1 /* 2 * arch/microblaze/mm/fault.c 3 * 4 * Copyright (C) 2007 Xilinx, Inc. All rights reserved. 5 * 6 * Derived from "arch/ppc/mm/fault.c" 7 * Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org) 8 * 9 * Derived from "arch/i386/mm/fault.c" 10 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 11 * 12 * Modified by Cort Dougan and Paul Mackerras. 13 * 14 * This file is subject to the terms and conditions of the GNU General 15 * Public License. See the file COPYING in the main directory of this 16 * archive for more details. 17 * 18 */ 19 20 #include <linux/extable.h> 21 #include <linux/signal.h> 22 #include <linux/sched.h> 23 #include <linux/kernel.h> 24 #include <linux/errno.h> 25 #include <linux/string.h> 26 #include <linux/types.h> 27 #include <linux/ptrace.h> 28 #include <linux/mman.h> 29 #include <linux/mm.h> 30 #include <linux/interrupt.h> 31 32 #include <asm/page.h> 33 #include <asm/pgtable.h> 34 #include <asm/mmu.h> 35 #include <linux/mmu_context.h> 36 #include <linux/uaccess.h> 37 #include <asm/exceptions.h> 38 39 static unsigned long pte_misses; /* updated by do_page_fault() */ 40 static unsigned long pte_errors; /* updated by do_page_fault() */ 41 42 /* 43 * Check whether the instruction at regs->pc is a store using 44 * an update addressing form which will update r1. 45 */ 46 static int store_updates_sp(struct pt_regs *regs) 47 { 48 unsigned int inst; 49 50 if (get_user(inst, (unsigned int __user *)regs->pc)) 51 return 0; 52 /* check for 1 in the rD field */ 53 if (((inst >> 21) & 0x1f) != 1) 54 return 0; 55 /* check for store opcodes */ 56 if ((inst & 0xd0000000) == 0xd0000000) 57 return 1; 58 return 0; 59 } 60 61 62 /* 63 * bad_page_fault is called when we have a bad access from the kernel. 64 * It is called from do_page_fault above and from some of the procedures 65 * in traps.c. 66 */ 67 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig) 68 { 69 const struct exception_table_entry *fixup; 70 /* MS: no context */ 71 /* Are we prepared to handle this fault? */ 72 fixup = search_exception_tables(regs->pc); 73 if (fixup) { 74 regs->pc = fixup->fixup; 75 return; 76 } 77 78 /* kernel has accessed a bad area */ 79 die("kernel access of bad area", regs, sig); 80 } 81 82 /* 83 * The error_code parameter is ESR for a data fault, 84 * 0 for an instruction fault. 85 */ 86 void do_page_fault(struct pt_regs *regs, unsigned long address, 87 unsigned long error_code) 88 { 89 struct vm_area_struct *vma; 90 struct mm_struct *mm = current->mm; 91 int code = SEGV_MAPERR; 92 int is_write = error_code & ESR_S; 93 vm_fault_t fault; 94 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; 95 96 regs->ear = address; 97 regs->esr = error_code; 98 99 /* On a kernel SLB miss we can only check for a valid exception entry */ 100 if (unlikely(kernel_mode(regs) && (address >= TASK_SIZE))) { 101 pr_warn("kernel task_size exceed"); 102 _exception(SIGSEGV, regs, code, address); 103 } 104 105 /* for instr TLB miss and instr storage exception ESR_S is undefined */ 106 if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11) 107 is_write = 0; 108 109 if (unlikely(faulthandler_disabled() || !mm)) { 110 if (kernel_mode(regs)) 111 goto bad_area_nosemaphore; 112 113 /* faulthandler_disabled() in user mode is really bad, 114 as is current->mm == NULL. */ 115 pr_emerg("Page fault in user mode with faulthandler_disabled(), mm = %p\n", 116 mm); 117 pr_emerg("r15 = %lx MSR = %lx\n", 118 regs->r15, regs->msr); 119 die("Weird page fault", regs, SIGSEGV); 120 } 121 122 if (user_mode(regs)) 123 flags |= FAULT_FLAG_USER; 124 125 /* When running in the kernel we expect faults to occur only to 126 * addresses in user space. All other faults represent errors in the 127 * kernel and should generate an OOPS. Unfortunately, in the case of an 128 * erroneous fault occurring in a code path which already holds mmap_sem 129 * we will deadlock attempting to validate the fault against the 130 * address space. Luckily the kernel only validly references user 131 * space from well defined areas of code, which are listed in the 132 * exceptions table. 133 * 134 * As the vast majority of faults will be valid we will only perform 135 * the source reference check when there is a possibility of a deadlock. 136 * Attempt to lock the address space, if we cannot we then validate the 137 * source. If this is invalid we can skip the address space check, 138 * thus avoiding the deadlock. 139 */ 140 if (unlikely(!down_read_trylock(&mm->mmap_sem))) { 141 if (kernel_mode(regs) && !search_exception_tables(regs->pc)) 142 goto bad_area_nosemaphore; 143 144 retry: 145 down_read(&mm->mmap_sem); 146 } 147 148 vma = find_vma(mm, address); 149 if (unlikely(!vma)) 150 goto bad_area; 151 152 if (vma->vm_start <= address) 153 goto good_area; 154 155 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) 156 goto bad_area; 157 158 if (unlikely(!is_write)) 159 goto bad_area; 160 161 /* 162 * N.B. The ABI allows programs to access up to 163 * a few hundred bytes below the stack pointer (TBD). 164 * The kernel signal delivery code writes up to about 1.5kB 165 * below the stack pointer (r1) before decrementing it. 166 * The exec code can write slightly over 640kB to the stack 167 * before setting the user r1. Thus we allow the stack to 168 * expand to 1MB without further checks. 169 */ 170 if (unlikely(address + 0x100000 < vma->vm_end)) { 171 172 /* get user regs even if this fault is in kernel mode */ 173 struct pt_regs *uregs = current->thread.regs; 174 if (uregs == NULL) 175 goto bad_area; 176 177 /* 178 * A user-mode access to an address a long way below 179 * the stack pointer is only valid if the instruction 180 * is one which would update the stack pointer to the 181 * address accessed if the instruction completed, 182 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb 183 * (or the byte, halfword, float or double forms). 184 * 185 * If we don't check this then any write to the area 186 * between the last mapped region and the stack will 187 * expand the stack rather than segfaulting. 188 */ 189 if (address + 2048 < uregs->r1 190 && (kernel_mode(regs) || !store_updates_sp(regs))) 191 goto bad_area; 192 } 193 if (expand_stack(vma, address)) 194 goto bad_area; 195 196 good_area: 197 code = SEGV_ACCERR; 198 199 /* a write */ 200 if (unlikely(is_write)) { 201 if (unlikely(!(vma->vm_flags & VM_WRITE))) 202 goto bad_area; 203 flags |= FAULT_FLAG_WRITE; 204 /* a read */ 205 } else { 206 /* protection fault */ 207 if (unlikely(error_code & 0x08000000)) 208 goto bad_area; 209 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC)))) 210 goto bad_area; 211 } 212 213 /* 214 * If for any reason at all we couldn't handle the fault, 215 * make sure we exit gracefully rather than endlessly redo 216 * the fault. 217 */ 218 fault = handle_mm_fault(vma, address, flags); 219 220 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) 221 return; 222 223 if (unlikely(fault & VM_FAULT_ERROR)) { 224 if (fault & VM_FAULT_OOM) 225 goto out_of_memory; 226 else if (fault & VM_FAULT_SIGSEGV) 227 goto bad_area; 228 else if (fault & VM_FAULT_SIGBUS) 229 goto do_sigbus; 230 BUG(); 231 } 232 233 if (flags & FAULT_FLAG_ALLOW_RETRY) { 234 if (unlikely(fault & VM_FAULT_MAJOR)) 235 current->maj_flt++; 236 else 237 current->min_flt++; 238 if (fault & VM_FAULT_RETRY) { 239 flags &= ~FAULT_FLAG_ALLOW_RETRY; 240 flags |= FAULT_FLAG_TRIED; 241 242 /* 243 * No need to up_read(&mm->mmap_sem) as we would 244 * have already released it in __lock_page_or_retry 245 * in mm/filemap.c. 246 */ 247 248 goto retry; 249 } 250 } 251 252 up_read(&mm->mmap_sem); 253 254 /* 255 * keep track of tlb+htab misses that are good addrs but 256 * just need pte's created via handle_mm_fault() 257 * -- Cort 258 */ 259 pte_misses++; 260 return; 261 262 bad_area: 263 up_read(&mm->mmap_sem); 264 265 bad_area_nosemaphore: 266 pte_errors++; 267 268 /* User mode accesses cause a SIGSEGV */ 269 if (user_mode(regs)) { 270 _exception(SIGSEGV, regs, code, address); 271 return; 272 } 273 274 bad_page_fault(regs, address, SIGSEGV); 275 return; 276 277 /* 278 * We ran out of memory, or some other thing happened to us that made 279 * us unable to handle the page fault gracefully. 280 */ 281 out_of_memory: 282 up_read(&mm->mmap_sem); 283 if (!user_mode(regs)) 284 bad_page_fault(regs, address, SIGKILL); 285 else 286 pagefault_out_of_memory(); 287 return; 288 289 do_sigbus: 290 up_read(&mm->mmap_sem); 291 if (user_mode(regs)) { 292 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address, current); 293 return; 294 } 295 bad_page_fault(regs, address, SIGBUS); 296 } 297