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Linux/arch/um/kernel/trap.c

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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  */
 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 
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 
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 
173 void fatal_sigsegv(void)
174 {
175         force_sigsegv(SIGSEGV, current);
176         do_signal();
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 
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  */
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 
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 
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 
331 void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
332 {
333         do_IRQ(WINCH_IRQ, regs);
334 }
335 
336 void trap_init(void)
337 {
338 }
339 

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