(void)
 330 {
 331         extern char __vsyscall_page;
 332         unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
 333
 334         __set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
 335                      vsyscall_mode == NATIVE
 336                      ? PAGE_KERNEL_VSYSCALL
 337                      : PAGE_KERNEL_VVAR);
 338         BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
 339                      (unsigned long)VSYSCALL_ADDR);
 340 }
 341
 342 static int __init vsyscall_init(void)
 343 {
 344         cpu_notifier_register_begin();
 345
 346         on_each_cpu(cpu_vsyscall_init, NULL, 1);
 347         /* notifier priority > KVM */
 348         __hotcpu_notifier(cpu_vsyscall_notifier, 30);
 349
 350         cpu_notifier_register_done();
 351
 352         return 0;
 353 }
 354 __initcall(vsyscall_init);