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