// SPDX-License-Identifier: GPL-2.0-only
/*
 *  mm/userfaultfd.c
 *
 *  Copyright (C) 2015  Red Hat, Inc.
 */

#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/userfaultfd_k.h>
#include <linux/mmu_notifier.h>
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <asm/tlbflush.h>
#include "internal.h"

static __always_inline
struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
                                    unsigned long dst_start,
                                    unsigned long len)
{
        /*
         * Make sure that the dst range is both valid and fully within a
         * single existing vma.
         */
        struct vm_area_struct *dst_vma;

        dst_vma = find_vma(dst_mm, dst_start);
        if (!dst_vma)
                return NULL;

        if (dst_start < dst_vma->vm_start ||
            dst_start + len > dst_vma->vm_end)
                return NULL;

        /*
         * Check the vma is registered in uffd, this is required to
         * enforce the VM_MAYWRITE check done at uffd registration
         * time.
         */
        if (!dst_vma->vm_userfaultfd_ctx.ctx)
                return NULL;

        return dst_vma;
}

/*
 * Install PTEs, to map dst_addr (within dst_vma) to page.
 *
 * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
 * and anon, and for both shared and private VMAs.
 */
int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
                             struct vm_area_struct *dst_vma,
                             unsigned long dst_addr, struct page *page,
                             bool newly_allocated, bool wp_copy)
{
        int ret;
        pte_t _dst_pte, *dst_pte;
        bool writable = dst_vma->vm_flags & VM_WRITE;
        bool vm_shared = dst_vma->vm_flags & VM_SHARED;
        bool page_in_cache = page->mapping;
        spinlock_t *ptl;
        struct inode *inode;
        pgoff_t offset, max_off;

        _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
        if (page_in_cache && !vm_shared)
                writable = false;
        if (writable || !page_in_cache)
                _dst_pte = pte_mkdirty(_dst_pte);
        if (writable) {
                if (wp_copy)
                        _dst_pte = pte_mkuffd_wp(_dst_pte);
                else
                        _dst_pte = pte_mkwrite(_dst_pte);
        }

        dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);

        if (vma_is_shmem(dst_vma)) {
                /* serialize against truncate with the page table lock */
                inode = dst_vma->vm_file->f_inode;
                offset = linear_page_index(dst_vma, dst_addr);
                max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
                ret = -EFAULT;
                if (unlikely(offset >= max_off))
                        goto out_unlock;
        }

        ret = -EEXIST;
        if (!pte_none(*dst_pte))
                goto out_unlock;

        if (page_in_cache)
                page_add_file_rmap(page, false);
        else
                page_add_new_anon_rmap(page, dst_vma, dst_addr, false);

        /*
         * Must happen after rmap, as mm_counter() checks mapping (via
         * PageAnon()), which is set by __page_set_anon_rmap().
         */
        inc_mm_counter(dst_mm, mm_counter(page));

        if (newly_allocated)
                lru_cache_add_inactive_or_unevictable(page, dst_vma);

        set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);
        ret = 0;
out_unlock:
        pte_unmap_unlock(dst_pte, ptl);
        return ret;
}

static int mcopy_atomic_pte(struct mm_struct *dst_mm,
                            pmd_t *dst_pmd,
                            struct vm_area_struct *dst_vma,
                            unsigned long dst_addr,
                            unsigned long src_addr,
                            struct page **pagep,
                            bool wp_copy)
{
        void *page_kaddr;
        int ret;
        struct page *page;

        if (!*pagep) {
                ret = -ENOMEM;
                page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
                if (!page)
                        goto out;

                page_kaddr = kmap_atomic(page);
                ret = copy_from_user(page_kaddr,
                                     (const void __user *) src_addr,
                                     PAGE_SIZE);
                kunmap_atomic(page_kaddr);

                /* fallback to copy_from_user outside mmap_lock */
                if (unlikely(ret)) {
                        ret = -ENOENT;
                        *pagep = page;
                        /* don't free the page */
                        goto out;
                }
        } else {
                page = *pagep;
                *pagep = NULL;
        }

        /*
         * The memory barrier inside __SetPageUptodate makes sure that
         * preceding stores to the page contents become visible before
         * the set_pte_at() write.
         */
        __SetPageUptodate(page);

        ret = -ENOMEM;
        if (mem_cgroup_charge(page, dst_mm, GFP_KERNEL))
                goto out_release;

        ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
                                       page, true, wp_copy);
        if (ret)
                goto out_release;
out:
        return ret;
out_release:
        put_page(page);
        goto out;
}

static int mfill_zeropage_pte(struct mm_struct *dst_mm,
                              pmd_t *dst_pmd,
                              struct vm_area_struct *dst_vma,
                              unsigned long dst_addr)
{
        pte_t _dst_pte, *dst_pte;
        spinlock_t *ptl;
        int ret;
        pgoff_t offset, max_off;
        struct inode *inode;

        _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
                                         dst_vma->vm_page_prot));
        dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
        if (dst_vma->vm_file) {
                /* the shmem MAP_PRIVATE case requires checking the i_size */
                inode = dst_vma->vm_file->f_inode;
                offset = linear_page_index(dst_vma, dst_addr);
                max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
                ret = -EFAULT;
                if (unlikely(offset >= max_off))
                        goto out_unlock;
        }
        ret = -EEXIST;
        if (!pte_none(*dst_pte))
                goto out_unlock;
        set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);
        ret = 0;
out_unlock:
        pte_unmap_unlock(dst_pte, ptl);
        return ret;
}

/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
static int mcontinue_atomic_pte(struct mm_struct *dst_mm,
                                pmd_t *dst_pmd,
                                struct vm_area_struct *dst_vma,
                                unsigned long dst_addr,
                                bool wp_copy)
{
        struct inode *inode = file_inode(dst_vma->vm_file);
        pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
        struct page *page;
        int ret;

        ret = shmem_getpage(inode, pgoff, &page, SGP_READ);
        if (ret)
                goto out;
        if (!page) {
                ret = -EFAULT;
                goto out;
        }

        ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
                                       page, false, wp_copy);
        if (ret)
                goto out_release;

        unlock_page(page);
        ret = 0;
out:
        return ret;
out_release:
        unlock_page(page);
        put_page(page);
        goto out;
}

static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
{
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;

        pgd = pgd_offset(mm, address);
        p4d = p4d_alloc(mm, pgd, address);
        if (!p4d)
                return NULL;
        pud = pud_alloc(mm, p4d, address);
        if (!pud)
                return NULL;
        /*
         * Note that we didn't run this because the pmd was
         * missing, the *pmd may be already established and in
         * turn it may also be a trans_huge_pmd.
         */
        return pmd_alloc(mm, pud, address);
}

#ifdef CONFIG_HUGETLB_PAGE
/*
 * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
 * called with mmap_lock held, it will release mmap_lock before returning.
 */
static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
                                              struct vm_area_struct *dst_vma,
                                              unsigned long dst_start,
                                              unsigned long src_start,
                                              unsigned long len,
                                              enum mcopy_atomic_mode mode)
{
        int vm_shared = dst_vma->vm_flags & VM_SHARED;
        ssize_t err;
        pte_t *dst_pte;
        unsigned long src_addr, dst_addr;
        long copied;
        struct page *page;
        unsigned long vma_hpagesize;
        pgoff_t idx;
        u32 hash;
        struct address_space *mapping;

        /*
         * There is no default zero huge page for all huge page sizes as
         * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
         * by THP.  Since we can not reliably insert a zero page, this
         * feature is not supported.
         */
        if (mode == MCOPY_ATOMIC_ZEROPAGE) {
                mmap_read_unlock(dst_mm);
                return -EINVAL;
        }

        src_addr = src_start;
        dst_addr = dst_start;
        copied = 0;
        page = NULL;
        vma_hpagesize = vma_kernel_pagesize(dst_vma);

        /*
         * Validate alignment based on huge page size
         */
        err = -EINVAL;
        if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
                goto out_unlock;

retry:
        /*
         * On routine entry dst_vma is set.  If we had to drop mmap_lock and
         * retry, dst_vma will be set to NULL and we must lookup again.
         */
        if (!dst_vma) {
                err = -ENOENT;
                dst_vma = find_dst_vma(dst_mm, dst_start, len);
                if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
                        goto out_unlock;

                err = -EINVAL;
                if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
                        goto out_unlock;

                vm_shared = dst_vma->vm_flags & VM_SHARED;
        }

        /*
         * If not shared, ensure the dst_vma has a anon_vma.
         */
        err = -ENOMEM;
        if (!vm_shared) {
                if (unlikely(anon_vma_prepare(dst_vma)))
                        goto out_unlock;
        }

        while (src_addr < src_start + len) {
                BUG_ON(dst_addr >= dst_start + len);

                /*
                 * Serialize via i_mmap_rwsem and hugetlb_fault_mutex.
                 * i_mmap_rwsem ensures the dst_pte remains valid even
                 * in the case of shared pmds.  fault mutex prevents
                 * races with other faulting threads.
                 */
                mapping = dst_vma->vm_file->f_mapping;
                i_mmap_lock_read(mapping);
                idx = linear_page_index(dst_vma, dst_addr);
                hash = hugetlb_fault_mutex_hash(mapping, idx);
                mutex_lock(&hugetlb_fault_mutex_table[hash]);

                err = -ENOMEM;
                dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize);
                if (!dst_pte) {
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        i_mmap_unlock_read(mapping);
                        goto out_unlock;
                }

                if (mode != MCOPY_ATOMIC_CONTINUE &&
                    !huge_pte_none(huge_ptep_get(dst_pte))) {
                        err = -EEXIST;
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        i_mmap_unlock_read(mapping);
                        goto out_unlock;
                }

                err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
                                               dst_addr, src_addr, mode, &page);

                mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                i_mmap_unlock_read(mapping);

                cond_resched();

                if (unlikely(err == -ENOENT)) {
                        mmap_read_unlock(dst_mm);
                        BUG_ON(!page);

                        err = copy_huge_page_from_user(page,
                                                (const void __user *)src_addr,
                                                vma_hpagesize / PAGE_SIZE,
                                                true);
                        if (unlikely(err)) {
                                err = -EFAULT;
                                goto out;
                        }
                        mmap_read_lock(dst_mm);

                        dst_vma = NULL;
                        goto retry;
                } else
                        BUG_ON(page);

                if (!err) {
                        dst_addr += vma_hpagesize;
                        src_addr += vma_hpagesize;
                        copied += vma_hpagesize;

                        if (fatal_signal_pending(current))
                                err = -EINTR;
                }
                if (err)
                        break;
        }

out_unlock:
        mmap_read_unlock(dst_mm);
out:
        if (page)
                put_page(page);
        BUG_ON(copied < 0);
        BUG_ON(err > 0);
        BUG_ON(!copied && !err);
        return copied ? copied : err;
}
#else /* !CONFIG_HUGETLB_PAGE */
/* fail at build time if gcc attempts to use this */
extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
                                      struct vm_area_struct *dst_vma,
                                      unsigned long dst_start,
                                      unsigned long src_start,
                                      unsigned long len,
                                      enum mcopy_atomic_mode mode);
#endif /* CONFIG_HUGETLB_PAGE */

static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
                                                pmd_t *dst_pmd,
                                                struct vm_area_struct *dst_vma,
                                                unsigned long dst_addr,
                                                unsigned long src_addr,
                                                struct page **page,
                                                enum mcopy_atomic_mode mode,
                                                bool wp_copy)
{
        ssize_t err;

        if (mode == MCOPY_ATOMIC_CONTINUE) {
                return mcontinue_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
                                            wp_copy);
        }

        /*
         * The normal page fault path for a shmem will invoke the
         * fault, fill the hole in the file and COW it right away. The
         * result generates plain anonymous memory. So when we are
         * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll
         * generate anonymous memory directly without actually filling
         * the hole. For the MAP_PRIVATE case the robustness check
         * only happens in the pagetable (to verify it's still none)
         * and not in the radix tree.
         */
        if (!(dst_vma->vm_flags & VM_SHARED)) {
                if (mode == MCOPY_ATOMIC_NORMAL)
                        err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
                                               dst_addr, src_addr, page,
                                               wp_copy);
                else
                        err = mfill_zeropage_pte(dst_mm, dst_pmd,
                                                 dst_vma, dst_addr);
        } else {
                VM_WARN_ON_ONCE(wp_copy);
                err = shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
                                             dst_addr, src_addr,
                                             mode != MCOPY_ATOMIC_NORMAL,
                                             page);
        }

        return err;
}

static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
                                              unsigned long dst_start,
                                              unsigned long src_start,
                                              unsigned long len,
                                              enum mcopy_atomic_mode mcopy_mode,
                                              atomic_t *mmap_changing,
                                              __u64 mode)
{
        struct vm_area_struct *dst_vma;
        ssize_t err;
        pmd_t *dst_pmd;
        unsigned long src_addr, dst_addr;
        long copied;
        struct page *page;
        bool wp_copy;

        /*
         * Sanitize the command parameters:
         */
        BUG_ON(dst_start & ~PAGE_MASK);
        BUG_ON(len & ~PAGE_MASK);

        /* Does the address range wrap, or is the span zero-sized? */
        BUG_ON(src_start + len <= src_start);
        BUG_ON(dst_start + len <= dst_start);

        src_addr = src_start;
        dst_addr = dst_start;
        copied = 0;
        page = NULL;
retry:
        mmap_read_lock(dst_mm);

        /*
         * If memory mappings are changing because of non-cooperative
         * operation (e.g. mremap) running in parallel, bail out and
         * request the user to retry later
         */
        err = -EAGAIN;
        if (mmap_changing && atomic_read(mmap_changing))
                goto out_unlock;

        /*
         * Make sure the vma is not shared, that the dst range is
         * both valid and fully within a single existing vma.
         */
        err = -ENOENT;
        dst_vma = find_dst_vma(dst_mm, dst_start, len);
        if (!dst_vma)
                goto out_unlock;

        err = -EINVAL;
        /*
         * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
         * it will overwrite vm_ops, so vma_is_anonymous must return false.
         */
        if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
            dst_vma->vm_flags & VM_SHARED))
                goto out_unlock;

        /*
         * validate 'mode' now that we know the dst_vma: don't allow
         * a wrprotect copy if the userfaultfd didn't register as WP.
         */
        wp_copy = mode & UFFDIO_COPY_MODE_WP;
        if (wp_copy && !(dst_vma->vm_flags & VM_UFFD_WP))
                goto out_unlock;

        /*
         * If this is a HUGETLB vma, pass off to appropriate routine
         */
        if (is_vm_hugetlb_page(dst_vma))
                return  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
                                                src_start, len, mcopy_mode);

        if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
                goto out_unlock;
        if (!vma_is_shmem(dst_vma) && mcopy_mode == MCOPY_ATOMIC_CONTINUE)
                goto out_unlock;

        /*
         * Ensure the dst_vma has a anon_vma or this page
         * would get a NULL anon_vma when moved in the
         * dst_vma.
         */
        err = -ENOMEM;
        if (!(dst_vma->vm_flags & VM_SHARED) &&
            unlikely(anon_vma_prepare(dst_vma)))
                goto out_unlock;

        while (src_addr < src_start + len) {
                pmd_t dst_pmdval;

                BUG_ON(dst_addr >= dst_start + len);

                dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
                if (unlikely(!dst_pmd)) {
                        err = -ENOMEM;
                        break;
                }

                dst_pmdval = pmd_read_atomic(dst_pmd);
                /*
                 * If the dst_pmd is mapped as THP don't
                 * override it and just be strict.
                 */
                if (unlikely(pmd_trans_huge(dst_pmdval))) {
                        err = -EEXIST;
                        break;
                }
                if (unlikely(pmd_none(dst_pmdval)) &&
                    unlikely(__pte_alloc(dst_mm, dst_pmd))) {
                        err = -ENOMEM;
                        break;
                }
                /* If an huge pmd materialized from under us fail */
                if (unlikely(pmd_trans_huge(*dst_pmd))) {
                        err = -EFAULT;
                        break;
                }

                BUG_ON(pmd_none(*dst_pmd));
                BUG_ON(pmd_trans_huge(*dst_pmd));

                err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
                                       src_addr, &page, mcopy_mode, wp_copy);
                cond_resched();

                if (unlikely(err == -ENOENT)) {
                        void *page_kaddr;

                        mmap_read_unlock(dst_mm);
                        BUG_ON(!page);

                        page_kaddr = kmap(page);
                        err = copy_from_user(page_kaddr,
                                             (const void __user *) src_addr,
                                             PAGE_SIZE);
                        kunmap(page);
                        if (unlikely(err)) {
                                err = -EFAULT;
                                goto out;
                        }
                        goto retry;
                } else
                        BUG_ON(page);

                if (!err) {
                        dst_addr += PAGE_SIZE;
                        src_addr += PAGE_SIZE;
                        copied += PAGE_SIZE;

                        if (fatal_signal_pending(current))
                                err = -EINTR;
                }
                if (err)
                        break;
        }

out_unlock:
        mmap_read_unlock(dst_mm);
out:
        if (page)
                put_page(page);
        BUG_ON(copied < 0);
        BUG_ON(err > 0);
        BUG_ON(!copied && !err);
        return copied ? copied : err;
}

ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
                     unsigned long src_start, unsigned long len,
                     atomic_t *mmap_changing, __u64 mode)
{
        return __mcopy_atomic(dst_mm, dst_start, src_start, len,
                              MCOPY_ATOMIC_NORMAL, mmap_changing, mode);
}

ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
                       unsigned long len, atomic_t *mmap_changing)
{
        return __mcopy_atomic(dst_mm, start, 0, len, MCOPY_ATOMIC_ZEROPAGE,
                              mmap_changing, 0);
}

ssize_t mcopy_continue(struct mm_struct *dst_mm, unsigned long start,
                       unsigned long len, atomic_t *mmap_changing)
{
        return __mcopy_atomic(dst_mm, start, 0, len, MCOPY_ATOMIC_CONTINUE,
                              mmap_changing, 0);
}

int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
                        unsigned long len, bool enable_wp,
                        atomic_t *mmap_changing)
{
        struct vm_area_struct *dst_vma;
        pgprot_t newprot;
        int err;

        /*
         * Sanitize the command parameters:
         */
        BUG_ON(start & ~PAGE_MASK);
        BUG_ON(len & ~PAGE_MASK);

        /* Does the address range wrap, or is the span zero-sized? */
        BUG_ON(start + len <= start);

        mmap_read_lock(dst_mm);

        /*
         * If memory mappings are changing because of non-cooperative
         * operation (e.g. mremap) running in parallel, bail out and
         * request the user to retry later
         */
        err = -EAGAIN;
        if (mmap_changing && atomic_read(mmap_changing))
                goto out_unlock;

        err = -ENOENT;
        dst_vma = find_dst_vma(dst_mm, start, len);
        /*
         * Make sure the vma is not shared, that the dst range is
         * both valid and fully within a single existing vma.
         */
        if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
                goto out_unlock;
        if (!userfaultfd_wp(dst_vma))
                goto out_unlock;
        if (!vma_is_anonymous(dst_vma))
                goto out_unlock;

        if (enable_wp)
                newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
        else
                newprot = vm_get_page_prot(dst_vma->vm_flags);

        change_protection(dst_vma, start, start + len, newprot,
                          enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE);

        err = 0;
out_unlock:
        mmap_read_unlock(dst_mm);
        return err;
}