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1da177e4 | 1 | /* |
95c46b56 AL |
2 | * Copyright (c) 2012-2014 Andy Lutomirski <luto@amacapital.net> |
3 | * | |
4 | * Based on the original implementation which is: | |
1da177e4 LT |
5 | * Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE |
6 | * Copyright 2003 Andi Kleen, SuSE Labs. | |
7 | * | |
95c46b56 AL |
8 | * Parts of the original code have been moved to arch/x86/vdso/vma.c |
9 | * | |
10 | * This file implements vsyscall emulation. vsyscalls are a legacy ABI: | |
11 | * Userspace can request certain kernel services by calling fixed | |
12 | * addresses. This concept is problematic: | |
5cec93c2 | 13 | * |
95c46b56 AL |
14 | * - It interferes with ASLR. |
15 | * - It's awkward to write code that lives in kernel addresses but is | |
16 | * callable by userspace at fixed addresses. | |
17 | * - The whole concept is impossible for 32-bit compat userspace. | |
18 | * - UML cannot easily virtualize a vsyscall. | |
1da177e4 | 19 | * |
95c46b56 AL |
20 | * As of mid-2014, I believe that there is no new userspace code that |
21 | * will use a vsyscall if the vDSO is present. I hope that there will | |
22 | * soon be no new userspace code that will ever use a vsyscall. | |
1da177e4 | 23 | * |
95c46b56 AL |
24 | * The code in this file emulates vsyscalls when notified of a page |
25 | * fault to a vsyscall address. | |
1da177e4 LT |
26 | */ |
27 | ||
1da177e4 LT |
28 | #include <linux/kernel.h> |
29 | #include <linux/timer.h> | |
3f07c014 | 30 | #include <linux/sched/signal.h> |
589ee628 | 31 | #include <linux/mm_types.h> |
5cec93c2 AL |
32 | #include <linux/syscalls.h> |
33 | #include <linux/ratelimit.h> | |
1da177e4 LT |
34 | |
35 | #include <asm/vsyscall.h> | |
7460ed28 | 36 | #include <asm/unistd.h> |
1da177e4 | 37 | #include <asm/fixmap.h> |
5cec93c2 | 38 | #include <asm/traps.h> |
1da177e4 | 39 | |
c149a665 AL |
40 | #define CREATE_TRACE_POINTS |
41 | #include "vsyscall_trace.h" | |
42 | ||
3dc33bd3 | 43 | static enum { EMULATE, NATIVE, NONE } vsyscall_mode = |
93f13a9f | 44 | #if defined(CONFIG_LEGACY_VSYSCALL_NATIVE) |
3dc33bd3 | 45 | NATIVE; |
93f13a9f | 46 | #elif defined(CONFIG_LEGACY_VSYSCALL_NONE) |
3dc33bd3 KC |
47 | NONE; |
48 | #else | |
49 | EMULATE; | |
50 | #endif | |
3ae36655 AL |
51 | |
52 | static int __init vsyscall_setup(char *str) | |
53 | { | |
54 | if (str) { | |
55 | if (!strcmp("emulate", str)) | |
56 | vsyscall_mode = EMULATE; | |
57 | else if (!strcmp("native", str)) | |
58 | vsyscall_mode = NATIVE; | |
59 | else if (!strcmp("none", str)) | |
60 | vsyscall_mode = NONE; | |
61 | else | |
62 | return -EINVAL; | |
63 | ||
64 | return 0; | |
65 | } | |
66 | ||
67 | return -EINVAL; | |
68 | } | |
69 | early_param("vsyscall", vsyscall_setup); | |
70 | ||
5cec93c2 AL |
71 | static void warn_bad_vsyscall(const char *level, struct pt_regs *regs, |
72 | const char *message) | |
1da177e4 | 73 | { |
c767a54b | 74 | if (!show_unhandled_signals) |
5cec93c2 | 75 | return; |
1da177e4 | 76 | |
53b884ac AL |
77 | printk_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n", |
78 | level, current->comm, task_pid_nr(current), | |
79 | message, regs->ip, regs->cs, | |
80 | regs->sp, regs->ax, regs->si, regs->di); | |
c9712944 AL |
81 | } |
82 | ||
83 | static int addr_to_vsyscall_nr(unsigned long addr) | |
84 | { | |
85 | int nr; | |
86 | ||
f40c3300 | 87 | if ((addr & ~0xC00UL) != VSYSCALL_ADDR) |
c9712944 AL |
88 | return -EINVAL; |
89 | ||
90 | nr = (addr & 0xC00UL) >> 10; | |
91 | if (nr >= 3) | |
92 | return -EINVAL; | |
93 | ||
94 | return nr; | |
1da177e4 LT |
95 | } |
96 | ||
4fc34901 AL |
97 | static bool write_ok_or_segv(unsigned long ptr, size_t size) |
98 | { | |
99 | /* | |
100 | * XXX: if access_ok, get_user, and put_user handled | |
2a53ccbc | 101 | * sig_on_uaccess_err, this could go away. |
4fc34901 AL |
102 | */ |
103 | ||
104 | if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) { | |
105 | siginfo_t info; | |
106 | struct thread_struct *thread = ¤t->thread; | |
107 | ||
108 | thread->error_code = 6; /* user fault, no page, write */ | |
109 | thread->cr2 = ptr; | |
51e7dc70 | 110 | thread->trap_nr = X86_TRAP_PF; |
4fc34901 AL |
111 | |
112 | memset(&info, 0, sizeof(info)); | |
113 | info.si_signo = SIGSEGV; | |
114 | info.si_errno = 0; | |
115 | info.si_code = SEGV_MAPERR; | |
116 | info.si_addr = (void __user *)ptr; | |
117 | ||
118 | force_sig_info(SIGSEGV, &info, current); | |
119 | return false; | |
120 | } else { | |
121 | return true; | |
122 | } | |
123 | } | |
124 | ||
3ae36655 | 125 | bool emulate_vsyscall(struct pt_regs *regs, unsigned long address) |
1da177e4 | 126 | { |
5cec93c2 AL |
127 | struct task_struct *tsk; |
128 | unsigned long caller; | |
87b526d3 | 129 | int vsyscall_nr, syscall_nr, tmp; |
2a53ccbc | 130 | int prev_sig_on_uaccess_err; |
5cec93c2 AL |
131 | long ret; |
132 | ||
3ae36655 AL |
133 | /* |
134 | * No point in checking CS -- the only way to get here is a user mode | |
135 | * trap to a high address, which means that we're in 64-bit user code. | |
136 | */ | |
5cec93c2 | 137 | |
3ae36655 | 138 | WARN_ON_ONCE(address != regs->ip); |
c9712944 | 139 | |
3ae36655 AL |
140 | if (vsyscall_mode == NONE) { |
141 | warn_bad_vsyscall(KERN_INFO, regs, | |
142 | "vsyscall attempted with vsyscall=none"); | |
143 | return false; | |
c9712944 AL |
144 | } |
145 | ||
3ae36655 | 146 | vsyscall_nr = addr_to_vsyscall_nr(address); |
c149a665 AL |
147 | |
148 | trace_emulate_vsyscall(vsyscall_nr); | |
149 | ||
c9712944 AL |
150 | if (vsyscall_nr < 0) { |
151 | warn_bad_vsyscall(KERN_WARNING, regs, | |
3ae36655 | 152 | "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround"); |
5cec93c2 AL |
153 | goto sigsegv; |
154 | } | |
d0aff6e6 | 155 | |
5cec93c2 | 156 | if (get_user(caller, (unsigned long __user *)regs->sp) != 0) { |
3ae36655 AL |
157 | warn_bad_vsyscall(KERN_WARNING, regs, |
158 | "vsyscall with bad stack (exploit attempt?)"); | |
5cec93c2 AL |
159 | goto sigsegv; |
160 | } | |
8c73626a | 161 | |
5cec93c2 | 162 | tsk = current; |
4fc34901 AL |
163 | |
164 | /* | |
87b526d3 AL |
165 | * Check for access_ok violations and find the syscall nr. |
166 | * | |
46ed99d1 | 167 | * NULL is a valid user pointer (in the access_ok sense) on 32-bit and |
4fc34901 | 168 | * 64-bit, so we don't need to special-case it here. For all the |
46ed99d1 | 169 | * vsyscalls, NULL means "don't write anything" not "write it at |
4fc34901 AL |
170 | * address 0". |
171 | */ | |
5cec93c2 AL |
172 | switch (vsyscall_nr) { |
173 | case 0: | |
4fc34901 | 174 | if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) || |
87b526d3 AL |
175 | !write_ok_or_segv(regs->si, sizeof(struct timezone))) { |
176 | ret = -EFAULT; | |
177 | goto check_fault; | |
178 | } | |
4fc34901 | 179 | |
87b526d3 AL |
180 | syscall_nr = __NR_gettimeofday; |
181 | break; | |
182 | ||
183 | case 1: | |
184 | if (!write_ok_or_segv(regs->di, sizeof(time_t))) { | |
185 | ret = -EFAULT; | |
186 | goto check_fault; | |
187 | } | |
188 | ||
189 | syscall_nr = __NR_time; | |
190 | break; | |
191 | ||
192 | case 2: | |
193 | if (!write_ok_or_segv(regs->di, sizeof(unsigned)) || | |
194 | !write_ok_or_segv(regs->si, sizeof(unsigned))) { | |
195 | ret = -EFAULT; | |
196 | goto check_fault; | |
197 | } | |
198 | ||
199 | syscall_nr = __NR_getcpu; | |
200 | break; | |
201 | } | |
202 | ||
203 | /* | |
204 | * Handle seccomp. regs->ip must be the original value. | |
205 | * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt. | |
206 | * | |
207 | * We could optimize the seccomp disabled case, but performance | |
208 | * here doesn't matter. | |
209 | */ | |
210 | regs->orig_ax = syscall_nr; | |
211 | regs->ax = -ENOSYS; | |
2f275de5 | 212 | tmp = secure_computing(NULL); |
87b526d3 AL |
213 | if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) { |
214 | warn_bad_vsyscall(KERN_DEBUG, regs, | |
215 | "seccomp tried to change syscall nr or ip"); | |
216 | do_exit(SIGSYS); | |
217 | } | |
26893107 | 218 | regs->orig_ax = -1; |
87b526d3 AL |
219 | if (tmp) |
220 | goto do_ret; /* skip requested */ | |
221 | ||
222 | /* | |
223 | * With a real vsyscall, page faults cause SIGSEGV. We want to | |
224 | * preserve that behavior to make writing exploits harder. | |
225 | */ | |
2a53ccbc IM |
226 | prev_sig_on_uaccess_err = current->thread.sig_on_uaccess_err; |
227 | current->thread.sig_on_uaccess_err = 1; | |
87b526d3 AL |
228 | |
229 | ret = -EFAULT; | |
230 | switch (vsyscall_nr) { | |
231 | case 0: | |
5cec93c2 AL |
232 | ret = sys_gettimeofday( |
233 | (struct timeval __user *)regs->di, | |
234 | (struct timezone __user *)regs->si); | |
235 | break; | |
236 | ||
237 | case 1: | |
5cec93c2 AL |
238 | ret = sys_time((time_t __user *)regs->di); |
239 | break; | |
240 | ||
241 | case 2: | |
5cec93c2 AL |
242 | ret = sys_getcpu((unsigned __user *)regs->di, |
243 | (unsigned __user *)regs->si, | |
46ed99d1 | 244 | NULL); |
5cec93c2 | 245 | break; |
5cec93c2 | 246 | } |
8c73626a | 247 | |
2a53ccbc | 248 | current->thread.sig_on_uaccess_err = prev_sig_on_uaccess_err; |
4fc34901 | 249 | |
87b526d3 | 250 | check_fault: |
5cec93c2 | 251 | if (ret == -EFAULT) { |
4fc34901 | 252 | /* Bad news -- userspace fed a bad pointer to a vsyscall. */ |
5cec93c2 AL |
253 | warn_bad_vsyscall(KERN_INFO, regs, |
254 | "vsyscall fault (exploit attempt?)"); | |
4fc34901 AL |
255 | |
256 | /* | |
257 | * If we failed to generate a signal for any reason, | |
258 | * generate one here. (This should be impossible.) | |
259 | */ | |
260 | if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) && | |
261 | !sigismember(&tsk->pending.signal, SIGSEGV))) | |
262 | goto sigsegv; | |
263 | ||
264 | return true; /* Don't emulate the ret. */ | |
5cec93c2 | 265 | } |
8c73626a | 266 | |
5cec93c2 | 267 | regs->ax = ret; |
1da177e4 | 268 | |
5651721e | 269 | do_ret: |
5cec93c2 AL |
270 | /* Emulate a ret instruction. */ |
271 | regs->ip = caller; | |
272 | regs->sp += 8; | |
3ae36655 | 273 | return true; |
5cec93c2 AL |
274 | |
275 | sigsegv: | |
5cec93c2 | 276 | force_sig(SIGSEGV, current); |
3ae36655 | 277 | return true; |
1da177e4 LT |
278 | } |
279 | ||
b9359090 AL |
280 | /* |
281 | * A pseudo VMA to allow ptrace access for the vsyscall page. This only | |
282 | * covers the 64bit vsyscall page now. 32bit has a real VMA now and does | |
283 | * not need special handling anymore: | |
284 | */ | |
285 | static const char *gate_vma_name(struct vm_area_struct *vma) | |
286 | { | |
287 | return "[vsyscall]"; | |
288 | } | |
7cbea8dc | 289 | static const struct vm_operations_struct gate_vma_ops = { |
b9359090 AL |
290 | .name = gate_vma_name, |
291 | }; | |
292 | static struct vm_area_struct gate_vma = { | |
293 | .vm_start = VSYSCALL_ADDR, | |
294 | .vm_end = VSYSCALL_ADDR + PAGE_SIZE, | |
295 | .vm_page_prot = PAGE_READONLY_EXEC, | |
296 | .vm_flags = VM_READ | VM_EXEC, | |
297 | .vm_ops = &gate_vma_ops, | |
298 | }; | |
299 | ||
300 | struct vm_area_struct *get_gate_vma(struct mm_struct *mm) | |
301 | { | |
c338867d | 302 | #ifdef CONFIG_COMPAT |
b9359090 AL |
303 | if (!mm || mm->context.ia32_compat) |
304 | return NULL; | |
305 | #endif | |
87983c66 AL |
306 | if (vsyscall_mode == NONE) |
307 | return NULL; | |
b9359090 AL |
308 | return &gate_vma; |
309 | } | |
310 | ||
311 | int in_gate_area(struct mm_struct *mm, unsigned long addr) | |
312 | { | |
313 | struct vm_area_struct *vma = get_gate_vma(mm); | |
314 | ||
315 | if (!vma) | |
316 | return 0; | |
317 | ||
318 | return (addr >= vma->vm_start) && (addr < vma->vm_end); | |
319 | } | |
320 | ||
321 | /* | |
322 | * Use this when you have no reliable mm, typically from interrupt | |
323 | * context. It is less reliable than using a task's mm and may give | |
324 | * false positives. | |
325 | */ | |
326 | int in_gate_area_no_mm(unsigned long addr) | |
327 | { | |
87983c66 | 328 | return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR; |
b9359090 AL |
329 | } |
330 | ||
e4026440 | 331 | void __init map_vsyscall(void) |
1da177e4 | 332 | { |
3ae36655 AL |
333 | extern char __vsyscall_page; |
334 | unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page); | |
1da177e4 | 335 | |
87983c66 AL |
336 | if (vsyscall_mode != NONE) |
337 | __set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall, | |
338 | vsyscall_mode == NATIVE | |
339 | ? PAGE_KERNEL_VSYSCALL | |
340 | : PAGE_KERNEL_VVAR); | |
341 | ||
f40c3300 AL |
342 | BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) != |
343 | (unsigned long)VSYSCALL_ADDR); | |
1da177e4 | 344 | } |