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 siginfo_t info; 92 int code = SEGV_MAPERR; 93 int is_write = error_code & ESR_S; 94 int fault; 95 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; 96 97 regs->ear = address; 98 regs->esr = error_code; 99 100 /* On a kernel SLB miss we can only check for a valid exception entry */ 101 if (unlikely(kernel_mode(regs) && (address >= TASK_SIZE))) { 102 pr_warn("kernel task_size exceed"); 103 _exception(SIGSEGV, regs, code, address); 104 } 105 106 /* for instr TLB miss and instr storage exception ESR_S is undefined */ 107 if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11) 108 is_write = 0; 109 110 if (unlikely(faulthandler_disabled() || !mm)) { 111 if (kernel_mode(regs)) 112 goto bad_area_nosemaphore; 113 114 /* faulthandler_disabled() in user mode is really bad, 115 as is current->mm == NULL. */ 116 pr_emerg("Page fault in user mode with faulthandler_disabled(), mm = %p\n", 117 mm); 118 pr_emerg("r15 = %lx MSR = %lx\n", 119 regs->r15, regs->msr); 120 die("Weird page fault", regs, SIGSEGV); 121 } 122 123 if (user_mode(regs)) 124 flags |= FAULT_FLAG_USER; 125 126 /* When running in the kernel we expect faults to occur only to 127 * addresses in user space. All other faults represent errors in the 128 * kernel and should generate an OOPS. Unfortunately, in the case of an 129 * erroneous fault occurring in a code path which already holds mmap_sem 130 * we will deadlock attempting to validate the fault against the 131 * address space. Luckily the kernel only validly references user 132 * space from well defined areas of code, which are listed in the 133 * exceptions table. 134 * 135 * As the vast majority of faults will be valid we will only perform 136 * the source reference check when there is a possibility of a deadlock. 137 * Attempt to lock the address space, if we cannot we then validate the 138 * source. If this is invalid we can skip the address space check, 139 * thus avoiding the deadlock. 140 */ 141 if (unlikely(!down_read_trylock(&mm->mmap_sem))) { 142 if (kernel_mode(regs) && !search_exception_tables(regs->pc)) 143 goto bad_area_nosemaphore; 144 145 retry: 146 down_read(&mm->mmap_sem); 147 } 148 149 vma = find_vma(mm, address); 150 if (unlikely(!vma)) 151 goto bad_area; 152 153 if (vma->vm_start <= address) 154 goto good_area; 155 156 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) 157 goto bad_area; 158 159 if (unlikely(!is_write)) 160 goto bad_area; 161 162 /* 163 * N.B. The ABI allows programs to access up to 164 * a few hundred bytes below the stack pointer (TBD). 165 * The kernel signal delivery code writes up to about 1.5kB 166 * below the stack pointer (r1) before decrementing it. 167 * The exec code can write slightly over 640kB to the stack 168 * before setting the user r1. Thus we allow the stack to 169 * expand to 1MB without further checks. 170 */ 171 if (unlikely(address + 0x100000 < vma->vm_end)) { 172 173 /* get user regs even if this fault is in kernel mode */ 174 struct pt_regs *uregs = current->thread.regs; 175 if (uregs == NULL) 176 goto bad_area; 177 178 /* 179 * A user-mode access to an address a long way below 180 * the stack pointer is only valid if the instruction 181 * is one which would update the stack pointer to the 182 * address accessed if the instruction completed, 183 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb 184 * (or the byte, halfword, float or double forms). 185 * 186 * If we don't check this then any write to the area 187 * between the last mapped region and the stack will 188 * expand the stack rather than segfaulting. 189 */ 190 if (address + 2048 < uregs->r1 191 && (kernel_mode(regs) || !store_updates_sp(regs))) 192 goto bad_area; 193 } 194 if (expand_stack(vma, address)) 195 goto bad_area; 196 197 good_area: 198 code = SEGV_ACCERR; 199 200 /* a write */ 201 if (unlikely(is_write)) { 202 if (unlikely(!(vma->vm_flags & VM_WRITE))) 203 goto bad_area; 204 flags |= FAULT_FLAG_WRITE; 205 /* a read */ 206 } else { 207 /* protection fault */ 208 if (unlikely(error_code & 0x08000000)) 209 goto bad_area; 210 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC)))) 211 goto bad_area; 212 } 213 214 /* 215 * If for any reason at all we couldn't handle the fault, 216 * make sure we exit gracefully rather than endlessly redo 217 * the fault. 218 */ 219 fault = handle_mm_fault(vma, address, flags); 220 221 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) 222 return; 223 224 if (unlikely(fault & VM_FAULT_ERROR)) { 225 if (fault & VM_FAULT_OOM) 226 goto out_of_memory; 227 else if (fault & VM_FAULT_SIGSEGV) 228 goto bad_area; 229 else if (fault & VM_FAULT_SIGBUS) 230 goto do_sigbus; 231 BUG(); 232 } 233 234 if (flags & FAULT_FLAG_ALLOW_RETRY) { 235 if (unlikely(fault & VM_FAULT_MAJOR)) 236 current->maj_flt++; 237 else 238 current->min_flt++; 239 if (fault & VM_FAULT_RETRY) { 240 flags &= ~FAULT_FLAG_ALLOW_RETRY; 241 flags |= FAULT_FLAG_TRIED; 242 243 /* 244 * No need to up_read(&mm->mmap_sem) as we would 245 * have already released it in __lock_page_or_retry 246 * in mm/filemap.c. 247 */ 248 249 goto retry; 250 } 251 } 252 253 up_read(&mm->mmap_sem); 254 255 /* 256 * keep track of tlb+htab misses that are good addrs but 257 * just need pte's created via handle_mm_fault() 258 * -- Cort 259 */ 260 pte_misses++; 261 return; 262 263 bad_area: 264 up_read(&mm->mmap_sem); 265 266 bad_area_nosemaphore: 267 pte_errors++; 268 269 /* User mode accesses cause a SIGSEGV */ 270 if (user_mode(regs)) { 271 _exception(SIGSEGV, regs, code, address); 272 /* info.si_signo = SIGSEGV; 273 info.si_errno = 0; 274 info.si_code = code; 275 info.si_addr = (void *) address; 276 force_sig_info(SIGSEGV, &info, current);*/ 277 return; 278 } 279 280 bad_page_fault(regs, address, SIGSEGV); 281 return; 282 283 /* 284 * We ran out of memory, or some other thing happened to us that made 285 * us unable to handle the page fault gracefully. 286 */ 287 out_of_memory: 288 up_read(&mm->mmap_sem); 289 if (!user_mode(regs)) 290 bad_page_fault(regs, address, SIGKILL); 291 else 292 pagefault_out_of_memory(); 293 return; 294 295 do_sigbus: 296 up_read(&mm->mmap_sem); 297 if (user_mode(regs)) { 298 info.si_signo = SIGBUS; 299 info.si_errno = 0; 300 info.si_code = BUS_ADRERR; 301 info.si_addr = (void __user *)address; 302 force_sig_info(SIGBUS, &info, current); 303 return; 304 } 305 bad_page_fault(regs, address, SIGBUS); 306 } 307