/*
 *  linux/arch/i386/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 */

#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/smp.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/tty.h>
#include <linux/vt_kern.h>              /* For unblank_screen() */
#include <linux/highmem.h>
#include <linux/bootmem.h>              /* for max_low_pfn */
#include <linux/vmalloc.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>

#include <asm/system.h>
#include <asm/desc.h>
#include <asm/segment.h>

extern void die(const char *,struct pt_regs *,long);

static ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);

int register_page_fault_notifier(struct notifier_block *nb)
{
        vmalloc_sync_all();
        return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
}
EXPORT_SYMBOL_GPL(register_page_fault_notifier);

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

static inline int notify_page_fault(struct pt_regs *regs, long err)
{
        struct die_args args = {
                .regs = regs,
                .str = "page fault",
                .err = err,
                .trapnr = 14,
                .signr = SIGSEGV
        };
        return atomic_notifier_call_chain(&notify_page_fault_chain,
                                          DIE_PAGE_FAULT, &args);
}

/*
 * Return EIP plus the CS segment base.  The segment limit is also
 * adjusted, clamped to the kernel/user address space (whichever is
 * appropriate), and returned in *eip_limit.
 *
 * The segment is checked, because it might have been changed by another
 * task between the original faulting instruction and here.
 *
 * If CS is no longer a valid code segment, or if EIP is beyond the
 * limit, or if it is a kernel address when CS is not a kernel segment,
 * then the returned value will be greater than *eip_limit.
 * 
 * This is slow, but is very rarely executed.
 */
static inline unsigned long get_segment_eip(struct pt_regs *regs,
                                            unsigned long *eip_limit)
{
        unsigned long eip = regs->eip;
        unsigned seg = regs->xcs & 0xffff;
        u32 seg_ar, seg_limit, base, *desc;

        /* Unlikely, but must come before segment checks. */
        if (unlikely(regs->eflags & VM_MASK)) {
                base = seg << 4;
                *eip_limit = base + 0xffff;
                return base + (eip & 0xffff);
        }

        /* The standard kernel/user address space limit. */
        *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg;
        
        /* By far the most common cases. */
        if (likely(SEGMENT_IS_FLAT_CODE(seg)))
                return eip;

        /* Check the segment exists, is within the current LDT/GDT size,
           that kernel/user (ring 0..3) has the appropriate privilege,
           that it's a code segment, and get the limit. */
        __asm__ ("larl %3,%0; lsll %3,%1"
                 : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
        if ((~seg_ar & 0x9800) || eip > seg_limit) {
                *eip_limit = 0;
                return 1;        /* So that returned eip > *eip_limit. */
        }

        /* Get the GDT/LDT descriptor base. 
           When you look for races in this code remember that
           LDT and other horrors are only used in user space. */
        if (seg & (1<<2)) {
                /* Must lock the LDT while reading it. */
                down(&current->mm->context.sem);
                desc = current->mm->context.ldt;
                desc = (void *)desc + (seg & ~7);
        } else {
                /* Must disable preemption while reading the GDT. */
                desc = (u32 *)get_cpu_gdt_table(get_cpu());
                desc = (void *)desc + (seg & ~7);
        }

        /* Decode the code segment base from the descriptor */
        base = get_desc_base((unsigned long *)desc);

        if (seg & (1<<2)) { 
                up(&current->mm->context.sem);
        } else
                put_cpu();

        /* Adjust EIP and segment limit, and clamp at the kernel limit.
           It's legitimate for segments to wrap at 0xffffffff. */
        seg_limit += base;
        if (seg_limit < *eip_limit && seg_limit >= base)
                *eip_limit = seg_limit;
        return eip + base;
}

/* 
 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
 * Check that here and ignore it.
 */
static int __is_prefetch(struct pt_regs *regs, unsigned long addr)
{ 
        unsigned long limit;
        unsigned char *instr = (unsigned char *)get_segment_eip (regs, &limit);
        int scan_more = 1;
        int prefetch = 0; 
        int i;

        for (i = 0; scan_more && i < 15; i++) { 
                unsigned char opcode;
                unsigned char instr_hi;
                unsigned char instr_lo;

                if (instr > (unsigned char *)limit)
                        break;
                if (probe_kernel_address(instr, opcode))
                        break; 

                instr_hi = opcode & 0xf0; 
                instr_lo = opcode & 0x0f; 
                instr++;

                switch (instr_hi) { 
                case 0x20:
                case 0x30:
                        /* Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. */
                        scan_more = ((instr_lo & 7) == 0x6);
                        break;
                        
                case 0x60:
                        /* 0x64 thru 0x67 are valid prefixes in all modes. */
                        scan_more = (instr_lo & 0xC) == 0x4;
                        break;          
                case 0xF0:
                        /* 0xF0, 0xF2, and 0xF3 are valid prefixes */
                        scan_more = !instr_lo || (instr_lo>>1) == 1;
                        break;                  
                case 0x00:
                        /* Prefetch instruction is 0x0F0D or 0x0F18 */
                        scan_more = 0;
                        if (instr > (unsigned char *)limit)
                                break;
                        if (probe_kernel_address(instr, opcode))
                                break;
                        prefetch = (instr_lo == 0xF) &&
                                (opcode == 0x0D || opcode == 0x18);
                        break;                  
                default:
                        scan_more = 0;
                        break;
                } 
        }
        return prefetch;
}

static inline int is_prefetch(struct pt_regs *regs, unsigned long addr,
                              unsigned long error_code)
{
        if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
                     boot_cpu_data.x86 >= 6)) {
                /* Catch an obscure case of prefetch inside an NX page. */
                if (nx_enabled && (error_code & 16))
                        return 0;
                return __is_prefetch(regs, addr);
        }
        return 0;
} 

static noinline void force_sig_info_fault(int si_signo, int si_code,
        unsigned long address, struct task_struct *tsk)
{
        siginfo_t info;

        info.si_signo = si_signo;
        info.si_errno = 0;
        info.si_code = si_code;
        info.si_addr = (void __user *)address;
        force_sig_info(si_signo, &info, tsk);
}

fastcall void do_invalid_op(struct pt_regs *, unsigned long);

static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
{
        unsigned index = pgd_index(address);
        pgd_t *pgd_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;

        pgd += index;
        pgd_k = init_mm.pgd + index;

        if (!pgd_present(*pgd_k))
                return NULL;

        /*
         * set_pgd(pgd, *pgd_k); here would be useless on PAE
         * and redundant with the set_pmd() on non-PAE. As would
         * set_pud.
         */

        pud = pud_offset(pgd, address);
        pud_k = pud_offset(pgd_k, address);
        if (!pud_present(*pud_k))
                return NULL;

        pmd = pmd_offset(pud, address);
        pmd_k = pmd_offset(pud_k, address);
        if (!pmd_present(*pmd_k))
                return NULL;
        if (!pmd_present(*pmd)) {
                set_pmd(pmd, *pmd_k);
                arch_flush_lazy_mmu_mode();
        } else
                BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
        return pmd_k;
}

/*
 * Handle a fault on the vmalloc or module mapping area
 *
 * This assumes no large pages in there.
 */
static inline int vmalloc_fault(unsigned long address)
{
        unsigned long pgd_paddr;
        pmd_t *pmd_k;
        pte_t *pte_k;
        /*
         * Synchronize this task's top level page-table
         * with the 'reference' page table.
         *
         * Do _not_ use "current" here. We might be inside
         * an interrupt in the middle of a task switch..
         */
        pgd_paddr = read_cr3();
        pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
        if (!pmd_k)
                return -1;
        pte_k = pte_offset_kernel(pmd_k, address);
        if (!pte_present(*pte_k))
                return -1;
        return 0;
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * error_code:
 *      bit 0 == 0 means no page found, 1 means protection fault
 *      bit 1 == 0 means read, 1 means write
 *      bit 2 == 0 means kernel, 1 means user-mode
 *      bit 3 == 1 means use of reserved bit detected
 *      bit 4 == 1 means fault was an instruction fetch
 */
fastcall void __kprobes do_page_fault(struct pt_regs *regs,
                                      unsigned long error_code)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct * vma;
        unsigned long address;
        int write, si_code;

        /* get the address */
        address = read_cr2();

        tsk = current;

        si_code = SEGV_MAPERR;

        /*
         * We fault-in kernel-space virtual memory on-demand. The
         * 'reference' page table is init_mm.pgd.
         *
         * NOTE! We MUST NOT take any locks for this case. We may
         * be in an interrupt or a critical region, and should
         * only copy the information from the master page table,
         * nothing more.
         *
         * This verifies that the fault happens in kernel space
         * (error_code & 4) == 0, and that the fault was not a
         * protection error (error_code & 9) == 0.
         */
        if (unlikely(address >= TASK_SIZE)) {
                if (!(error_code & 0x0000000d) && vmalloc_fault(address) >= 0)
                        return;
                if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
                        return;
                /*
                 * Don't take the mm semaphore here. If we fixup a prefetch
                 * fault we could otherwise deadlock.
                 */
                goto bad_area_nosemaphore;
        }

        if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
                return;

        /* It's safe to allow irq's after cr2 has been saved and the vmalloc
           fault has been handled. */
        if (regs->eflags & (X86_EFLAGS_IF|VM_MASK))
                local_irq_enable();

        mm = tsk->mm;

        /*
         * If we're in an interrupt, have no user context or are running in an
         * atomic region then we must not take the fault..
         */
        if (in_atomic() || !mm)
                goto bad_area_nosemaphore;

        /* 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.  Unfortunatly, 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 possibilty 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 ((error_code & 4) == 0 &&
                    !search_exception_tables(regs->eip))
                        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;
        if (error_code & 4) {
                /*
                 * Accessing the stack below %esp is always a bug.
                 * The large cushion allows instructions like enter
                 * and pusha to work.  ("enter $65535,$31" pushes
                 * 32 pointers and then decrements %esp by 65535.)
                 */
                if (address + 65536 + 32 * sizeof(unsigned long) < regs->esp)
                        goto bad_area;
        }
        if (expand_stack(vma, address))
                goto bad_area;
/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
        si_code = SEGV_ACCERR;
        write = 0;
        switch (error_code & 3) {
                default:        /* 3: write, present */
                                /* fall through */
                case 2:         /* write, not present */
                        if (!(vma->vm_flags & VM_WRITE))
                                goto bad_area;
                        write++;
                        break;
                case 1:         /* read, present */
                        goto bad_area;
                case 0:         /* read, not present */
                        if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                                goto bad_area;
        }

 survive:
        /*
         * If for any reason at all we couldn't handle the fault,
         * make sure we exit gracefully rather than endlessly redo
         * the fault.
         */
        switch (handle_mm_fault(mm, vma, address, write)) {
                case VM_FAULT_MINOR:
                        tsk->min_flt++;
                        break;
                case VM_FAULT_MAJOR:
                        tsk->maj_flt++;
                        break;
                case VM_FAULT_SIGBUS:
                        goto do_sigbus;
                case VM_FAULT_OOM:
                        goto out_of_memory;
                default:
                        BUG();
        }

        /*
         * Did it hit the DOS screen memory VA from vm86 mode?
         */
        if (regs->eflags & VM_MASK) {
                unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
                if (bit < 32)
                        tsk->thread.screen_bitmap |= 1 << bit;
        }
        up_read(&mm->mmap_sem);
        return;

/*
 * Something tried to access memory that isn't in our memory map..
 * Fix it, but check if it's kernel or user first..
 */
bad_area:
        up_read(&mm->mmap_sem);

bad_area_nosemaphore:
        /* User mode accesses just cause a SIGSEGV */
        if (error_code & 4) {
                /*
                 * It's possible to have interrupts off here.
                 */
                local_irq_enable();

                /* 
                 * Valid to do another page fault here because this one came 
                 * from user space.
                 */
                if (is_prefetch(regs, address, error_code))
                        return;

                tsk->thread.cr2 = address;
                /* Kernel addresses are always protection faults */
                tsk->thread.error_code = error_code | (address >= TASK_SIZE);
                tsk->thread.trap_no = 14;
                force_sig_info_fault(SIGSEGV, si_code, address, tsk);
                return;
        }

#ifdef CONFIG_X86_F00F_BUG
        /*
         * Pentium F0 0F C7 C8 bug workaround.
         */
        if (boot_cpu_data.f00f_bug) {
                unsigned long nr;
                
                nr = (address - idt_descr.address) >> 3;

                if (nr == 6) {
                        do_invalid_op(regs, 0);
                        return;
                }
        }
#endif

no_context:
        /* Are we prepared to handle this kernel fault?  */
        if (fixup_exception(regs))
                return;

        /* 
         * Valid to do another page fault here, because if this fault
         * had been triggered by is_prefetch fixup_exception would have 
         * handled it.
         */
        if (is_prefetch(regs, address, error_code))
                return;

/*
 * Oops. The kernel tried to access some bad page. We'll have to
 * terminate things with extreme prejudice.
 */

        bust_spinlocks(1);

        if (oops_may_print()) {
                __typeof__(pte_val(__pte(0))) page;

#ifdef CONFIG_X86_PAE
                if (error_code & 16) {
                        pte_t *pte = lookup_address(address);

                        if (pte && pte_present(*pte) && !pte_exec_kernel(*pte))
                                printk(KERN_CRIT "kernel tried to execute "
                                        "NX-protected page - exploit attempt? "
                                        "(uid: %d)\n", current->uid);
                }
#endif
                if (address < PAGE_SIZE)
                        printk(KERN_ALERT "BUG: unable to handle kernel NULL "
                                        "pointer dereference");
                else
                        printk(KERN_ALERT "BUG: unable to handle kernel paging"
                                        " request");
                printk(" at virtual address %08lx\n",address);
                printk(KERN_ALERT " printing eip:\n");
                printk("%08lx\n", regs->eip);

                page = read_cr3();
                page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
#ifdef CONFIG_X86_PAE
                printk(KERN_ALERT "*pdpt = %016Lx\n", page);
                if ((page >> PAGE_SHIFT) < max_low_pfn
                    && page & _PAGE_PRESENT) {
                        page &= PAGE_MASK;
                        page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT)
                                                                 & (PTRS_PER_PMD - 1)];
                        printk(KERN_ALERT "*pde = %016Lx\n", page);
                        page &= ~_PAGE_NX;
                }
#else
                printk(KERN_ALERT "*pde = %08lx\n", page);
#endif

                /*
                 * We must not directly access the pte in the highpte
                 * case if the page table is located in highmem.
                 * And let's rather not kmap-atomic the pte, just in case
                 * it's allocated already.
                 */
                if ((page >> PAGE_SHIFT) < max_low_pfn
                    && (page & _PAGE_PRESENT)) {
                        page &= PAGE_MASK;
                        page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT)
                                                                 & (PTRS_PER_PTE - 1)];
                        printk(KERN_ALERT "*pte = %0*Lx\n", sizeof(page)*2, (u64)page);
                }
        }

        tsk->thread.cr2 = address;
        tsk->thread.trap_no = 14;
        tsk->thread.error_code = error_code;
        die("Oops", regs, error_code);
        bust_spinlocks(0);
        do_exit(SIGKILL);

/*
 * 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(tsk)) {
                yield();
                down_read(&mm->mmap_sem);
                goto survive;
        }
        printk("VM: killing process %s\n", tsk->comm);
        if (error_code & 4)
                do_exit(SIGKILL);
        goto no_context;

do_sigbus:
        up_read(&mm->mmap_sem);

        /* Kernel mode? Handle exceptions or die */
        if (!(error_code & 4))
                goto no_context;

        /* User space => ok to do another page fault */
        if (is_prefetch(regs, address, error_code))
                return;

        tsk->thread.cr2 = address;
        tsk->thread.error_code = error_code;
        tsk->thread.trap_no = 14;
        force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
}

void vmalloc_sync_all(void)
{
        /*
         * Note that races in the updates of insync and start aren't
         * problematic: insync can only get set bits added, and updates to
         * start are only improving performance (without affecting correctness
         * if undone).
         */
        static DECLARE_BITMAP(insync, PTRS_PER_PGD);
        static unsigned long start = TASK_SIZE;
        unsigned long address;

        if (SHARED_KERNEL_PMD)
                return;

        BUILD_BUG_ON(TASK_SIZE & ~PGDIR_MASK);
        for (address = start; address >= TASK_SIZE; address += PGDIR_SIZE) {
                if (!test_bit(pgd_index(address), insync)) {
                        unsigned long flags;
                        struct page *page;

                        spin_lock_irqsave(&pgd_lock, flags);
                        for (page = pgd_list; page; page =
                                        (struct page *)page->index)
                                if (!vmalloc_sync_one(page_address(page),
                                                                address)) {
                                        BUG_ON(page != pgd_list);
                                        break;
                                }
                        spin_unlock_irqrestore(&pgd_lock, flags);
                        if (!page)
                                set_bit(pgd_index(address), insync);
                }
                if (address == start && test_bit(pgd_index(address), insync))
                        start = address + PGDIR_SIZE;
        }
}