kernel/linux.git/mm/memfd.c, branch v6.1.168

mm: reinstate ability to map write-sealed memfd mappings read-only

2025-08-28T14:26:12+00:00

[ Upstream commit 8ec396d05d1b737c87311fb7311f753b02c2a6b1 ] Patch series "mm: reinstate ability to map write-sealed memfd mappings read-only". In commit 158978945f31 ("mm: perform the mapping_map_writable() check after call_mmap()") (and preceding changes in the same series) it became possible to mmap() F_SEAL_WRITE sealed memfd mappings read-only. Commit 5de195060b2e ("mm: resolve faulty mmap_region() error path behaviour") unintentionally undid this logic by moving the mapping_map_writable() check before the shmem_mmap() hook is invoked, thereby regressing this change. This series reworks how we both permit write-sealed mappings being mapped read-only and disallow mprotect() from undoing the write-seal, fixing this regression. We also add a regression test to ensure that we do not accidentally regress this in future. Thanks to Julian Orth for reporting this regression. This patch (of 2): In commit 158978945f31 ("mm: perform the mapping_map_writable() check after call_mmap()") (and preceding changes in the same series) it became possible to mmap() F_SEAL_WRITE sealed memfd mappings read-only. This was previously unnecessarily disallowed, despite the man page documentation indicating that it would be, thereby limiting the usefulness of F_SEAL_WRITE logic. We fixed this by adapting logic that existed for the F_SEAL_FUTURE_WRITE seal (one which disallows future writes to the memfd) to also be used for F_SEAL_WRITE. For background - the F_SEAL_FUTURE_WRITE seal clears VM_MAYWRITE for a read-only mapping to disallow mprotect() from overriding the seal - an operation performed by seal_check_write(), invoked from shmem_mmap(), the f_op->mmap() hook used by shmem mappings. By extending this to F_SEAL_WRITE and critically - checking mapping_map_writable() to determine if we may map the memfd AFTER we invoke shmem_mmap() - the desired logic becomes possible. This is because mapping_map_writable() explicitly checks for VM_MAYWRITE, which we will have cleared. Commit 5de195060b2e ("mm: resolve faulty mmap_region() error path behaviour") unintentionally undid this logic by moving the mapping_map_writable() check before the shmem_mmap() hook is invoked, thereby regressing this change. We reinstate this functionality by moving the check out of shmem_mmap() and instead performing it in do_mmap() at the point at which VMA flags are being determined, which seems in any case to be a more appropriate place in which to make this determination. In order to achieve this we rework memfd seal logic to allow us access to this information using existing logic and eliminate the clearing of VM_MAYWRITE from seal_check_write() which we are performing in do_mmap() instead. Link: https://lkml.kernel.org/r/99fc35d2c62bd2e05571cf60d9f8b843c56069e0.1732804776.git.lorenzo.stoakes@oracle.com Fixes: 5de195060b2e ("mm: resolve faulty mmap_region() error path behaviour") Signed-off-by: Lorenzo Stoakes Reported-by: Julian Orth Closes: https://lore.kernel.org/all/CAHijbEUMhvJTN9Xw1GmbM266FXXv=U7s4L_Jem5x3AaPZxrYpQ@mail.gmail.com/ Cc: Jann Horn Cc: Liam R. Howlett Cc: Linus Torvalds Cc: Shuah Khan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Isaac J. Manjarres Signed-off-by: Greg Kroah-Hartman

memfd: check for non-NULL file_seals in memfd_create() syscall

2023-06-28T09:12:27+00:00

[ Upstream commit 935d44acf621aa0688fef8312dec3e5940f38f4e ] Ensure that file_seals is non-NULL before using it in the memfd_create() syscall. One situation in which memfd_file_seals_ptr() could return a NULL pointer when CONFIG_SHMEM=n, oopsing the kernel. Link: https://lkml.kernel.org/r/20230607132427.2867435-1-roberto.sassu@huaweicloud.com Fixes: 47b9012ecdc7 ("shmem: add sealing support to hugetlb-backed memfd") Signed-off-by: Roberto Sassu Cc: Marc-Andr Lureau Cc: Mike Kravetz Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin

memfd: fix F_SEAL_WRITE after shmem huge page allocated

2022-03-05T19:08:32+00:00

Wangyong reports: after enabling tmpfs filesystem to support transparent hugepage with the following command: echo always > /sys/kernel/mm/transparent_hugepage/shmem_enabled the docker program tries to add F_SEAL_WRITE through the following command, but it fails unexpectedly with errno EBUSY: fcntl(5, F_ADD_SEALS, F_SEAL_WRITE) = -1. That is because memfd_tag_pins() and memfd_wait_for_pins() were never updated for shmem huge pages: checking page_mapcount() against page_count() is hopeless on THP subpages - they need to check total_mapcount() against page_count() on THP heads only. Make memfd_tag_pins() (compared > 1) as strict as memfd_wait_for_pins() (compared != 1): either can be justified, but given the non-atomic total_mapcount() calculation, it is better now to be strict. Bear in mind that total_mapcount() itself scans all of the THP subpages, when choosing to take an XA_CHECK_SCHED latency break. Also fix the unlikely xa_is_value() case in memfd_wait_for_pins(): if a page has been swapped out since memfd_tag_pins(), then its refcount must have fallen, and so it can safely be untagged. Link: https://lkml.kernel.org/r/a4f79248-df75-2c8c-3df-ba3317ccb5da@google.com Signed-off-by: Hugh Dickins Reported-by: Zeal Robot Reported-by: wangyong Cc: Mike Kravetz Cc: Matthew Wilcox (Oracle) Cc: CGEL ZTE Cc: Kirill A. Shutemov Cc: Song Liu Cc: Yang Yang Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm,hugetlb: remove mlock ulimit for SHM_HUGETLB

2021-11-09T18:02:48+00:00

Commit 21a3c273f88c ("mm, hugetlb: add thread name and pid to SHM_HUGETLB mlock rlimit warning") marked this as deprecated in 2012, but it is not deleted yet. Mike says he still sees that message in log files on occasion, so maybe we should preserve this warning. Also remove hugetlbfs related user_shm_unlock in ipc/shm.c and remove the user_shm_unlock after out. Link: https://lkml.kernel.org/r/20211103105857.25041-1-zhangyiru3@huawei.com Signed-off-by: zhangyiru Reviewed-by: Mike Kravetz Cc: Hugh Dickins Cc: Liu Zixian Cc: Michal Hocko Cc: wuxu.wu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Reimplement RLIMIT_MEMLOCK on top of ucounts

2021-04-30T19:14:02+00:00

The rlimit counter is tied to uid in the user_namespace. This allows rlimit values to be specified in userns even if they are already globally exceeded by the user. However, the value of the previous user_namespaces cannot be exceeded. Changelog v11: * Fix issue found by lkp robot. v8: * Fix issues found by lkp-tests project. v7: * Keep only ucounts for RLIMIT_MEMLOCK checks instead of struct cred. v6: * Fix bug in hugetlb_file_setup() detected by trinity. Reported-by: kernel test robot Reported-by: kernel test robot Signed-off-by: Alexey Gladkov Link: https://lkml.kernel.org/r/970d50c70c71bfd4496e0e8d2a0a32feebebb350.1619094428.git.legion@kernel.org Signed-off-by: Eric W. Biederman

mm: page cache: store only head pages in i_pages

2019-09-24T22:54:08+00:00

Transparent Huge Pages are currently stored in i_pages as pointers to consecutive subpages. This patch changes that to storing consecutive pointers to the head page in preparation for storing huge pages more efficiently in i_pages. Large parts of this are "inspired" by Kirill's patch https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/ Kirill and Huang Ying contributed several fixes. [willy@infradead.org: use compound_nr, squish uninit-var warning] Link: http://lkml.kernel.org/r/20190731210400.7419-1-willy@infradead.org Signed-off-by: Matthew Wilcox Acked-by: Jan Kara Reviewed-by: Kirill Shutemov Reviewed-by: Song Liu Tested-by: Song Liu Tested-by: William Kucharski Reviewed-by: William Kucharski Tested-by: Qian Cai Tested-by: Mikhail Gavrilov Cc: Hugh Dickins Cc: Chris Wilson Cc: Song Liu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Revert "mm: page cache: store only head pages in i_pages"

2019-07-06T02:55:18+00:00

This reverts commit 5fd4ca2d84b249f0858ce28cf637cf25b61a398f. Mikhail Gavrilov reports that it causes the VM_BUG_ON_PAGE() in __delete_from_swap_cache() to trigger: page:ffffd6d34dff0000 refcount:1 mapcount:1 mapping:ffff97812323a689 index:0xfecec363 anon flags: 0x17fffe00080034(uptodate|lru|active|swapbacked) raw: 0017fffe00080034 ffffd6d34c67c508 ffffd6d3504b8d48 ffff97812323a689 raw: 00000000fecec363 0000000000000000 0000000100000000 ffff978433ace000 page dumped because: VM_BUG_ON_PAGE(entry != page) page->mem_cgroup:ffff978433ace000 ------------[ cut here ]------------ kernel BUG at mm/swap_state.c:170! invalid opcode: 0000 [#1] SMP NOPTI CPU: 1 PID: 221 Comm: kswapd0 Not tainted 5.2.0-0.rc2.git0.1.fc31.x86_64 #1 Hardware name: System manufacturer System Product Name/ROG STRIX X470-I GAMING, BIOS 2202 04/11/2019 RIP: 0010:__delete_from_swap_cache+0x20d/0x240 Code: 30 65 48 33 04 25 28 00 00 00 75 4a 48 83 c4 38 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 c7 c6 2f dc 0f 8a 48 89 c7 e8 93 1b fd ff <0f> 0b 48 c7 c6 a8 74 0f 8a e8 85 1b fd ff 0f 0b 48 c7 c6 a8 7d 0f RSP: 0018:ffffa982036e7980 EFLAGS: 00010046 RAX: 0000000000000021 RBX: 0000000000000040 RCX: 0000000000000006 RDX: 0000000000000000 RSI: 0000000000000086 RDI: ffff97843d657900 RBP: 0000000000000001 R08: ffffa982036e7835 R09: 0000000000000535 R10: ffff97845e21a46c R11: ffffa982036e7835 R12: ffff978426387120 R13: 0000000000000000 R14: ffffd6d34dff0040 R15: ffffd6d34dff0000 FS: 0000000000000000(0000) GS:ffff97843d640000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00002cba88ef5000 CR3: 000000078a97c000 CR4: 00000000003406e0 Call Trace: delete_from_swap_cache+0x46/0xa0 try_to_free_swap+0xbc/0x110 swap_writepage+0x13/0x70 pageout.isra.0+0x13c/0x350 shrink_page_list+0xc14/0xdf0 shrink_inactive_list+0x1e5/0x3c0 shrink_node_memcg+0x202/0x760 shrink_node+0xe0/0x470 balance_pgdat+0x2d1/0x510 kswapd+0x220/0x420 kthread+0xfb/0x130 ret_from_fork+0x22/0x40 and it's not immediately obvious why it happens. It's too late in the rc cycle to do anything but revert for now. Link: https://lore.kernel.org/lkml/CABXGCsN9mYmBD-4GaaeW_NrDu+FDXLzr_6x+XNxfmFV6QkYCDg@mail.gmail.com/ Reported-and-bisected-by: Mikhail Gavrilov Suggested-by: Jan Kara Cc: Michal Hocko Cc: Vlastimil Babka Cc: Matthew Wilcox Cc: Kirill Shutemov Cc: William Kucharski Cc: Andrew Morton Signed-off-by: Linus Torvalds

mm: page cache: store only head pages in i_pages

2019-05-14T16:47:45+00:00

Transparent Huge Pages are currently stored in i_pages as pointers to consecutive subpages. This patch changes that to storing consecutive pointers to the head page in preparation for storing huge pages more efficiently in i_pages. Large parts of this are "inspired" by Kirill's patch https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/ [willy@infradead.org: fix swapcache pages] Link: http://lkml.kernel.org/r/20190324155441.GF10344@bombadil.infradead.org [kirill@shutemov.name: hugetlb stores pages in page cache differently] Link: http://lkml.kernel.org/r/20190404134553.vuvhgmghlkiw2hgl@kshutemo-mobl1 Link: http://lkml.kernel.org/r/20190307153051.18815-1-willy@infradead.org Signed-off-by: Matthew Wilcox Acked-by: Jan Kara Reviewed-by: Kirill Shutemov Reviewed-and-tested-by: Song Liu Tested-by: William Kucharski Reviewed-by: William Kucharski Tested-by: Qian Cai Cc: Hugh Dickins Cc: Song Liu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd

2019-03-06T05:07:19+00:00

Android uses ashmem for sharing memory regions. We are looking forward to migrating all usecases of ashmem to memfd so that we can possibly remove the ashmem driver in the future from staging while also benefiting from using memfd and contributing to it. Note staging drivers are also not ABI and generally can be removed at anytime. One of the main usecases Android has is the ability to create a region and mmap it as writeable, then add protection against making any "future" writes while keeping the existing already mmap'ed writeable-region active. This allows us to implement a usecase where receivers of the shared memory buffer can get a read-only view, while the sender continues to write to the buffer. See CursorWindow documentation in Android for more details: https://developer.android.com/reference/android/database/CursorWindow This usecase cannot be implemented with the existing F_SEAL_WRITE seal. To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal which prevents any future mmap and write syscalls from succeeding while keeping the existing mmap active. A better way to do F_SEAL_FUTURE_WRITE seal was discussed [1] last week where we don't need to modify core VFS structures to get the same behavior of the seal. This solves several side-effects pointed by Andy. self-tests are provided in later patch to verify the expected semantics. [1] https://lore.kernel.org/lkml/20181111173650.GA256781@google.com/ Thanks a lot to Andy for suggestions to improve code. Link: http://lkml.kernel.org/r/20190112203816.85534-2-joel@joelfernandes.org Signed-off-by: Joel Fernandes (Google) Acked-by: John Stultz Cc: Andy Lutomirski Cc: Minchan Kim Cc: Jann Horn Cc: Al Viro Cc: Andy Lutomirski Cc: Hugh Dickins Cc: J. Bruce Fields Cc: Jeff Layton Cc: Marc-Andr Lureau Cc: Matthew Wilcox Cc: Mike Kravetz Cc: Shuah Khan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

memfd: Convert memfd_tag_pins to XArray

2018-10-21T14:46:41+00:00

Switch to a batch-processing model like memfd_wait_for_pins() and use the xa_state previously set up by memfd_wait_for_pins(). Signed-off-by: Matthew Wilcox Reviewed-by: Mike Kravetz