arch/um/kernel/trap.c

   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, -EACCESS, -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                 int 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 %p sp %p 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         struct siginfo si;
 166
 167         si.si_signo = SIGSEGV;
 168         si.si_code = SEGV_ACCERR;
 169         si.si_addr = (void __user *) FAULT_ADDRESS(fi);
 170         current->thread.arch.faultinfo = fi;
 171         force_sig_info(SIGSEGV, &si, current);
 172 }
 173
 174 void fatal_sigsegv(void)
 175 {
 176         force_sigsegv(SIGSEGV, current);
 177         do_signal(&current->thread.regs);
 178         /*
 179          * This is to tell gcc that we're not returning - do_signal
 180          * can, in general, return, but in this case, it's not, since
 181          * we just got a fatal SIGSEGV queued.
 182          */
 183         os_dump_core();
 184 }
 185
 186 void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 187 {
 188         struct faultinfo * fi = UPT_FAULTINFO(regs);
 189
 190         if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
 191                 show_segv_info(regs);
 192                 bad_segv(*fi, UPT_IP(regs));
 193                 return;
 194         }
 195         segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
 196 }
 197
 198 /*
 199  * We give a *copy* of the faultinfo in the regs to segv.
 200  * This must be done, since nesting SEGVs could overwrite
 201  * the info in the regs. A pointer to the info then would
 202  * give us bad data!
 203  */
 204 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 205                    struct uml_pt_regs *regs)
 206 {
 207         struct siginfo si;
 208         jmp_buf *catcher;
 209         int err;
 210         int is_write = FAULT_WRITE(fi);
 211         unsigned long address = FAULT_ADDRESS(fi);
 212
 213         if (!is_user && regs)
 214                 current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
 215
 216         if (!is_user && (address >= start_vm) && (address < end_vm)) {
 217                 flush_tlb_kernel_vm();
 218                 goto out;
 219         }
 220         else if (current->mm == NULL) {
 221                 show_regs(container_of(regs, struct pt_regs, regs));
 222                 panic("Segfault with no mm");
 223         }
 224         else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
 225                 show_regs(container_of(regs, struct pt_regs, regs));
 226                 panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
 227                        address, ip);
 228         }
 229
 230         if (SEGV_IS_FIXABLE(&fi))
 231                 err = handle_page_fault(address, ip, is_write, is_user,
 232                                         &si.si_code);
 233         else {
 234                 err = -EFAULT;
 235                 /*
 236                  * A thread accessed NULL, we get a fault, but CR2 is invalid.
 237                  * This code is used in __do_copy_from_user() of TT mode.
 238                  * XXX tt mode is gone, so maybe this isn't needed any more
 239                  */
 240                 address = 0;
 241         }
 242
 243         catcher = current->thread.fault_catcher;
 244         if (!err)
 245                 goto out;
 246         else if (catcher != NULL) {
 247                 current->thread.fault_addr = (void *) address;
 248                 UML_LONGJMP(catcher, 1);
 249         }
 250         else if (current->thread.fault_addr != NULL)
 251                 panic("fault_addr set but no fault catcher");
 252         else if (!is_user && arch_fixup(ip, regs))
 253                 goto out;
 254
 255         if (!is_user) {
 256                 show_regs(container_of(regs, struct pt_regs, regs));
 257                 panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
 258                       address, ip);
 259         }
 260
 261         show_segv_info(regs);
 262
 263         if (err == -EACCES) {
 264                 si.si_signo = SIGBUS;
 265                 si.si_errno = 0;
 266                 si.si_code = BUS_ADRERR;
 267                 si.si_addr = (void __user *)address;
 268                 current->thread.arch.faultinfo = fi;
 269                 force_sig_info(SIGBUS, &si, current);
 270         } else {
 271                 BUG_ON(err != -EFAULT);
 272                 si.si_signo = SIGSEGV;
 273                 si.si_addr = (void __user *) address;
 274                 current->thread.arch.faultinfo = fi;
 275                 force_sig_info(SIGSEGV, &si, current);
 276         }
 277
 278 out:
 279         if (regs)
 280                 current->thread.segv_regs = NULL;
 281
 282         return 0;
 283 }
 284
 285 void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
 286 {
 287         struct faultinfo *fi;
 288         struct siginfo clean_si;
 289
 290         if (!UPT_IS_USER(regs)) {
 291                 if (sig == SIGBUS)
 292                         printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
 293                                "mount likely just ran out of space\n");
 294                 panic("Kernel mode signal %d", sig);
 295         }
 296
 297         arch_examine_signal(sig, regs);
 298
 299         memset(&clean_si, 0, sizeof(clean_si));
 300         clean_si.si_signo = si->si_signo;
 301         clean_si.si_errno = si->si_errno;
 302         clean_si.si_code = si->si_code;
 303         switch (sig) {
 304         case SIGILL:
 305         case SIGFPE:
 306         case SIGSEGV:
 307         case SIGBUS:
 308         case SIGTRAP:
 309                 fi = UPT_FAULTINFO(regs);
 310                 clean_si.si_addr = (void __user *) FAULT_ADDRESS(*fi);
 311                 current->thread.arch.faultinfo = *fi;
 312 #ifdef __ARCH_SI_TRAPNO
 313                 clean_si.si_trapno = si->si_trapno;
 314 #endif
 315                 break;
 316         default:
 317                 printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d)\n",
 318                         sig, si->si_code);
 319         }
 320
 321         force_sig_info(sig, &clean_si, current);
 322 }
 323
 324 void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
 325 {
 326         if (current->thread.fault_catcher != NULL)
 327                 UML_LONGJMP(current->thread.fault_catcher, 1);
 328         else
 329                 relay_signal(sig, si, regs);
 330 }
 331
 332 void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 333 {
 334         do_IRQ(WINCH_IRQ, regs);
 335 }
 336
 337 void trap_init(void)
 338 {
 339 }