arch/riscv/mm/fault.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2009 Sunplus Core Technology Co., Ltd.
   4  *  Lennox Wu <lennox.wu@sunplusct.com>
   5  *  Chen Liqin <liqin.chen@sunplusct.com>
   6  * Copyright (C) 2012 Regents of the University of California
   7  */
   8
   9
  10 #include <linux/mm.h>
  11 #include <linux/kernel.h>
  12 #include <linux/interrupt.h>
  13 #include <linux/perf_event.h>
  14 #include <linux/signal.h>
  15 #include <linux/uaccess.h>
  16
  17 #include <asm/ptrace.h>
  18 #include <asm/tlbflush.h>
  19
  20 #include "../kernel/head.h"
  21
  22 static inline void no_context(struct pt_regs *regs, unsigned long addr)
  23 {
  24         /* Are we prepared to handle this kernel fault? */
  25         if (fixup_exception(regs))
  26                 return;
  27
  28         /*
  29          * Oops. The kernel tried to access some bad page. We'll have to
  30          * terminate things with extreme prejudice.
  31          */
  32         bust_spinlocks(1);
  33         pr_alert("Unable to handle kernel %s at virtual address " REG_FMT "\n",
  34                 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
  35                 "paging request", addr);
  36         die(regs, "Oops");
  37         do_exit(SIGKILL);
  38 }
  39
  40 static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_fault_t fault)
  41 {
  42         if (fault & VM_FAULT_OOM) {
  43                 /*
  44                  * We ran out of memory, call the OOM killer, and return the userspace
  45                  * (which will retry the fault, or kill us if we got oom-killed).
  46                  */
  47                 if (!user_mode(regs)) {
  48                         no_context(regs, addr);
  49                         return;
  50                 }
  51                 pagefault_out_of_memory();
  52                 return;
  53         } else if (fault & VM_FAULT_SIGBUS) {
  54                 /* Kernel mode? Handle exceptions or die */
  55                 if (!user_mode(regs)) {
  56                         no_context(regs, addr);
  57                         return;
  58                 }
  59                 do_trap(regs, SIGBUS, BUS_ADRERR, addr);
  60                 return;
  61         }
  62         BUG();
  63 }
  64
  65 static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code, unsigned long addr)
  66 {
  67         /*
  68          * Something tried to access memory that isn't in our memory map.
  69          * Fix it, but check if it's kernel or user first.
  70          */
  71         mmap_read_unlock(mm);
  72         /* User mode accesses just cause a SIGSEGV */
  73         if (user_mode(regs)) {
  74                 do_trap(regs, SIGSEGV, code, addr);
  75                 return;
  76         }
  77
  78         no_context(regs, addr);
  79 }
  80
  81 static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
  82 {
  83         pgd_t *pgd, *pgd_k;
  84         pud_t *pud, *pud_k;
  85         p4d_t *p4d, *p4d_k;
  86         pmd_t *pmd, *pmd_k;
  87         pte_t *pte_k;
  88         int index;
  89         unsigned long pfn;
  90
  91         /* User mode accesses just cause a SIGSEGV */
  92         if (user_mode(regs))
  93                 return do_trap(regs, SIGSEGV, code, addr);
  94
  95         /*
  96          * Synchronize this task's top level page-table
  97          * with the 'reference' page table.
  98          *
  99          * Do _not_ use "tsk->active_mm->pgd" here.
 100          * We might be inside an interrupt in the middle
 101          * of a task switch.
 102          */
 103         index = pgd_index(addr);
 104         pfn = csr_read(CSR_SATP) & SATP_PPN;
 105         pgd = (pgd_t *)pfn_to_virt(pfn) + index;
 106         pgd_k = init_mm.pgd + index;
 107
 108         if (!pgd_present(*pgd_k)) {
 109                 no_context(regs, addr);
 110                 return;
 111         }
 112         set_pgd(pgd, *pgd_k);
 113
 114         p4d = p4d_offset(pgd, addr);
 115         p4d_k = p4d_offset(pgd_k, addr);
 116         if (!p4d_present(*p4d_k)) {
 117                 no_context(regs, addr);
 118                 return;
 119         }
 120
 121         pud = pud_offset(p4d, addr);
 122         pud_k = pud_offset(p4d_k, addr);
 123         if (!pud_present(*pud_k)) {
 124                 no_context(regs, addr);
 125                 return;
 126         }
 127
 128         /*
 129          * Since the vmalloc area is global, it is unnecessary
 130          * to copy individual PTEs
 131          */
 132         pmd = pmd_offset(pud, addr);
 133         pmd_k = pmd_offset(pud_k, addr);
 134         if (!pmd_present(*pmd_k)) {
 135                 no_context(regs, addr);
 136                 return;
 137         }
 138         set_pmd(pmd, *pmd_k);
 139
 140         /*
 141          * Make sure the actual PTE exists as well to
 142          * catch kernel vmalloc-area accesses to non-mapped
 143          * addresses. If we don't do this, this will just
 144          * silently loop forever.
 145          */
 146         pte_k = pte_offset_kernel(pmd_k, addr);
 147         if (!pte_present(*pte_k)) {
 148                 no_context(regs, addr);
 149                 return;
 150         }
 151
 152         /*
 153          * The kernel assumes that TLBs don't cache invalid
 154          * entries, but in RISC-V, SFENCE.VMA specifies an
 155          * ordering constraint, not a cache flush; it is
 156          * necessary even after writing invalid entries.
 157          */
 158         local_flush_tlb_page(addr);
 159 }
 160
 161 static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
 162 {
 163         switch (cause) {
 164         case EXC_INST_PAGE_FAULT:
 165                 if (!(vma->vm_flags & VM_EXEC)) {
 166                         return true;
 167                 }
 168                 break;
 169         case EXC_LOAD_PAGE_FAULT:
 170                 if (!(vma->vm_flags & VM_READ)) {
 171                         return true;
 172                 }
 173                 break;
 174         case EXC_STORE_PAGE_FAULT:
 175                 if (!(vma->vm_flags & VM_WRITE)) {
 176                         return true;
 177                 }
 178                 break;
 179         default:
 180                 panic("%s: unhandled cause %lu", __func__, cause);
 181         }
 182         return false;
 183 }
 184
 185 /*
 186  * This routine handles page faults.  It determines the address and the
 187  * problem, and then passes it off to one of the appropriate routines.
 188  */
 189 asmlinkage void do_page_fault(struct pt_regs *regs)
 190 {
 191         struct task_struct *tsk;
 192         struct vm_area_struct *vma;
 193         struct mm_struct *mm;
 194         unsigned long addr, cause;
 195         unsigned int flags = FAULT_FLAG_DEFAULT;
 196         int code = SEGV_MAPERR;
 197         vm_fault_t fault;
 198
 199         cause = regs->cause;
 200         addr = regs->badaddr;
 201
 202         tsk = current;
 203         mm = tsk->mm;
 204
 205         /*
 206          * Fault-in kernel-space virtual memory on-demand.
 207          * The 'reference' page table is init_mm.pgd.
 208          *
 209          * NOTE! We MUST NOT take any locks for this case. We may
 210          * be in an interrupt or a critical region, and should
 211          * only copy the information from the master page table,
 212          * nothing more.
 213          */
 214         if (unlikely((addr >= VMALLOC_START) && (addr <= VMALLOC_END))) {
 215                 vmalloc_fault(regs, code, addr);
 216                 return;
 217         }
 218
 219         /* Enable interrupts if they were enabled in the parent context. */
 220         if (likely(regs->status & SR_PIE))
 221                 local_irq_enable();
 222
 223         /*
 224          * If we're in an interrupt, have no user context, or are running
 225          * in an atomic region, then we must not take the fault.
 226          */
 227         if (unlikely(faulthandler_disabled() || !mm)) {
 228                 no_context(regs, addr);
 229                 return;
 230         }
 231
 232         if (user_mode(regs))
 233                 flags |= FAULT_FLAG_USER;
 234
 235         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 236
 237         if (cause == EXC_STORE_PAGE_FAULT)
 238                 flags |= FAULT_FLAG_WRITE;
 239         else if (cause == EXC_INST_PAGE_FAULT)
 240                 flags |= FAULT_FLAG_INSTRUCTION;
 241 retry:
 242         mmap_read_lock(mm);
 243         vma = find_vma(mm, addr);
 244         if (unlikely(!vma)) {
 245                 bad_area(regs, mm, code, addr);
 246                 return;
 247         }
 248         if (likely(vma->vm_start <= addr))
 249                 goto good_area;
 250         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
 251                 bad_area(regs, mm, code, addr);
 252                 return;
 253         }
 254         if (unlikely(expand_stack(vma, addr))) {
 255                 bad_area(regs, mm, code, addr);
 256                 return;
 257         }
 258
 259         /*
 260          * Ok, we have a good vm_area for this memory access, so
 261          * we can handle it.
 262          */
 263 good_area:
 264         code = SEGV_ACCERR;
 265
 266         if (unlikely(access_error(cause, vma))) {
 267                 bad_area(regs, mm, code, addr);
 268                 return;
 269         }
 270
 271         /*
 272          * If for any reason at all we could not handle the fault,
 273          * make sure we exit gracefully rather than endlessly redo
 274          * the fault.
 275          */
 276         fault = handle_mm_fault(vma, addr, flags, regs);
 277
 278         /*
 279          * If we need to retry but a fatal signal is pending, handle the
 280          * signal first. We do not need to release the mmap_lock because it
 281          * would already be released in __lock_page_or_retry in mm/filemap.c.
 282          */
 283         if (fault_signal_pending(fault, regs))
 284                 return;
 285
 286         if (unlikely((fault & VM_FAULT_RETRY) && (flags & FAULT_FLAG_ALLOW_RETRY))) {
 287                 flags |= FAULT_FLAG_TRIED;
 288
 289                 /*
 290                  * No need to mmap_read_unlock(mm) as we would
 291                  * have already released it in __lock_page_or_retry
 292                  * in mm/filemap.c.
 293                  */
 294                 goto retry;
 295         }
 296
 297         mmap_read_unlock(mm);
 298
 299         if (unlikely(fault & VM_FAULT_ERROR)) {
 300                 mm_fault_error(regs, addr, fault);
 301                 return;
 302         }
 303         return;
 304 }