linux.git/mm/userfaultfd.c, branch v6.8

mm: userfaultfd: fix unexpected change to src_folio when UFFDIO_MOVE fails

2024-03-05T00:40:33+00:00

After ptep_clear_flush(), if we find that src_folio is pinned we will fail
UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
src_folio->{mapping,index} is not restored in this process. This is not
what we expected, so fix it.

This can cause the rmap for that page to be invalid, possibly resulting
in memory corruption.  At least swapout+migration would no longer work,
because we might fail to locate the mappings of that folio.

Link: https://lkml.kernel.org/r/20240222080815.46291-1-zhengqi.arch@bytedance.com
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Qi Zheng 
Reviewed-by: David Hildenbrand 
Reviewed-by: Suren Baghdasaryan 
Cc: Andrea Arcangeli 
Cc: 
Signed-off-by: Andrew Morton

mm/userfaultfd: UFFDIO_MOVE implementation should use ptep_get()

2024-02-08T05:20:33+00:00

Commit c33c794828f2 ("mm: ptep_get() conversion") converted all (non-arch)
call sites to use ptep_get() instead of doing a direct dereference of the
pte.  Full rationale can be found in that commit's log.

Since then, UFFDIO_MOVE has been implemented which does 7 direct pte
dereferences.  Let's fix those up to use ptep_get().

I've asserted in the past that there is no reliable automated mechanism to
catch these; I'm relying on a combination of Coccinelle (which throws up a
lot of false positives) and some compiler magic to force a compiler error
on dereference.  But given the frequency with which new issues are coming
up, I'll add it to my todo list to try to find an automated solution.

Link: https://lkml.kernel.org/r/20240123141755.3836179-1-ryan.roberts@arm.com
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Ryan Roberts 
Reviewed-by: Suren Baghdasaryan 
Cc: Andrea Arcangeli 
Cc: David Hildenbrand 
Signed-off-by: Andrew Morton

userfaultfd: fix mmap_changing checking in mfill_atomic_hugetlb

2024-01-26T07:52:21+00:00

In mfill_atomic_hugetlb(), mmap_changing isn't being checked
again if we drop mmap_lock and reacquire it. When the lock is not held,
mmap_changing could have been incremented. This is also inconsistent
with the behavior in mfill_atomic().

Link: https://lkml.kernel.org/r/20240117223729.1444522-1-lokeshgidra@google.com
Fixes: df2cc96e77011 ("userfaultfd: prevent non-cooperative events vs mcopy_atomic races") 
Signed-off-by: Lokesh Gidra 
Cc: Andrea Arcangeli 
Cc: Mike Rapoport 
Cc: Axel Rasmussen 
Cc: Brian Geffon 
Cc: David Hildenbrand 
Cc: Jann Horn 
Cc: Kalesh Singh 
Cc: Matthew Wilcox (Oracle) 
Cc: Nicolas Geoffray 
Cc: Peter Xu 
Cc: Suren Baghdasaryan 
Cc: 
Signed-off-by: Andrew Morton

userfaultfd: avoid huge_zero_page in UFFDIO_MOVE

2024-01-12T23:20:49+00:00

While testing UFFDIO_MOVE ioctl, syzbot triggered VM_BUG_ON_PAGE caused by
a call to PageAnonExclusive() with a huge_zero_page as a parameter. 
UFFDIO_MOVE does not yet handle zeropages and returns EBUSY when one is
encountered.  Add an early huge_zero_page check in the PMD move path to
avoid this situation.

Link: https://lkml.kernel.org/r/20240112013935.1474648-1-surenb@google.com
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
Signed-off-by: Suren Baghdasaryan 
Acked-by: David Hildenbrand 
Cc: Andrea Arcangeli 
Cc: Peter Xu 
Cc: Stephen Rothwell 
Signed-off-by: Andrew Morton

userfaultfd: fix move_pages_pte() splitting folio under RCU read lock

2024-01-05T18:17:43+00:00

While testing the split PMD path with lockdep enabled I've got an "Invalid
wait context" error caused by split_huge_page_to_list() trying to lock
anon_vma->rwsem while inside RCU read section.  The issues is due to
move_pages_pte() calling split_folio() under RCU read lock.  Fix this by
unmapping the PTEs and exiting RCU read section before splitting the folio
and then retrying.  The same retry pattern is used when locking the folio
or anon_vma in this function.  After splitting the large folio we unlock
and release it because after the split the old folio might not be the one
that contains the src_addr.

Link: https://lkml.kernel.org/r/20240102233256.1077959-1-surenb@google.com
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Suren Baghdasaryan 
Reviewed-by: Peter Xu 
Cc: Al Viro 
Cc: Andrea Arcangeli 
Cc: Axel Rasmussen 
Cc: Brian Geffon 
Cc: Christian Brauner 
Cc: David Hildenbrand 
Cc: Hugh Dickins 
Cc: Jann Horn 
Cc: Kalesh Singh 
Cc: Liam R. Howlett 
Cc: Lokesh Gidra 
Cc: Matthew Wilcox (Oracle) 
Cc: Michal Hocko 
Cc: Mike Rapoport (IBM) 
Cc: Nicolas Geoffray 
Cc: Ryan Roberts 
Cc: Shuah Khan 
Cc: ZhangPeng 
Signed-off-by: Andrew Morton

mm/userfaultfd: page_add_file_rmap() -> folio_add_file_rmap_pte()

2023-12-29T19:58:49+00:00

Let's convert mfill_atomic_install_pte().

Link: https://lkml.kernel.org/r/20231220224504.646757-12-david@redhat.com
Signed-off-by: David Hildenbrand 
Reviewed-by: Yin Fengwei 
Reviewed-by: Ryan Roberts 
Cc: Hugh Dickins 
Cc: Matthew Wilcox (Oracle) 
Cc: Muchun Song 
Cc: Muchun Song 
Cc: Peter Xu 
Signed-off-by: Andrew Morton

mm: remove some calls to page_add_new_anon_rmap()

2023-12-29T19:58:25+00:00

We already have the folio in these functions, we just need to use it. 
folio_add_new_anon_rmap() didn't exist at the time they were converted to
folios.

Link: https://lkml.kernel.org/r/20231211162214.2146080-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Reviewed-by: David Hildenbrand 
Signed-off-by: Andrew Morton

userfaultfd: UFFDIO_MOVE uABI

2023-12-29T19:58:24+00:00

Implement the uABI of UFFDIO_MOVE ioctl.
UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application
needs pages to be allocated [1]. However, with UFFDIO_MOVE, if pages are
available (in userspace) for recycling, as is usually the case in heap
compaction algorithms, then we can avoid the page allocation and memcpy
(done by UFFDIO_COPY). Also, since the pages are recycled in the
userspace, we avoid the need to release (via madvise) the pages back to
the kernel [2].

We see over 40% reduction (on a Google pixel 6 device) in the compacting
thread's completion time by using UFFDIO_MOVE vs.  UFFDIO_COPY.  This was
measured using a benchmark that emulates a heap compaction implementation
using userfaultfd (to allow concurrent accesses by application threads). 
More details of the usecase are explained in [2].  Furthermore,
UFFDIO_MOVE enables moving swapped-out pages without touching them within
the same vma.  Today, it can only be done by mremap, however it forces
splitting the vma.

[1] https://lore.kernel.org/all/1425575884-2574-1-git-send-email-aarcange@redhat.com/
[2] https://lore.kernel.org/linux-mm/CA+EESO4uO84SSnBhArH4HvLNhaUQ5nZKNKXqxRCyjniNVjp0Aw@mail.gmail.com/

Update for the ioctl_userfaultfd(2)  manpage:

   UFFDIO_MOVE
       (Since Linux xxx)  Move a continuous memory chunk into the
       userfault registered range and optionally wake up the blocked
       thread. The source and destination addresses and the number of
       bytes to move are specified by the src, dst, and len fields of
       the uffdio_move structure pointed to by argp:

           struct uffdio_move {
               __u64 dst;    /* Destination of move */
               __u64 src;    /* Source of move */
               __u64 len;    /* Number of bytes to move */
               __u64 mode;   /* Flags controlling behavior of move */
               __s64 move;   /* Number of bytes moved, or negated error */
           };

       The following value may be bitwise ORed in mode to change the
       behavior of the UFFDIO_MOVE operation:

       UFFDIO_MOVE_MODE_DONTWAKE
              Do not wake up the thread that waits for page-fault
              resolution

       UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES
              Allow holes in the source virtual range that is being moved.
              When not specified, the holes will result in ENOENT error.
              When specified, the holes will be accounted as successfully
              moved memory. This is mostly useful to move hugepage aligned
              virtual regions without knowing if there are transparent
              hugepages in the regions or not, but preventing the risk of
              having to split the hugepage during the operation.

       The move field is used by the kernel to return the number of
       bytes that was actually moved, or an error (a negated errno-
       style value).  If the value returned in move doesn't match the
       value that was specified in len, the operation fails with the
       error EAGAIN.  The move field is output-only; it is not read by
       the UFFDIO_MOVE operation.

       The operation may fail for various reasons. Usually, remapping of
       pages that are not exclusive to the given process fail; once KSM
       might deduplicate pages or fork() COW-shares pages during fork()
       with child processes, they are no longer exclusive. Further, the
       kernel might only perform lightweight checks for detecting whether
       the pages are exclusive, and return -EBUSY in case that check fails.
       To make the operation more likely to succeed, KSM should be
       disabled, fork() should be avoided or MADV_DONTFORK should be
       configured for the source VMA before fork().

       This ioctl(2) operation returns 0 on success.  In this case, the
       entire area was moved.  On error, -1 is returned and errno is
       set to indicate the error.  Possible errors include:

       EAGAIN The number of bytes moved (i.e., the value returned in
              the move field) does not equal the value that was
              specified in the len field.

       EINVAL Either dst or len was not a multiple of the system page
              size, or the range specified by src and len or dst and len
              was invalid.

       EINVAL An invalid bit was specified in the mode field.

       ENOENT
              The source virtual memory range has unmapped holes and
              UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES is not set.

       EEXIST
              The destination virtual memory range is fully or partially
              mapped.

       EBUSY
              The pages in the source virtual memory range are either
              pinned or not exclusive to the process. The kernel might
              only perform lightweight checks for detecting whether the
              pages are exclusive. To make the operation more likely to
              succeed, KSM should be disabled, fork() should be avoided
              or MADV_DONTFORK should be configured for the source virtual
              memory area before fork().

       ENOMEM Allocating memory needed for the operation failed.

       ESRCH
              The target process has exited at the time of a UFFDIO_MOVE
              operation.

Link: https://lkml.kernel.org/r/20231206103702.3873743-3-surenb@google.com
Signed-off-by: Andrea Arcangeli 
Signed-off-by: Suren Baghdasaryan 
Cc: Al Viro 
Cc: Axel Rasmussen 
Cc: Brian Geffon 
Cc: Christian Brauner 
Cc: David Hildenbrand 
Cc: Hugh Dickins 
Cc: Jann Horn 
Cc: Kalesh Singh 
Cc: Liam R. Howlett 
Cc: Lokesh Gidra 
Cc: Matthew Wilcox (Oracle) 
Cc: Michal Hocko 
Cc: Mike Rapoport (IBM) 
Cc: Nicolas Geoffray 
Cc: Peter Xu 
Cc: Ryan Roberts 
Cc: Shuah Khan 
Cc: ZhangPeng 
Signed-off-by: Andrew Morton

mm: more ptep_get() conversion

2023-11-15T23:30:09+00:00

Commit c33c794828f2 ("mm: ptep_get() conversion") converted all (non-arch)
call sites to use ptep_get() instead of doing a direct dereference of the
pte.  Full rationale can be found in that commit's log.

Since then, three new call sites have snuck in, which directly dereference
the pte, so let's fix those up.

Unfortunately there is no reliable automated mechanism to catch these; I'm
relying on a combination of Coccinelle (which throws up a lot of false
positives) and some compiler magic to force a compiler error on
dereference (While this approach finds dereferences, it also yields a
non-booting kernel so can't be committed).

Link: https://lkml.kernel.org/r/20231114154945.490401-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts 
Cc: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

Merge tag 'x86_shstk_for_6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2023-08-31T19:20:12+00:00

Pull x86 shadow stack support from Dave Hansen:
 "This is the long awaited x86 shadow stack support, part of Intel's
  Control-flow Enforcement Technology (CET).

  CET consists of two related security features: shadow stacks and
  indirect branch tracking. This series implements just the shadow stack
  part of this feature, and just for userspace.

  The main use case for shadow stack is providing protection against
  return oriented programming attacks. It works by maintaining a
  secondary (shadow) stack using a special memory type that has
  protections against modification. When executing a CALL instruction,
  the processor pushes the return address to both the normal stack and
  to the special permission shadow stack. Upon RET, the processor pops
  the shadow stack copy and compares it to the normal stack copy.

  For more information, refer to the links below for the earlier
  versions of this patch set"

Link: https://lore.kernel.org/lkml/20220130211838.8382-1-rick.p.edgecombe@intel.com/
Link: https://lore.kernel.org/lkml/20230613001108.3040476-1-rick.p.edgecombe@intel.com/

* tag 'x86_shstk_for_6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (47 commits)
  x86/shstk: Change order of __user in type
  x86/ibt: Convert IBT selftest to asm
  x86/shstk: Don't retry vm_munmap() on -EINTR
  x86/kbuild: Fix Documentation/ reference
  x86/shstk: Move arch detail comment out of core mm
  x86/shstk: Add ARCH_SHSTK_STATUS
  x86/shstk: Add ARCH_SHSTK_UNLOCK
  x86: Add PTRACE interface for shadow stack
  selftests/x86: Add shadow stack test
  x86/cpufeatures: Enable CET CR4 bit for shadow stack
  x86/shstk: Wire in shadow stack interface
  x86: Expose thread features in /proc/$PID/status
  x86/shstk: Support WRSS for userspace
  x86/shstk: Introduce map_shadow_stack syscall
  x86/shstk: Check that signal frame is shadow stack mem
  x86/shstk: Check that SSP is aligned on sigreturn
  x86/shstk: Handle signals for shadow stack
  x86/shstk: Introduce routines modifying shstk
  x86/shstk: Handle thread shadow stack
  x86/shstk: Add user-mode shadow stack support
  ...