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