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
die_kernel_fault(const char * msg,unsigned long addr,struct pt_regs * regs)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
no_context(struct pt_regs * regs,unsigned long addr)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
mm_fault_error(struct pt_regs * regs,unsigned long addr,vm_fault_t fault)62 static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_fault_t fault)
63 {
64 if (!user_mode(regs)) {
65 no_context(regs, addr);
66 return;
67 }
68
69 if (fault & VM_FAULT_OOM) {
70 /*
71 * We ran out of memory, call the OOM killer, and return the userspace
72 * (which will retry the fault, or kill us if we got oom-killed).
73 */
74 pagefault_out_of_memory();
75 return;
76 } else if (fault & (VM_FAULT_SIGBUS | VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) {
77 /* Kernel mode? Handle exceptions or die */
78 do_trap(regs, SIGBUS, BUS_ADRERR, addr);
79 return;
80 } else if (fault & VM_FAULT_SIGSEGV) {
81 do_trap(regs, SIGSEGV, SEGV_MAPERR, addr);
82 return;
83 }
84
85 BUG();
86 }
87
88 static inline void
bad_area_nosemaphore(struct pt_regs * regs,int code,unsigned long addr)89 bad_area_nosemaphore(struct pt_regs *regs, int code, unsigned long addr)
90 {
91 /*
92 * Something tried to access memory that isn't in our memory map.
93 * Fix it, but check if it's kernel or user first.
94 */
95 /* User mode accesses just cause a SIGSEGV */
96 if (user_mode(regs)) {
97 do_trap(regs, SIGSEGV, code, addr);
98 return;
99 }
100
101 no_context(regs, addr);
102 }
103
104 static inline void
bad_area(struct pt_regs * regs,struct mm_struct * mm,int code,unsigned long addr)105 bad_area(struct pt_regs *regs, struct mm_struct *mm, int code,
106 unsigned long addr)
107 {
108 mmap_read_unlock(mm);
109
110 bad_area_nosemaphore(regs, code, addr);
111 }
112
vmalloc_fault(struct pt_regs * regs,int code,unsigned long addr)113 static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
114 {
115 pgd_t *pgd, *pgd_k;
116 pud_t *pud_k;
117 p4d_t *p4d_k;
118 pmd_t *pmd_k;
119 pte_t *pte_k;
120 int index;
121 unsigned long pfn;
122
123 /* User mode accesses just cause a SIGSEGV */
124 if (user_mode(regs))
125 return do_trap(regs, SIGSEGV, code, addr);
126
127 /*
128 * Synchronize this task's top level page-table
129 * with the 'reference' page table.
130 *
131 * Do _not_ use "tsk->active_mm->pgd" here.
132 * We might be inside an interrupt in the middle
133 * of a task switch.
134 */
135 index = pgd_index(addr);
136 pfn = csr_read(CSR_SATP) & SATP_PPN;
137 pgd = (pgd_t *)pfn_to_virt(pfn) + index;
138 pgd_k = init_mm.pgd + index;
139
140 if (!pgd_present(*pgd_k)) {
141 no_context(regs, addr);
142 return;
143 }
144 set_pgd(pgd, *pgd_k);
145
146 p4d_k = p4d_offset(pgd_k, addr);
147 if (!p4d_present(*p4d_k)) {
148 no_context(regs, addr);
149 return;
150 }
151
152 pud_k = pud_offset(p4d_k, addr);
153 if (!pud_present(*pud_k)) {
154 no_context(regs, addr);
155 return;
156 }
157 if (pud_leaf(*pud_k))
158 goto flush_tlb;
159
160 /*
161 * Since the vmalloc area is global, it is unnecessary
162 * to copy individual PTEs
163 */
164 pmd_k = pmd_offset(pud_k, addr);
165 if (!pmd_present(*pmd_k)) {
166 no_context(regs, addr);
167 return;
168 }
169 if (pmd_leaf(*pmd_k))
170 goto flush_tlb;
171
172 /*
173 * Make sure the actual PTE exists as well to
174 * catch kernel vmalloc-area accesses to non-mapped
175 * addresses. If we don't do this, this will just
176 * silently loop forever.
177 */
178 pte_k = pte_offset_kernel(pmd_k, addr);
179 if (!pte_present(*pte_k)) {
180 no_context(regs, addr);
181 return;
182 }
183
184 /*
185 * The kernel assumes that TLBs don't cache invalid
186 * entries, but in RISC-V, SFENCE.VMA specifies an
187 * ordering constraint, not a cache flush; it is
188 * necessary even after writing invalid entries.
189 */
190 flush_tlb:
191 local_flush_tlb_page(addr);
192 }
193
access_error(unsigned long cause,struct vm_area_struct * vma)194 static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
195 {
196 switch (cause) {
197 case EXC_INST_PAGE_FAULT:
198 if (!(vma->vm_flags & VM_EXEC)) {
199 return true;
200 }
201 break;
202 case EXC_LOAD_PAGE_FAULT:
203 /* Write implies read */
204 if (!(vma->vm_flags & (VM_READ | VM_WRITE))) {
205 return true;
206 }
207 break;
208 case EXC_STORE_PAGE_FAULT:
209 if (!(vma->vm_flags & VM_WRITE)) {
210 return true;
211 }
212 break;
213 default:
214 panic("%s: unhandled cause %lu", __func__, cause);
215 }
216 return false;
217 }
218
219 /*
220 * This routine handles page faults. It determines the address and the
221 * problem, and then passes it off to one of the appropriate routines.
222 */
handle_page_fault(struct pt_regs * regs)223 void handle_page_fault(struct pt_regs *regs)
224 {
225 struct task_struct *tsk;
226 struct vm_area_struct *vma;
227 struct mm_struct *mm;
228 unsigned long addr, cause;
229 unsigned int flags = FAULT_FLAG_DEFAULT;
230 int code = SEGV_MAPERR;
231 vm_fault_t fault;
232
233 cause = regs->cause;
234 addr = regs->badaddr;
235
236 tsk = current;
237 mm = tsk->mm;
238
239 if (kprobe_page_fault(regs, cause))
240 return;
241
242 /*
243 * Fault-in kernel-space virtual memory on-demand.
244 * The 'reference' page table is init_mm.pgd.
245 *
246 * NOTE! We MUST NOT take any locks for this case. We may
247 * be in an interrupt or a critical region, and should
248 * only copy the information from the master page table,
249 * nothing more.
250 */
251 if ((!IS_ENABLED(CONFIG_MMU) || !IS_ENABLED(CONFIG_64BIT)) &&
252 unlikely(addr >= VMALLOC_START && addr < VMALLOC_END)) {
253 vmalloc_fault(regs, code, addr);
254 return;
255 }
256
257 /* Enable interrupts if they were enabled in the parent context. */
258 if (!regs_irqs_disabled(regs))
259 local_irq_enable();
260
261 /*
262 * If we're in an interrupt, have no user context, or are running
263 * in an atomic region, then we must not take the fault.
264 */
265 if (unlikely(faulthandler_disabled() || !mm)) {
266 tsk->thread.bad_cause = cause;
267 no_context(regs, addr);
268 return;
269 }
270
271 if (user_mode(regs))
272 flags |= FAULT_FLAG_USER;
273
274 if (!user_mode(regs) && addr < TASK_SIZE && unlikely(!(regs->status & SR_SUM))) {
275 if (fixup_exception(regs))
276 return;
277
278 die_kernel_fault("access to user memory without uaccess routines", addr, regs);
279 }
280
281 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
282
283 if (cause == EXC_STORE_PAGE_FAULT)
284 flags |= FAULT_FLAG_WRITE;
285 else if (cause == EXC_INST_PAGE_FAULT)
286 flags |= FAULT_FLAG_INSTRUCTION;
287 if (!(flags & FAULT_FLAG_USER))
288 goto lock_mmap;
289
290 vma = lock_vma_under_rcu(mm, addr);
291 if (!vma)
292 goto lock_mmap;
293
294 if (unlikely(access_error(cause, vma))) {
295 vma_end_read(vma);
296 goto lock_mmap;
297 }
298
299 fault = handle_mm_fault(vma, addr, flags | FAULT_FLAG_VMA_LOCK, regs);
300 if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
301 vma_end_read(vma);
302
303 if (!(fault & VM_FAULT_RETRY)) {
304 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
305 goto done;
306 }
307 count_vm_vma_lock_event(VMA_LOCK_RETRY);
308 if (fault & VM_FAULT_MAJOR)
309 flags |= FAULT_FLAG_TRIED;
310
311 if (fault_signal_pending(fault, regs)) {
312 if (!user_mode(regs))
313 no_context(regs, addr);
314 return;
315 }
316 lock_mmap:
317
318 retry:
319 vma = lock_mm_and_find_vma(mm, addr, regs);
320 if (unlikely(!vma)) {
321 tsk->thread.bad_cause = cause;
322 bad_area_nosemaphore(regs, code, addr);
323 return;
324 }
325
326 /*
327 * Ok, we have a good vm_area for this memory access, so
328 * we can handle it.
329 */
330 code = SEGV_ACCERR;
331
332 if (unlikely(access_error(cause, vma))) {
333 tsk->thread.bad_cause = cause;
334 bad_area(regs, mm, code, addr);
335 return;
336 }
337
338 /*
339 * If for any reason at all we could not handle the fault,
340 * make sure we exit gracefully rather than endlessly redo
341 * the fault.
342 */
343 fault = handle_mm_fault(vma, addr, flags, regs);
344
345 /*
346 * If we need to retry but a fatal signal is pending, handle the
347 * signal first. We do not need to release the mmap_lock because it
348 * would already be released in __lock_page_or_retry in mm/filemap.c.
349 */
350 if (fault_signal_pending(fault, regs)) {
351 if (!user_mode(regs))
352 no_context(regs, addr);
353 return;
354 }
355
356 /* The fault is fully completed (including releasing mmap lock) */
357 if (fault & VM_FAULT_COMPLETED)
358 return;
359
360 if (unlikely(fault & VM_FAULT_RETRY)) {
361 flags |= FAULT_FLAG_TRIED;
362
363 /*
364 * No need to mmap_read_unlock(mm) as we would
365 * have already released it in __lock_page_or_retry
366 * in mm/filemap.c.
367 */
368 goto retry;
369 }
370
371 mmap_read_unlock(mm);
372
373 done:
374 if (unlikely(fault & VM_FAULT_ERROR)) {
375 tsk->thread.bad_cause = cause;
376 mm_fault_error(regs, addr, fault);
377 return;
378 }
379 return;
380 }
381