xref: /openbmc/linux/arch/microblaze/mm/fault.c (revision 4800cd83)
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 <asm/mmu_context.h>
36 #include <asm/system.h>
37 #include <linux/uaccess.h>
38 #include <asm/exceptions.h>
39 
40 static unsigned long pte_misses;	/* updated by do_page_fault() */
41 static unsigned long pte_errors;	/* updated by do_page_fault() */
42 
43 /*
44  * Check whether the instruction at regs->pc is a store using
45  * an update addressing form which will update r1.
46  */
47 static int store_updates_sp(struct pt_regs *regs)
48 {
49 	unsigned int inst;
50 
51 	if (get_user(inst, (unsigned int *)regs->pc))
52 		return 0;
53 	/* check for 1 in the rD field */
54 	if (((inst >> 21) & 0x1f) != 1)
55 		return 0;
56 	/* check for store opcodes */
57 	if ((inst & 0xd0000000) == 0xd0000000)
58 		return 1;
59 	return 0;
60 }
61 
62 
63 /*
64  * bad_page_fault is called when we have a bad access from the kernel.
65  * It is called from do_page_fault above and from some of the procedures
66  * in traps.c.
67  */
68 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
69 {
70 	const struct exception_table_entry *fixup;
71 /* MS: no context */
72 	/* Are we prepared to handle this fault?  */
73 	fixup = search_exception_tables(regs->pc);
74 	if (fixup) {
75 		regs->pc = fixup->fixup;
76 		return;
77 	}
78 
79 	/* kernel has accessed a bad area */
80 	die("kernel access of bad area", regs, sig);
81 }
82 
83 /*
84  * The error_code parameter is ESR for a data fault,
85  * 0 for an instruction fault.
86  */
87 void do_page_fault(struct pt_regs *regs, unsigned long address,
88 		   unsigned long error_code)
89 {
90 	struct vm_area_struct *vma;
91 	struct mm_struct *mm = current->mm;
92 	siginfo_t info;
93 	int code = SEGV_MAPERR;
94 	int is_write = error_code & ESR_S;
95 	int fault;
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 		printk(KERN_WARNING "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(in_atomic() || !mm)) {
111 		if (kernel_mode(regs))
112 			goto bad_area_nosemaphore;
113 
114 		/* in_atomic() in user mode is really bad,
115 		   as is current->mm == NULL. */
116 		printk(KERN_EMERG "Page fault in user mode with "
117 		       "in_atomic(), mm = %p\n", mm);
118 		printk(KERN_EMERG "r15 = %lx  MSR = %lx\n",
119 		       regs->r15, regs->msr);
120 		die("Weird page fault", regs, SIGSEGV);
121 	}
122 
123 	/* When running in the kernel we expect faults to occur only to
124 	 * addresses in user space.  All other faults represent errors in the
125 	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
126 	 * erroneous fault occurring in a code path which already holds mmap_sem
127 	 * we will deadlock attempting to validate the fault against the
128 	 * address space.  Luckily the kernel only validly references user
129 	 * space from well defined areas of code, which are listed in the
130 	 * exceptions table.
131 	 *
132 	 * As the vast majority of faults will be valid we will only perform
133 	 * the source reference check when there is a possibility of a deadlock.
134 	 * Attempt to lock the address space, if we cannot we then validate the
135 	 * source.  If this is invalid we can skip the address space check,
136 	 * thus avoiding the deadlock.
137 	 */
138 	if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
139 		if (kernel_mode(regs) && !search_exception_tables(regs->pc))
140 			goto bad_area_nosemaphore;
141 
142 		down_read(&mm->mmap_sem);
143 	}
144 
145 	vma = find_vma(mm, address);
146 	if (unlikely(!vma))
147 		goto bad_area;
148 
149 	if (vma->vm_start <= address)
150 		goto good_area;
151 
152 	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
153 		goto bad_area;
154 
155 	if (unlikely(!is_write))
156 		goto bad_area;
157 
158 	/*
159 	 * N.B. The ABI allows programs to access up to
160 	 * a few hundred bytes below the stack pointer (TBD).
161 	 * The kernel signal delivery code writes up to about 1.5kB
162 	 * below the stack pointer (r1) before decrementing it.
163 	 * The exec code can write slightly over 640kB to the stack
164 	 * before setting the user r1.  Thus we allow the stack to
165 	 * expand to 1MB without further checks.
166 	 */
167 	if (unlikely(address + 0x100000 < vma->vm_end)) {
168 
169 		/* get user regs even if this fault is in kernel mode */
170 		struct pt_regs *uregs = current->thread.regs;
171 		if (uregs == NULL)
172 			goto bad_area;
173 
174 		/*
175 		 * A user-mode access to an address a long way below
176 		 * the stack pointer is only valid if the instruction
177 		 * is one which would update the stack pointer to the
178 		 * address accessed if the instruction completed,
179 		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
180 		 * (or the byte, halfword, float or double forms).
181 		 *
182 		 * If we don't check this then any write to the area
183 		 * between the last mapped region and the stack will
184 		 * expand the stack rather than segfaulting.
185 		 */
186 		if (address + 2048 < uregs->r1
187 			&& (kernel_mode(regs) || !store_updates_sp(regs)))
188 				goto bad_area;
189 	}
190 	if (expand_stack(vma, address))
191 		goto bad_area;
192 
193 good_area:
194 	code = SEGV_ACCERR;
195 
196 	/* a write */
197 	if (unlikely(is_write)) {
198 		if (unlikely(!(vma->vm_flags & VM_WRITE)))
199 			goto bad_area;
200 	/* a read */
201 	} else {
202 		/* protection fault */
203 		if (unlikely(error_code & 0x08000000))
204 			goto bad_area;
205 		if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC))))
206 			goto bad_area;
207 	}
208 
209 	/*
210 	 * If for any reason at all we couldn't handle the fault,
211 	 * make sure we exit gracefully rather than endlessly redo
212 	 * the fault.
213 	 */
214 	fault = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
215 	if (unlikely(fault & VM_FAULT_ERROR)) {
216 		if (fault & VM_FAULT_OOM)
217 			goto out_of_memory;
218 		else if (fault & VM_FAULT_SIGBUS)
219 			goto do_sigbus;
220 		BUG();
221 	}
222 	if (unlikely(fault & VM_FAULT_MAJOR))
223 		current->maj_flt++;
224 	else
225 		current->min_flt++;
226 	up_read(&mm->mmap_sem);
227 	/*
228 	 * keep track of tlb+htab misses that are good addrs but
229 	 * just need pte's created via handle_mm_fault()
230 	 * -- Cort
231 	 */
232 	pte_misses++;
233 	return;
234 
235 bad_area:
236 	up_read(&mm->mmap_sem);
237 
238 bad_area_nosemaphore:
239 	pte_errors++;
240 
241 	/* User mode accesses cause a SIGSEGV */
242 	if (user_mode(regs)) {
243 		_exception(SIGSEGV, regs, code, address);
244 /*		info.si_signo = SIGSEGV;
245 		info.si_errno = 0;
246 		info.si_code = code;
247 		info.si_addr = (void *) address;
248 		force_sig_info(SIGSEGV, &info, current);*/
249 		return;
250 	}
251 
252 	bad_page_fault(regs, address, SIGSEGV);
253 	return;
254 
255 /*
256  * We ran out of memory, or some other thing happened to us that made
257  * us unable to handle the page fault gracefully.
258  */
259 out_of_memory:
260 	up_read(&mm->mmap_sem);
261 	if (!user_mode(regs))
262 		bad_page_fault(regs, address, SIGKILL);
263 	else
264 		pagefault_out_of_memory();
265 	return;
266 
267 do_sigbus:
268 	up_read(&mm->mmap_sem);
269 	if (user_mode(regs)) {
270 		info.si_signo = SIGBUS;
271 		info.si_errno = 0;
272 		info.si_code = BUS_ADRERR;
273 		info.si_addr = (void __user *)address;
274 		force_sig_info(SIGBUS, &info, current);
275 		return;
276 	}
277 	bad_page_fault(regs, address, SIGBUS);
278 }
279