/*
 *  linux/arch/arm/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *  Modifications for ARM processor (c) 1995-2004 Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/extable.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/page-flags.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
#include <linux/highmem.h>
#include <linux/perf_event.h>

#include <asm/pgtable.h>
#include <asm/system_misc.h>
#include <asm/system_info.h>
#include <asm/tlbflush.h>

#include "fault.h"

#ifdef CONFIG_MMU

#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs, unsigned int fsr)
{
        int ret = 0;

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

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

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
void show_pte(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;

        if (!mm)
                mm = &init_mm;

        pr_alert("pgd = %p\n", mm->pgd);
        pgd = pgd_offset(mm, addr);
        pr_alert("[%08lx] *pgd=%08llx",
                        addr, (long long)pgd_val(*pgd));

        do {
                pud_t *pud;
                pmd_t *pmd;
                pte_t *pte;

                if (pgd_none(*pgd))
                        break;

                if (pgd_bad(*pgd)) {
                        pr_cont("(bad)");
                        break;
                }

                pud = pud_offset(pgd, addr);
                if (PTRS_PER_PUD != 1)
                        pr_cont(", *pud=%08llx", (long long)pud_val(*pud));

                if (pud_none(*pud))
                        break;

                if (pud_bad(*pud)) {
                        pr_cont("(bad)");
                        break;
                }

                pmd = pmd_offset(pud, addr);
                if (PTRS_PER_PMD != 1)
                        pr_cont(", *pmd=%08llx", (long long)pmd_val(*pmd));

                if (pmd_none(*pmd))
                        break;

                if (pmd_bad(*pmd)) {
                        pr_cont("(bad)");
                        break;
                }

                /* We must not map this if we have highmem enabled */
                if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
                        break;

                pte = pte_offset_map(pmd, addr);
                pr_cont(", *pte=%08llx", (long long)pte_val(*pte));
#ifndef CONFIG_ARM_LPAE
                pr_cont(", *ppte=%08llx",
                       (long long)pte_val(pte[PTE_HWTABLE_PTRS]));
#endif
                pte_unmap(pte);
        } while(0);

        pr_cont("\n");
}
#else                                   /* CONFIG_MMU */
void show_pte(struct mm_struct *mm, unsigned long addr)
{ }
#endif                                  /* CONFIG_MMU */

/*
 * Oops.  The kernel tried to access some page that wasn't present.
 */
static void
__do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
                  struct pt_regs *regs)
{
        /*
         * Are we prepared to handle this kernel fault?
         */
        if (fixup_exception(regs))
                return;

        /*
         * No handler, we'll have to terminate things with extreme prejudice.
         */
        bust_spinlocks(1);
        pr_alert("Unable to handle kernel %s at virtual address %08lx\n",
                 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
                 "paging request", addr);

        show_pte(mm, addr);
        die("Oops", regs, fsr);
        bust_spinlocks(0);
        do_exit(SIGKILL);
}

/*
 * Something tried to access memory that isn't in our memory map..
 * User mode accesses just cause a SIGSEGV
 */
static void
__do_user_fault(struct task_struct *tsk, unsigned long addr,
                unsigned int fsr, unsigned int sig, int code,
                struct pt_regs *regs)
{
        if (addr > TASK_SIZE)
                harden_branch_predictor();

#ifdef CONFIG_DEBUG_USER
        if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) ||
            ((user_debug & UDBG_BUS)  && (sig == SIGBUS))) {
                printk(KERN_DEBUG "%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
                       tsk->comm, sig, addr, fsr);
                show_pte(tsk->mm, addr);
                show_regs(regs);
        }
#endif

        tsk->thread.address = addr;
        tsk->thread.error_code = fsr;
        tsk->thread.trap_no = 14;
        force_sig_fault(sig, code, (void __user *)addr, tsk);
}

void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->active_mm;

        /*
         * If we are in kernel mode at this point, we
         * have no context to handle this fault with.
         */
        if (user_mode(regs))
                __do_user_fault(tsk, addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
        else
                __do_kernel_fault(mm, addr, fsr, regs);
}

#ifdef CONFIG_MMU
#define VM_FAULT_BADMAP         0x010000
#define VM_FAULT_BADACCESS      0x020000

/*
 * Check that the permissions on the VMA allow for the fault which occurred.
 * If we encountered a write fault, we must have write permission, otherwise
 * we allow any permission.
 */
static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
{
        unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;

        if (fsr & FSR_WRITE)
                mask = VM_WRITE;
        if (fsr & FSR_LNX_PF)
                mask = VM_EXEC;

        return vma->vm_flags & mask ? false : true;
}

static vm_fault_t __kprobes
__do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
                unsigned int flags, struct task_struct *tsk)
{
        struct vm_area_struct *vma;
        vm_fault_t fault;

        vma = find_vma(mm, addr);
        fault = VM_FAULT_BADMAP;
        if (unlikely(!vma))
                goto out;
        if (unlikely(vma->vm_start > addr))
                goto check_stack;

        /*
         * Ok, we have a good vm_area for this
         * memory access, so we can handle it.
         */
good_area:
        if (access_error(fsr, vma)) {
                fault = VM_FAULT_BADACCESS;
                goto out;
        }

        return handle_mm_fault(vma, addr & PAGE_MASK, flags);

check_stack:
        /* Don't allow expansion below FIRST_USER_ADDRESS */
        if (vma->vm_flags & VM_GROWSDOWN &&
            addr >= FIRST_USER_ADDRESS && !expand_stack(vma, addr))
                goto good_area;
out:
        return fault;
}

static int __kprobes
do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        int sig, code;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        if (notify_page_fault(regs, fsr))
                return 0;

        tsk = current;
        mm  = tsk->mm;

        /* Enable interrupts if they were enabled in the parent context. */
        if (interrupts_enabled(regs))
                local_irq_enable();

        /*
         * If we're in an interrupt or have no user
         * context, we must not take the fault..
         */
        if (faulthandler_disabled() || !mm)
                goto no_context;

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;
        if (fsr & FSR_WRITE)
                flags |= FAULT_FLAG_WRITE;

        /*
         * As per x86, we may deadlock here.  However, since the kernel only
         * validly references user space from well defined areas of the code,
         * we can bug out early if this is from code which shouldn't.
         */
        if (!down_read_trylock(&mm->mmap_sem)) {
                if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc))
                        goto no_context;
retry:
                down_read(&mm->mmap_sem);
        } else {
                /*
                 * The above down_read_trylock() might have succeeded in
                 * which case, we'll have missed the might_sleep() from
                 * down_read()
                 */
                might_sleep();
#ifdef CONFIG_DEBUG_VM
                if (!user_mode(regs) &&
                    !search_exception_tables(regs->ARM_pc))
                        goto no_context;
#endif
        }

        fault = __do_page_fault(mm, addr, fsr, flags, tsk);

        /* If we need to retry but a fatal signal is pending, handle the
         * signal first. We do not need to release the mmap_sem because
         * it would already be released in __lock_page_or_retry in
         * mm/filemap.c. */
        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
                if (!user_mode(regs))
                        goto no_context;
                return 0;
        }

        /*
         * Major/minor page fault accounting is only done on the
         * initial attempt. If we go through a retry, it is extremely
         * likely that the page will be found in page cache at that point.
         */

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
        if (!(fault & VM_FAULT_ERROR) && flags & FAULT_FLAG_ALLOW_RETRY) {
                if (fault & VM_FAULT_MAJOR) {
                        tsk->maj_flt++;
                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
                                        regs, addr);
                } else {
                        tsk->min_flt++;
                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
                                        regs, addr);
                }
                if (fault & VM_FAULT_RETRY) {
                        /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
                        * of starvation. */
                        flags &= ~FAULT_FLAG_ALLOW_RETRY;
                        flags |= FAULT_FLAG_TRIED;
                        goto retry;
                }
        }

        up_read(&mm->mmap_sem);

        /*
         * Handle the "normal" case first - VM_FAULT_MAJOR
         */
        if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
                return 0;

        /*
         * If we are in kernel mode at this point, we
         * have no context to handle this fault with.
         */
        if (!user_mode(regs))
                goto no_context;

        if (fault & VM_FAULT_OOM) {
                /*
                 * We ran out of memory, call the OOM killer, and return to
                 * userspace (which will retry the fault, or kill us if we
                 * got oom-killed)
                 */
                pagefault_out_of_memory();
                return 0;
        }

        if (fault & VM_FAULT_SIGBUS) {
                /*
                 * We had some memory, but were unable to
                 * successfully fix up this page fault.
                 */
                sig = SIGBUS;
                code = BUS_ADRERR;
        } else {
                /*
                 * Something tried to access memory that
                 * isn't in our memory map..
                 */
                sig = SIGSEGV;
                code = fault == VM_FAULT_BADACCESS ?
                        SEGV_ACCERR : SEGV_MAPERR;
        }

        __do_user_fault(tsk, addr, fsr, sig, code, regs);
        return 0;

no_context:
        __do_kernel_fault(mm, addr, fsr, regs);
        return 0;
}
#else                                   /* CONFIG_MMU */
static int
do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        return 0;
}
#endif                                  /* CONFIG_MMU */

/*
 * First Level Translation Fault Handler
 *
 * We enter here because the first level page table doesn't contain
 * a valid entry for the address.
 *
 * If the address is in kernel space (>= TASK_SIZE), then we are
 * probably faulting in the vmalloc() area.
 *
 * If the init_task's first level page tables contains the relevant
 * entry, we copy the it to this task.  If not, we send the process
 * a signal, fixup the exception, or oops the kernel.
 *
 * 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.
 */
#ifdef CONFIG_MMU
static int __kprobes
do_translation_fault(unsigned long addr, unsigned int fsr,
                     struct pt_regs *regs)
{
        unsigned int index;
        pgd_t *pgd, *pgd_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;

        if (addr < TASK_SIZE)
                return do_page_fault(addr, fsr, regs);

        if (user_mode(regs))
                goto bad_area;

        index = pgd_index(addr);

        pgd = cpu_get_pgd() + index;
        pgd_k = init_mm.pgd + index;

        if (pgd_none(*pgd_k))
                goto bad_area;
        if (!pgd_present(*pgd))
                set_pgd(pgd, *pgd_k);

        pud = pud_offset(pgd, addr);
        pud_k = pud_offset(pgd_k, addr);

        if (pud_none(*pud_k))
                goto bad_area;
        if (!pud_present(*pud))
                set_pud(pud, *pud_k);

        pmd = pmd_offset(pud, addr);
        pmd_k = pmd_offset(pud_k, addr);

#ifdef CONFIG_ARM_LPAE
        /*
         * Only one hardware entry per PMD with LPAE.
         */
        index = 0;
#else
        /*
         * On ARM one Linux PGD entry contains two hardware entries (see page
         * tables layout in pgtable.h). We normally guarantee that we always
         * fill both L1 entries. But create_mapping() doesn't follow the rule.
         * It can create inidividual L1 entries, so here we have to call
         * pmd_none() check for the entry really corresponded to address, not
         * for the first of pair.
         */
        index = (addr >> SECTION_SHIFT) & 1;
#endif
        if (pmd_none(pmd_k[index]))
                goto bad_area;

        copy_pmd(pmd, pmd_k);
        return 0;

bad_area:
        do_bad_area(addr, fsr, regs);
        return 0;
}
#else                                   /* CONFIG_MMU */
static int
do_translation_fault(unsigned long addr, unsigned int fsr,
                     struct pt_regs *regs)
{
        return 0;
}
#endif                                  /* CONFIG_MMU */

/*
 * Some section permission faults need to be handled gracefully.
 * They can happen due to a __{get,put}_user during an oops.
 */
#ifndef CONFIG_ARM_LPAE
static int
do_sect_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        do_bad_area(addr, fsr, regs);
        return 0;
}
#endif /* CONFIG_ARM_LPAE */

/*
 * This abort handler always returns "fault".
 */
static int
do_bad(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        return 1;
}

struct fsr_info {
        int     (*fn)(unsigned long addr, unsigned int fsr, struct pt_regs *regs);
        int     sig;
        int     code;
        const char *name;
};

/* FSR definition */
#ifdef CONFIG_ARM_LPAE
#include "fsr-3level.c"
#else
#include "fsr-2level.c"
#endif

void __init
hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
                int sig, int code, const char *name)
{
        if (nr < 0 || nr >= ARRAY_SIZE(fsr_info))
                BUG();

        fsr_info[nr].fn   = fn;
        fsr_info[nr].sig  = sig;
        fsr_info[nr].code = code;
        fsr_info[nr].name = name;
}

/*
 * Dispatch a data abort to the relevant handler.
 */
asmlinkage void
do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        const struct fsr_info *inf = fsr_info + fsr_fs(fsr);

        if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
                return;

        pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
                inf->name, fsr, addr);
        show_pte(current->mm, addr);

        arm_notify_die("", regs, inf->sig, inf->code, (void __user *)addr,
                       fsr, 0);
}

void __init
hook_ifault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
                 int sig, int code, const char *name)
{
        if (nr < 0 || nr >= ARRAY_SIZE(ifsr_info))
                BUG();

        ifsr_info[nr].fn   = fn;
        ifsr_info[nr].sig  = sig;
        ifsr_info[nr].code = code;
        ifsr_info[nr].name = name;
}

asmlinkage void
do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
{
        const struct fsr_info *inf = ifsr_info + fsr_fs(ifsr);

        if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
                return;

        pr_alert("Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
                inf->name, ifsr, addr);

        arm_notify_die("", regs, inf->sig, inf->code, (void __user *)addr,
                       ifsr, 0);
}

/*
 * Abort handler to be used only during first unmasking of asynchronous aborts
 * on the boot CPU. This makes sure that the machine will not die if the
 * firmware/bootloader left an imprecise abort pending for us to trip over.
 */
static int __init early_abort_handler(unsigned long addr, unsigned int fsr,
                                      struct pt_regs *regs)
{
        pr_warn("Hit pending asynchronous external abort (FSR=0x%08x) during "
                "first unmask, this is most likely caused by a "
                "firmware/bootloader bug.\n", fsr);

        return 0;
}

void __init early_abt_enable(void)
{
        fsr_info[FSR_FS_AEA].fn = early_abort_handler;
        local_abt_enable();
        fsr_info[FSR_FS_AEA].fn = do_bad;
}

#ifndef CONFIG_ARM_LPAE
static int __init exceptions_init(void)
{
        if (cpu_architecture() >= CPU_ARCH_ARMv6) {
                hook_fault_code(4, do_translation_fault, SIGSEGV, SEGV_MAPERR,
                                "I-cache maintenance fault");
        }

        if (cpu_architecture() >= CPU_ARCH_ARMv7) {
                /*
                 * TODO: Access flag faults introduced in ARMv6K.
                 * Runtime check for 'K' extension is needed
                 */
                hook_fault_code(3, do_bad, SIGSEGV, SEGV_MAPERR,
                                "section access flag fault");
                hook_fault_code(6, do_bad, SIGSEGV, SEGV_MAPERR,
                                "section access flag fault");
        }

        return 0;
}

arch_initcall(exceptions_init);
#endif