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 #include <linux/perf_event.h> 32 33 #include <asm/page.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_DEFAULT; 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 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 126 127 /* When running in the kernel we expect faults to occur only to 128 * addresses in user space. All other faults represent errors in the 129 * kernel and should generate an OOPS. Unfortunately, in the case of an 130 * erroneous fault occurring in a code path which already holds mmap_lock 131 * we will deadlock attempting to validate the fault against the 132 * address space. Luckily the kernel only validly references user 133 * space from well defined areas of code, which are listed in the 134 * exceptions table. 135 * 136 * As the vast majority of faults will be valid we will only perform 137 * the source reference check when there is a possibility of a deadlock. 138 * Attempt to lock the address space, if we cannot we then validate the 139 * source. If this is invalid we can skip the address space check, 140 * thus avoiding the deadlock. 141 */ 142 if (unlikely(!mmap_read_trylock(mm))) { 143 if (kernel_mode(regs) && !search_exception_tables(regs->pc)) 144 goto bad_area_nosemaphore; 145 146 retry: 147 mmap_read_lock(mm); 148 } 149 150 vma = find_vma(mm, address); 151 if (unlikely(!vma)) 152 goto bad_area; 153 154 if (vma->vm_start <= address) 155 goto good_area; 156 157 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) 158 goto bad_area; 159 160 if (unlikely(!is_write)) 161 goto bad_area; 162 163 /* 164 * N.B. The ABI allows programs to access up to 165 * a few hundred bytes below the stack pointer (TBD). 166 * The kernel signal delivery code writes up to about 1.5kB 167 * below the stack pointer (r1) before decrementing it. 168 * The exec code can write slightly over 640kB to the stack 169 * before setting the user r1. Thus we allow the stack to 170 * expand to 1MB without further checks. 171 */ 172 if (unlikely(address + 0x100000 < vma->vm_end)) { 173 174 /* get user regs even if this fault is in kernel mode */ 175 struct pt_regs *uregs = current->thread.regs; 176 if (uregs == NULL) 177 goto bad_area; 178 179 /* 180 * A user-mode access to an address a long way below 181 * the stack pointer is only valid if the instruction 182 * is one which would update the stack pointer to the 183 * address accessed if the instruction completed, 184 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb 185 * (or the byte, halfword, float or double forms). 186 * 187 * If we don't check this then any write to the area 188 * between the last mapped region and the stack will 189 * expand the stack rather than segfaulting. 190 */ 191 if (address + 2048 < uregs->r1 192 && (kernel_mode(regs) || !store_updates_sp(regs))) 193 goto bad_area; 194 } 195 if (expand_stack(vma, address)) 196 goto bad_area; 197 198 good_area: 199 code = SEGV_ACCERR; 200 201 /* a write */ 202 if (unlikely(is_write)) { 203 if (unlikely(!(vma->vm_flags & VM_WRITE))) 204 goto bad_area; 205 flags |= FAULT_FLAG_WRITE; 206 /* a read */ 207 } else { 208 /* protection fault */ 209 if (unlikely(error_code & 0x08000000)) 210 goto bad_area; 211 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC)))) 212 goto bad_area; 213 } 214 215 /* 216 * If for any reason at all we couldn't handle the fault, 217 * make sure we exit gracefully rather than endlessly redo 218 * the fault. 219 */ 220 fault = handle_mm_fault(vma, address, flags, regs); 221 222 if (fault_signal_pending(fault, regs)) { 223 if (!user_mode(regs)) 224 bad_page_fault(regs, address, SIGBUS); 225 return; 226 } 227 228 /* The fault is fully completed (including releasing mmap lock) */ 229 if (fault & VM_FAULT_COMPLETED) 230 return; 231 232 if (unlikely(fault & VM_FAULT_ERROR)) { 233 if (fault & VM_FAULT_OOM) 234 goto out_of_memory; 235 else if (fault & VM_FAULT_SIGSEGV) 236 goto bad_area; 237 else if (fault & VM_FAULT_SIGBUS) 238 goto do_sigbus; 239 BUG(); 240 } 241 242 if (fault & VM_FAULT_RETRY) { 243 flags |= FAULT_FLAG_TRIED; 244 245 /* 246 * No need to mmap_read_unlock(mm) as we would 247 * have already released it in __lock_page_or_retry 248 * in mm/filemap.c. 249 */ 250 251 goto retry; 252 } 253 254 mmap_read_unlock(mm); 255 256 /* 257 * keep track of tlb+htab misses that are good addrs but 258 * just need pte's created via handle_mm_fault() 259 * -- Cort 260 */ 261 pte_misses++; 262 return; 263 264 bad_area: 265 mmap_read_unlock(mm); 266 267 bad_area_nosemaphore: 268 pte_errors++; 269 270 /* User mode accesses cause a SIGSEGV */ 271 if (user_mode(regs)) { 272 _exception(SIGSEGV, regs, code, address); 273 return; 274 } 275 276 bad_page_fault(regs, address, SIGSEGV); 277 return; 278 279 /* 280 * We ran out of memory, or some other thing happened to us that made 281 * us unable to handle the page fault gracefully. 282 */ 283 out_of_memory: 284 mmap_read_unlock(mm); 285 if (!user_mode(regs)) 286 bad_page_fault(regs, address, SIGKILL); 287 else 288 pagefault_out_of_memory(); 289 return; 290 291 do_sigbus: 292 mmap_read_unlock(mm); 293 if (user_mode(regs)) { 294 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 295 return; 296 } 297 bad_page_fault(regs, address, SIGBUS); 298 } 299