// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/arch/arm/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *  Modifications for ARM processor (c) 1995-2004 Russell King
 */
#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 <linux/kfence.h>

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

#include "fault.h"

#ifdef CONFIG_MMU

bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
{
        unsigned long addr = (unsigned long)unsafe_src;

        return addr >= TASK_SIZE && ULONG_MAX - addr >= size;
}

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

        if (!mm)
                mm = &init_mm;

        pgd = pgd_offset(mm, addr);
        printk("%s[%08lx] *pgd=%08llx", lvl, addr, (long long)pgd_val(*pgd));

        do {
                p4d_t *p4d;
                pud_t *pud;
                pmd_t *pmd;
                pte_t *pte;

                p4d = p4d_offset(pgd, addr);
                if (p4d_none(*p4d))
                        break;

                if (p4d_bad(*p4d)) {
                        pr_cont("(bad)");
                        break;
                }

                pud = pud_offset(p4d, 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);
                if (!pte)
                        break;

                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(const char *lvl, struct mm_struct *mm, unsigned long addr)
{ }
#endif                                  /* CONFIG_MMU */

static inline bool is_write_fault(unsigned int fsr)
{
        return (fsr & FSR_WRITE) && !(fsr & FSR_CM);
}

static inline bool is_translation_fault(unsigned int fsr)
{
        int fs = fsr_fs(fsr);
#ifdef CONFIG_ARM_LPAE
        if ((fs & FS_MMU_NOLL_MASK) == FS_TRANS_NOLL)
                return true;
#else
        if (fs == FS_L1_TRANS || fs == FS_L2_TRANS)
                return true;
#endif
        return false;
}

static inline bool is_permission_fault(unsigned int fsr)
{
        int fs = fsr_fs(fsr);
#ifdef CONFIG_ARM_LPAE
        if ((fs & FS_MMU_NOLL_MASK) == FS_PERM_NOLL)
                return true;
#else
        if (fs == FS_L1_PERM || fs == FS_L2_PERM)
                return true;
#endif
        return false;
}

static void die_kernel_fault(const char *msg, struct mm_struct *mm,
                             unsigned long addr, unsigned int fsr,
                             struct pt_regs *regs)
{
        bust_spinlocks(1);
        pr_alert("8<--- cut here ---\n");
        pr_alert("Unable to handle kernel %s at virtual address %08lx when %s\n",
                 msg, addr, fsr & FSR_LNX_PF ? "execute" : str_write_read(fsr & FSR_WRITE));

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

/*
 * 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)
{
        const char *msg;
        /*
         * Are we prepared to handle this kernel fault?
         */
        if (fixup_exception(regs))
                return;

        /*
         * No handler, we'll have to terminate things with extreme prejudice.
         */
        if (addr < PAGE_SIZE) {
                msg = "NULL pointer dereference";
        } else if (is_permission_fault(fsr) && fsr & FSR_LNX_PF) {
                msg = "execution of memory";
        } else {
                if (is_translation_fault(fsr) &&
                    kfence_handle_page_fault(addr, is_write_fault(fsr), regs))
                        return;

                msg = "paging request";
        }

        die_kernel_fault(msg, mm, addr, fsr, regs);
}

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

#ifdef CONFIG_DEBUG_USER
        if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) ||
            ((user_debug & UDBG_BUS)  && (sig == SIGBUS))) {
                pr_err("8<--- cut here ---\n");
                pr_err("%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
                       tsk->comm, sig, addr, fsr);
                show_pte(KERN_ERR, tsk->mm, addr);
                show_regs(regs);
        }
#endif
#ifndef CONFIG_KUSER_HELPERS
        if ((sig == SIGSEGV) && ((addr & PAGE_MASK) == 0xffff0000))
                printk_ratelimited(KERN_DEBUG
                                   "%s: CONFIG_KUSER_HELPERS disabled at 0x%08lx\n",
                                   tsk->comm, addr);
#endif

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

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(addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
        else
                __do_kernel_fault(mm, addr, fsr, regs);
}

#ifdef CONFIG_MMU
#ifdef CONFIG_CPU_TTBR0_PAN
static inline bool ttbr0_usermode_access_allowed(struct pt_regs *regs)
{
        struct svc_pt_regs *svcregs;

        /* If we are in user mode: permission granted */
        if (user_mode(regs))
                return true;

        /* uaccess state saved above pt_regs on SVC exception entry */
        svcregs = to_svc_pt_regs(regs);

        return !(svcregs->ttbcr & TTBCR_EPD0);
}
#else
static inline bool ttbr0_usermode_access_allowed(struct pt_regs *regs)
{
        return true;
}
#endif

static int __kprobes
do_kernel_address_page_fault(struct mm_struct *mm, unsigned long addr,
                             unsigned int fsr, struct pt_regs *regs)
{
        if (user_mode(regs)) {
                /*
                 * Fault from user mode for a kernel space address. User mode
                 * should not be faulting in kernel space, which includes the
                 * vector/khelper page. Handle the branch predictor hardening
                 * while interrupts are still disabled, then send a SIGSEGV.
                 */
                harden_branch_predictor();
                __do_user_fault(addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
        } else {
                /*
                 * Fault from kernel mode. Enable interrupts if they were
                 * enabled in the parent context. Section (upper page table)
                 * translation faults are handled via do_translation_fault(),
                 * so we will only get here for a non-present kernel space
                 * PTE or PTE permission fault. This may happen in exceptional
                 * circumstances and need the fixup tables to be walked.
                 */
                if (interrupts_enabled(regs))
                        local_irq_enable();

                __do_kernel_fault(mm, addr, fsr, regs);
        }

        return 0;
}

static int __kprobes
do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        int sig, code;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_DEFAULT;
        vm_flags_t vm_flags = VM_ACCESS_FLAGS;

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

        /*
         * Handle kernel addresses faults separately, which avoids touching
         * the mmap lock from contexts that are not able to sleep.
         */
        if (addr >= TASK_SIZE)
                return do_kernel_address_page_fault(mm, addr, fsr, regs);

        /* 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 (is_write_fault(fsr)) {
                flags |= FAULT_FLAG_WRITE;
                vm_flags = VM_WRITE;
        }

        if (fsr & FSR_LNX_PF) {
                vm_flags = VM_EXEC;

                if (is_permission_fault(fsr) && !user_mode(regs))
                        die_kernel_fault("execution of memory",
                                         mm, addr, fsr, regs);
        }

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);

        /*
         * Privileged access aborts with CONFIG_CPU_TTBR0_PAN enabled are
         * routed via the translation fault mechanism. Check whether uaccess
         * is disabled while in kernel mode.
         */
        if (!ttbr0_usermode_access_allowed(regs))
                goto no_context;

        if (!(flags & FAULT_FLAG_USER))
                goto lock_mmap;

        vma = lock_vma_under_rcu(mm, addr);
        if (!vma)
                goto lock_mmap;

        if (!(vma->vm_flags & vm_flags)) {
                vma_end_read(vma);
                count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
                fault = 0;
                code = SEGV_ACCERR;
                goto bad_area;
        }
        fault = handle_mm_fault(vma, addr, flags | FAULT_FLAG_VMA_LOCK, regs);
        if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
                vma_end_read(vma);

        if (!(fault & VM_FAULT_RETRY)) {
                count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
                goto done;
        }
        count_vm_vma_lock_event(VMA_LOCK_RETRY);
        if (fault & VM_FAULT_MAJOR)
                flags |= FAULT_FLAG_TRIED;

        /* Quick path to respond to signals */
        if (fault_signal_pending(fault, regs)) {
                if (!user_mode(regs))
                        goto no_context;
                return 0;
        }
lock_mmap:

retry:
        vma = lock_mm_and_find_vma(mm, addr, regs);
        if (unlikely(!vma)) {
                fault = 0;
                code = SEGV_MAPERR;
                goto bad_area;
        }

        /*
         * ok, we have a good vm_area for this memory access, check the
         * permissions on the VMA allow for the fault which occurred.
         */
        if (!(vma->vm_flags & vm_flags)) {
                mmap_read_unlock(mm);
                fault = 0;
                code = SEGV_ACCERR;
                goto bad_area;
        }

        fault = handle_mm_fault(vma, addr & PAGE_MASK, flags, regs);

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

        /* The fault is fully completed (including releasing mmap lock) */
        if (fault & VM_FAULT_COMPLETED)
                return 0;

        if (!(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_RETRY) {
                        flags |= FAULT_FLAG_TRIED;
                        goto retry;
                }
        }

        mmap_read_unlock(mm);
done:

        /* Handle the "normal" case first */
        if (likely(!(fault & VM_FAULT_ERROR)))
                return 0;

        code = SEGV_MAPERR;
bad_area:
        /*
         * 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;
        }

        __do_user_fault(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 this is a user address (addr < TASK_SIZE), we handle this as a
 * normal page fault. This leaves the remainder of the function to handle
 * kernel address translation faults.
 *
 * Since user mode is not permitted to access kernel addresses, pass these
 * directly to do_kernel_address_page_fault() to handle.
 *
 * Otherwise, we're probably faulting in the vmalloc() area, so try to fix
 * that up. Note that we must not take any locks or enable interrupts in
 * this case.
 *
 * If vmalloc() fixup fails, that means the non-leaf page tables did not
 * contain an entry for this address, so handle this via
 * do_kernel_address_page_fault().
 */
#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;
        p4d_t *p4d, *p4d_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;

        p4d = p4d_offset(pgd, addr);
        p4d_k = p4d_offset(pgd_k, addr);

        if (p4d_none(*p4d_k))
                goto bad_area;
        if (!p4d_present(*p4d))
                set_p4d(p4d, *p4d_k);

        pud = pud_offset(p4d, addr);
        pud_k = pud_offset(p4d_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_kernel_address_page_fault(current->mm, 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)
{
        /*
         * If this is a kernel address, but from user mode, then userspace
         * is trying bad stuff. Invoke the branch predictor handling.
         * Interrupts are disabled here.
         */
        if (addr >= TASK_SIZE && user_mode(regs))
                harden_branch_predictor();

        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("8<--- cut here ---\n");
        pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
                inf->name, fsr, addr);
        show_pte(KERN_ALERT, 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("8<--- cut here ---\n");
        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