[net-next-2.6.git] / arch / powerpc / mm / fault.c

/*
 *  PowerPC version
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *
 *  Derived from "arch/i386/mm/fault.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Modified by Cort Dougan and Paul Mackerras.
 *
 *  Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/highmem.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>

#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/tlbflush.h>
#include <asm/siginfo.h>

#ifdef CONFIG_KPROBES
ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);

/* Hook to register for page fault notifications */
int register_page_fault_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
}

int unregister_page_fault_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
}

static inline int notify_page_fault(enum die_val val, const char *str,
			struct pt_regs *regs, long err, int trap, int sig)
{
	struct die_args args = {
		.regs = regs,
		.str = str,
		.err = err,
		.trapnr = trap,
		.signr = sig
	};
	return atomic_notifier_call_chain(&notify_page_fault_chain, val, &args);
}
#else
static inline int notify_page_fault(enum die_val val, const char *str,
			struct pt_regs *regs, long err, int trap, int sig)
{
	return NOTIFY_DONE;
}
#endif

/*
 * Check whether the instruction at regs->nip is a store using
 * an update addressing form which will update r1.
 */
static int store_updates_sp(struct pt_regs *regs)
{
	unsigned int inst;

	if (get_user(inst, (unsigned int __user *)regs->nip))
		return 0;
	/* check for 1 in the rA field */
	if (((inst >> 16) & 0x1f) != 1)
		return 0;
	/* check major opcode */
	switch (inst >> 26) {
	case 37:	/* stwu */
	case 39:	/* stbu */
	case 45:	/* sthu */
	case 53:	/* stfsu */
	case 55:	/* stfdu */
		return 1;
	case 62:	/* std or stdu */
		return (inst & 3) == 1;
	case 31:
		/* check minor opcode */
		switch ((inst >> 1) & 0x3ff) {
		case 181:	/* stdux */
		case 183:	/* stwux */
		case 247:	/* stbux */
		case 439:	/* sthux */
		case 695:	/* stfsux */
		case 759:	/* stfdux */
			return 1;
		}
	}
	return 0;
}

#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
static void do_dabr(struct pt_regs *regs, unsigned long address,
		    unsigned long error_code)
{
	siginfo_t info;

	if (notify_die(DIE_DABR_MATCH, "dabr_match", regs, error_code,
			11, SIGSEGV) == NOTIFY_STOP)
		return;

	if (debugger_dabr_match(regs))
		return;

	/* Clear the DABR */
	set_dabr(0);

	/* Deliver the signal to userspace */
	info.si_signo = SIGTRAP;
	info.si_errno = 0;
	info.si_code = TRAP_HWBKPT;
	info.si_addr = (void __user *)address;
	force_sig_info(SIGTRAP, &info, current);
}
#endif /* !(CONFIG_4xx || CONFIG_BOOKE)*/

/*
 * For 600- and 800-family processors, the error_code parameter is DSISR
 * for a data fault, SRR1 for an instruction fault. For 400-family processors
 * the error_code parameter is ESR for a data fault, 0 for an instruction
 * fault.
 * For 64-bit processors, the error_code parameter is
 *  - DSISR for a non-SLB data access fault,
 *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
 *  - 0 any SLB fault.
 *
 * The return value is 0 if the fault was handled, or the signal
 * number if this is a kernel fault that can't be handled here.
 */
int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
			    unsigned long error_code)
{
	struct vm_area_struct * vma;
	struct mm_struct *mm = current->mm;
	siginfo_t info;
	int code = SEGV_MAPERR;
	int is_write = 0;
	int trap = TRAP(regs);
 	int is_exec = trap == 0x400;

#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
	/*
	 * Fortunately the bit assignments in SRR1 for an instruction
	 * fault and DSISR for a data fault are mostly the same for the
	 * bits we are interested in.  But there are some bits which
	 * indicate errors in DSISR but can validly be set in SRR1.
	 */
	if (trap == 0x400)
		error_code &= 0x48200000;
	else
		is_write = error_code & DSISR_ISSTORE;
#else
	is_write = error_code & ESR_DST;
#endif /* CONFIG_4xx || CONFIG_BOOKE */

	if (notify_page_fault(DIE_PAGE_FAULT, "page_fault", regs, error_code,
				11, SIGSEGV) == NOTIFY_STOP)
		return 0;

	if (trap == 0x300) {
		if (debugger_fault_handler(regs))
			return 0;
	}

	/* On a kernel SLB miss we can only check for a valid exception entry */
	if (!user_mode(regs) && (address >= TASK_SIZE))
		return SIGSEGV;

#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
  	if (error_code & DSISR_DABRMATCH) {
		/* DABR match */
		do_dabr(regs, address, error_code);
		return 0;
	}
#endif /* !(CONFIG_4xx || CONFIG_BOOKE)*/

	if (in_atomic() || mm == NULL) {
		if (!user_mode(regs))
			return SIGSEGV;
		/* in_atomic() in user mode is really bad,
		   as is current->mm == NULL. */
		printk(KERN_EMERG "Page fault in user mode with"
		       "in_atomic() = %d mm = %p\n", in_atomic(), mm);
		printk(KERN_EMERG "NIP = %lx  MSR = %lx\n",
		       regs->nip, regs->msr);
		die("Weird page fault", regs, SIGSEGV);
	}

	/* When running in the kernel we expect faults to occur only to
	 * addresses in user space.  All other faults represent errors in the
	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
	 * erroneous fault occurring in a code path which already holds mmap_sem
	 * we will deadlock attempting to validate the fault against the
	 * address space.  Luckily the kernel only validly references user
	 * space from well defined areas of code, which are listed in the
	 * exceptions table.
	 *
	 * As the vast majority of faults will be valid we will only perform
	 * the source reference check when there is a possibility of a deadlock.
	 * Attempt to lock the address space, if we cannot we then validate the
	 * source.  If this is invalid we can skip the address space check,
	 * thus avoiding the deadlock.
	 */
	if (!down_read_trylock(&mm->mmap_sem)) {
		if (!user_mode(regs) && !search_exception_tables(regs->nip))
			goto bad_area_nosemaphore;

		down_read(&mm->mmap_sem);
	}

	vma = find_vma(mm, address);
	if (!vma)
		goto bad_area;
	if (vma->vm_start <= address)
		goto good_area;
	if (!(vma->vm_flags & VM_GROWSDOWN))
		goto bad_area;

	/*
	 * N.B. The POWER/Open ABI allows programs to access up to
	 * 288 bytes below the stack pointer.
	 * The kernel signal delivery code writes up to about 1.5kB
	 * below the stack pointer (r1) before decrementing it.
	 * The exec code can write slightly over 640kB to the stack
	 * before setting the user r1.  Thus we allow the stack to
	 * expand to 1MB without further checks.
	 */
	if (address + 0x100000 < vma->vm_end) {
		/* get user regs even if this fault is in kernel mode */
		struct pt_regs *uregs = current->thread.regs;
		if (uregs == NULL)
			goto bad_area;

		/*
		 * A user-mode access to an address a long way below
		 * the stack pointer is only valid if the instruction
		 * is one which would update the stack pointer to the
		 * address accessed if the instruction completed,
		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
		 * (or the byte, halfword, float or double forms).
		 *
		 * If we don't check this then any write to the area
		 * between the last mapped region and the stack will
		 * expand the stack rather than segfaulting.
		 */
		if (address + 2048 < uregs->gpr[1]
		    && (!user_mode(regs) || !store_updates_sp(regs)))
			goto bad_area;
	}
	if (expand_stack(vma, address))
		goto bad_area;

good_area:
	code = SEGV_ACCERR;
#if defined(CONFIG_6xx)
	if (error_code & 0x95700000)
		/* an error such as lwarx to I/O controller space,
		   address matching DABR, eciwx, etc. */
		goto bad_area;
#endif /* CONFIG_6xx */
#if defined(CONFIG_8xx)
        /* The MPC8xx seems to always set 0x80000000, which is
         * "undefined".  Of those that can be set, this is the only
         * one which seems bad.
         */
	if (error_code & 0x10000000)
                /* Guarded storage error. */
		goto bad_area;
#endif /* CONFIG_8xx */

	if (is_exec) {
#ifdef CONFIG_PPC64
		/* protection fault */
		if (error_code & DSISR_PROTFAULT)
			goto bad_area;
		if (!(vma->vm_flags & VM_EXEC))
			goto bad_area;
#endif
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
		pte_t *ptep;
		pmd_t *pmdp;

		/* Since 4xx/Book-E supports per-page execute permission,
		 * we lazily flush dcache to icache. */
		ptep = NULL;
		if (get_pteptr(mm, address, &ptep, &pmdp)) {
			spinlock_t *ptl = pte_lockptr(mm, pmdp);
			spin_lock(ptl);
			if (pte_present(*ptep)) {
				struct page *page = pte_page(*ptep);

				if (!test_bit(PG_arch_1, &page->flags)) {
					flush_dcache_icache_page(page);
					set_bit(PG_arch_1, &page->flags);
				}
				pte_update(ptep, 0, _PAGE_HWEXEC);
				_tlbie(address);
				pte_unmap_unlock(ptep, ptl);
				up_read(&mm->mmap_sem);
				return 0;
			}
			pte_unmap_unlock(ptep, ptl);
		}
#endif
	/* a write */
	} else if (is_write) {
		if (!(vma->vm_flags & VM_WRITE))
			goto bad_area;
	/* a read */
	} else {
		/* protection fault */
		if (error_code & 0x08000000)
			goto bad_area;
		if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
			goto bad_area;
	}

	/*
	 * If for any reason at all we couldn't handle the fault,
	 * make sure we exit gracefully rather than endlessly redo
	 * the fault.
	 */
 survive:
	switch (handle_mm_fault(mm, vma, address, is_write)) {

	case VM_FAULT_MINOR:
		current->min_flt++;
		break;
	case VM_FAULT_MAJOR:
		current->maj_flt++;
		break;
	case VM_FAULT_SIGBUS:
		goto do_sigbus;
	case VM_FAULT_OOM:
		goto out_of_memory;
	default:
		BUG();
	}

	up_read(&mm->mmap_sem);
	return 0;

bad_area:
	up_read(&mm->mmap_sem);

bad_area_nosemaphore:
	/* User mode accesses cause a SIGSEGV */
	if (user_mode(regs)) {
		_exception(SIGSEGV, regs, code, address);
		return 0;
	}

	if (is_exec && (error_code & DSISR_PROTFAULT)
	    && printk_ratelimit())
		printk(KERN_CRIT "kernel tried to execute NX-protected"
		       " page (%lx) - exploit attempt? (uid: %d)\n",
		       address, current->uid);

	return SIGSEGV;

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
	up_read(&mm->mmap_sem);
	if (is_init(current)) {
		yield();
		down_read(&mm->mmap_sem);
		goto survive;
	}
	printk("VM: killing process %s\n", current->comm);
	if (user_mode(regs))
		do_exit(SIGKILL);
	return SIGKILL;

do_sigbus:
	up_read(&mm->mmap_sem);
	if (user_mode(regs)) {
		info.si_signo = SIGBUS;
		info.si_errno = 0;
		info.si_code = BUS_ADRERR;
		info.si_addr = (void __user *)address;
		force_sig_info(SIGBUS, &info, current);
		return 0;
	}
	return SIGBUS;
}

/*
 * bad_page_fault is called when we have a bad access from the kernel.
 * It is called from the DSI and ISI handlers in head.S and from some
 * of the procedures in traps.c.
 */
void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
	const struct exception_table_entry *entry;

	/* Are we prepared to handle this fault?  */
	if ((entry = search_exception_tables(regs->nip)) != NULL) {
		regs->nip = entry->fixup;
		return;
	}

	/* kernel has accessed a bad area */

	switch (regs->trap) {
	case 0x300:
	case 0x380:
		printk(KERN_ALERT "Unable to handle kernel paging request for "
			"data at address 0x%08lx\n", regs->dar);
		break;
	case 0x400:
	case 0x480:
		printk(KERN_ALERT "Unable to handle kernel paging request for "
			"instruction fetch\n");
		break;
	default:
		printk(KERN_ALERT "Unable to handle kernel paging request for "
			"unknown fault\n");
		break;
	}
	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
		regs->nip);

	die("Kernel access of bad area", regs, sig);
}
Commit	Line	Data
14cf11af	1	/*
14cf11af PM	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
14cf11af PM	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>
1eeb66a1	31	#include <linux/kdebug.h>
14cf11af PM	32
	33	#include <asm/page.h>
	34	#include <asm/pgtable.h>
	35	#include <asm/mmu.h>
	36	#include <asm/mmu_context.h>
	37	#include <asm/system.h>
	38	#include <asm/uaccess.h>
	39	#include <asm/tlbflush.h>
14cf11af PM	40	#include <asm/siginfo.h>
14cf11af PM	41
4f9e87c0 AK	42	#ifdef CONFIG_KPROBES
	43	ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
	44
	45	/* Hook to register for page fault notifications */
	46	int register_page_fault_notifier(struct notifier_block *nb)
	47	{
	48	return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
	49	}
	50
	51	int unregister_page_fault_notifier(struct notifier_block *nb)
	52	{
	53	return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
	54	}
	55
	56	static inline int notify_page_fault(enum die_val val, const char *str,
	57	struct pt_regs *regs, long err, int trap, int sig)
	58	{
	59	struct die_args args = {
	60	.regs = regs,
	61	.str = str,
	62	.err = err,
	63	.trapnr = trap,
	64	.signr = sig
	65	};
	66	return atomic_notifier_call_chain(&notify_page_fault_chain, val, &args);
	67	}
	68	#else
	69	static inline int notify_page_fault(enum die_val val, const char *str,
	70	struct pt_regs *regs, long err, int trap, int sig)
	71	{
	72	return NOTIFY_DONE;
	73	}
	74	#endif
	75
14cf11af PM	76	/*
	77	* Check whether the instruction at regs->nip is a store using
	78	* an update addressing form which will update r1.
	79	*/
	80	static int store_updates_sp(struct pt_regs *regs)
	81	{
	82	unsigned int inst;
	83
	84	if (get_user(inst, (unsigned int __user *)regs->nip))
	85	return 0;
	86	/* check for 1 in the rA field */
	87	if (((inst >> 16) & 0x1f) != 1)
	88	return 0;
	89	/* check major opcode */
	90	switch (inst >> 26) {
	91	case 37: /* stwu */
	92	case 39: /* stbu */
	93	case 45: /* sthu */
	94	case 53: /* stfsu */
	95	case 55: /* stfdu */
	96	return 1;
	97	case 62: /* std or stdu */
	98	return (inst & 3) == 1;
	99	case 31:
	100	/* check minor opcode */
	101	switch ((inst >> 1) & 0x3ff) {
	102	case 181: /* stdux */
	103	case 183: /* stwux */
	104	case 247: /* stbux */
	105	case 439: /* sthux */
	106	case 695: /* stfsux */
	107	case 759: /* stfdux */
	108	return 1;
	109	}
	110	}
	111	return 0;
	112	}
	113
cffb09ce	114	#if !(defined(CONFIG_4xx) \|\| defined(CONFIG_BOOKE))
bce6c5fd AB	115	static void do_dabr(struct pt_regs *regs, unsigned long address,
bce6c5fd AB	116	unsigned long error_code)
14cf11af PM	117	{
	118	siginfo_t info;
	119
	120	if (notify_die(DIE_DABR_MATCH, "dabr_match", regs, error_code,
	121	11, SIGSEGV) == NOTIFY_STOP)
	122	return;
	123
	124	if (debugger_dabr_match(regs))
	125	return;
	126
	127	/* Clear the DABR */
	128	set_dabr(0);
	129
	130	/* Deliver the signal to userspace */
	131	info.si_signo = SIGTRAP;
	132	info.si_errno = 0;
	133	info.si_code = TRAP_HWBKPT;
bce6c5fd	134	info.si_addr = (void __user *)address;
14cf11af PM	135	force_sig_info(SIGTRAP, &info, current);
14cf11af PM	136	}
cffb09ce	137	#endif /* !(CONFIG_4xx \|\| CONFIG_BOOKE)*/
14cf11af PM	138
	139	/*
	140	* For 600- and 800-family processors, the error_code parameter is DSISR
	141	* for a data fault, SRR1 for an instruction fault. For 400-family processors
	142	* the error_code parameter is ESR for a data fault, 0 for an instruction
	143	* fault.
	144	* For 64-bit processors, the error_code parameter is
	145	* - DSISR for a non-SLB data access fault,
	146	* - SRR1 & 0x08000000 for a non-SLB instruction access fault
	147	* - 0 any SLB fault.
	148	*
	149	* The return value is 0 if the fault was handled, or the signal
	150	* number if this is a kernel fault that can't be handled here.
	151	*/
	152	int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
	153	unsigned long error_code)
	154	{
	155	struct vm_area_struct * vma;
	156	struct mm_struct *mm = current->mm;
	157	siginfo_t info;
	158	int code = SEGV_MAPERR;
	159	int is_write = 0;
	160	int trap = TRAP(regs);
	161	int is_exec = trap == 0x400;
	162
	163	#if !(defined(CONFIG_4xx) \|\| defined(CONFIG_BOOKE))
	164	/*
	165	* Fortunately the bit assignments in SRR1 for an instruction
	166	* fault and DSISR for a data fault are mostly the same for the
	167	* bits we are interested in. But there are some bits which
	168	* indicate errors in DSISR but can validly be set in SRR1.
	169	*/
	170	if (trap == 0x400)
	171	error_code &= 0x48200000;
	172	else
	173	is_write = error_code & DSISR_ISSTORE;
	174	#else
	175	is_write = error_code & ESR_DST;
	176	#endif /* CONFIG_4xx \|\| CONFIG_BOOKE */
	177
4f9e87c0	178	if (notify_page_fault(DIE_PAGE_FAULT, "page_fault", regs, error_code,
14cf11af PM	179	11, SIGSEGV) == NOTIFY_STOP)
	180	return 0;
	181
	182	if (trap == 0x300) {
	183	if (debugger_fault_handler(regs))
	184	return 0;
	185	}
	186
	187	/* On a kernel SLB miss we can only check for a valid exception entry */
	188	if (!user_mode(regs) && (address >= TASK_SIZE))
	189	return SIGSEGV;
	190
	191	#if !(defined(CONFIG_4xx) \|\| defined(CONFIG_BOOKE))
	192	if (error_code & DSISR_DABRMATCH) {
	193	/* DABR match */
bce6c5fd	194	do_dabr(regs, address, error_code);
14cf11af PM	195	return 0;
	196	}
	197	#endif /* !(CONFIG_4xx \|\| CONFIG_BOOKE)*/
	198
	199	if (in_atomic() \|\| mm == NULL) {
	200	if (!user_mode(regs))
	201	return SIGSEGV;
	202	/* in_atomic() in user mode is really bad,
	203	as is current->mm == NULL. */
	204	printk(KERN_EMERG "Page fault in user mode with"
	205	"in_atomic() = %d mm = %p\n", in_atomic(), mm);
	206	printk(KERN_EMERG "NIP = %lx MSR = %lx\n",
	207	regs->nip, regs->msr);
	208	die("Weird page fault", regs, SIGSEGV);
	209	}
	210
	211	/* When running in the kernel we expect faults to occur only to
	212	* addresses in user space. All other faults represent errors in the
fc5266ea AB	213	* kernel and should generate an OOPS. Unfortunately, in the case of an
fc5266ea AB	214	* erroneous fault occurring in a code path which already holds mmap_sem
14cf11af PM	215	* we will deadlock attempting to validate the fault against the
	216	* address space. Luckily the kernel only validly references user
	217	* space from well defined areas of code, which are listed in the
	218	* exceptions table.
	219	*
	220	* As the vast majority of faults will be valid we will only perform
fc5266ea	221	* the source reference check when there is a possibility of a deadlock.
14cf11af PM	222	* Attempt to lock the address space, if we cannot we then validate the
	223	* source. If this is invalid we can skip the address space check,
	224	* thus avoiding the deadlock.
	225	*/
	226	if (!down_read_trylock(&mm->mmap_sem)) {
	227	if (!user_mode(regs) && !search_exception_tables(regs->nip))
	228	goto bad_area_nosemaphore;
	229
	230	down_read(&mm->mmap_sem);
	231	}
	232
	233	vma = find_vma(mm, address);
	234	if (!vma)
	235	goto bad_area;
	236	if (vma->vm_start <= address)
	237	goto good_area;
	238	if (!(vma->vm_flags & VM_GROWSDOWN))
	239	goto bad_area;
	240
	241	/*
	242	* N.B. The POWER/Open ABI allows programs to access up to
	243	* 288 bytes below the stack pointer.
	244	* The kernel signal delivery code writes up to about 1.5kB
	245	* below the stack pointer (r1) before decrementing it.
	246	* The exec code can write slightly over 640kB to the stack
	247	* before setting the user r1. Thus we allow the stack to
	248	* expand to 1MB without further checks.
	249	*/
	250	if (address + 0x100000 < vma->vm_end) {
	251	/* get user regs even if this fault is in kernel mode */
	252	struct pt_regs *uregs = current->thread.regs;
	253	if (uregs == NULL)
	254	goto bad_area;
	255
	256	/*
	257	* A user-mode access to an address a long way below
	258	* the stack pointer is only valid if the instruction
	259	* is one which would update the stack pointer to the
	260	* address accessed if the instruction completed,
	261	* i.e. either stwu rs,n(r1) or stwux rs,r1,rb
	262	* (or the byte, halfword, float or double forms).
	263	*
	264	* If we don't check this then any write to the area
	265	* between the last mapped region and the stack will
	266	* expand the stack rather than segfaulting.
	267	*/
	268	if (address + 2048 < uregs->gpr[1]
	269	&& (!user_mode(regs) \|\| !store_updates_sp(regs)))
	270	goto bad_area;
	271	}
	272	if (expand_stack(vma, address))
	273	goto bad_area;
	274
	275	good_area:
	276	code = SEGV_ACCERR;
	277	#if defined(CONFIG_6xx)
	278	if (error_code & 0x95700000)
	279	/* an error such as lwarx to I/O controller space,
	280	address matching DABR, eciwx, etc. */
	281	goto bad_area;
	282	#endif /* CONFIG_6xx */
	283	#if defined(CONFIG_8xx)
	284	/* The MPC8xx seems to always set 0x80000000, which is
	285	* "undefined". Of those that can be set, this is the only
286	* one which seems bad.
287	*/
288	if (error_code & 0x10000000)
289	/* Guarded storage error. */
290	goto bad_area;
291	#endif /* CONFIG_8xx */
292
293	if (is_exec) {
294	#ifdef CONFIG_PPC64
295	/* protection fault */
296	if (error_code & DSISR_PROTFAULT)
297	goto bad_area;
298	if (!(vma->vm_flags & VM_EXEC))
299	goto bad_area;
300	#endif
301	#if defined(CONFIG_4xx) \|\| defined(CONFIG_BOOKE)
302	pte_t *ptep;
bab70a4a	303	pmd_t *pmdp;
14cf11af PM	304
	305	/* Since 4xx/Book-E supports per-page execute permission,
	306	* we lazily flush dcache to icache. */
	307	ptep = NULL;
bab70a4a ES	308	if (get_pteptr(mm, address, &ptep, &pmdp)) {
	309	spinlock_t *ptl = pte_lockptr(mm, pmdp);
	310	spin_lock(ptl);
	311	if (pte_present(*ptep)) {
	312	struct page page = pte_page(ptep);
14cf11af	313
bab70a4a ES	314	if (!test_bit(PG_arch_1, &page->flags)) {
	315	flush_dcache_icache_page(page);
	316	set_bit(PG_arch_1, &page->flags);
	317	}
	318	pte_update(ptep, 0, _PAGE_HWEXEC);
	319	_tlbie(address);
	320	pte_unmap_unlock(ptep, ptl);
	321	up_read(&mm->mmap_sem);
	322	return 0;
14cf11af	323	}
bab70a4a	324	pte_unmap_unlock(ptep, ptl);
14cf11af	325	}
14cf11af PM	326	#endif
	327	/* a write */
	328	} else if (is_write) {
	329	if (!(vma->vm_flags & VM_WRITE))
	330	goto bad_area;
	331	/* a read */
	332	} else {
	333	/* protection fault */
	334	if (error_code & 0x08000000)
	335	goto bad_area;
df67b3da	336	if (!(vma->vm_flags & (VM_READ \| VM_EXEC \| VM_WRITE)))
14cf11af PM	337	goto bad_area;
	338	}
	339
	340	/*
	341	* If for any reason at all we couldn't handle the fault,
	342	* make sure we exit gracefully rather than endlessly redo
	343	* the fault.
	344	*/
	345	survive:
	346	switch (handle_mm_fault(mm, vma, address, is_write)) {
	347
	348	case VM_FAULT_MINOR:
	349	current->min_flt++;
	350	break;
	351	case VM_FAULT_MAJOR:
	352	current->maj_flt++;
	353	break;
	354	case VM_FAULT_SIGBUS:
	355	goto do_sigbus;
	356	case VM_FAULT_OOM:
	357	goto out_of_memory;
	358	default:
	359	BUG();
	360	}
	361
	362	up_read(&mm->mmap_sem);
	363	return 0;
	364
	365	bad_area:
	366	up_read(&mm->mmap_sem);
	367
	368	bad_area_nosemaphore:
	369	/* User mode accesses cause a SIGSEGV */
	370	if (user_mode(regs)) {
	371	_exception(SIGSEGV, regs, code, address);
	372	return 0;
	373	}
	374
	375	if (is_exec && (error_code & DSISR_PROTFAULT)
	376	&& printk_ratelimit())
	377	printk(KERN_CRIT "kernel tried to execute NX-protected"
	378	" page (%lx) - exploit attempt? (uid: %d)\n",
	379	address, current->uid);
	380
	381	return SIGSEGV;
	382
	383	/*
	384	* We ran out of memory, or some other thing happened to us that made
	385	* us unable to handle the page fault gracefully.
	386	*/
	387	out_of_memory:
	388	up_read(&mm->mmap_sem);
f400e198	389	if (is_init(current)) {
14cf11af PM	390	yield();
	391	down_read(&mm->mmap_sem);
	392	goto survive;
	393	}
	394	printk("VM: killing process %s\n", current->comm);
	395	if (user_mode(regs))
	396	do_exit(SIGKILL);
	397	return SIGKILL;
	398
	399	do_sigbus:
	400	up_read(&mm->mmap_sem);
	401	if (user_mode(regs)) {
	402	info.si_signo = SIGBUS;
	403	info.si_errno = 0;
	404	info.si_code = BUS_ADRERR;
	405	info.si_addr = (void __user *)address;
	406	force_sig_info(SIGBUS, &info, current);
	407	return 0;
	408	}
	409	return SIGBUS;
	410	}
	411
	412	/*
	413	* bad_page_fault is called when we have a bad access from the kernel.
	414	* It is called from the DSI and ISI handlers in head.S and from some
	415	* of the procedures in traps.c.
	416	*/
	417	void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
	418	{
	419	const struct exception_table_entry *entry;
	420
	421	/* Are we prepared to handle this fault? */
	422	if ((entry = search_exception_tables(regs->nip)) != NULL) {
	423	regs->nip = entry->fixup;
	424	return;
	425	}
	426
	427	/* kernel has accessed a bad area */
723925b7	428
723925b7	429	switch (regs->trap) {
a416dd8d ME	430	case 0x300:
	431	case 0x380:
	432	printk(KERN_ALERT "Unable to handle kernel paging request for "
	433	"data at address 0x%08lx\n", regs->dar);
	434	break;
	435	case 0x400:
	436	case 0x480:
	437	printk(KERN_ALERT "Unable to handle kernel paging request for "
	438	"instruction fetch\n");
	439	break;
	440	default:
	441	printk(KERN_ALERT "Unable to handle kernel paging request for "
	442	"unknown fault\n");
	443	break;
723925b7 OJ	444	}
	445	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
	446	regs->nip);
	447
14cf11af PM	448	die("Kernel access of bad area", regs, sig);
14cf11af PM	449	}