+ mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch added to mm-hotfixes-unstable branch

* + mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch added to mm-hotfixes-unstable branch
@ 2022-11-25 23:40 Andrew Morton
  0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2022-11-25 23:40 UTC (permalink / raw)
  To: mm-commits, stable, shy828301, peterx, jhubbard, david, jannh, akpm


The patch titled
     Subject: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Jann Horn <jannh@google.com>
Subject: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths
Date: Fri, 25 Nov 2022 22:37:14 +0100

Any codepath that zaps page table entries must invoke MMU notifiers to
ensure that secondary MMUs (like KVM) don't keep accessing pages which
aren't mapped anymore.  Secondary MMUs don't hold their own references to
pages that are mirrored over, so failing to notify them can lead to page
use-after-free.

I'm marking this as addressing an issue introduced in commit f3f0e1d2150b
("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of
the security impact of this only came in commit 27e1f8273113 ("khugepaged:
enable collapse pmd for pte-mapped THP"), which actually omitted flushes
for the removal of present PTEs, not just for the removal of empty page
tables.

Link: https://lkml.kernel.org/r/20221125213714.4115729-3-jannh@google.com
Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Jann Horn <jannh@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Yang Shi <shy828301@gmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/khugepaged.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/mm/khugepaged.c~mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths
+++ a/mm/khugepaged.c
@@ -1399,6 +1399,7 @@ static void collapse_and_free_pmd(struct
 				  unsigned long addr, pmd_t *pmdp)
 {
 	pmd_t pmd;
+	struct mmu_notifier_range range;
 
 	mmap_assert_write_locked(mm);
 	if (vma->vm_file)
@@ -1410,8 +1411,12 @@ static void collapse_and_free_pmd(struct
 	if (vma->anon_vma)
 		lockdep_assert_held_write(&vma->anon_vma->root->rwsem);
 
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, addr,
+				addr + HPAGE_PMD_SIZE);
+	mmu_notifier_invalidate_range_start(&range);
 	pmd = pmdp_collapse_flush(vma, addr, pmdp);
 	tlb_remove_table_sync_one();
+	mmu_notifier_invalidate_range_end(&range);
 	mm_dec_nr_ptes(mm);
 	page_table_check_pte_clear_range(mm, addr, pmd);
 	pte_free(mm, pmd_pgtable(pmd));
_

Patches currently in -mm which might be from jannh@google.com are

mm-khugepaged-take-the-right-locks-for-page-table-retraction.patch
mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi.patch
mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch


^ permalink raw reply	[flat|nested] 2+ messages in thread