1 /* 2 * Copyright (C) 2009 Wind River Systems Inc 3 * Implemented by fredrik.markstrom@gmail.com and ivarholmqvist@gmail.com 4 * 5 * based on arch/mips/mm/fault.c which is: 6 * 7 * Copyright (C) 1995-2000 Ralf Baechle 8 * 9 * This file is subject to the terms and conditions of the GNU General Public 10 * License. See the file "COPYING" in the main directory of this archive 11 * for more details. 12 */ 13 14 #include <linux/signal.h> 15 #include <linux/sched.h> 16 #include <linux/sched/debug.h> 17 #include <linux/interrupt.h> 18 #include <linux/kernel.h> 19 #include <linux/errno.h> 20 #include <linux/string.h> 21 #include <linux/types.h> 22 #include <linux/ptrace.h> 23 #include <linux/mman.h> 24 #include <linux/mm.h> 25 #include <linux/extable.h> 26 #include <linux/uaccess.h> 27 #include <linux/ptrace.h> 28 29 #include <asm/mmu_context.h> 30 #include <asm/traps.h> 31 32 #define EXC_SUPERV_INSN_ACCESS 9 /* Supervisor only instruction address */ 33 #define EXC_SUPERV_DATA_ACCESS 11 /* Supervisor only data address */ 34 #define EXC_X_PROTECTION_FAULT 13 /* TLB permission violation (x) */ 35 #define EXC_R_PROTECTION_FAULT 14 /* TLB permission violation (r) */ 36 #define EXC_W_PROTECTION_FAULT 15 /* TLB permission violation (w) */ 37 38 /* 39 * This routine handles page faults. It determines the address, 40 * and the problem, and then passes it off to one of the appropriate 41 * routines. 42 */ 43 asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause, 44 unsigned long address) 45 { 46 struct vm_area_struct *vma = NULL; 47 struct task_struct *tsk = current; 48 struct mm_struct *mm = tsk->mm; 49 int code = SEGV_MAPERR; 50 int fault; 51 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; 52 53 cause >>= 2; 54 55 /* Restart the instruction */ 56 regs->ea -= 4; 57 58 /* 59 * We fault-in kernel-space virtual memory on-demand. The 60 * 'reference' page table is init_mm.pgd. 61 * 62 * NOTE! We MUST NOT take any locks for this case. We may 63 * be in an interrupt or a critical region, and should 64 * only copy the information from the master page table, 65 * nothing more. 66 */ 67 if (unlikely(address >= VMALLOC_START && address <= VMALLOC_END)) { 68 if (user_mode(regs)) 69 goto bad_area_nosemaphore; 70 else 71 goto vmalloc_fault; 72 } 73 74 if (unlikely(address >= TASK_SIZE)) 75 goto bad_area_nosemaphore; 76 77 /* 78 * If we're in an interrupt or have no user 79 * context, we must not take the fault.. 80 */ 81 if (faulthandler_disabled() || !mm) 82 goto bad_area_nosemaphore; 83 84 if (user_mode(regs)) 85 flags |= FAULT_FLAG_USER; 86 87 if (!down_read_trylock(&mm->mmap_sem)) { 88 if (!user_mode(regs) && !search_exception_tables(regs->ea)) 89 goto bad_area_nosemaphore; 90 retry: 91 down_read(&mm->mmap_sem); 92 } 93 94 vma = find_vma(mm, address); 95 if (!vma) 96 goto bad_area; 97 if (vma->vm_start <= address) 98 goto good_area; 99 if (!(vma->vm_flags & VM_GROWSDOWN)) 100 goto bad_area; 101 if (expand_stack(vma, address)) 102 goto bad_area; 103 /* 104 * Ok, we have a good vm_area for this memory access, so 105 * we can handle it.. 106 */ 107 good_area: 108 code = SEGV_ACCERR; 109 110 switch (cause) { 111 case EXC_SUPERV_INSN_ACCESS: 112 goto bad_area; 113 case EXC_SUPERV_DATA_ACCESS: 114 goto bad_area; 115 case EXC_X_PROTECTION_FAULT: 116 if (!(vma->vm_flags & VM_EXEC)) 117 goto bad_area; 118 break; 119 case EXC_R_PROTECTION_FAULT: 120 if (!(vma->vm_flags & VM_READ)) 121 goto bad_area; 122 break; 123 case EXC_W_PROTECTION_FAULT: 124 if (!(vma->vm_flags & VM_WRITE)) 125 goto bad_area; 126 flags = FAULT_FLAG_WRITE; 127 break; 128 } 129 130 /* 131 * If for any reason at all we couldn't handle the fault, 132 * make sure we exit gracefully rather than endlessly redo 133 * the fault. 134 */ 135 fault = handle_mm_fault(vma, address, flags); 136 137 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) 138 return; 139 140 if (unlikely(fault & VM_FAULT_ERROR)) { 141 if (fault & VM_FAULT_OOM) 142 goto out_of_memory; 143 else if (fault & VM_FAULT_SIGSEGV) 144 goto bad_area; 145 else if (fault & VM_FAULT_SIGBUS) 146 goto do_sigbus; 147 BUG(); 148 } 149 150 /* 151 * Major/minor page fault accounting is only done on the 152 * initial attempt. If we go through a retry, it is extremely 153 * likely that the page will be found in page cache at that point. 154 */ 155 if (flags & FAULT_FLAG_ALLOW_RETRY) { 156 if (fault & VM_FAULT_MAJOR) 157 current->maj_flt++; 158 else 159 current->min_flt++; 160 if (fault & VM_FAULT_RETRY) { 161 /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk 162 * of starvation. */ 163 flags &= ~FAULT_FLAG_ALLOW_RETRY; 164 flags |= FAULT_FLAG_TRIED; 165 166 /* 167 * No need to up_read(&mm->mmap_sem) as we would 168 * have already released it in __lock_page_or_retry 169 * in mm/filemap.c. 170 */ 171 172 goto retry; 173 } 174 } 175 176 up_read(&mm->mmap_sem); 177 return; 178 179 /* 180 * Something tried to access memory that isn't in our memory map.. 181 * Fix it, but check if it's kernel or user first.. 182 */ 183 bad_area: 184 up_read(&mm->mmap_sem); 185 186 bad_area_nosemaphore: 187 /* User mode accesses just cause a SIGSEGV */ 188 if (user_mode(regs)) { 189 if (unhandled_signal(current, SIGSEGV) && printk_ratelimit()) { 190 pr_info("%s: unhandled page fault (%d) at 0x%08lx, " 191 "cause %ld\n", current->comm, SIGSEGV, address, cause); 192 show_regs(regs); 193 } 194 _exception(SIGSEGV, regs, code, address); 195 return; 196 } 197 198 no_context: 199 /* Are we prepared to handle this kernel fault? */ 200 if (fixup_exception(regs)) 201 return; 202 203 /* 204 * Oops. The kernel tried to access some bad page. We'll have to 205 * terminate things with extreme prejudice. 206 */ 207 bust_spinlocks(1); 208 209 pr_alert("Unable to handle kernel %s at virtual address %08lx", 210 address < PAGE_SIZE ? "NULL pointer dereference" : 211 "paging request", address); 212 pr_alert("ea = %08lx, ra = %08lx, cause = %ld\n", regs->ea, regs->ra, 213 cause); 214 panic("Oops"); 215 return; 216 217 /* 218 * We ran out of memory, or some other thing happened to us that made 219 * us unable to handle the page fault gracefully. 220 */ 221 out_of_memory: 222 up_read(&mm->mmap_sem); 223 if (!user_mode(regs)) 224 goto no_context; 225 pagefault_out_of_memory(); 226 return; 227 228 do_sigbus: 229 up_read(&mm->mmap_sem); 230 231 /* Kernel mode? Handle exceptions or die */ 232 if (!user_mode(regs)) 233 goto no_context; 234 235 _exception(SIGBUS, regs, BUS_ADRERR, address); 236 return; 237 238 vmalloc_fault: 239 { 240 /* 241 * Synchronize this task's top level page-table 242 * with the 'reference' page table. 243 * 244 * Do _not_ use "tsk" here. We might be inside 245 * an interrupt in the middle of a task switch.. 246 */ 247 int offset = pgd_index(address); 248 pgd_t *pgd, *pgd_k; 249 pud_t *pud, *pud_k; 250 pmd_t *pmd, *pmd_k; 251 pte_t *pte_k; 252 253 pgd = pgd_current + offset; 254 pgd_k = init_mm.pgd + offset; 255 256 if (!pgd_present(*pgd_k)) 257 goto no_context; 258 set_pgd(pgd, *pgd_k); 259 260 pud = pud_offset(pgd, address); 261 pud_k = pud_offset(pgd_k, address); 262 if (!pud_present(*pud_k)) 263 goto no_context; 264 pmd = pmd_offset(pud, address); 265 pmd_k = pmd_offset(pud_k, address); 266 if (!pmd_present(*pmd_k)) 267 goto no_context; 268 set_pmd(pmd, *pmd_k); 269 270 pte_k = pte_offset_kernel(pmd_k, address); 271 if (!pte_present(*pte_k)) 272 goto no_context; 273 274 flush_tlb_one(address); 275 return; 276 } 277 } 278