linux-stable.git/fs/userfaultfd.c, branch v6.3.9

mm/uffd: fix vma operation where start addr cuts part of vma

2023-06-21T14:02:08+00:00

commit 270aa010620697fb27b8f892cc4e194bc2b7d134 upstream.

Patch series "mm/uffd: Fix vma merge/split", v2.

This series contains two patches that fix vma merge/split for userfaultfd
on two separate issues.

Patch 1 fixes a regression since 6.1+ due to something we overlooked when
converting to maple tree apis.  The plan is we use patch 1 to replace the
commit "2f628010799e (mm: userfaultfd: avoid passing an invalid range to
vma_merge())" in mm-hostfixes-unstable tree if possible, so as to bring
uffd vma operations back aligned with the rest code again.

Patch 2 fixes a long standing issue that vma can be left unmerged even if
we can for either uffd register or unregister.

Many thanks to Lorenzo on either noticing this issue from the assert
movement patch, looking at this problem, and also provided a reproducer on
the unmerged vma issue [1].

[1] https://gist.github.com/lorenzo-stoakes/a11a10f5f479e7a977fc456331266e0e


This patch (of 2):

It seems vma merging with uffd paths is broken with either
register/unregister, where right now we can feed wrong parameters to
vma_merge() and it's found by recent patch which moved asserts upwards in
vma_merge() by Lorenzo Stoakes:

https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/

It's possible that "start" is contained within vma but not clamped to its
start.  We need to convert this into either "cannot merge" case or "can
merge" case 4 which permits subdivision of prev by assigning vma to prev.
As we loop, each subsequent VMA will be clamped to the start.

This patch will eliminate the report and make sure vma_merge() calls will
become legal again.

One thing to mention is that the "Fixes: 29417d292bd0" below is there only
to help explain where the warning can start to trigger, the real commit to
fix should be 69dbe6daf104.  Commit 29417d292bd0 helps us to identify the
issue, but unfortunately we may want to keep it in Fixes too just to ease
kernel backporters for easier tracking.

Link: https://lkml.kernel.org/r/20230517190916.3429499-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20230517190916.3429499-2-peterx@redhat.com
Fixes: 69dbe6daf104 ("userfaultfd: use maple tree iterator to iterate VMAs")
Signed-off-by: Peter Xu 
Reported-by: Mark Rutland 
Reviewed-by: Lorenzo Stoakes 
Reviewed-by: Liam R. Howlett 
Closes: https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/
Cc: Lorenzo Stoakes 
Cc: Mike Rapoport (IBM) 
Cc: Liam R. Howlett 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Greg Kroah-Hartman

Revert "userfaultfd: don't fail on unrecognized features"

2023-04-16T17:41:26+00:00

This is a proposal to revert commit 914eedcb9ba0ff53c33808.

I found this when writing a simple UFFDIO_API test to be the first unit
test in this set.  Two things breaks with the commit:

  - UFFDIO_API check was lost and missing.  According to man page, the
  kernel should reject ioctl(UFFDIO_API) if uffdio_api.api != 0xaa.  This
  check is needed if the api version will be extended in the future, or
  user app won't be able to identify which is a new kernel.

  - Feature flags checks were removed, which means UFFDIO_API with a
  feature that does not exist will also succeed.  According to the man
  page, we should (and it makes sense) to reject ioctl(UFFDIO_API) if
  unknown features passed in.

Link: https://lore.kernel.org/r/20220722201513.1624158-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20230412163922.327282-2-peterx@redhat.com
Fixes: 914eedcb9ba0 ("userfaultfd: don't fail on unrecognized features")
Signed-off-by: Peter Xu 
Acked-by: David Hildenbrand 
Cc: Axel Rasmussen 
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Mike Kravetz 
Cc: Mike Rapoport (IBM) 
Cc: Zach O'Keefe 
Cc: 
Signed-off-by: Andrew Morton

mm: replace vma->vm_flags direct modifications with modifier calls

2023-02-10T00:51:39+00:00

Replace direct modifications to vma->vm_flags with calls to modifier
functions to be able to track flag changes and to keep vma locking
correctness.

[akpm@linux-foundation.org: fix drivers/misc/open-dice.c, per Hyeonggon Yoo]
Link: https://lkml.kernel.org/r/20230126193752.297968-5-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Acked-by: Michal Hocko 
Acked-by: Mel Gorman 
Acked-by: Mike Rapoport (IBM) 
Acked-by: Sebastian Reichel 
Reviewed-by: Liam R. Howlett 
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Andy Lutomirski 
Cc: Arjun Roy 
Cc: Axel Rasmussen 
Cc: David Hildenbrand 
Cc: David Howells 
Cc: Davidlohr Bueso 
Cc: David Rientjes 
Cc: Eric Dumazet 
Cc: Greg Thelen 
Cc: Hugh Dickins 
Cc: Ingo Molnar 
Cc: Jann Horn 
Cc: Joel Fernandes 
Cc: Johannes Weiner 
Cc: Kent Overstreet 
Cc: Laurent Dufour 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox 
Cc: Minchan Kim 
Cc: Paul E. McKenney 
Cc: Peter Oskolkov 
Cc: Peter Xu 
Cc: Peter Zijlstra 
Cc: Punit Agrawal 
Cc: Sebastian Andrzej Siewior 
Cc: Shakeel Butt 
Cc: Soheil Hassas Yeganeh 
Cc: Song Liu 
Cc: Vlastimil Babka 
Cc: Will Deacon 
Signed-off-by: Andrew Morton

mm: switch vma_merge(), split_vma(), and __split_vma to vma iterator

2023-02-10T00:51:35+00:00

Drop the vmi_* functions and transition all users to use the vma iterator
directly.

Link: https://lkml.kernel.org/r/20230120162650.984577-30-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett 
Signed-off-by: Andrew Morton

userfaultfd: use vma iterator

2023-02-10T00:51:33+00:00

Use the vma iterator so that the iterator can be invalidated or updated to
avoid each caller doing so.

Link: https://lkml.kernel.org/r/20230120162650.984577-17-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett 
Signed-off-by: Andrew Morton

mm/hugetlb: introduce hugetlb_walk()

2023-01-19T01:12:39+00:00

huge_pte_offset() is the main walker function for hugetlb pgtables.  The
name is not really representing what it does, though.

Instead of renaming it, introduce a wrapper function called hugetlb_walk()
which will use huge_pte_offset() inside.  Assert on the locks when walking
the pgtable.

Note, the vma lock assertion will be a no-op for private mappings.

Document the last special case in the page_vma_mapped_walk() path where we
don't need any more lock to call hugetlb_walk().

Taking vma lock there is not needed because either: (1) potential callers
of hugetlb pvmw holds i_mmap_rwsem already (from one rmap_walk()), or (2)
the caller will not walk a hugetlb vma at all so the hugetlb code path not
reachable (e.g.  in ksm or uprobe paths).

It's slightly implicit for future page_vma_mapped_walk() callers on that
lock requirement.  But anyway, when one day this rule breaks, one will get
a straightforward warning in hugetlb_walk() with lockdep, then there'll be
a way out.

[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/20221216155229.2043750-1-peterx@redhat.com
Signed-off-by: Peter Xu 
Reviewed-by: Mike Kravetz 
Reviewed-by: John Hubbard 
Reviewed-by: David Hildenbrand 
Cc: Andrea Arcangeli 
Cc: James Houghton 
Cc: Jann Horn 
Cc: Miaohe Lin 
Cc: Muchun Song 
Cc: Nadav Amit 
Cc: Rik van Riel 
Signed-off-by: Andrew Morton

mm/hugetlb: make userfaultfd_huge_must_wait() safe to pmd unshare

2023-01-19T01:12:38+00:00

We can take the hugetlb walker lock, here taking vma lock directly.

Link: https://lkml.kernel.org/r/20221216155217.2043700-1-peterx@redhat.com
Signed-off-by: Peter Xu 
Reviewed-by: David Hildenbrand 
Reviewed-by: Mike Kravetz 
Reviewed-by: John Hubbard 
Cc: Andrea Arcangeli 
Cc: James Houghton 
Cc: Jann Horn 
Cc: Miaohe Lin 
Cc: Muchun Song 
Cc: Nadav Amit 
Cc: Rik van Riel 
Signed-off-by: Andrew Morton

mm/userfaultfd: enable writenotify while userfaultfd-wp is enabled for a VMA

2023-01-12T00:14:20+00:00

Currently, we don't enable writenotify when enabling userfaultfd-wp on a
shared writable mapping (for now only shmem and hugetlb).  The consequence
is that vma->vm_page_prot will still include write permissions, to be set
as default for all PTEs that get remapped (e.g., mprotect(), NUMA hinting,
page migration, ...).

So far, vma->vm_page_prot is assumed to be a safe default, meaning that we
only add permissions (e.g., mkwrite) but not remove permissions (e.g.,
wrprotect).  For example, when enabling softdirty tracking, we enable
writenotify.  With uffd-wp on shared mappings, that changed.  More details
on vma->vm_page_prot semantics were summarized in [1].

This is problematic for uffd-wp: we'd have to manually check for a uffd-wp
PTEs/PMDs and manually write-protect PTEs/PMDs, which is error prone. 
Prone to such issues is any code that uses vma->vm_page_prot to set PTE
permissions: primarily pte_modify() and mk_pte().

Instead, let's enable writenotify such that PTEs/PMDs/...  will be mapped
write-protected as default and we will only allow selected PTEs that are
definitely safe to be mapped without write-protection (see
can_change_pte_writable()) to be writable.  In the future, we might want
to enable write-bit recovery -- e.g., can_change_pte_writable() -- at more
locations, for example, also when removing uffd-wp protection.

This fixes two known cases:

(a) remove_migration_pte() mapping uffd-wp'ed PTEs writable, resulting
    in uffd-wp not triggering on write access.
(b) do_numa_page() / do_huge_pmd_numa_page() mapping uffd-wp'ed PTEs/PMDs
    writable, resulting in uffd-wp not triggering on write access.

Note that do_numa_page() / do_huge_pmd_numa_page() can be reached even
without NUMA hinting (which currently doesn't seem to be applicable to
shmem), for example, by using uffd-wp with a PROT_WRITE shmem VMA.  On
such a VMA, userfaultfd-wp is currently non-functional.

Note that when enabling userfaultfd-wp, there is no need to walk page
tables to enforce the new default protection for the PTEs: we know that
they cannot be uffd-wp'ed yet, because that can only happen after enabling
uffd-wp for the VMA in general.

Also note that this makes mprotect() on ranges with uffd-wp'ed PTEs not
accidentally set the write bit -- which would result in uffd-wp not
triggering on later write access.  This commit makes uffd-wp on shmem
behave just like uffd-wp on anonymous memory in that regard, even though,
mixing mprotect with uffd-wp is controversial.

[1] https://lkml.kernel.org/r/92173bad-caa3-6b43-9d1e-9a471fdbc184@redhat.com

Link: https://lkml.kernel.org/r/20221209080912.7968-1-david@redhat.com
Fixes: b1f9e876862d ("mm/uffd: enable write protection for shmem & hugetlbfs")
Signed-off-by: David Hildenbrand 
Reported-by: Ives van Hoorne 
Debugged-by: Peter Xu 
Acked-by: Peter Xu 
Cc: Hugh Dickins 
Cc: Alistair Popple 
Cc: Mike Rapoport 
Cc: Nadav Amit 
Cc: Andrea Arcangeli 
Cc: 
Signed-off-by: Andrew Morton

fs/userfaultfd: Fix maple tree iterator in userfaultfd_unregister()

2022-11-07T20:58:26+00:00

When iterating the VMAs, the maple state needs to be invalidated if the
tree is modified by a split or merge to ensure the maple tree node
contained in the maple state is still valid.  These invalidations were
missed, so add them to the paths which alter the tree.

Reported-by: syzbot+0d2014e4da2ccced5b41@syzkaller.appspotmail.com
Fixes: 69dbe6daf104 (userfaultfd: use maple tree iterator to iterate VMAs)
Signed-off-by: Liam R. Howlett 
Signed-off-by: Linus Torvalds

Merge tag 'mm-stable-2022-10-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2022-10-11T00:53:04+00:00

Pull MM updates from Andrew Morton:

- Yu Zhao's Multi-Gen LRU patches are here. They've been under test in
linux-next for a couple of months without, to my knowledge, any
negative reports (or any positive ones, come to that).

- Also the Maple Tree from Liam Howlett. An overlapping range-based
tree for vmas. It it apparently slightly more efficient in its own
right, but is mainly targeted at enabling work to reduce mmap_lock
contention.

Liam has identified a number of other tree users in the kernel which
could be beneficially onverted to mapletrees.

Yu Zhao has identified a hard-to-hit but "easy to fix" lockdep splat
at [1]. This has yet to be addressed due to Liam's unfortunately
timed vacation. He is now back and we'll get this fixed up.

- Dmitry Vyukov introduces KMSAN: the Kernel Memory Sanitizer. It uses
clang-generated instrumentation to detect used-unintialized bugs down
to the single bit level.

KMSAN keeps finding bugs. New ones, as well as the legacy ones.

- Yang Shi adds a userspace mechanism (madvise) to induce a collapse of
memory into THPs.

- Zach O'Keefe has expanded Yang Shi's madvise(MADV_COLLAPSE) to
support file/shmem-backed pages.

- userfaultfd updates from Axel Rasmussen

- zsmalloc cleanups from Alexey Romanov

- cleanups from Miaohe Lin: vmscan, hugetlb_cgroup, hugetlb and
memory-failure

- Huang Ying adds enhancements to NUMA balancing memory tiering mode's
page promotion, with a new way of detecting hot pages.

- memcg updates from Shakeel Butt: charging optimizations and reduced
memory consumption.

- memcg cleanups from Kairui Song.

- memcg fixes and cleanups from Johannes Weiner.

- Vishal Moola provides more folio conversions

- Zhang Yi removed ll_rw_block() :(

- migration enhancements from Peter Xu

- migration error-path bugfixes from Huang Ying

- Aneesh Kumar added ability for a device driver to alter the memory
tiering promotion paths. For optimizations by PMEM drivers, DRM
drivers, etc.

- vma merging improvements from Jakub Matěn.

- NUMA hinting cleanups from David Hildenbrand.

- xu xin added aditional userspace visibility into KSM merging
activity.

- THP & KSM code consolidation from Qi Zheng.

- more folio work from Matthew Wilcox.

- KASAN updates from Andrey Konovalov.

- DAMON cleanups from Kaixu Xia.

- DAMON work from SeongJae Park: fixes, cleanups.

- hugetlb sysfs cleanups from Muchun Song.

- Mike Kravetz fixes locking issues in hugetlbfs and in hugetlb core.

Link: https://lkml.kernel.org/r/CAOUHufZabH85CeUN-MEMgL8gJGzJEWUrkiM58JkTbBhh-jew0Q@mail.gmail.com [1]

* tag 'mm-stable-2022-10-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (555 commits)
hugetlb: allocate vma lock for all sharable vmas
hugetlb: take hugetlb vma_lock when clearing vma_lock->vma pointer
hugetlb: fix vma lock handling during split vma and range unmapping
mglru: mm/vmscan.c: fix imprecise comments
mm/mglru: don't sync disk for each aging cycle
mm: memcontrol: drop dead CONFIG_MEMCG_SWAP config symbol
mm: memcontrol: use do_memsw_account() in a few more places
mm: memcontrol: deprecate swapaccounting=0 mode
mm: memcontrol: don't allocate cgroup swap arrays when memcg is disabled
mm/secretmem: remove reduntant return value
mm/hugetlb: add available_huge_pages() func
mm: remove unused inline functions from include/linux/mm_inline.h
selftests/vm: add selftest for MADV_COLLAPSE of uffd-minor memory
selftests/vm: add file/shmem MADV_COLLAPSE selftest for cleared pmd
selftests/vm: add thp collapse shmem testing
selftests/vm: add thp collapse file and tmpfs testing
selftests/vm: modularize thp collapse memory operations
selftests/vm: dedup THP helpers
mm/khugepaged: add tracepoint to hpage_collapse_scan_file()
mm/madvise: add file and shmem support to MADV_COLLAPSE
...