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
no_context(struct pt_regs * regs,unsigned long write,unsigned long address)34 static void __kprobes no_context(struct pt_regs *regs,
35 unsigned long write, unsigned long address)
36 {
37 const int field = sizeof(unsigned long) * 2;
38
39 /* Are we prepared to handle this kernel fault? */
40 if (fixup_exception(regs))
41 return;
42
43 if (kfence_handle_page_fault(address, write, 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 bust_spinlocks(1);
51
52 pr_alert("CPU %d Unable to handle kernel paging request at "
53 "virtual address %0*lx, era == %0*lx, ra == %0*lx\n",
54 raw_smp_processor_id(), field, address, field, regs->csr_era,
55 field, regs->regs[1]);
56 die("Oops", regs);
57 }
58
do_out_of_memory(struct pt_regs * regs,unsigned long write,unsigned long address)59 static void __kprobes do_out_of_memory(struct pt_regs *regs,
60 unsigned long write, unsigned long address)
61 {
62 /*
63 * We ran out of memory, call the OOM killer, and return the userspace
64 * (which will retry the fault, or kill us if we got oom-killed).
65 */
66 if (!user_mode(regs)) {
67 no_context(regs, write, address);
68 return;
69 }
70 pagefault_out_of_memory();
71 }
72
do_sigbus(struct pt_regs * regs,unsigned long write,unsigned long address,int si_code)73 static void __kprobes do_sigbus(struct pt_regs *regs,
74 unsigned long write, unsigned long address, int si_code)
75 {
76 /* Kernel mode? Handle exceptions or die */
77 if (!user_mode(regs)) {
78 no_context(regs, write, address);
79 return;
80 }
81
82 /*
83 * Send a sigbus, regardless of whether we were in kernel
84 * or user mode.
85 */
86 current->thread.csr_badvaddr = address;
87 current->thread.trap_nr = read_csr_excode();
88 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
89 }
90
do_sigsegv(struct pt_regs * regs,unsigned long write,unsigned long address,int si_code)91 static void __kprobes do_sigsegv(struct pt_regs *regs,
92 unsigned long write, unsigned long address, int si_code)
93 {
94 const int field = sizeof(unsigned long) * 2;
95 static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
96
97 /* Kernel mode? Handle exceptions or die */
98 if (!user_mode(regs)) {
99 no_context(regs, write, address);
100 return;
101 }
102
103 /* User mode accesses just cause a SIGSEGV */
104 current->thread.csr_badvaddr = address;
105 if (!write)
106 current->thread.error_code = 1;
107 else
108 current->thread.error_code = 2;
109 current->thread.trap_nr = read_csr_excode();
110
111 if (show_unhandled_signals &&
112 unhandled_signal(current, SIGSEGV) && __ratelimit(&ratelimit_state)) {
113 pr_info("do_page_fault(): sending SIGSEGV to %s for invalid %s %0*lx\n",
114 current->comm,
115 write ? "write access to" : "read access from",
116 field, address);
117 pr_info("era = %0*lx in", field,
118 (unsigned long) regs->csr_era);
119 print_vma_addr(KERN_CONT " ", regs->csr_era);
120 pr_cont("\n");
121 pr_info("ra = %0*lx in", field,
122 (unsigned long) regs->regs[1]);
123 print_vma_addr(KERN_CONT " ", regs->regs[1]);
124 pr_cont("\n");
125 }
126 force_sig_fault(SIGSEGV, si_code, (void __user *)address);
127 }
128
129 /*
130 * This routine handles page faults. It determines the address,
131 * and the problem, and then passes it off to one of the appropriate
132 * routines.
133 */
__do_page_fault(struct pt_regs * regs,unsigned long write,unsigned long address)134 static void __kprobes __do_page_fault(struct pt_regs *regs,
135 unsigned long write, unsigned long address)
136 {
137 int si_code = SEGV_MAPERR;
138 unsigned int flags = FAULT_FLAG_DEFAULT;
139 struct task_struct *tsk = current;
140 struct mm_struct *mm = tsk->mm;
141 struct vm_area_struct *vma = NULL;
142 vm_fault_t fault;
143
144 if (kprobe_page_fault(regs, current->thread.trap_nr))
145 return;
146
147 /*
148 * We fault-in kernel-space virtual memory on-demand. The
149 * 'reference' page table is init_mm.pgd.
150 *
151 * NOTE! We MUST NOT take any locks for this case. We may
152 * be in an interrupt or a critical region, and should
153 * only copy the information from the master page table,
154 * nothing more.
155 */
156 if (address & __UA_LIMIT) {
157 if (!user_mode(regs))
158 no_context(regs, write, address);
159 else
160 do_sigsegv(regs, write, address, si_code);
161 return;
162 }
163
164 /*
165 * If we're in an interrupt or have no user
166 * context, we must not take the fault..
167 */
168 if (faulthandler_disabled() || !mm) {
169 do_sigsegv(regs, write, address, si_code);
170 return;
171 }
172
173 if (user_mode(regs))
174 flags |= FAULT_FLAG_USER;
175
176 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
177 retry:
178 vma = lock_mm_and_find_vma(mm, address, regs);
179 if (unlikely(!vma))
180 goto bad_area_nosemaphore;
181 goto good_area;
182
183 /*
184 * Something tried to access memory that isn't in our memory map..
185 * Fix it, but check if it's kernel or user first..
186 */
187 bad_area:
188 mmap_read_unlock(mm);
189 bad_area_nosemaphore:
190 do_sigsegv(regs, write, address, si_code);
191 return;
192
193 /*
194 * Ok, we have a good vm_area for this memory access, so
195 * we can handle it..
196 */
197 good_area:
198 si_code = SEGV_ACCERR;
199
200 if (write) {
201 flags |= FAULT_FLAG_WRITE;
202 if (!(vma->vm_flags & VM_WRITE))
203 goto bad_area;
204 } else {
205 if (!(vma->vm_flags & VM_READ) && address != exception_era(regs))
206 goto bad_area;
207 if (!(vma->vm_flags & VM_EXEC) && address == exception_era(regs))
208 goto bad_area;
209 }
210
211 /*
212 * If for any reason at all we couldn't handle the fault,
213 * make sure we exit gracefully rather than endlessly redo
214 * the fault.
215 */
216 fault = handle_mm_fault(vma, address, flags, regs);
217
218 if (fault_signal_pending(fault, regs)) {
219 if (!user_mode(regs))
220 no_context(regs, write, address);
221 return;
222 }
223
224 /* The fault is fully completed (including releasing mmap lock) */
225 if (fault & VM_FAULT_COMPLETED)
226 return;
227
228 if (unlikely(fault & VM_FAULT_RETRY)) {
229 flags |= FAULT_FLAG_TRIED;
230
231 /*
232 * No need to mmap_read_unlock(mm) as we would
233 * have already released it in __lock_page_or_retry
234 * in mm/filemap.c.
235 */
236 goto retry;
237 }
238 if (unlikely(fault & VM_FAULT_ERROR)) {
239 mmap_read_unlock(mm);
240 if (fault & VM_FAULT_OOM) {
241 do_out_of_memory(regs, write, address);
242 return;
243 } else if (fault & VM_FAULT_SIGSEGV) {
244 do_sigsegv(regs, write, address, si_code);
245 return;
246 } else if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
247 do_sigbus(regs, write, address, si_code);
248 return;
249 }
250 BUG();
251 }
252
253 mmap_read_unlock(mm);
254 }
255
do_page_fault(struct pt_regs * regs,unsigned long write,unsigned long address)256 asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
257 unsigned long write, unsigned long address)
258 {
259 irqentry_state_t state = irqentry_enter(regs);
260
261 /* Enable interrupt if enabled in parent context */
262 if (likely(regs->csr_prmd & CSR_PRMD_PIE))
263 local_irq_enable();
264
265 __do_page_fault(regs, write, address);
266
267 local_irq_disable();
268
269 irqentry_exit(regs, state);
270 }
271
