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69604fe76e
linux/mm/userfaultfd.c
Peter Xu f369b07c86 mm/uffd: reset write protection when unregister with wp-mode 
The motivation of this patch comes from a recent report and patchfix from
David Hildenbrand on hugetlb shared handling of wr-protected page [1].

With the reproducer provided in commit message of [1], one can leverage
the uffd-wp lazy-reset of ptes to trigger a hugetlb issue which can affect
not only the attacker process, but also the whole system.

The lazy-reset mechanism of uffd-wp was used to make unregister faster,
meanwhile it has an assumption that any leftover pgtable entries should
only affect the process on its own, so not only the user should be aware
of anything it does, but also it should not affect outside of the process.

But it seems that this is not true, and it can also be utilized to make
some exploit easier.

So far there's no clue showing that the lazy-reset is important to any
userfaultfd users because normally the unregister will only happen once
for a specific range of memory of the lifecycle of the process.

Considering all above, what this patch proposes is to do explicit pte
resets when unregister an uffd region with wr-protect mode enabled.

It should be the same as calling ioctl(UFFDIO_WRITEPROTECT, wp=false)
right before ioctl(UFFDIO_UNREGISTER) for the user.  So potentially it'll
make the unregister slower.  From that pov it's a very slight abi change,
but hopefully nothing should break with this change either.

Regarding to the change itself - core of uffd write [un]protect operation
is moved into a separate function (uffd_wp_range()) and it is reused in
the unregister code path.

Note that the new function will not check for anything, e.g.  ranges or
memory types, because they should have been checked during the previous
UFFDIO_REGISTER or it should have failed already.  It also doesn't check
mmap_changing because we're with mmap write lock held anyway.

I added a Fixes upon introducing of uffd-wp shmem+hugetlbfs because that's
the only issue reported so far and that's the commit David's reproducer
will start working (v5.19+).  But the whole idea actually applies to not
only file memories but also anonymous.  It's just that we don't need to
fix anonymous prior to v5.19- because there's no known way to exploit.

IOW, this patch can also fix the issue reported in [1] as the patch 2 does.

[1] https://lore.kernel.org/all/20220811103435.188481-3-david@redhat.com/

Link: https://lkml.kernel.org/r/20220811201340.39342-1-peterx@redhat.com
Fixes: b1f9e87686 ("mm/uffd: enable write protection for shmem & hugetlbfs")
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-08-20 15:17:45 -07:00

775 lines
19 KiB
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// 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 <asm/tlb.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);
_dst_pte = pte_mkdirty(_dst_pte);
if (page_in_cache && !vm_shared)
writable = false;
/*
* Always mark a PTE as write-protected when needed, regardless of
* VM_WRITE, which the user might change.
*/
if (wp_copy) {
_dst_pte = pte_mkuffd_wp(_dst_pte);
writable = false;
}
if (writable)
_dst_pte = pte_mkwrite(_dst_pte);
else
/*
* We need this to make sure write bit removed; as mk_pte()
* could return a pte with write bit set.
*/
_dst_pte = pte_wrprotect(_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;
/*
* We allow to overwrite a pte marker: consider when both MISSING|WP
* registered, we firstly wr-protect a none pte which has no page cache
* page backing it, then access the page.
*/
if (!pte_none_mostly(*dst_pte))
goto out_unlock;
if (page_in_cache) {
/* Usually, cache pages are already added to LRU */
if (newly_allocated)
lru_cache_add(page);
page_add_file_rmap(page, dst_vma, false);
} else {
page_add_new_anon_rmap(page, dst_vma, dst_addr);
lru_cache_add_inactive_or_unevictable(page, dst_vma);
}
/*
* 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));
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;
}
flush_dcache_page(page);
} 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_folio(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_NOALLOC);
/* Our caller expects us to return -EFAULT if we failed to find page. */
if (ret == -ENOENT)
ret = -EFAULT;
if (ret)
goto out;
if (!page) {
ret = -EFAULT;
goto out;
}
if (PageHWPoison(page)) {
ret = -EIO;
goto out_release;
}
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,
bool wp_copy)
{
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_mostly(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,
wp_copy);
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,
bool wp_copy);
#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 {
err = shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
dst_addr, src_addr,
mode != MCOPY_ATOMIC_NORMAL,
wp_copy, 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,
wp_copy);
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;
}
flush_dcache_page(page);
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);
}
void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma,
unsigned long start, unsigned long len, bool enable_wp)
{
struct mmu_gather tlb;
pgprot_t newprot;
if (enable_wp)
newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
else
newprot = vm_get_page_prot(dst_vma->vm_flags);
tlb_gather_mmu(&tlb, dst_mm);
change_protection(&tlb, dst_vma, start, start + len, newprot,
enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE);
tlb_finish_mmu(&tlb);
}
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;
unsigned long page_mask;
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);
if (!dst_vma)
goto out_unlock;
if (!userfaultfd_wp(dst_vma))
goto out_unlock;
if (!vma_can_userfault(dst_vma, dst_vma->vm_flags))
goto out_unlock;
if (is_vm_hugetlb_page(dst_vma)) {
err = -EINVAL;
page_mask = vma_kernel_pagesize(dst_vma) - 1;
if ((start & page_mask) || (len & page_mask))
goto out_unlock;
}
uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp);
err = 0;
out_unlock:
mmap_read_unlock(dst_mm);
return err;
}
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