// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 */

#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/hardirq.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/sched/debug.h>
#include <asm/current.h>
#include <asm/tlbflush.h>
#include <arch.h>
#include <as-layout.h>
#include <kern_util.h>
#include <os.h>
#include <skas.h>

/*
 * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
 * segv().
 */
int handle_page_fault(unsigned long address, unsigned long ip,
                      int is_write, int is_user, int *code_out)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        pmd_t *pmd;
        pte_t *pte;
        int err = -EFAULT;
        unsigned int flags = FAULT_FLAG_DEFAULT;

        *code_out = SEGV_MAPERR;

        /*
         * If the fault was with pagefaults disabled, don't take the fault, just
         * fail.
         */
        if (faulthandler_disabled())
                goto out_nosemaphore;

        if (is_user)
                flags |= FAULT_FLAG_USER;
retry:
        mmap_read_lock(mm);
        vma = find_vma(mm, address);
        if (!vma)
                goto out;
        else if (vma->vm_start <= address)
                goto good_area;
        else if (!(vma->vm_flags & VM_GROWSDOWN))
                goto out;
        else if (is_user && !ARCH_IS_STACKGROW(address))
                goto out;
        else if (expand_stack(vma, address))
                goto out;

good_area:
        *code_out = SEGV_ACCERR;
        if (is_write) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto out;
                flags |= FAULT_FLAG_WRITE;
        } else {
                /* Don't require VM_READ|VM_EXEC for write faults! */
                if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
                        goto out;
        }

        do {
                vm_fault_t fault;

                fault = handle_mm_fault(vma, address, flags, NULL);

                if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
                        goto out_nosemaphore;

                if (unlikely(fault & VM_FAULT_ERROR)) {
                        if (fault & VM_FAULT_OOM) {
                                goto out_of_memory;
                        } else if (fault & VM_FAULT_SIGSEGV) {
                                goto out;
                        } else if (fault & VM_FAULT_SIGBUS) {
                                err = -EACCES;
                                goto out;
                        }
                        BUG();
                }
                if (flags & FAULT_FLAG_ALLOW_RETRY) {
                        if (fault & VM_FAULT_RETRY) {
                                flags |= FAULT_FLAG_TRIED;

                                goto retry;
                        }
                }

                pmd = pmd_off(mm, address);
                pte = pte_offset_kernel(pmd, address);
        } while (!pte_present(*pte));
        err = 0;
        /*
         * The below warning was added in place of
         *      pte_mkyoung(); if (is_write) pte_mkdirty();
         * If it's triggered, we'd see normally a hang here (a clean pte is
         * marked read-only to emulate the dirty bit).
         * However, the generic code can mark a PTE writable but clean on a
         * concurrent read fault, triggering this harmlessly. So comment it out.
         */
#if 0
        WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
#endif
        flush_tlb_page(vma, address);
out:
        mmap_read_unlock(mm);
out_nosemaphore:
        return err;

out_of_memory:
        /*
         * We ran out of memory, call the OOM killer, and return the userspace
         * (which will retry the fault, or kill us if we got oom-killed).
         */
        mmap_read_unlock(mm);
        if (!is_user)
                goto out_nosemaphore;
        pagefault_out_of_memory();
        return 0;
}
EXPORT_SYMBOL(handle_page_fault);

static void show_segv_info(struct uml_pt_regs *regs)
{
        struct task_struct *tsk = current;
        struct faultinfo *fi = UPT_FAULTINFO(regs);

        if (!unhandled_signal(tsk, SIGSEGV))
                return;

        if (!printk_ratelimit())
                return;

        printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x",
                task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
                tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
                (void *)UPT_IP(regs), (void *)UPT_SP(regs),
                fi->error_code);

        print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
        printk(KERN_CONT "\n");
}

static void bad_segv(struct faultinfo fi, unsigned long ip)
{
        current->thread.arch.faultinfo = fi;
        force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
}

void fatal_sigsegv(void)
{
        force_sigsegv(SIGSEGV);
        do_signal(&current->thread.regs);
        /*
         * This is to tell gcc that we're not returning - do_signal
         * can, in general, return, but in this case, it's not, since
         * we just got a fatal SIGSEGV queued.
         */
        os_dump_core();
}

/**
 * segv_handler() - the SIGSEGV handler
 * @sig:        the signal number
 * @unused_si:  the signal info struct; unused in this handler
 * @regs:       the ptrace register information
 *
 * The handler first extracts the faultinfo from the UML ptrace regs struct.
 * If the userfault did not happen in an UML userspace process, bad_segv is called.
 * Otherwise the signal did happen in a cloned userspace process, handle it.
 */
void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
        struct faultinfo * fi = UPT_FAULTINFO(regs);

        if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
                show_segv_info(regs);
                bad_segv(*fi, UPT_IP(regs));
                return;
        }
        segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
}

/*
 * We give a *copy* of the faultinfo in the regs to segv.
 * This must be done, since nesting SEGVs could overwrite
 * the info in the regs. A pointer to the info then would
 * give us bad data!
 */
unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
                   struct uml_pt_regs *regs)
{
        jmp_buf *catcher;
        int si_code;
        int err;
        int is_write = FAULT_WRITE(fi);
        unsigned long address = FAULT_ADDRESS(fi);

        if (!is_user && regs)
                current->thread.segv_regs = container_of(regs, struct pt_regs, regs);

        if (!is_user && (address >= start_vm) && (address < end_vm)) {
                flush_tlb_kernel_vm();
                goto out;
        }
        else if (current->mm == NULL) {
                show_regs(container_of(regs, struct pt_regs, regs));
                panic("Segfault with no mm");
        }
        else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
                show_regs(container_of(regs, struct pt_regs, regs));
                panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
                       address, ip);
        }

        if (SEGV_IS_FIXABLE(&fi))
                err = handle_page_fault(address, ip, is_write, is_user,
                                        &si_code);
        else {
                err = -EFAULT;
                /*
                 * A thread accessed NULL, we get a fault, but CR2 is invalid.
                 * This code is used in __do_copy_from_user() of TT mode.
                 * XXX tt mode is gone, so maybe this isn't needed any more
                 */
                address = 0;
        }

        catcher = current->thread.fault_catcher;
        if (!err)
                goto out;
        else if (catcher != NULL) {
                current->thread.fault_addr = (void *) address;
                UML_LONGJMP(catcher, 1);
        }
        else if (current->thread.fault_addr != NULL)
                panic("fault_addr set but no fault catcher");
        else if (!is_user && arch_fixup(ip, regs))
                goto out;

        if (!is_user) {
                show_regs(container_of(regs, struct pt_regs, regs));
                panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
                      address, ip);
        }

        show_segv_info(regs);

        if (err == -EACCES) {
                current->thread.arch.faultinfo = fi;
                force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
        } else {
                BUG_ON(err != -EFAULT);
                current->thread.arch.faultinfo = fi;
                force_sig_fault(SIGSEGV, si_code, (void __user *) address);
        }

out:
        if (regs)
                current->thread.segv_regs = NULL;

        return 0;
}

void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
{
        int code, err;
        if (!UPT_IS_USER(regs)) {
                if (sig == SIGBUS)
                        printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
                               "mount likely just ran out of space\n");
                panic("Kernel mode signal %d", sig);
        }

        arch_examine_signal(sig, regs);

        /* Is the signal layout for the signal known?
         * Signal data must be scrubbed to prevent information leaks.
         */
        code = si->si_code;
        err = si->si_errno;
        if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
                struct faultinfo *fi = UPT_FAULTINFO(regs);
                current->thread.arch.faultinfo = *fi;
                force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
        } else {
                printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
                       sig, code, err);
                force_sig(sig);
        }
}

void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
{
        if (current->thread.fault_catcher != NULL)
                UML_LONGJMP(current->thread.fault_catcher, 1);
        else
                relay_signal(sig, si, regs);
}

void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
        do_IRQ(WINCH_IRQ, regs);
}