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Linux/arch/x86/kernel/vsyscall_64.c

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  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         printk_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 __cpuinit 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 __cpuinit 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 __cpuinit
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);
403 

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