1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
4 *
5 * Derived from MIPS:
6 * Copyright (C) 1995 - 2000 by Ralf Baechle
7 */
8 #include <linux/context_tracking.h>
9 #include <linux/signal.h>
10 #include <linux/sched.h>
11 #include <linux/interrupt.h>
12 #include <linux/kernel.h>
13 #include <linux/entry-common.h>
14 #include <linux/errno.h>
15 #include <linux/string.h>
16 #include <linux/types.h>
17 #include <linux/ptrace.h>
18 #include <linux/ratelimit.h>
19 #include <linux/mman.h>
20 #include <linux/mm.h>
21 #include <linux/smp.h>
22 #include <linux/kdebug.h>
23 #include <linux/perf_event.h>
24 #include <linux/uaccess.h>
25 #include <linux/kfence.h>
26
27 #include <asm/branch.h>
28 #include <asm/exception.h>
29 #include <asm/mmu_context.h>
30 #include <asm/ptrace.h>
31
32 int show_unhandled_signals = 1;
33
spurious_fault(unsigned long write,unsigned long address)34 static int __kprobes spurious_fault(unsigned long write, unsigned long address)
35 {
36 pgd_t *pgd;
37 p4d_t *p4d;
38 pud_t *pud;
39 pmd_t *pmd;
40 pte_t *pte;
41
42 if (!(address & __UA_LIMIT))
43 return 0;
44
45 pgd = pgd_offset_k(address);
46 if (!pgd_present(pgdp_get(pgd)))
47 return 0;
48
49 p4d = p4d_offset(pgd, address);
50 if (!p4d_present(p4dp_get(p4d)))
51 return 0;
52
53 pud = pud_offset(p4d, address);
54 if (!pud_present(pudp_get(pud)))
55 return 0;
56
57 pmd = pmd_offset(pud, address);
58 if (!pmd_present(pmdp_get(pmd)))
59 return 0;
60
61 if (pmd_leaf(*pmd)) {
62 return write ? pmd_write(pmdp_get(pmd)) : 1;
63 } else {
64 pte = pte_offset_kernel(pmd, address);
65 if (!pte_present(ptep_get(pte)))
66 return 0;
67
68 return write ? pte_write(ptep_get(pte)) : 1;
69 }
70 }
71
no_context(struct pt_regs * regs,unsigned long write,unsigned long address)72 static void __kprobes no_context(struct pt_regs *regs,
73 unsigned long write, unsigned long address)
74 {
75 const int field = sizeof(unsigned long) * 2;
76
77 if (spurious_fault(write, address))
78 return;
79
80 /* Are we prepared to handle this kernel fault? */
81 if (fixup_exception(regs))
82 return;
83
84 if (kfence_handle_page_fault(address, write, regs))
85 return;
86
87 /*
88 * Oops. The kernel tried to access some bad page. We'll have to
89 * terminate things with extreme prejudice.
90 */
91 bust_spinlocks(1);
92
93 pr_alert("CPU %d Unable to handle kernel paging request at "
94 "virtual address %0*lx, era == %0*lx, ra == %0*lx\n",
95 raw_smp_processor_id(), field, address, field, regs->csr_era,
96 field, regs->regs[1]);
97 die("Oops", regs);
98 }
99
do_out_of_memory(struct pt_regs * regs,unsigned long write,unsigned long address)100 static void __kprobes do_out_of_memory(struct pt_regs *regs,
101 unsigned long write, unsigned long address)
102 {
103 /*
104 * We ran out of memory, call the OOM killer, and return the userspace
105 * (which will retry the fault, or kill us if we got oom-killed).
106 */
107 if (!user_mode(regs)) {
108 no_context(regs, write, address);
109 return;
110 }
111 pagefault_out_of_memory();
112 }
113
do_sigbus(struct pt_regs * regs,unsigned long write,unsigned long address,int si_code)114 static void __kprobes do_sigbus(struct pt_regs *regs,
115 unsigned long write, unsigned long address, int si_code)
116 {
117 /* Kernel mode? Handle exceptions or die */
118 if (!user_mode(regs)) {
119 no_context(regs, write, address);
120 return;
121 }
122
123 /*
124 * Send a sigbus, regardless of whether we were in kernel
125 * or user mode.
126 */
127 current->thread.csr_badvaddr = address;
128 current->thread.trap_nr = read_csr_excode();
129 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
130 }
131
do_sigsegv(struct pt_regs * regs,unsigned long write,unsigned long address,int si_code)132 static void __kprobes do_sigsegv(struct pt_regs *regs,
133 unsigned long write, unsigned long address, int si_code)
134 {
135 const int field = sizeof(unsigned long) * 2;
136 static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
137
138 /* Kernel mode? Handle exceptions or die */
139 if (!user_mode(regs)) {
140 no_context(regs, write, address);
141 return;
142 }
143
144 /* User mode accesses just cause a SIGSEGV */
145 current->thread.csr_badvaddr = address;
146 if (!write)
147 current->thread.error_code = 1;
148 else
149 current->thread.error_code = 2;
150 current->thread.trap_nr = read_csr_excode();
151
152 if (show_unhandled_signals &&
153 unhandled_signal(current, SIGSEGV) && __ratelimit(&ratelimit_state)) {
154 pr_info("do_page_fault(): sending SIGSEGV to %s for invalid %s %0*lx\n",
155 current->comm,
156 write ? "write access to" : "read access from",
157 field, address);
158 pr_info("era = %0*lx in", field,
159 (unsigned long) regs->csr_era);
160 print_vma_addr(KERN_CONT " ", regs->csr_era);
161 pr_cont("\n");
162 pr_info("ra = %0*lx in", field,
163 (unsigned long) regs->regs[1]);
164 print_vma_addr(KERN_CONT " ", regs->regs[1]);
165 pr_cont("\n");
166 }
167 force_sig_fault(SIGSEGV, si_code, (void __user *)address);
168 }
169
170 /*
171 * This routine handles page faults. It determines the address,
172 * and the problem, and then passes it off to one of the appropriate
173 * routines.
174 */
__do_page_fault(struct pt_regs * regs,unsigned long write,unsigned long address)175 static void __kprobes __do_page_fault(struct pt_regs *regs,
176 unsigned long write, unsigned long address)
177 {
178 int si_code = SEGV_MAPERR;
179 unsigned int flags = FAULT_FLAG_DEFAULT;
180 struct task_struct *tsk = current;
181 struct mm_struct *mm = tsk->mm;
182 struct vm_area_struct *vma = NULL;
183 vm_fault_t fault;
184
185 if (kprobe_page_fault(regs, current->thread.trap_nr))
186 return;
187
188 /*
189 * We fault-in kernel-space virtual memory on-demand. The
190 * 'reference' page table is init_mm.pgd.
191 *
192 * NOTE! We MUST NOT take any locks for this case. We may
193 * be in an interrupt or a critical region, and should
194 * only copy the information from the master page table,
195 * nothing more.
196 */
197 if (address & __UA_LIMIT) {
198 if (!user_mode(regs))
199 no_context(regs, write, address);
200 else
201 do_sigsegv(regs, write, address, si_code);
202 return;
203 }
204
205 /*
206 * If we're in an interrupt or have no user
207 * context, we must not take the fault..
208 */
209 if (faulthandler_disabled() || !mm) {
210 do_sigsegv(regs, write, address, si_code);
211 return;
212 }
213
214 if (user_mode(regs))
215 flags |= FAULT_FLAG_USER;
216
217 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
218
219 if (!(flags & FAULT_FLAG_USER))
220 goto lock_mmap;
221
222 vma = lock_vma_under_rcu(mm, address);
223 if (!vma)
224 goto lock_mmap;
225
226 if (write) {
227 flags |= FAULT_FLAG_WRITE;
228 if (!(vma->vm_flags & VM_WRITE)) {
229 vma_end_read(vma);
230 si_code = SEGV_ACCERR;
231 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
232 goto bad_area_nosemaphore;
233 }
234 } else {
235 if (!(vma->vm_flags & VM_EXEC) && address == exception_era(regs)) {
236 vma_end_read(vma);
237 si_code = SEGV_ACCERR;
238 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
239 goto bad_area_nosemaphore;
240 }
241 if (!(vma->vm_flags & (VM_READ | VM_WRITE)) && address != exception_era(regs)) {
242 vma_end_read(vma);
243 si_code = SEGV_ACCERR;
244 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
245 goto bad_area_nosemaphore;
246 }
247 }
248
249 fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
250 if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
251 vma_end_read(vma);
252
253 if (!(fault & VM_FAULT_RETRY)) {
254 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
255 goto done;
256 }
257
258 count_vm_vma_lock_event(VMA_LOCK_RETRY);
259 if (fault & VM_FAULT_MAJOR)
260 flags |= FAULT_FLAG_TRIED;
261
262 /* Quick path to respond to signals */
263 if (fault_signal_pending(fault, regs)) {
264 if (!user_mode(regs))
265 no_context(regs, write, address);
266 return;
267 }
268 lock_mmap:
269
270 retry:
271 vma = lock_mm_and_find_vma(mm, address, regs);
272 if (unlikely(!vma))
273 goto bad_area_nosemaphore;
274 goto good_area;
275
276 /*
277 * Something tried to access memory that isn't in our memory map..
278 * Fix it, but check if it's kernel or user first..
279 */
280 bad_area:
281 mmap_read_unlock(mm);
282 bad_area_nosemaphore:
283 do_sigsegv(regs, write, address, si_code);
284 return;
285
286 /*
287 * Ok, we have a good vm_area for this memory access, so
288 * we can handle it..
289 */
290 good_area:
291 si_code = SEGV_ACCERR;
292
293 if (write) {
294 flags |= FAULT_FLAG_WRITE;
295 if (!(vma->vm_flags & VM_WRITE))
296 goto bad_area;
297 } else {
298 if (!(vma->vm_flags & VM_EXEC) && address == exception_era(regs))
299 goto bad_area;
300 if (!(vma->vm_flags & (VM_READ | VM_WRITE)) && address != exception_era(regs))
301 goto bad_area;
302 }
303
304 /*
305 * If for any reason at all we couldn't handle the fault,
306 * make sure we exit gracefully rather than endlessly redo
307 * the fault.
308 */
309 fault = handle_mm_fault(vma, address, flags, regs);
310
311 if (fault_signal_pending(fault, regs)) {
312 if (!user_mode(regs))
313 no_context(regs, write, address);
314 return;
315 }
316
317 /* The fault is fully completed (including releasing mmap lock) */
318 if (fault & VM_FAULT_COMPLETED)
319 return;
320
321 if (unlikely(fault & VM_FAULT_RETRY)) {
322 flags |= FAULT_FLAG_TRIED;
323
324 /*
325 * No need to mmap_read_unlock(mm) as we would
326 * have already released it in __lock_page_or_retry
327 * in mm/filemap.c.
328 */
329 goto retry;
330 }
331 mmap_read_unlock(mm);
332
333 done:
334 if (unlikely(fault & VM_FAULT_ERROR)) {
335 if (fault & VM_FAULT_OOM) {
336 do_out_of_memory(regs, write, address);
337 return;
338 } else if (fault & VM_FAULT_SIGSEGV) {
339 do_sigsegv(regs, write, address, si_code);
340 return;
341 } else if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
342 do_sigbus(regs, write, address, si_code);
343 return;
344 }
345 BUG();
346 }
347 }
348
do_page_fault(struct pt_regs * regs,unsigned long write,unsigned long address)349 asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
350 unsigned long write, unsigned long address)
351 {
352 irqentry_state_t state = irqentry_enter(regs);
353
354 /* Enable interrupt if enabled in parent context */
355 if (likely(regs->csr_prmd & CSR_PRMD_PIE))
356 local_irq_enable();
357
358 __do_page_fault(regs, write, address);
359
360 local_irq_disable();
361
362 irqentry_exit(regs, state);
363 }
364