diff options
author | Kirill A. Shutemov <kirill@shutemov.name> | 2020-03-06 07:28:32 +0100 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-03-06 14:06:09 +0100 |
commit | c3e5ea6ee574ae5e845a40ac8198de1fb63bb3ab (patch) | |
tree | ec7eb9d9a887d28057702901810fcd74fecfb679 | |
parent | mm: fix possible PMD dirty bit lost in set_pmd_migration_entry() (diff) | |
download | linux-c3e5ea6ee574ae5e845a40ac8198de1fb63bb3ab.tar.xz linux-c3e5ea6ee574ae5e845a40ac8198de1fb63bb3ab.zip |
mm: avoid data corruption on CoW fault into PFN-mapped VMA
Jeff Moyer has reported that one of xfstests triggers a warning when run
on DAX-enabled filesystem:
WARNING: CPU: 76 PID: 51024 at mm/memory.c:2317 wp_page_copy+0xc40/0xd50
...
wp_page_copy+0x98c/0xd50 (unreliable)
do_wp_page+0xd8/0xad0
__handle_mm_fault+0x748/0x1b90
handle_mm_fault+0x120/0x1f0
__do_page_fault+0x240/0xd70
do_page_fault+0x38/0xd0
handle_page_fault+0x10/0x30
The warning happens on failed __copy_from_user_inatomic() which tries to
copy data into a CoW page.
This happens because of race between MADV_DONTNEED and CoW page fault:
CPU0 CPU1
handle_mm_fault()
do_wp_page()
wp_page_copy()
do_wp_page()
madvise(MADV_DONTNEED)
zap_page_range()
zap_pte_range()
ptep_get_and_clear_full()
<TLB flush>
__copy_from_user_inatomic()
sees empty PTE and fails
WARN_ON_ONCE(1)
clear_page()
The solution is to re-try __copy_from_user_inatomic() under PTL after
checking that PTE is matches the orig_pte.
The second copy attempt can still fail, like due to non-readable PTE, but
there's nothing reasonable we can do about, except clearing the CoW page.
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Jeff Moyer <jmoyer@redhat.com>
Cc: <stable@vger.kernel.org>
Cc: Justin He <Justin.He@arm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Link: http://lkml.kernel.org/r/20200218154151.13349-1-kirill.shutemov@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to '')
-rw-r--r-- | mm/memory.c | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/mm/memory.c b/mm/memory.c index 0bccc622e482..e8bfdf0d9d1d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2257,7 +2257,7 @@ static inline bool cow_user_page(struct page *dst, struct page *src, bool ret; void *kaddr; void __user *uaddr; - bool force_mkyoung; + bool locked = false; struct vm_area_struct *vma = vmf->vma; struct mm_struct *mm = vma->vm_mm; unsigned long addr = vmf->address; @@ -2282,11 +2282,11 @@ static inline bool cow_user_page(struct page *dst, struct page *src, * On architectures with software "accessed" bits, we would * take a double page fault, so mark it accessed here. */ - force_mkyoung = arch_faults_on_old_pte() && !pte_young(vmf->orig_pte); - if (force_mkyoung) { + if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) { pte_t entry; vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl); + locked = true; if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) { /* * Other thread has already handled the fault @@ -2310,18 +2310,37 @@ static inline bool cow_user_page(struct page *dst, struct page *src, * zeroes. */ if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { + if (locked) + goto warn; + + /* Re-validate under PTL if the page is still mapped */ + vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl); + locked = true; + if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) { + /* The PTE changed under us. Retry page fault. */ + ret = false; + goto pte_unlock; + } + /* - * Give a warn in case there can be some obscure - * use-case + * The same page can be mapped back since last copy attampt. + * Try to copy again under PTL. */ - WARN_ON_ONCE(1); - clear_page(kaddr); + if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { + /* + * Give a warn in case there can be some obscure + * use-case + */ +warn: + WARN_ON_ONCE(1); + clear_page(kaddr); + } } ret = true; pte_unlock: - if (force_mkyoung) + if (locked) pte_unmap_unlock(vmf->pte, vmf->ptl); kunmap_atomic(kaddr); flush_dcache_page(dst); |