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authorPeter Xu <peterx@redhat.com>2023-03-21 22:18:40 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-04-06 04:06:22 +0300
commit60d5b473d61be61ac315e544fcd6a8234a79500e (patch)
treed884fd3eeae807d93c4cdcf83202a4d9673a9b47 /mm/hugetlb.c
parent3dd4432549415f3c65dd52d5c687629efbf4ece1 (diff)
downloadlinux-60d5b473d61be61ac315e544fcd6a8234a79500e.tar.xz
mm/hugetlb: fix uffd wr-protection for CoW optimization path
This patch fixes an issue that a hugetlb uffd-wr-protected mapping can be writable even with uffd-wp bit set. It only happens with hugetlb private mappings, when someone firstly wr-protects a missing pte (which will install a pte marker), then a write to the same page without any prior access to the page. Userfaultfd-wp trap for hugetlb was implemented in hugetlb_fault() before reaching hugetlb_wp() to avoid taking more locks that userfault won't need. However there's one CoW optimization path that can trigger hugetlb_wp() inside hugetlb_no_page(), which will bypass the trap. This patch skips hugetlb_wp() for CoW and retries the fault if uffd-wp bit is detected. The new path will only trigger in the CoW optimization path because generic hugetlb_fault() (e.g. when a present pte was wr-protected) will resolve the uffd-wp bit already. Also make sure anonymous UNSHARE won't be affected and can still be resolved, IOW only skip CoW not CoR. This patch will be needed for v5.19+ hence copy stable. [peterx@redhat.com: v2] Link: https://lkml.kernel.org/r/ZBzOqwF2wrHgBVZb@x1n [peterx@redhat.com: v3] Link: https://lkml.kernel.org/r/20230324142620.2344140-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20230321191840.1897940-1-peterx@redhat.com Fixes: 166f3ecc0daf ("mm/hugetlb: hook page faults for uffd write protection") Signed-off-by: Peter Xu <peterx@redhat.com> Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com> Tested-by: Muhammad Usama Anjum <usama.anjum@collabora.com> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r--mm/hugetlb.c14
1 files changed, 12 insertions, 2 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 07abcb6eb203..245038a9fe4e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5478,7 +5478,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
struct folio *pagecache_folio, spinlock_t *ptl)
{
const bool unshare = flags & FAULT_FLAG_UNSHARE;
- pte_t pte;
+ pte_t pte = huge_ptep_get(ptep);
struct hstate *h = hstate_vma(vma);
struct page *old_page;
struct folio *new_folio;
@@ -5488,6 +5488,17 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
struct mmu_notifier_range range;
/*
+ * Never handle CoW for uffd-wp protected pages. It should be only
+ * handled when the uffd-wp protection is removed.
+ *
+ * Note that only the CoW optimization path (in hugetlb_no_page())
+ * can trigger this, because hugetlb_fault() will always resolve
+ * uffd-wp bit first.
+ */
+ if (!unshare && huge_pte_uffd_wp(pte))
+ return 0;
+
+ /*
* hugetlb does not support FOLL_FORCE-style write faults that keep the
* PTE mapped R/O such as maybe_mkwrite() would do.
*/
@@ -5500,7 +5511,6 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
return 0;
}
- pte = huge_ptep_get(ptep);
old_page = pte_page(pte);
delayacct_wpcopy_start();