arch/um/kernel/trap.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   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 }