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1 /*
2  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
3  * Licensed under the GPL
4  */
5 
6 #include <linux/mm.h>
7 #include <linux/sched.h>
8 #include <linux/hardirq.h>
9 #include <linux/module.h>
10 #include <linux/uaccess.h>
11 #include <asm/current.h>
12 #include <asm/pgtable.h>
13 #include <asm/tlbflush.h>
14 #include <arch.h>
15 #include <as-layout.h>
16 #include <kern_util.h>
17 #include <os.h>
18 #include <skas.h>
19 
20 /*
21  * Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by
22  * segv().
23  */
handle_page_fault(unsigned long address,unsigned long ip,int is_write,int is_user,int * code_out)24 int handle_page_fault(unsigned long address, unsigned long ip,
25 		      int is_write, int is_user, int *code_out)
26 {
27 	struct mm_struct *mm = current->mm;
28 	struct vm_area_struct *vma;
29 	pgd_t *pgd;
30 	pud_t *pud;
31 	pmd_t *pmd;
32 	pte_t *pte;
33 	int err = -EFAULT;
34 	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
35 
36 	*code_out = SEGV_MAPERR;
37 
38 	/*
39 	 * If the fault was with pagefaults disabled, don't take the fault, just
40 	 * fail.
41 	 */
42 	if (faulthandler_disabled())
43 		goto out_nosemaphore;
44 
45 	if (is_user)
46 		flags |= FAULT_FLAG_USER;
47 retry:
48 	down_read(&mm->mmap_sem);
49 	vma = find_vma(mm, address);
50 	if (!vma)
51 		goto out;
52 	else if (vma->vm_start <= address)
53 		goto good_area;
54 	else if (!(vma->vm_flags & VM_GROWSDOWN))
55 		goto out;
56 	else if (is_user && !ARCH_IS_STACKGROW(address))
57 		goto out;
58 	else if (expand_stack(vma, address))
59 		goto out;
60 
61 good_area:
62 	*code_out = SEGV_ACCERR;
63 	if (is_write) {
64 		if (!(vma->vm_flags & VM_WRITE))
65 			goto out;
66 		flags |= FAULT_FLAG_WRITE;
67 	} else {
68 		/* Don't require VM_READ|VM_EXEC for write faults! */
69 		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
70 			goto out;
71 	}
72 
73 	do {
74 		int fault;
75 
76 		fault = handle_mm_fault(mm, vma, address, flags);
77 
78 		if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
79 			goto out_nosemaphore;
80 
81 		if (unlikely(fault & VM_FAULT_ERROR)) {
82 			if (fault & VM_FAULT_OOM) {
83 				goto out_of_memory;
84 			} else if (fault & VM_FAULT_SIGSEGV) {
85 				goto out;
86 			} else if (fault & VM_FAULT_SIGBUS) {
87 				err = -EACCES;
88 				goto out;
89 			}
90 			BUG();
91 		}
92 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
93 			if (fault & VM_FAULT_MAJOR)
94 				current->maj_flt++;
95 			else
96 				current->min_flt++;
97 			if (fault & VM_FAULT_RETRY) {
98 				flags &= ~FAULT_FLAG_ALLOW_RETRY;
99 				flags |= FAULT_FLAG_TRIED;
100 
101 				goto retry;
102 			}
103 		}
104 
105 		pgd = pgd_offset(mm, address);
106 		pud = pud_offset(pgd, address);
107 		pmd = pmd_offset(pud, address);
108 		pte = pte_offset_kernel(pmd, address);
109 	} while (!pte_present(*pte));
110 	err = 0;
111 	/*
112 	 * The below warning was added in place of
113 	 *	pte_mkyoung(); if (is_write) pte_mkdirty();
114 	 * If it's triggered, we'd see normally a hang here (a clean pte is
115 	 * marked read-only to emulate the dirty bit).
116 	 * However, the generic code can mark a PTE writable but clean on a
117 	 * concurrent read fault, triggering this harmlessly. So comment it out.
118 	 */
119 #if 0
120 	WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
121 #endif
122 	flush_tlb_page(vma, address);
123 out:
124 	up_read(&mm->mmap_sem);
125 out_nosemaphore:
126 	return err;
127 
128 out_of_memory:
129 	/*
130 	 * We ran out of memory, call the OOM killer, and return the userspace
131 	 * (which will retry the fault, or kill us if we got oom-killed).
132 	 */
133 	up_read(&mm->mmap_sem);
134 	if (!is_user)
135 		goto out_nosemaphore;
136 	pagefault_out_of_memory();
137 	return 0;
138 }
139 EXPORT_SYMBOL(handle_page_fault);
140 
show_segv_info(struct uml_pt_regs * regs)141 static void show_segv_info(struct uml_pt_regs *regs)
142 {
143 	struct task_struct *tsk = current;
144 	struct faultinfo *fi = UPT_FAULTINFO(regs);
145 
146 	if (!unhandled_signal(tsk, SIGSEGV))
147 		return;
148 
149 	if (!printk_ratelimit())
150 		return;
151 
152 	printk("%s%s[%d]: segfault at %lx ip %p sp %p error %x",
153 		task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
154 		tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
155 		(void *)UPT_IP(regs), (void *)UPT_SP(regs),
156 		fi->error_code);
157 
158 	print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
159 	printk(KERN_CONT "\n");
160 }
161 
bad_segv(struct faultinfo fi,unsigned long ip)162 static void bad_segv(struct faultinfo fi, unsigned long ip)
163 {
164 	struct siginfo si;
165 
166 	si.si_signo = SIGSEGV;
167 	si.si_code = SEGV_ACCERR;
168 	si.si_addr = (void __user *) FAULT_ADDRESS(fi);
169 	current->thread.arch.faultinfo = fi;
170 	force_sig_info(SIGSEGV, &si, current);
171 }
172 
fatal_sigsegv(void)173 void fatal_sigsegv(void)
174 {
175 	force_sigsegv(SIGSEGV, current);
176 	do_signal(&current->thread.regs);
177 	/*
178 	 * This is to tell gcc that we're not returning - do_signal
179 	 * can, in general, return, but in this case, it's not, since
180 	 * we just got a fatal SIGSEGV queued.
181 	 */
182 	os_dump_core();
183 }
184 
segv_handler(int sig,struct siginfo * unused_si,struct uml_pt_regs * regs)185 void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
186 {
187 	struct faultinfo * fi = UPT_FAULTINFO(regs);
188 
189 	if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
190 		show_segv_info(regs);
191 		bad_segv(*fi, UPT_IP(regs));
192 		return;
193 	}
194 	segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
195 }
196 
197 /*
198  * We give a *copy* of the faultinfo in the regs to segv.
199  * This must be done, since nesting SEGVs could overwrite
200  * the info in the regs. A pointer to the info then would
201  * give us bad data!
202  */
segv(struct faultinfo fi,unsigned long ip,int is_user,struct uml_pt_regs * regs)203 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
204 		   struct uml_pt_regs *regs)
205 {
206 	struct siginfo si;
207 	jmp_buf *catcher;
208 	int err;
209 	int is_write = FAULT_WRITE(fi);
210 	unsigned long address = FAULT_ADDRESS(fi);
211 
212 	if (!is_user && regs)
213 		current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
214 
215 	if (!is_user && (address >= start_vm) && (address < end_vm)) {
216 		flush_tlb_kernel_vm();
217 		goto out;
218 	}
219 	else if (current->mm == NULL) {
220 		show_regs(container_of(regs, struct pt_regs, regs));
221 		panic("Segfault with no mm");
222 	}
223 	else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
224 		show_regs(container_of(regs, struct pt_regs, regs));
225 		panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
226 		       address, ip);
227 	}
228 
229 	if (SEGV_IS_FIXABLE(&fi))
230 		err = handle_page_fault(address, ip, is_write, is_user,
231 					&si.si_code);
232 	else {
233 		err = -EFAULT;
234 		/*
235 		 * A thread accessed NULL, we get a fault, but CR2 is invalid.
236 		 * This code is used in __do_copy_from_user() of TT mode.
237 		 * XXX tt mode is gone, so maybe this isn't needed any more
238 		 */
239 		address = 0;
240 	}
241 
242 	catcher = current->thread.fault_catcher;
243 	if (!err)
244 		goto out;
245 	else if (catcher != NULL) {
246 		current->thread.fault_addr = (void *) address;
247 		UML_LONGJMP(catcher, 1);
248 	}
249 	else if (current->thread.fault_addr != NULL)
250 		panic("fault_addr set but no fault catcher");
251 	else if (!is_user && arch_fixup(ip, regs))
252 		goto out;
253 
254 	if (!is_user) {
255 		show_regs(container_of(regs, struct pt_regs, regs));
256 		panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
257 		      address, ip);
258 	}
259 
260 	show_segv_info(regs);
261 
262 	if (err == -EACCES) {
263 		si.si_signo = SIGBUS;
264 		si.si_errno = 0;
265 		si.si_code = BUS_ADRERR;
266 		si.si_addr = (void __user *)address;
267 		current->thread.arch.faultinfo = fi;
268 		force_sig_info(SIGBUS, &si, current);
269 	} else {
270 		BUG_ON(err != -EFAULT);
271 		si.si_signo = SIGSEGV;
272 		si.si_addr = (void __user *) address;
273 		current->thread.arch.faultinfo = fi;
274 		force_sig_info(SIGSEGV, &si, current);
275 	}
276 
277 out:
278 	if (regs)
279 		current->thread.segv_regs = NULL;
280 
281 	return 0;
282 }
283 
relay_signal(int sig,struct siginfo * si,struct uml_pt_regs * regs)284 void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
285 {
286 	struct faultinfo *fi;
287 	struct siginfo clean_si;
288 
289 	if (!UPT_IS_USER(regs)) {
290 		if (sig == SIGBUS)
291 			printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
292 			       "mount likely just ran out of space\n");
293 		panic("Kernel mode signal %d", sig);
294 	}
295 
296 	arch_examine_signal(sig, regs);
297 
298 	memset(&clean_si, 0, sizeof(clean_si));
299 	clean_si.si_signo = si->si_signo;
300 	clean_si.si_errno = si->si_errno;
301 	clean_si.si_code = si->si_code;
302 	switch (sig) {
303 	case SIGILL:
304 	case SIGFPE:
305 	case SIGSEGV:
306 	case SIGBUS:
307 	case SIGTRAP:
308 		fi = UPT_FAULTINFO(regs);
309 		clean_si.si_addr = (void __user *) FAULT_ADDRESS(*fi);
310 		current->thread.arch.faultinfo = *fi;
311 #ifdef __ARCH_SI_TRAPNO
312 		clean_si.si_trapno = si->si_trapno;
313 #endif
314 		break;
315 	default:
316 		printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d)\n",
317 			sig, si->si_code);
318 	}
319 
320 	force_sig_info(sig, &clean_si, current);
321 }
322 
bus_handler(int sig,struct siginfo * si,struct uml_pt_regs * regs)323 void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
324 {
325 	if (current->thread.fault_catcher != NULL)
326 		UML_LONGJMP(current->thread.fault_catcher, 1);
327 	else
328 		relay_signal(sig, si, regs);
329 }
330 
winch(int sig,struct siginfo * unused_si,struct uml_pt_regs * regs)331 void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
332 {
333 	do_IRQ(WINCH_IRQ, regs);
334 }
335 
trap_init(void)336 void trap_init(void)
337 {
338 }
339