1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
4 */
5
6 #include <linux/mm.h>
7 #include <linux/sched/signal.h>
8 #include <linux/hardirq.h>
9 #include <linux/module.h>
10 #include <linux/uaccess.h>
11 #include <linux/sched/debug.h>
12 #include <asm/current.h>
13 #include <asm/tlbflush.h>
14 #include <arch.h>
15 #include <as-layout.h>
16 #include <kern_util.h>
17 #include <os.h>
18 #include <skas.h>
19
20 /*
21 * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
22 * segv().
23 */
handle_page_fault(unsigned long address,unsigned long ip,int is_write,int is_user,int * code_out)24 int handle_page_fault(unsigned long address, unsigned long ip,
25 int is_write, int is_user, int *code_out)
26 {
27 struct mm_struct *mm = current->mm;
28 struct vm_area_struct *vma;
29 pmd_t *pmd;
30 pte_t *pte;
31 int err = -EFAULT;
32 unsigned int flags = FAULT_FLAG_DEFAULT;
33
34 *code_out = SEGV_MAPERR;
35
36 /*
37 * If the fault was with pagefaults disabled, don't take the fault, just
38 * fail.
39 */
40 if (faulthandler_disabled())
41 goto out_nosemaphore;
42
43 if (is_user)
44 flags |= FAULT_FLAG_USER;
45 retry:
46 mmap_read_lock(mm);
47 vma = find_vma(mm, address);
48 if (!vma)
49 goto out;
50 else if (vma->vm_start <= address)
51 goto good_area;
52 else if (!(vma->vm_flags & VM_GROWSDOWN))
53 goto out;
54 else if (is_user && !ARCH_IS_STACKGROW(address))
55 goto out;
56 else if (expand_stack(vma, address))
57 goto out;
58
59 good_area:
60 *code_out = SEGV_ACCERR;
61 if (is_write) {
62 if (!(vma->vm_flags & VM_WRITE))
63 goto out;
64 flags |= FAULT_FLAG_WRITE;
65 } else {
66 /* Don't require VM_READ|VM_EXEC for write faults! */
67 if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
68 goto out;
69 }
70
71 do {
72 vm_fault_t fault;
73
74 fault = handle_mm_fault(vma, address, flags, NULL);
75
76 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
77 goto out_nosemaphore;
78
79 /* The fault is fully completed (including releasing mmap lock) */
80 if (fault & VM_FAULT_COMPLETED)
81 return 0;
82
83 if (unlikely(fault & VM_FAULT_ERROR)) {
84 if (fault & VM_FAULT_OOM) {
85 goto out_of_memory;
86 } else if (fault & VM_FAULT_SIGSEGV) {
87 goto out;
88 } else if (fault & VM_FAULT_SIGBUS) {
89 err = -EACCES;
90 goto out;
91 }
92 BUG();
93 }
94 if (fault & VM_FAULT_RETRY) {
95 flags |= FAULT_FLAG_TRIED;
96
97 goto retry;
98 }
99
100 pmd = pmd_off(mm, address);
101 pte = pte_offset_kernel(pmd, address);
102 } while (!pte_present(*pte));
103 err = 0;
104 /*
105 * The below warning was added in place of
106 * pte_mkyoung(); if (is_write) pte_mkdirty();
107 * If it's triggered, we'd see normally a hang here (a clean pte is
108 * marked read-only to emulate the dirty bit).
109 * However, the generic code can mark a PTE writable but clean on a
110 * concurrent read fault, triggering this harmlessly. So comment it out.
111 */
112 #if 0
113 WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
114 #endif
115 flush_tlb_page(vma, address);
116 out:
117 mmap_read_unlock(mm);
118 out_nosemaphore:
119 return err;
120
121 out_of_memory:
122 /*
123 * We ran out of memory, call the OOM killer, and return the userspace
124 * (which will retry the fault, or kill us if we got oom-killed).
125 */
126 mmap_read_unlock(mm);
127 if (!is_user)
128 goto out_nosemaphore;
129 pagefault_out_of_memory();
130 return 0;
131 }
132
show_segv_info(struct uml_pt_regs * regs)133 static void show_segv_info(struct uml_pt_regs *regs)
134 {
135 struct task_struct *tsk = current;
136 struct faultinfo *fi = UPT_FAULTINFO(regs);
137
138 if (!unhandled_signal(tsk, SIGSEGV))
139 return;
140
141 if (!printk_ratelimit())
142 return;
143
144 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x",
145 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
146 tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
147 (void *)UPT_IP(regs), (void *)UPT_SP(regs),
148 fi->error_code);
149
150 print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
151 printk(KERN_CONT "\n");
152 }
153
bad_segv(struct faultinfo fi,unsigned long ip)154 static void bad_segv(struct faultinfo fi, unsigned long ip)
155 {
156 current->thread.arch.faultinfo = fi;
157 force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
158 }
159
fatal_sigsegv(void)160 void fatal_sigsegv(void)
161 {
162 force_fatal_sig(SIGSEGV);
163 do_signal(¤t->thread.regs);
164 /*
165 * This is to tell gcc that we're not returning - do_signal
166 * can, in general, return, but in this case, it's not, since
167 * we just got a fatal SIGSEGV queued.
168 */
169 os_dump_core();
170 }
171
172 /**
173 * segv_handler() - the SIGSEGV handler
174 * @sig: the signal number
175 * @unused_si: the signal info struct; unused in this handler
176 * @regs: the ptrace register information
177 *
178 * The handler first extracts the faultinfo from the UML ptrace regs struct.
179 * If the userfault did not happen in an UML userspace process, bad_segv is called.
180 * Otherwise the signal did happen in a cloned userspace process, handle it.
181 */
segv_handler(int sig,struct siginfo * unused_si,struct uml_pt_regs * regs)182 void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
183 {
184 struct faultinfo * fi = UPT_FAULTINFO(regs);
185
186 if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
187 show_segv_info(regs);
188 bad_segv(*fi, UPT_IP(regs));
189 return;
190 }
191 segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
192 }
193
194 /*
195 * We give a *copy* of the faultinfo in the regs to segv.
196 * This must be done, since nesting SEGVs could overwrite
197 * the info in the regs. A pointer to the info then would
198 * give us bad data!
199 */
segv(struct faultinfo fi,unsigned long ip,int is_user,struct uml_pt_regs * regs)200 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
201 struct uml_pt_regs *regs)
202 {
203 jmp_buf *catcher;
204 int si_code;
205 int err;
206 int is_write = FAULT_WRITE(fi);
207 unsigned long address = FAULT_ADDRESS(fi);
208
209 if (!is_user && regs)
210 current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
211
212 if (!is_user && (address >= start_vm) && (address < end_vm)) {
213 flush_tlb_kernel_vm();
214 goto out;
215 }
216 else if (current->mm == NULL) {
217 show_regs(container_of(regs, struct pt_regs, regs));
218 panic("Segfault with no mm");
219 }
220 else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
221 show_regs(container_of(regs, struct pt_regs, regs));
222 panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
223 address, ip);
224 }
225
226 if (SEGV_IS_FIXABLE(&fi))
227 err = handle_page_fault(address, ip, is_write, is_user,
228 &si_code);
229 else {
230 err = -EFAULT;
231 /*
232 * A thread accessed NULL, we get a fault, but CR2 is invalid.
233 * This code is used in __do_copy_from_user() of TT mode.
234 * XXX tt mode is gone, so maybe this isn't needed any more
235 */
236 address = 0;
237 }
238
239 catcher = current->thread.fault_catcher;
240 if (!err)
241 goto out;
242 else if (catcher != NULL) {
243 current->thread.fault_addr = (void *) address;
244 UML_LONGJMP(catcher, 1);
245 }
246 else if (current->thread.fault_addr != NULL)
247 panic("fault_addr set but no fault catcher");
248 else if (!is_user && arch_fixup(ip, regs))
249 goto out;
250
251 if (!is_user) {
252 show_regs(container_of(regs, struct pt_regs, regs));
253 panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
254 address, ip);
255 }
256
257 show_segv_info(regs);
258
259 if (err == -EACCES) {
260 current->thread.arch.faultinfo = fi;
261 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
262 } else {
263 BUG_ON(err != -EFAULT);
264 current->thread.arch.faultinfo = fi;
265 force_sig_fault(SIGSEGV, si_code, (void __user *) address);
266 }
267
268 out:
269 if (regs)
270 current->thread.segv_regs = NULL;
271
272 return 0;
273 }
274
relay_signal(int sig,struct siginfo * si,struct uml_pt_regs * regs)275 void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
276 {
277 int code, err;
278 if (!UPT_IS_USER(regs)) {
279 if (sig == SIGBUS)
280 printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
281 "mount likely just ran out of space\n");
282 panic("Kernel mode signal %d", sig);
283 }
284
285 arch_examine_signal(sig, regs);
286
287 /* Is the signal layout for the signal known?
288 * Signal data must be scrubbed to prevent information leaks.
289 */
290 code = si->si_code;
291 err = si->si_errno;
292 if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
293 struct faultinfo *fi = UPT_FAULTINFO(regs);
294 current->thread.arch.faultinfo = *fi;
295 force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
296 } else {
297 printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
298 sig, code, err);
299 force_sig(sig);
300 }
301 }
302
bus_handler(int sig,struct siginfo * si,struct uml_pt_regs * regs)303 void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
304 {
305 if (current->thread.fault_catcher != NULL)
306 UML_LONGJMP(current->thread.fault_catcher, 1);
307 else
308 relay_signal(sig, si, regs);
309 }
310
winch(int sig,struct siginfo * unused_si,struct uml_pt_regs * regs)311 void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
312 {
313 do_IRQ(WINCH_IRQ, regs);
314 }
315