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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> | |
5cec93c2 AL |
30 | #include <linux/syscalls.h> |
31 | #include <linux/ratelimit.h> | |
1da177e4 LT |
32 | |
33 | #include <asm/vsyscall.h> | |
7460ed28 | 34 | #include <asm/unistd.h> |
1da177e4 | 35 | #include <asm/fixmap.h> |
5cec93c2 | 36 | #include <asm/traps.h> |
1da177e4 | 37 | |
c149a665 AL |
38 | #define CREATE_TRACE_POINTS |
39 | #include "vsyscall_trace.h" | |
40 | ||
2e57ae05 | 41 | static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE; |
3ae36655 AL |
42 | |
43 | static int __init vsyscall_setup(char *str) | |
44 | { | |
45 | if (str) { | |
46 | if (!strcmp("emulate", str)) | |
47 | vsyscall_mode = EMULATE; | |
48 | else if (!strcmp("native", str)) | |
49 | vsyscall_mode = NATIVE; | |
50 | else if (!strcmp("none", str)) | |
51 | vsyscall_mode = NONE; | |
52 | else | |
53 | return -EINVAL; | |
54 | ||
55 | return 0; | |
56 | } | |
57 | ||
58 | return -EINVAL; | |
59 | } | |
60 | early_param("vsyscall", vsyscall_setup); | |
61 | ||
5cec93c2 AL |
62 | static void warn_bad_vsyscall(const char *level, struct pt_regs *regs, |
63 | const char *message) | |
1da177e4 | 64 | { |
c767a54b | 65 | if (!show_unhandled_signals) |
5cec93c2 | 66 | return; |
1da177e4 | 67 | |
53b884ac AL |
68 | printk_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n", |
69 | level, current->comm, task_pid_nr(current), | |
70 | message, regs->ip, regs->cs, | |
71 | regs->sp, regs->ax, regs->si, regs->di); | |
c9712944 AL |
72 | } |
73 | ||
74 | static int addr_to_vsyscall_nr(unsigned long addr) | |
75 | { | |
76 | int nr; | |
77 | ||
f40c3300 | 78 | if ((addr & ~0xC00UL) != VSYSCALL_ADDR) |
c9712944 AL |
79 | return -EINVAL; |
80 | ||
81 | nr = (addr & 0xC00UL) >> 10; | |
82 | if (nr >= 3) | |
83 | return -EINVAL; | |
84 | ||
85 | return nr; | |
1da177e4 LT |
86 | } |
87 | ||
4fc34901 AL |
88 | static bool write_ok_or_segv(unsigned long ptr, size_t size) |
89 | { | |
90 | /* | |
91 | * XXX: if access_ok, get_user, and put_user handled | |
92 | * sig_on_uaccess_error, this could go away. | |
93 | */ | |
94 | ||
95 | if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) { | |
96 | siginfo_t info; | |
97 | struct thread_struct *thread = ¤t->thread; | |
98 | ||
99 | thread->error_code = 6; /* user fault, no page, write */ | |
100 | thread->cr2 = ptr; | |
51e7dc70 | 101 | thread->trap_nr = X86_TRAP_PF; |
4fc34901 AL |
102 | |
103 | memset(&info, 0, sizeof(info)); | |
104 | info.si_signo = SIGSEGV; | |
105 | info.si_errno = 0; | |
106 | info.si_code = SEGV_MAPERR; | |
107 | info.si_addr = (void __user *)ptr; | |
108 | ||
109 | force_sig_info(SIGSEGV, &info, current); | |
110 | return false; | |
111 | } else { | |
112 | return true; | |
113 | } | |
114 | } | |
115 | ||
3ae36655 | 116 | bool emulate_vsyscall(struct pt_regs *regs, unsigned long address) |
1da177e4 | 117 | { |
5cec93c2 AL |
118 | struct task_struct *tsk; |
119 | unsigned long caller; | |
87b526d3 | 120 | int vsyscall_nr, syscall_nr, tmp; |
4fc34901 | 121 | int prev_sig_on_uaccess_error; |
5cec93c2 AL |
122 | long ret; |
123 | ||
3ae36655 AL |
124 | /* |
125 | * No point in checking CS -- the only way to get here is a user mode | |
126 | * trap to a high address, which means that we're in 64-bit user code. | |
127 | */ | |
5cec93c2 | 128 | |
3ae36655 | 129 | WARN_ON_ONCE(address != regs->ip); |
c9712944 | 130 | |
3ae36655 AL |
131 | if (vsyscall_mode == NONE) { |
132 | warn_bad_vsyscall(KERN_INFO, regs, | |
133 | "vsyscall attempted with vsyscall=none"); | |
134 | return false; | |
c9712944 AL |
135 | } |
136 | ||
3ae36655 | 137 | vsyscall_nr = addr_to_vsyscall_nr(address); |
c149a665 AL |
138 | |
139 | trace_emulate_vsyscall(vsyscall_nr); | |
140 | ||
c9712944 AL |
141 | if (vsyscall_nr < 0) { |
142 | warn_bad_vsyscall(KERN_WARNING, regs, | |
3ae36655 | 143 | "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround"); |
5cec93c2 AL |
144 | goto sigsegv; |
145 | } | |
d0aff6e6 | 146 | |
5cec93c2 | 147 | if (get_user(caller, (unsigned long __user *)regs->sp) != 0) { |
3ae36655 AL |
148 | warn_bad_vsyscall(KERN_WARNING, regs, |
149 | "vsyscall with bad stack (exploit attempt?)"); | |
5cec93c2 AL |
150 | goto sigsegv; |
151 | } | |
8c73626a | 152 | |
5cec93c2 | 153 | tsk = current; |
4fc34901 AL |
154 | |
155 | /* | |
87b526d3 AL |
156 | * Check for access_ok violations and find the syscall nr. |
157 | * | |
46ed99d1 | 158 | * NULL is a valid user pointer (in the access_ok sense) on 32-bit and |
4fc34901 | 159 | * 64-bit, so we don't need to special-case it here. For all the |
46ed99d1 | 160 | * vsyscalls, NULL means "don't write anything" not "write it at |
4fc34901 AL |
161 | * address 0". |
162 | */ | |
5cec93c2 AL |
163 | switch (vsyscall_nr) { |
164 | case 0: | |
4fc34901 | 165 | if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) || |
87b526d3 AL |
166 | !write_ok_or_segv(regs->si, sizeof(struct timezone))) { |
167 | ret = -EFAULT; | |
168 | goto check_fault; | |
169 | } | |
4fc34901 | 170 | |
87b526d3 AL |
171 | syscall_nr = __NR_gettimeofday; |
172 | break; | |
173 | ||
174 | case 1: | |
175 | if (!write_ok_or_segv(regs->di, sizeof(time_t))) { | |
176 | ret = -EFAULT; | |
177 | goto check_fault; | |
178 | } | |
179 | ||
180 | syscall_nr = __NR_time; | |
181 | break; | |
182 | ||
183 | case 2: | |
184 | if (!write_ok_or_segv(regs->di, sizeof(unsigned)) || | |
185 | !write_ok_or_segv(regs->si, sizeof(unsigned))) { | |
186 | ret = -EFAULT; | |
187 | goto check_fault; | |
188 | } | |
189 | ||
190 | syscall_nr = __NR_getcpu; | |
191 | break; | |
192 | } | |
193 | ||
194 | /* | |
195 | * Handle seccomp. regs->ip must be the original value. | |
196 | * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt. | |
197 | * | |
198 | * We could optimize the seccomp disabled case, but performance | |
199 | * here doesn't matter. | |
200 | */ | |
201 | regs->orig_ax = syscall_nr; | |
202 | regs->ax = -ENOSYS; | |
a4412fc9 | 203 | tmp = secure_computing(); |
87b526d3 AL |
204 | if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) { |
205 | warn_bad_vsyscall(KERN_DEBUG, regs, | |
206 | "seccomp tried to change syscall nr or ip"); | |
207 | do_exit(SIGSYS); | |
208 | } | |
26893107 | 209 | regs->orig_ax = -1; |
87b526d3 AL |
210 | if (tmp) |
211 | goto do_ret; /* skip requested */ | |
212 | ||
213 | /* | |
214 | * With a real vsyscall, page faults cause SIGSEGV. We want to | |
215 | * preserve that behavior to make writing exploits harder. | |
216 | */ | |
217 | prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error; | |
218 | current_thread_info()->sig_on_uaccess_error = 1; | |
219 | ||
220 | ret = -EFAULT; | |
221 | switch (vsyscall_nr) { | |
222 | case 0: | |
5cec93c2 AL |
223 | ret = sys_gettimeofday( |
224 | (struct timeval __user *)regs->di, | |
225 | (struct timezone __user *)regs->si); | |
226 | break; | |
227 | ||
228 | case 1: | |
5cec93c2 AL |
229 | ret = sys_time((time_t __user *)regs->di); |
230 | break; | |
231 | ||
232 | case 2: | |
5cec93c2 AL |
233 | ret = sys_getcpu((unsigned __user *)regs->di, |
234 | (unsigned __user *)regs->si, | |
46ed99d1 | 235 | NULL); |
5cec93c2 | 236 | break; |
5cec93c2 | 237 | } |
8c73626a | 238 | |
4fc34901 AL |
239 | current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error; |
240 | ||
87b526d3 | 241 | check_fault: |
5cec93c2 | 242 | if (ret == -EFAULT) { |
4fc34901 | 243 | /* Bad news -- userspace fed a bad pointer to a vsyscall. */ |
5cec93c2 AL |
244 | warn_bad_vsyscall(KERN_INFO, regs, |
245 | "vsyscall fault (exploit attempt?)"); | |
4fc34901 AL |
246 | |
247 | /* | |
248 | * If we failed to generate a signal for any reason, | |
249 | * generate one here. (This should be impossible.) | |
250 | */ | |
251 | if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) && | |
252 | !sigismember(&tsk->pending.signal, SIGSEGV))) | |
253 | goto sigsegv; | |
254 | ||
255 | return true; /* Don't emulate the ret. */ | |
5cec93c2 | 256 | } |
8c73626a | 257 | |
5cec93c2 | 258 | regs->ax = ret; |
1da177e4 | 259 | |
5651721e | 260 | do_ret: |
5cec93c2 AL |
261 | /* Emulate a ret instruction. */ |
262 | regs->ip = caller; | |
263 | regs->sp += 8; | |
3ae36655 | 264 | return true; |
5cec93c2 AL |
265 | |
266 | sigsegv: | |
5cec93c2 | 267 | force_sig(SIGSEGV, current); |
3ae36655 | 268 | return true; |
1da177e4 LT |
269 | } |
270 | ||
b9359090 AL |
271 | /* |
272 | * A pseudo VMA to allow ptrace access for the vsyscall page. This only | |
273 | * covers the 64bit vsyscall page now. 32bit has a real VMA now and does | |
274 | * not need special handling anymore: | |
275 | */ | |
276 | static const char *gate_vma_name(struct vm_area_struct *vma) | |
277 | { | |
278 | return "[vsyscall]"; | |
279 | } | |
280 | static struct vm_operations_struct gate_vma_ops = { | |
281 | .name = gate_vma_name, | |
282 | }; | |
283 | static struct vm_area_struct gate_vma = { | |
284 | .vm_start = VSYSCALL_ADDR, | |
285 | .vm_end = VSYSCALL_ADDR + PAGE_SIZE, | |
286 | .vm_page_prot = PAGE_READONLY_EXEC, | |
287 | .vm_flags = VM_READ | VM_EXEC, | |
288 | .vm_ops = &gate_vma_ops, | |
289 | }; | |
290 | ||
291 | struct vm_area_struct *get_gate_vma(struct mm_struct *mm) | |
292 | { | |
293 | #ifdef CONFIG_IA32_EMULATION | |
294 | if (!mm || mm->context.ia32_compat) | |
295 | return NULL; | |
296 | #endif | |
87983c66 AL |
297 | if (vsyscall_mode == NONE) |
298 | return NULL; | |
b9359090 AL |
299 | return &gate_vma; |
300 | } | |
301 | ||
302 | int in_gate_area(struct mm_struct *mm, unsigned long addr) | |
303 | { | |
304 | struct vm_area_struct *vma = get_gate_vma(mm); | |
305 | ||
306 | if (!vma) | |
307 | return 0; | |
308 | ||
309 | return (addr >= vma->vm_start) && (addr < vma->vm_end); | |
310 | } | |
311 | ||
312 | /* | |
313 | * Use this when you have no reliable mm, typically from interrupt | |
314 | * context. It is less reliable than using a task's mm and may give | |
315 | * false positives. | |
316 | */ | |
317 | int in_gate_area_no_mm(unsigned long addr) | |
318 | { | |
87983c66 | 319 | return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR; |
b9359090 AL |
320 | } |
321 | ||
e4026440 | 322 | void __init map_vsyscall(void) |
1da177e4 | 323 | { |
3ae36655 AL |
324 | extern char __vsyscall_page; |
325 | unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page); | |
1da177e4 | 326 | |
87983c66 AL |
327 | if (vsyscall_mode != NONE) |
328 | __set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall, | |
329 | vsyscall_mode == NATIVE | |
330 | ? PAGE_KERNEL_VSYSCALL | |
331 | : PAGE_KERNEL_VVAR); | |
332 | ||
f40c3300 AL |
333 | BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) != |
334 | (unsigned long)VSYSCALL_ADDR); | |
1da177e4 | 335 | } |