1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Copyright (C) 2009 Sunplus Core Technology Co., Ltd. 4 * Lennox Wu <lennox.wu@sunplusct.com> 5 * Chen Liqin <liqin.chen@sunplusct.com> 6 * Copyright (C) 2012 Regents of the University of California 7 */ 8 9 10 #include <linux/mm.h> 11 #include <linux/kernel.h> 12 #include <linux/interrupt.h> 13 #include <linux/perf_event.h> 14 #include <linux/signal.h> 15 #include <linux/uaccess.h> 16 #include <linux/kprobes.h> 17 #include <linux/kfence.h> 18 #include <linux/entry-common.h> 19 20 #include <asm/ptrace.h> 21 #include <asm/tlbflush.h> 22 23 #include "../kernel/head.h" 24 25 static void die_kernel_fault(const char *msg, unsigned long addr, 26 struct pt_regs *regs) 27 { 28 bust_spinlocks(1); 29 30 pr_alert("Unable to handle kernel %s at virtual address " REG_FMT "\n", msg, 31 addr); 32 33 bust_spinlocks(0); 34 die(regs, "Oops"); 35 make_task_dead(SIGKILL); 36 } 37 38 static inline void no_context(struct pt_regs *regs, unsigned long addr) 39 { 40 const char *msg; 41 42 /* Are we prepared to handle this kernel fault? */ 43 if (fixup_exception(regs)) 44 return; 45 46 /* 47 * Oops. The kernel tried to access some bad page. We'll have to 48 * terminate things with extreme prejudice. 49 */ 50 if (addr < PAGE_SIZE) 51 msg = "NULL pointer dereference"; 52 else { 53 if (kfence_handle_page_fault(addr, regs->cause == EXC_STORE_PAGE_FAULT, regs)) 54 return; 55 56 msg = "paging request"; 57 } 58 59 die_kernel_fault(msg, addr, regs); 60 } 61 62 static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_fault_t fault) 63 { 64 if (fault & VM_FAULT_OOM) { 65 /* 66 * We ran out of memory, call the OOM killer, and return the userspace 67 * (which will retry the fault, or kill us if we got oom-killed). 68 */ 69 if (!user_mode(regs)) { 70 no_context(regs, addr); 71 return; 72 } 73 pagefault_out_of_memory(); 74 return; 75 } else if (fault & VM_FAULT_SIGBUS) { 76 /* Kernel mode? Handle exceptions or die */ 77 if (!user_mode(regs)) { 78 no_context(regs, addr); 79 return; 80 } 81 do_trap(regs, SIGBUS, BUS_ADRERR, addr); 82 return; 83 } 84 BUG(); 85 } 86 87 static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code, unsigned long addr) 88 { 89 /* 90 * Something tried to access memory that isn't in our memory map. 91 * Fix it, but check if it's kernel or user first. 92 */ 93 mmap_read_unlock(mm); 94 /* User mode accesses just cause a SIGSEGV */ 95 if (user_mode(regs)) { 96 do_trap(regs, SIGSEGV, code, addr); 97 return; 98 } 99 100 no_context(regs, addr); 101 } 102 103 static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr) 104 { 105 pgd_t *pgd, *pgd_k; 106 pud_t *pud_k; 107 p4d_t *p4d_k; 108 pmd_t *pmd_k; 109 pte_t *pte_k; 110 int index; 111 unsigned long pfn; 112 113 /* User mode accesses just cause a SIGSEGV */ 114 if (user_mode(regs)) 115 return do_trap(regs, SIGSEGV, code, addr); 116 117 /* 118 * Synchronize this task's top level page-table 119 * with the 'reference' page table. 120 * 121 * Do _not_ use "tsk->active_mm->pgd" here. 122 * We might be inside an interrupt in the middle 123 * of a task switch. 124 */ 125 index = pgd_index(addr); 126 pfn = csr_read(CSR_SATP) & SATP_PPN; 127 pgd = (pgd_t *)pfn_to_virt(pfn) + index; 128 pgd_k = init_mm.pgd + index; 129 130 if (!pgd_present(*pgd_k)) { 131 no_context(regs, addr); 132 return; 133 } 134 set_pgd(pgd, *pgd_k); 135 136 p4d_k = p4d_offset(pgd_k, addr); 137 if (!p4d_present(*p4d_k)) { 138 no_context(regs, addr); 139 return; 140 } 141 142 pud_k = pud_offset(p4d_k, addr); 143 if (!pud_present(*pud_k)) { 144 no_context(regs, addr); 145 return; 146 } 147 if (pud_leaf(*pud_k)) 148 goto flush_tlb; 149 150 /* 151 * Since the vmalloc area is global, it is unnecessary 152 * to copy individual PTEs 153 */ 154 pmd_k = pmd_offset(pud_k, addr); 155 if (!pmd_present(*pmd_k)) { 156 no_context(regs, addr); 157 return; 158 } 159 if (pmd_leaf(*pmd_k)) 160 goto flush_tlb; 161 162 /* 163 * Make sure the actual PTE exists as well to 164 * catch kernel vmalloc-area accesses to non-mapped 165 * addresses. If we don't do this, this will just 166 * silently loop forever. 167 */ 168 pte_k = pte_offset_kernel(pmd_k, addr); 169 if (!pte_present(*pte_k)) { 170 no_context(regs, addr); 171 return; 172 } 173 174 /* 175 * The kernel assumes that TLBs don't cache invalid 176 * entries, but in RISC-V, SFENCE.VMA specifies an 177 * ordering constraint, not a cache flush; it is 178 * necessary even after writing invalid entries. 179 */ 180 flush_tlb: 181 local_flush_tlb_page(addr); 182 } 183 184 static inline bool access_error(unsigned long cause, struct vm_area_struct *vma) 185 { 186 switch (cause) { 187 case EXC_INST_PAGE_FAULT: 188 if (!(vma->vm_flags & VM_EXEC)) { 189 return true; 190 } 191 break; 192 case EXC_LOAD_PAGE_FAULT: 193 /* Write implies read */ 194 if (!(vma->vm_flags & (VM_READ | VM_WRITE))) { 195 return true; 196 } 197 break; 198 case EXC_STORE_PAGE_FAULT: 199 if (!(vma->vm_flags & VM_WRITE)) { 200 return true; 201 } 202 break; 203 default: 204 panic("%s: unhandled cause %lu", __func__, cause); 205 } 206 return false; 207 } 208 209 /* 210 * This routine handles page faults. It determines the address and the 211 * problem, and then passes it off to one of the appropriate routines. 212 */ 213 void handle_page_fault(struct pt_regs *regs) 214 { 215 struct task_struct *tsk; 216 struct vm_area_struct *vma; 217 struct mm_struct *mm; 218 unsigned long addr, cause; 219 unsigned int flags = FAULT_FLAG_DEFAULT; 220 int code = SEGV_MAPERR; 221 vm_fault_t fault; 222 223 cause = regs->cause; 224 addr = regs->badaddr; 225 226 tsk = current; 227 mm = tsk->mm; 228 229 if (kprobe_page_fault(regs, cause)) 230 return; 231 232 /* 233 * Fault-in kernel-space virtual memory on-demand. 234 * The 'reference' page table is init_mm.pgd. 235 * 236 * NOTE! We MUST NOT take any locks for this case. We may 237 * be in an interrupt or a critical region, and should 238 * only copy the information from the master page table, 239 * nothing more. 240 */ 241 if (unlikely((addr >= VMALLOC_START) && (addr < VMALLOC_END))) { 242 vmalloc_fault(regs, code, addr); 243 return; 244 } 245 246 #ifdef CONFIG_64BIT 247 /* 248 * Modules in 64bit kernels lie in their own virtual region which is not 249 * in the vmalloc region, but dealing with page faults in this region 250 * or the vmalloc region amounts to doing the same thing: checking that 251 * the mapping exists in init_mm.pgd and updating user page table, so 252 * just use vmalloc_fault. 253 */ 254 if (unlikely(addr >= MODULES_VADDR && addr < MODULES_END)) { 255 vmalloc_fault(regs, code, addr); 256 return; 257 } 258 #endif 259 /* Enable interrupts if they were enabled in the parent context. */ 260 if (!regs_irqs_disabled(regs)) 261 local_irq_enable(); 262 263 /* 264 * If we're in an interrupt, have no user context, or are running 265 * in an atomic region, then we must not take the fault. 266 */ 267 if (unlikely(faulthandler_disabled() || !mm)) { 268 tsk->thread.bad_cause = cause; 269 no_context(regs, addr); 270 return; 271 } 272 273 if (user_mode(regs)) 274 flags |= FAULT_FLAG_USER; 275 276 if (!user_mode(regs) && addr < TASK_SIZE && unlikely(!(regs->status & SR_SUM))) { 277 if (fixup_exception(regs)) 278 return; 279 280 die_kernel_fault("access to user memory without uaccess routines", addr, regs); 281 } 282 283 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr); 284 285 if (cause == EXC_STORE_PAGE_FAULT) 286 flags |= FAULT_FLAG_WRITE; 287 else if (cause == EXC_INST_PAGE_FAULT) 288 flags |= FAULT_FLAG_INSTRUCTION; 289 retry: 290 mmap_read_lock(mm); 291 vma = find_vma(mm, addr); 292 if (unlikely(!vma)) { 293 tsk->thread.bad_cause = cause; 294 bad_area(regs, mm, code, addr); 295 return; 296 } 297 if (likely(vma->vm_start <= addr)) 298 goto good_area; 299 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { 300 tsk->thread.bad_cause = cause; 301 bad_area(regs, mm, code, addr); 302 return; 303 } 304 if (unlikely(expand_stack(vma, addr))) { 305 tsk->thread.bad_cause = cause; 306 bad_area(regs, mm, code, addr); 307 return; 308 } 309 310 /* 311 * Ok, we have a good vm_area for this memory access, so 312 * we can handle it. 313 */ 314 good_area: 315 code = SEGV_ACCERR; 316 317 if (unlikely(access_error(cause, vma))) { 318 tsk->thread.bad_cause = cause; 319 bad_area(regs, mm, code, addr); 320 return; 321 } 322 323 /* 324 * If for any reason at all we could not handle the fault, 325 * make sure we exit gracefully rather than endlessly redo 326 * the fault. 327 */ 328 fault = handle_mm_fault(vma, addr, flags, regs); 329 330 /* 331 * If we need to retry but a fatal signal is pending, handle the 332 * signal first. We do not need to release the mmap_lock because it 333 * would already be released in __lock_page_or_retry in mm/filemap.c. 334 */ 335 if (fault_signal_pending(fault, regs)) { 336 if (!user_mode(regs)) 337 no_context(regs, addr); 338 return; 339 } 340 341 /* The fault is fully completed (including releasing mmap lock) */ 342 if (fault & VM_FAULT_COMPLETED) 343 return; 344 345 if (unlikely(fault & VM_FAULT_RETRY)) { 346 flags |= FAULT_FLAG_TRIED; 347 348 /* 349 * No need to mmap_read_unlock(mm) as we would 350 * have already released it in __lock_page_or_retry 351 * in mm/filemap.c. 352 */ 353 goto retry; 354 } 355 356 mmap_read_unlock(mm); 357 358 if (unlikely(fault & VM_FAULT_ERROR)) { 359 tsk->thread.bad_cause = cause; 360 mm_fault_error(regs, addr, fault); 361 return; 362 } 363 return; 364 } 365