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 #include <linux/time.h>
22 #include <linux/init.h>
23 #include <linux/kernel.h>
24 #include <linux/timer.h>
25 #include <linux/seqlock.h>
26 #include <linux/jiffies.h>
27 #include <linux/sysctl.h>
28 #include <linux/topology.h>
29 #include <linux/clocksource.h>
30 #include <linux/getcpu.h>
31 #include <linux/cpu.h>
32 #include <linux/smp.h>
33 #include <linux/notifier.h>
34 #include <linux/syscalls.h>
35 #include <linux/ratelimit.h>
36
37 #include <asm/vsyscall.h>
38 #include <asm/pgtable.h>
39 #include <asm/compat.h>
40 #include <asm/page.h>
41 #include <asm/unistd.h>
42 #include <asm/fixmap.h>
43 #include <asm/errno.h>
44 #include <asm/io.h>
45 #include <asm/segment.h>
46 #include <asm/desc.h>
47 #include <asm/topology.h>
48 #include <asm/vgtod.h>
49 #include <asm/traps.h>
50
51 #define CREATE_TRACE_POINTS
52 #include "vsyscall_trace.h"
53
54 DEFINE_VVAR(int, vgetcpu_mode);
55 DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
56 {
57 .lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
58 };
59
60 static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
61
vsyscall_setup(char * str)62 static int __init vsyscall_setup(char *str)
63 {
64 if (str) {
65 if (!strcmp("emulate", str))
66 vsyscall_mode = EMULATE;
67 else if (!strcmp("native", str))
68 vsyscall_mode = NATIVE;
69 else if (!strcmp("none", str))
70 vsyscall_mode = NONE;
71 else
72 return -EINVAL;
73
74 return 0;
75 }
76
77 return -EINVAL;
78 }
79 early_param("vsyscall", vsyscall_setup);
80
update_vsyscall_tz(void)81 void update_vsyscall_tz(void)
82 {
83 unsigned long flags;
84
85 write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
86 /* sys_tz has changed */
87 vsyscall_gtod_data.sys_tz = sys_tz;
88 write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
89 }
90
update_vsyscall(struct timespec * wall_time,struct timespec * wtm,struct clocksource * clock,u32 mult)91 void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
92 struct clocksource *clock, u32 mult)
93 {
94 unsigned long flags;
95
96 write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
97
98 /* copy vsyscall data */
99 vsyscall_gtod_data.clock.vclock_mode = clock->archdata.vclock_mode;
100 vsyscall_gtod_data.clock.cycle_last = clock->cycle_last;
101 vsyscall_gtod_data.clock.mask = clock->mask;
102 vsyscall_gtod_data.clock.mult = mult;
103 vsyscall_gtod_data.clock.shift = clock->shift;
104 vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
105 vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
106 vsyscall_gtod_data.wall_to_monotonic = *wtm;
107 vsyscall_gtod_data.wall_time_coarse = __current_kernel_time();
108
109 write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
110 }
111
warn_bad_vsyscall(const char * level,struct pt_regs * regs,const char * message)112 static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
113 const char *message)
114 {
115 static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);
116 struct task_struct *tsk;
117
118 if (!show_unhandled_signals || !__ratelimit(&rs))
119 return;
120
121 tsk = current;
122
123 printk("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
124 level, tsk->comm, task_pid_nr(tsk),
125 message, regs->ip, regs->cs,
126 regs->sp, regs->ax, regs->si, regs->di);
127 }
128
addr_to_vsyscall_nr(unsigned long addr)129 static int addr_to_vsyscall_nr(unsigned long addr)
130 {
131 int nr;
132
133 if ((addr & ~0xC00UL) != VSYSCALL_START)
134 return -EINVAL;
135
136 nr = (addr & 0xC00UL) >> 10;
137 if (nr >= 3)
138 return -EINVAL;
139
140 return nr;
141 }
142
write_ok_or_segv(unsigned long ptr,size_t size)143 static bool write_ok_or_segv(unsigned long ptr, size_t size)
144 {
145 /*
146 * XXX: if access_ok, get_user, and put_user handled
147 * sig_on_uaccess_error, this could go away.
148 */
149
150 if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
151 siginfo_t info;
152 struct thread_struct *thread = ¤t->thread;
153
154 thread->error_code = 6; /* user fault, no page, write */
155 thread->cr2 = ptr;
156 thread->trap_no = 14;
157
158 memset(&info, 0, sizeof(info));
159 info.si_signo = SIGSEGV;
160 info.si_errno = 0;
161 info.si_code = SEGV_MAPERR;
162 info.si_addr = (void __user *)ptr;
163
164 force_sig_info(SIGSEGV, &info, current);
165 return false;
166 } else {
167 return true;
168 }
169 }
170
emulate_vsyscall(struct pt_regs * regs,unsigned long address)171 bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
172 {
173 struct task_struct *tsk;
174 unsigned long caller;
175 int vsyscall_nr;
176 int prev_sig_on_uaccess_error;
177 long ret;
178
179 /*
180 * No point in checking CS -- the only way to get here is a user mode
181 * trap to a high address, which means that we're in 64-bit user code.
182 */
183
184 WARN_ON_ONCE(address != regs->ip);
185
186 if (vsyscall_mode == NONE) {
187 warn_bad_vsyscall(KERN_INFO, regs,
188 "vsyscall attempted with vsyscall=none");
189 return false;
190 }
191
192 vsyscall_nr = addr_to_vsyscall_nr(address);
193
194 trace_emulate_vsyscall(vsyscall_nr);
195
196 if (vsyscall_nr < 0) {
197 warn_bad_vsyscall(KERN_WARNING, regs,
198 "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
199 goto sigsegv;
200 }
201
202 if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
203 warn_bad_vsyscall(KERN_WARNING, regs,
204 "vsyscall with bad stack (exploit attempt?)");
205 goto sigsegv;
206 }
207
208 tsk = current;
209 if (seccomp_mode(&tsk->seccomp))
210 do_exit(SIGKILL);
211
212 /*
213 * With a real vsyscall, page faults cause SIGSEGV. We want to
214 * preserve that behavior to make writing exploits harder.
215 */
216 prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
217 current_thread_info()->sig_on_uaccess_error = 1;
218
219 /*
220 * 0 is a valid user pointer (in the access_ok sense) on 32-bit and
221 * 64-bit, so we don't need to special-case it here. For all the
222 * vsyscalls, 0 means "don't write anything" not "write it at
223 * address 0".
224 */
225 ret = -EFAULT;
226 switch (vsyscall_nr) {
227 case 0:
228 if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
229 !write_ok_or_segv(regs->si, sizeof(struct timezone)))
230 break;
231
232 ret = sys_gettimeofday(
233 (struct timeval __user *)regs->di,
234 (struct timezone __user *)regs->si);
235 break;
236
237 case 1:
238 if (!write_ok_or_segv(regs->di, sizeof(time_t)))
239 break;
240
241 ret = sys_time((time_t __user *)regs->di);
242 break;
243
244 case 2:
245 if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
246 !write_ok_or_segv(regs->si, sizeof(unsigned)))
247 break;
248
249 ret = sys_getcpu((unsigned __user *)regs->di,
250 (unsigned __user *)regs->si,
251 0);
252 break;
253 }
254
255 current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;
256
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 /* Emulate a ret instruction. */
276 regs->ip = caller;
277 regs->sp += 8;
278
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 */
vsyscall_set_cpu(int cpu)290 static void __cpuinit 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
cpu_vsyscall_init(void * arg)312 static void __cpuinit 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 __cpuinit
cpu_vsyscall_notifier(struct notifier_block * n,unsigned long action,void * arg)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
map_vsyscall(void)329 void __init map_vsyscall(void)
330 {
331 extern char __vsyscall_page;
332 unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
333 extern char __vvar_page;
334 unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);
335
336 __set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_vsyscall,
337 vsyscall_mode == NATIVE
338 ? PAGE_KERNEL_VSYSCALL
339 : PAGE_KERNEL_VVAR);
340 BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_FIRST_PAGE) !=
341 (unsigned long)VSYSCALL_START);
342
343 __set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
344 BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) !=
345 (unsigned long)VVAR_ADDRESS);
346 }
347
vsyscall_init(void)348 static int __init vsyscall_init(void)
349 {
350 BUG_ON(VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE));
351
352 on_each_cpu(cpu_vsyscall_init, NULL, 1);
353 /* notifier priority > KVM */
354 hotcpu_notifier(cpu_vsyscall_notifier, 30);
355
356 return 0;
357 }
358 __initcall(vsyscall_init);
359