1/*
2 *  arch/microblaze/mm/fault.c
3 *
4 *    Copyright (C) 2007 Xilinx, Inc.  All rights reserved.
5 *
6 *  Derived from "arch/ppc/mm/fault.c"
7 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
8 *
9 *  Derived from "arch/i386/mm/fault.c"
10 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
11 *
12 *  Modified by Cort Dougan and Paul Mackerras.
13 *
14 * This file is subject to the terms and conditions of the GNU General
15 * Public License.  See the file COPYING in the main directory of this
16 * archive for more details.
17 *
18 */
19
20#include <linux/module.h>
21#include <linux/signal.h>
22#include <linux/sched.h>
23#include <linux/kernel.h>
24#include <linux/errno.h>
25#include <linux/string.h>
26#include <linux/types.h>
27#include <linux/ptrace.h>
28#include <linux/mman.h>
29#include <linux/mm.h>
30#include <linux/interrupt.h>
31
32#include <asm/page.h>
33#include <asm/pgtable.h>
34#include <asm/mmu.h>
35#include <linux/mmu_context.h>
36#include <linux/uaccess.h>
37#include <asm/exceptions.h>
38
39static unsigned long pte_misses;	/* updated by do_page_fault() */
40static unsigned long pte_errors;	/* updated by do_page_fault() */
41
42/*
43 * Check whether the instruction at regs->pc is a store using
44 * an update addressing form which will update r1.
45 */
46static int store_updates_sp(struct pt_regs *regs)
47{
48	unsigned int inst;
49
50	if (get_user(inst, (unsigned int __user *)regs->pc))
51		return 0;
52	/* check for 1 in the rD field */
53	if (((inst >> 21) & 0x1f) != 1)
54		return 0;
55	/* check for store opcodes */
56	if ((inst & 0xd0000000) == 0xd0000000)
57		return 1;
58	return 0;
59}
60
61
62/*
63 * bad_page_fault is called when we have a bad access from the kernel.
64 * It is called from do_page_fault above and from some of the procedures
65 * in traps.c.
66 */
67void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
68{
69	const struct exception_table_entry *fixup;
70/* MS: no context */
71	/* Are we prepared to handle this fault?  */
72	fixup = search_exception_tables(regs->pc);
73	if (fixup) {
74		regs->pc = fixup->fixup;
75		return;
76	}
77
78	/* kernel has accessed a bad area */
79	die("kernel access of bad area", regs, sig);
80}
81
82/*
83 * The error_code parameter is ESR for a data fault,
84 * 0 for an instruction fault.
85 */
86void do_page_fault(struct pt_regs *regs, unsigned long address,
87		   unsigned long error_code)
88{
89	struct vm_area_struct *vma;
90	struct mm_struct *mm = current->mm;
91	siginfo_t info;
92	int code = SEGV_MAPERR;
93	int is_write = error_code & ESR_S;
94	int fault;
95	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
96
97	regs->ear = address;
98	regs->esr = error_code;
99
100	/* On a kernel SLB miss we can only check for a valid exception entry */
101	if (unlikely(kernel_mode(regs) && (address >= TASK_SIZE))) {
102		pr_warn("kernel task_size exceed");
103		_exception(SIGSEGV, regs, code, address);
104	}
105
106	/* for instr TLB miss and instr storage exception ESR_S is undefined */
107	if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
108		is_write = 0;
109
110	if (unlikely(faulthandler_disabled() || !mm)) {
111		if (kernel_mode(regs))
112			goto bad_area_nosemaphore;
113
114		/* faulthandler_disabled() in user mode is really bad,
115		   as is current->mm == NULL. */
116		pr_emerg("Page fault in user mode with faulthandler_disabled(), mm = %p\n",
117			 mm);
118		pr_emerg("r15 = %lx  MSR = %lx\n",
119		       regs->r15, regs->msr);
120		die("Weird page fault", regs, SIGSEGV);
121	}
122
123	if (user_mode(regs))
124		flags |= FAULT_FLAG_USER;
125
126	/* When running in the kernel we expect faults to occur only to
127	 * addresses in user space.  All other faults represent errors in the
128	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
129	 * erroneous fault occurring in a code path which already holds mmap_sem
130	 * we will deadlock attempting to validate the fault against the
131	 * address space.  Luckily the kernel only validly references user
132	 * space from well defined areas of code, which are listed in the
133	 * exceptions table.
134	 *
135	 * As the vast majority of faults will be valid we will only perform
136	 * the source reference check when there is a possibility of a deadlock.
137	 * Attempt to lock the address space, if we cannot we then validate the
138	 * source.  If this is invalid we can skip the address space check,
139	 * thus avoiding the deadlock.
140	 */
141	if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
142		if (kernel_mode(regs) && !search_exception_tables(regs->pc))
143			goto bad_area_nosemaphore;
144
145retry:
146		down_read(&mm->mmap_sem);
147	}
148
149	vma = find_vma(mm, address);
150	if (unlikely(!vma))
151		goto bad_area;
152
153	if (vma->vm_start <= address)
154		goto good_area;
155
156	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
157		goto bad_area;
158
159	if (unlikely(!is_write))
160		goto bad_area;
161
162	/*
163	 * N.B. The ABI allows programs to access up to
164	 * a few hundred bytes below the stack pointer (TBD).
165	 * The kernel signal delivery code writes up to about 1.5kB
166	 * below the stack pointer (r1) before decrementing it.
167	 * The exec code can write slightly over 640kB to the stack
168	 * before setting the user r1.  Thus we allow the stack to
169	 * expand to 1MB without further checks.
170	 */
171	if (unlikely(address + 0x100000 < vma->vm_end)) {
172
173		/* get user regs even if this fault is in kernel mode */
174		struct pt_regs *uregs = current->thread.regs;
175		if (uregs == NULL)
176			goto bad_area;
177
178		/*
179		 * A user-mode access to an address a long way below
180		 * the stack pointer is only valid if the instruction
181		 * is one which would update the stack pointer to the
182		 * address accessed if the instruction completed,
183		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
184		 * (or the byte, halfword, float or double forms).
185		 *
186		 * If we don't check this then any write to the area
187		 * between the last mapped region and the stack will
188		 * expand the stack rather than segfaulting.
189		 */
190		if (address + 2048 < uregs->r1
191			&& (kernel_mode(regs) || !store_updates_sp(regs)))
192				goto bad_area;
193	}
194	if (expand_stack(vma, address))
195		goto bad_area;
196
197good_area:
198	code = SEGV_ACCERR;
199
200	/* a write */
201	if (unlikely(is_write)) {
202		if (unlikely(!(vma->vm_flags & VM_WRITE)))
203			goto bad_area;
204		flags |= FAULT_FLAG_WRITE;
205	/* a read */
206	} else {
207		/* protection fault */
208		if (unlikely(error_code & 0x08000000))
209			goto bad_area;
210		if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC))))
211			goto bad_area;
212	}
213
214	/*
215	 * If for any reason at all we couldn't handle the fault,
216	 * make sure we exit gracefully rather than endlessly redo
217	 * the fault.
218	 */
219	fault = handle_mm_fault(mm, vma, address, flags);
220
221	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
222		return;
223
224	if (unlikely(fault & VM_FAULT_ERROR)) {
225		if (fault & VM_FAULT_OOM)
226			goto out_of_memory;
227		else if (fault & VM_FAULT_SIGSEGV)
228			goto bad_area;
229		else if (fault & VM_FAULT_SIGBUS)
230			goto do_sigbus;
231		BUG();
232	}
233
234	if (flags & FAULT_FLAG_ALLOW_RETRY) {
235		if (unlikely(fault & VM_FAULT_MAJOR))
236			current->maj_flt++;
237		else
238			current->min_flt++;
239		if (fault & VM_FAULT_RETRY) {
240			flags &= ~FAULT_FLAG_ALLOW_RETRY;
241			flags |= FAULT_FLAG_TRIED;
242
243			/*
244			 * No need to up_read(&mm->mmap_sem) as we would
245			 * have already released it in __lock_page_or_retry
246			 * in mm/filemap.c.
247			 */
248
249			goto retry;
250		}
251	}
252
253	up_read(&mm->mmap_sem);
254
255	/*
256	 * keep track of tlb+htab misses that are good addrs but
257	 * just need pte's created via handle_mm_fault()
258	 * -- Cort
259	 */
260	pte_misses++;
261	return;
262
263bad_area:
264	up_read(&mm->mmap_sem);
265
266bad_area_nosemaphore:
267	pte_errors++;
268
269	/* User mode accesses cause a SIGSEGV */
270	if (user_mode(regs)) {
271		_exception(SIGSEGV, regs, code, address);
272/*		info.si_signo = SIGSEGV;
273		info.si_errno = 0;
274		info.si_code = code;
275		info.si_addr = (void *) address;
276		force_sig_info(SIGSEGV, &info, current);*/
277		return;
278	}
279
280	bad_page_fault(regs, address, SIGSEGV);
281	return;
282
283/*
284 * We ran out of memory, or some other thing happened to us that made
285 * us unable to handle the page fault gracefully.
286 */
287out_of_memory:
288	up_read(&mm->mmap_sem);
289	if (!user_mode(regs))
290		bad_page_fault(regs, address, SIGKILL);
291	else
292		pagefault_out_of_memory();
293	return;
294
295do_sigbus:
296	up_read(&mm->mmap_sem);
297	if (user_mode(regs)) {
298		info.si_signo = SIGBUS;
299		info.si_errno = 0;
300		info.si_code = BUS_ADRERR;
301		info.si_addr = (void __user *)address;
302		force_sig_info(SIGBUS, &info, current);
303		return;
304	}
305	bad_page_fault(regs, address, SIGBUS);
306}
307