/*
 *  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
static inline int notify_page_fault(struct pt_regs *regs)
{
        int ret = 0;

        /* kprobe_running() needs smp_processor_id() */
        if (!user_mode(regs)) {
                preempt_disable();
                if (kprobe_running() && kprobe_fault_handler(regs, 11))
                        ret = 1;
                preempt_enable();
        }

        return ret;
}
#else
static inline int notify_page_fault(struct pt_regs *regs)
{
        return 0;
}
#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;
}

/*
 * 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, ret;
        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(regs))
                return 0;

        if (unlikely(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) {
#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
                /* protection fault */
                if (error_code & DSISR_PROTFAULT)
                        goto bad_area;
                /*
                 * Allow execution from readable areas if the MMU does not
                 * provide separate controls over reading and executing.
                 */
                if (!(vma->vm_flags & VM_EXEC) &&
                    (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
                     !(vma->vm_flags & (VM_READ | VM_WRITE))))
                        goto bad_area;
#else
                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 |
                                           _PAGE_ACCESSED);
                                _tlbie(address, mm->context.id);
                                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:
        ret = handle_mm_fault(mm, vma, address, is_write);
        if (unlikely(ret & VM_FAULT_ERROR)) {
                if (ret & VM_FAULT_OOM)
                        goto out_of_memory;
                else if (ret & VM_FAULT_SIGBUS)
                        goto do_sigbus;
                BUG();
        }
        if (ret & VM_FAULT_MAJOR)
                current->maj_flt++;
        else
                current->min_flt++;
        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_global_init(current)) {
                yield();
                down_read(&mm->mmap_sem);
                goto survive;
        }
        printk("VM: killing process %s\n", current->comm);
        if (user_mode(regs))
                do_group_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);
}