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

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