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(&current->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