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 */
24int 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;
45retry:
46	mmap_read_lock(mm);
47	vma = find_vma(mm, address);
48	if (!vma)
49		goto out;
50	if (vma->vm_start <= address)
51		goto good_area;
52	if (!(vma->vm_flags & VM_GROWSDOWN))
53		goto out;
54	if (is_user && !ARCH_IS_STACKGROW(address))
55		goto out;
56	vma = expand_stack(mm, address);
57	if (!vma)
58		goto out_nosemaphore;
59
60good_area:
61	*code_out = SEGV_ACCERR;
62	if (is_write) {
63		if (!(vma->vm_flags & VM_WRITE))
64			goto out;
65		flags |= FAULT_FLAG_WRITE;
66	} else {
67		/* Don't require VM_READ|VM_EXEC for write faults! */
68		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
69			goto out;
70	}
71
72	do {
73		vm_fault_t fault;
74
75		fault = handle_mm_fault(vma, address, flags, NULL);
76
77		if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
78			goto out_nosemaphore;
79
80		/* The fault is fully completed (including releasing mmap lock) */
81		if (fault & VM_FAULT_COMPLETED)
82			return 0;
83
84		if (unlikely(fault & VM_FAULT_ERROR)) {
85			if (fault & VM_FAULT_OOM) {
86				goto out_of_memory;
87			} else if (fault & VM_FAULT_SIGSEGV) {
88				goto out;
89			} else if (fault & VM_FAULT_SIGBUS) {
90				err = -EACCES;
91				goto out;
92			}
93			BUG();
94		}
95		if (fault & VM_FAULT_RETRY) {
96			flags |= FAULT_FLAG_TRIED;
97
98			goto retry;
99		}
100
101		pmd = pmd_off(mm, address);
102		pte = pte_offset_kernel(pmd, address);
103	} while (!pte_present(*pte));
104	err = 0;
105	/*
106	 * The below warning was added in place of
107	 *	pte_mkyoung(); if (is_write) pte_mkdirty();
108	 * If it's triggered, we'd see normally a hang here (a clean pte is
109	 * marked read-only to emulate the dirty bit).
110	 * However, the generic code can mark a PTE writable but clean on a
111	 * concurrent read fault, triggering this harmlessly. So comment it out.
112	 */
113#if 0
114	WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
115#endif
116	flush_tlb_page(vma, address);
117out:
118	mmap_read_unlock(mm);
119out_nosemaphore:
120	return err;
121
122out_of_memory:
123	/*
124	 * We ran out of memory, call the OOM killer, and return the userspace
125	 * (which will retry the fault, or kill us if we got oom-killed).
126	 */
127	mmap_read_unlock(mm);
128	if (!is_user)
129		goto out_nosemaphore;
130	pagefault_out_of_memory();
131	return 0;
132}
133
134static void show_segv_info(struct uml_pt_regs *regs)
135{
136	struct task_struct *tsk = current;
137	struct faultinfo *fi = UPT_FAULTINFO(regs);
138
139	if (!unhandled_signal(tsk, SIGSEGV))
140		return;
141
142	if (!printk_ratelimit())
143		return;
144
145	printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x",
146		task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
147		tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
148		(void *)UPT_IP(regs), (void *)UPT_SP(regs),
149		fi->error_code);
150
151	print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
152	printk(KERN_CONT "\n");
153}
154
155static void bad_segv(struct faultinfo fi, unsigned long ip)
156{
157	current->thread.arch.faultinfo = fi;
158	force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
159}
160
161void fatal_sigsegv(void)
162{
163	force_fatal_sig(SIGSEGV);
164	do_signal(&current->thread.regs);
165	/*
166	 * This is to tell gcc that we're not returning - do_signal
167	 * can, in general, return, but in this case, it's not, since
168	 * we just got a fatal SIGSEGV queued.
169	 */
170	os_dump_core();
171}
172
173/**
174 * segv_handler() - the SIGSEGV handler
175 * @sig:	the signal number
176 * @unused_si:	the signal info struct; unused in this handler
177 * @regs:	the ptrace register information
178 *
179 * The handler first extracts the faultinfo from the UML ptrace regs struct.
180 * If the userfault did not happen in an UML userspace process, bad_segv is called.
181 * Otherwise the signal did happen in a cloned userspace process, handle it.
182 */
183void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
184{
185	struct faultinfo * fi = UPT_FAULTINFO(regs);
186
187	if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
188		show_segv_info(regs);
189		bad_segv(*fi, UPT_IP(regs));
190		return;
191	}
192	segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
193}
194
195/*
196 * We give a *copy* of the faultinfo in the regs to segv.
197 * This must be done, since nesting SEGVs could overwrite
198 * the info in the regs. A pointer to the info then would
199 * give us bad data!
200 */
201unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
202		   struct uml_pt_regs *regs)
203{
204	jmp_buf *catcher;
205	int si_code;
206	int err;
207	int is_write = FAULT_WRITE(fi);
208	unsigned long address = FAULT_ADDRESS(fi);
209
210	if (!is_user && regs)
211		current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
212
213	if (!is_user && (address >= start_vm) && (address < end_vm)) {
214		flush_tlb_kernel_vm();
215		goto out;
216	}
217	else if (current->mm == NULL) {
218		show_regs(container_of(regs, struct pt_regs, regs));
219		panic("Segfault with no mm");
220	}
221	else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
222		show_regs(container_of(regs, struct pt_regs, regs));
223		panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
224		       address, ip);
225	}
226
227	if (SEGV_IS_FIXABLE(&fi))
228		err = handle_page_fault(address, ip, is_write, is_user,
229					&si_code);
230	else {
231		err = -EFAULT;
232		/*
233		 * A thread accessed NULL, we get a fault, but CR2 is invalid.
234		 * This code is used in __do_copy_from_user() of TT mode.
235		 * XXX tt mode is gone, so maybe this isn't needed any more
236		 */
237		address = 0;
238	}
239
240	catcher = current->thread.fault_catcher;
241	if (!err)
242		goto out;
243	else if (catcher != NULL) {
244		current->thread.fault_addr = (void *) address;
245		UML_LONGJMP(catcher, 1);
246	}
247	else if (current->thread.fault_addr != NULL)
248		panic("fault_addr set but no fault catcher");
249	else if (!is_user && arch_fixup(ip, regs))
250		goto out;
251
252	if (!is_user) {
253		show_regs(container_of(regs, struct pt_regs, regs));
254		panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
255		      address, ip);
256	}
257
258	show_segv_info(regs);
259
260	if (err == -EACCES) {
261		current->thread.arch.faultinfo = fi;
262		force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
263	} else {
264		BUG_ON(err != -EFAULT);
265		current->thread.arch.faultinfo = fi;
266		force_sig_fault(SIGSEGV, si_code, (void __user *) address);
267	}
268
269out:
270	if (regs)
271		current->thread.segv_regs = NULL;
272
273	return 0;
274}
275
276void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
277{
278	int code, err;
279	if (!UPT_IS_USER(regs)) {
280		if (sig == SIGBUS)
281			printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
282			       "mount likely just ran out of space\n");
283		panic("Kernel mode signal %d", sig);
284	}
285
286	arch_examine_signal(sig, regs);
287
288	/* Is the signal layout for the signal known?
289	 * Signal data must be scrubbed to prevent information leaks.
290	 */
291	code = si->si_code;
292	err = si->si_errno;
293	if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
294		struct faultinfo *fi = UPT_FAULTINFO(regs);
295		current->thread.arch.faultinfo = *fi;
296		force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
297	} else {
298		printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
299		       sig, code, err);
300		force_sig(sig);
301	}
302}
303
304void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
305{
306	if (current->thread.fault_catcher != NULL)
307		UML_LONGJMP(current->thread.fault_catcher, 1);
308	else
309		relay_signal(sig, si, regs);
310}
311
312void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
313{
314	do_IRQ(WINCH_IRQ, regs);
315}
316