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1 /*
2  *  PowerPC version
3  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
4  *
5  *  Derived from "arch/i386/mm/fault.c"
6  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
7  *
8  *  Modified by Cort Dougan and Paul Mackerras.
9  *
10  *  Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
11  *
12  *  This program is free software; you can redistribute it and/or
13  *  modify it under the terms of the GNU General Public License
14  *  as published by the Free Software Foundation; either version
15  *  2 of the License, or (at your option) any later version.
16  */
17 
18 #include <linux/signal.h>
19 #include <linux/sched.h>
20 #include <linux/kernel.h>
21 #include <linux/errno.h>
22 #include <linux/string.h>
23 #include <linux/types.h>
24 #include <linux/ptrace.h>
25 #include <linux/mman.h>
26 #include <linux/mm.h>
27 #include <linux/interrupt.h>
28 #include <linux/highmem.h>
29 #include <linux/module.h>
30 #include <linux/kprobes.h>
31 #include <linux/kdebug.h>
32 
33 #include <asm/firmware.h>
34 #include <asm/page.h>
35 #include <asm/pgtable.h>
36 #include <asm/mmu.h>
37 #include <asm/mmu_context.h>
38 #include <asm/system.h>
39 #include <asm/uaccess.h>
40 #include <asm/tlbflush.h>
41 #include <asm/siginfo.h>
42 
43 
44 #ifdef CONFIG_KPROBES
notify_page_fault(struct pt_regs * regs)45 static inline int notify_page_fault(struct pt_regs *regs)
46 {
47 	int ret = 0;
48 
49 	/* kprobe_running() needs smp_processor_id() */
50 	if (!user_mode(regs)) {
51 		preempt_disable();
52 		if (kprobe_running() && kprobe_fault_handler(regs, 11))
53 			ret = 1;
54 		preempt_enable();
55 	}
56 
57 	return ret;
58 }
59 #else
notify_page_fault(struct pt_regs * regs)60 static inline int notify_page_fault(struct pt_regs *regs)
61 {
62 	return 0;
63 }
64 #endif
65 
66 /*
67  * Check whether the instruction at regs->nip is a store using
68  * an update addressing form which will update r1.
69  */
store_updates_sp(struct pt_regs * regs)70 static int store_updates_sp(struct pt_regs *regs)
71 {
72 	unsigned int inst;
73 
74 	if (get_user(inst, (unsigned int __user *)regs->nip))
75 		return 0;
76 	/* check for 1 in the rA field */
77 	if (((inst >> 16) & 0x1f) != 1)
78 		return 0;
79 	/* check major opcode */
80 	switch (inst >> 26) {
81 	case 37:	/* stwu */
82 	case 39:	/* stbu */
83 	case 45:	/* sthu */
84 	case 53:	/* stfsu */
85 	case 55:	/* stfdu */
86 		return 1;
87 	case 62:	/* std or stdu */
88 		return (inst & 3) == 1;
89 	case 31:
90 		/* check minor opcode */
91 		switch ((inst >> 1) & 0x3ff) {
92 		case 181:	/* stdux */
93 		case 183:	/* stwux */
94 		case 247:	/* stbux */
95 		case 439:	/* sthux */
96 		case 695:	/* stfsux */
97 		case 759:	/* stfdux */
98 			return 1;
99 		}
100 	}
101 	return 0;
102 }
103 
104 /*
105  * For 600- and 800-family processors, the error_code parameter is DSISR
106  * for a data fault, SRR1 for an instruction fault. For 400-family processors
107  * the error_code parameter is ESR for a data fault, 0 for an instruction
108  * fault.
109  * For 64-bit processors, the error_code parameter is
110  *  - DSISR for a non-SLB data access fault,
111  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
112  *  - 0 any SLB fault.
113  *
114  * The return value is 0 if the fault was handled, or the signal
115  * number if this is a kernel fault that can't be handled here.
116  */
do_page_fault(struct pt_regs * regs,unsigned long address,unsigned long error_code)117 int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
118 			    unsigned long error_code)
119 {
120 	struct vm_area_struct * vma;
121 	struct mm_struct *mm = current->mm;
122 	siginfo_t info;
123 	int code = SEGV_MAPERR;
124 	int is_write = 0, ret;
125 	int trap = TRAP(regs);
126  	int is_exec = trap == 0x400;
127 
128 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
129 	/*
130 	 * Fortunately the bit assignments in SRR1 for an instruction
131 	 * fault and DSISR for a data fault are mostly the same for the
132 	 * bits we are interested in.  But there are some bits which
133 	 * indicate errors in DSISR but can validly be set in SRR1.
134 	 */
135 	if (trap == 0x400)
136 		error_code &= 0x48200000;
137 	else
138 		is_write = error_code & DSISR_ISSTORE;
139 #else
140 	is_write = error_code & ESR_DST;
141 #endif /* CONFIG_4xx || CONFIG_BOOKE */
142 
143 	if (notify_page_fault(regs))
144 		return 0;
145 
146 	if (unlikely(debugger_fault_handler(regs)))
147 		return 0;
148 
149 	/* On a kernel SLB miss we can only check for a valid exception entry */
150 	if (!user_mode(regs) && (address >= TASK_SIZE))
151 		return SIGSEGV;
152 
153 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
154   	if (error_code & DSISR_DABRMATCH) {
155 		/* DABR match */
156 		do_dabr(regs, address, error_code);
157 		return 0;
158 	}
159 #endif /* !(CONFIG_4xx || CONFIG_BOOKE)*/
160 
161 	if (in_atomic() || mm == NULL) {
162 		if (!user_mode(regs))
163 			return SIGSEGV;
164 		/* in_atomic() in user mode is really bad,
165 		   as is current->mm == NULL. */
166 		printk(KERN_EMERG "Page fault in user mode with "
167 		       "in_atomic() = %d mm = %p\n", in_atomic(), mm);
168 		printk(KERN_EMERG "NIP = %lx  MSR = %lx\n",
169 		       regs->nip, regs->msr);
170 		die("Weird page fault", regs, SIGSEGV);
171 	}
172 
173 	/* When running in the kernel we expect faults to occur only to
174 	 * addresses in user space.  All other faults represent errors in the
175 	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
176 	 * erroneous fault occurring in a code path which already holds mmap_sem
177 	 * we will deadlock attempting to validate the fault against the
178 	 * address space.  Luckily the kernel only validly references user
179 	 * space from well defined areas of code, which are listed in the
180 	 * exceptions table.
181 	 *
182 	 * As the vast majority of faults will be valid we will only perform
183 	 * the source reference check when there is a possibility of a deadlock.
184 	 * Attempt to lock the address space, if we cannot we then validate the
185 	 * source.  If this is invalid we can skip the address space check,
186 	 * thus avoiding the deadlock.
187 	 */
188 	if (!down_read_trylock(&mm->mmap_sem)) {
189 		if (!user_mode(regs) && !search_exception_tables(regs->nip))
190 			goto bad_area_nosemaphore;
191 
192 		down_read(&mm->mmap_sem);
193 	}
194 
195 	vma = find_vma(mm, address);
196 	if (!vma)
197 		goto bad_area;
198 	if (vma->vm_start <= address)
199 		goto good_area;
200 	if (!(vma->vm_flags & VM_GROWSDOWN))
201 		goto bad_area;
202 
203 	/*
204 	 * N.B. The POWER/Open ABI allows programs to access up to
205 	 * 288 bytes below the stack pointer.
206 	 * The kernel signal delivery code writes up to about 1.5kB
207 	 * below the stack pointer (r1) before decrementing it.
208 	 * The exec code can write slightly over 640kB to the stack
209 	 * before setting the user r1.  Thus we allow the stack to
210 	 * expand to 1MB without further checks.
211 	 */
212 	if (address + 0x100000 < vma->vm_end) {
213 		/* get user regs even if this fault is in kernel mode */
214 		struct pt_regs *uregs = current->thread.regs;
215 		if (uregs == NULL)
216 			goto bad_area;
217 
218 		/*
219 		 * A user-mode access to an address a long way below
220 		 * the stack pointer is only valid if the instruction
221 		 * is one which would update the stack pointer to the
222 		 * address accessed if the instruction completed,
223 		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
224 		 * (or the byte, halfword, float or double forms).
225 		 *
226 		 * If we don't check this then any write to the area
227 		 * between the last mapped region and the stack will
228 		 * expand the stack rather than segfaulting.
229 		 */
230 		if (address + 2048 < uregs->gpr[1]
231 		    && (!user_mode(regs) || !store_updates_sp(regs)))
232 			goto bad_area;
233 	}
234 	if (expand_stack(vma, address))
235 		goto bad_area;
236 
237 good_area:
238 	code = SEGV_ACCERR;
239 #if defined(CONFIG_6xx)
240 	if (error_code & 0x95700000)
241 		/* an error such as lwarx to I/O controller space,
242 		   address matching DABR, eciwx, etc. */
243 		goto bad_area;
244 #endif /* CONFIG_6xx */
245 #if defined(CONFIG_8xx)
246         /* The MPC8xx seems to always set 0x80000000, which is
247          * "undefined".  Of those that can be set, this is the only
248          * one which seems bad.
249          */
250 	if (error_code & 0x10000000)
251                 /* Guarded storage error. */
252 		goto bad_area;
253 #endif /* CONFIG_8xx */
254 
255 	if (is_exec) {
256 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
257 		/* protection fault */
258 		if (error_code & DSISR_PROTFAULT)
259 			goto bad_area;
260 		/*
261 		 * Allow execution from readable areas if the MMU does not
262 		 * provide separate controls over reading and executing.
263 		 */
264 		if (!(vma->vm_flags & VM_EXEC) &&
265 		    (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
266 		     !(vma->vm_flags & (VM_READ | VM_WRITE))))
267 			goto bad_area;
268 #else
269 		pte_t *ptep;
270 		pmd_t *pmdp;
271 
272 		/* Since 4xx/Book-E supports per-page execute permission,
273 		 * we lazily flush dcache to icache. */
274 		ptep = NULL;
275 		if (get_pteptr(mm, address, &ptep, &pmdp)) {
276 			spinlock_t *ptl = pte_lockptr(mm, pmdp);
277 			spin_lock(ptl);
278 			if (pte_present(*ptep)) {
279 				struct page *page = pte_page(*ptep);
280 
281 				if (!test_bit(PG_arch_1, &page->flags)) {
282 					flush_dcache_icache_page(page);
283 					set_bit(PG_arch_1, &page->flags);
284 				}
285 				pte_update(ptep, 0, _PAGE_HWEXEC |
286 					   _PAGE_ACCESSED);
287 				local_flush_tlb_page(vma, address);
288 				pte_unmap_unlock(ptep, ptl);
289 				up_read(&mm->mmap_sem);
290 				return 0;
291 			}
292 			pte_unmap_unlock(ptep, ptl);
293 		}
294 #endif
295 	/* a write */
296 	} else if (is_write) {
297 		if (!(vma->vm_flags & VM_WRITE))
298 			goto bad_area;
299 	/* a read */
300 	} else {
301 		/* protection fault */
302 		if (error_code & 0x08000000)
303 			goto bad_area;
304 		if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
305 			goto bad_area;
306 	}
307 
308 	/*
309 	 * If for any reason at all we couldn't handle the fault,
310 	 * make sure we exit gracefully rather than endlessly redo
311 	 * the fault.
312 	 */
313  survive:
314 	ret = handle_mm_fault(mm, vma, address, is_write);
315 	if (unlikely(ret & VM_FAULT_ERROR)) {
316 		if (ret & VM_FAULT_OOM)
317 			goto out_of_memory;
318 		else if (ret & VM_FAULT_SIGBUS)
319 			goto do_sigbus;
320 		BUG();
321 	}
322 	if (ret & VM_FAULT_MAJOR) {
323 		current->maj_flt++;
324 #ifdef CONFIG_PPC_SMLPAR
325 		if (firmware_has_feature(FW_FEATURE_CMO)) {
326 			preempt_disable();
327 			get_lppaca()->page_ins += (1 << PAGE_FACTOR);
328 			preempt_enable();
329 		}
330 #endif
331 	} else
332 		current->min_flt++;
333 	up_read(&mm->mmap_sem);
334 	return 0;
335 
336 bad_area:
337 	up_read(&mm->mmap_sem);
338 
339 bad_area_nosemaphore:
340 	/* User mode accesses cause a SIGSEGV */
341 	if (user_mode(regs)) {
342 		_exception(SIGSEGV, regs, code, address);
343 		return 0;
344 	}
345 
346 	if (is_exec && (error_code & DSISR_PROTFAULT)
347 	    && printk_ratelimit())
348 		printk(KERN_CRIT "kernel tried to execute NX-protected"
349 		       " page (%lx) - exploit attempt? (uid: %d)\n",
350 		       address, current_uid());
351 
352 	return SIGSEGV;
353 
354 /*
355  * We ran out of memory, or some other thing happened to us that made
356  * us unable to handle the page fault gracefully.
357  */
358 out_of_memory:
359 	up_read(&mm->mmap_sem);
360 	if (is_global_init(current)) {
361 		yield();
362 		down_read(&mm->mmap_sem);
363 		goto survive;
364 	}
365 	printk("VM: killing process %s\n", current->comm);
366 	if (user_mode(regs))
367 		do_group_exit(SIGKILL);
368 	return SIGKILL;
369 
370 do_sigbus:
371 	up_read(&mm->mmap_sem);
372 	if (user_mode(regs)) {
373 		info.si_signo = SIGBUS;
374 		info.si_errno = 0;
375 		info.si_code = BUS_ADRERR;
376 		info.si_addr = (void __user *)address;
377 		force_sig_info(SIGBUS, &info, current);
378 		return 0;
379 	}
380 	return SIGBUS;
381 }
382 
383 /*
384  * bad_page_fault is called when we have a bad access from the kernel.
385  * It is called from the DSI and ISI handlers in head.S and from some
386  * of the procedures in traps.c.
387  */
bad_page_fault(struct pt_regs * regs,unsigned long address,int sig)388 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
389 {
390 	const struct exception_table_entry *entry;
391 
392 	/* Are we prepared to handle this fault?  */
393 	if ((entry = search_exception_tables(regs->nip)) != NULL) {
394 		regs->nip = entry->fixup;
395 		return;
396 	}
397 
398 	/* kernel has accessed a bad area */
399 
400 	switch (regs->trap) {
401 	case 0x300:
402 	case 0x380:
403 		printk(KERN_ALERT "Unable to handle kernel paging request for "
404 			"data at address 0x%08lx\n", regs->dar);
405 		break;
406 	case 0x400:
407 	case 0x480:
408 		printk(KERN_ALERT "Unable to handle kernel paging request for "
409 			"instruction fetch\n");
410 		break;
411 	default:
412 		printk(KERN_ALERT "Unable to handle kernel paging request for "
413 			"unknown fault\n");
414 		break;
415 	}
416 	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
417 		regs->nip);
418 
419 	die("Kernel access of bad area", regs, sig);
420 }
421