kernel/linux.git/fs/userfaultfd.c, branch v5.15.209

userfaultfd: allow registration of ranges below mmap_min_addr

2026-06-01T15:35:16+00:00

commit 161ce69c2c89781784b945d8e281ff2da9dede9c upstream. The current implementation of validate_range() in fs/userfaultfd.c performs a hard check against mmap_min_addr. This is redundant because UFFDIO_REGISTER operates on memory ranges that must already be backed by a VMA. Enforcing mmap_min_addr or capability checks again in userfaultfd is unnecessary and prevents applications like binary compilers from using UFFD for valid memory regions mapped by application. Remove the redundant check for mmap_min_addr. We started using UFFD instead of the classic mprotect approach in the binary translator to track application writes. During development, we encountered this bug. The translator cannot control where the translated application chooses to map its memory and if the app requires a low-address area, UFFD fails, whereas mprotect would work just fine. I believe this is a genuine logic bug rather than an improvement, and I would appreciate including the fix in stable. Link: https://lore.kernel.org/20260409103345.15044-1-komlomal@gmail.com Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") Signed-off-by: Denis M. Karpov Reviewed-by: Lorenzo Stoakes Acked-by: Harry Yoo (Oracle) Reviewed-by: Pedro Falcato Reviewed-by: Liam R. Howlett Reviewed-by: Mike Rapoport (Microsoft) Cc: Alexander Viro Cc: Al Viro Cc: Christian Brauner Cc: Jan Kara Cc: Jann Horn Cc: Peter Xu Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

Fix userfaultfd_api to return EINVAL as expected

2024-07-18T11:07:42+00:00

commit 1723f04caacb32cadc4e063725d836a0c4450694 upstream. Currently if we request a feature that is not set in the Kernel config we fail silently and return all the available features. However, the man page indicates we should return an EINVAL. We need to fix this issue since we can end up with a Kernel warning should a program request the feature UFFD_FEATURE_WP_UNPOPULATED on a kernel with the config not set with this feature. [ 200.812896] WARNING: CPU: 91 PID: 13634 at mm/memory.c:1660 zap_pte_range+0x43d/0x660 [ 200.820738] Modules linked in: [ 200.869387] CPU: 91 PID: 13634 Comm: userfaultfd Kdump: loaded Not tainted 6.9.0-rc5+ #8 [ 200.877477] Hardware name: Dell Inc. PowerEdge R6525/0N7YGH, BIOS 2.7.3 03/30/2022 [ 200.885052] RIP: 0010:zap_pte_range+0x43d/0x660 Link: https://lkml.kernel.org/r/20240626130513.120193-1-audra@redhat.com Fixes: e06f1e1dd499 ("userfaultfd: wp: enabled write protection in userfaultfd API") Signed-off-by: Audra Mitchell Cc: Al Viro Cc: Andrea Arcangeli Cc: Christian Brauner Cc: Jan Kara Cc: Mike Rapoport Cc: Peter Xu Cc: Rafael Aquini Cc: Shaohua Li Cc: Shuah Khan Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

userfaultfd: open userfaultfds with O_RDONLY

2022-10-26T10:34:36+00:00

[ Upstream commit abec3d015fdfb7c63105c7e1c956188bf381aa55 ] Since userfaultfd doesn't implement a write operation, it is more appropriate to open it read-only. When userfaultfds are opened read-write like it is now, and such fd is passed from one process to another, SELinux will check both read and write permissions for the target process, even though it can't actually do any write operation on the fd later. Inspired by the following bug report, which has hit the SELinux scenario described above: https://bugzilla.redhat.com/show_bug.cgi?id=1974559 Reported-by: Robert O'Callahan Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") Signed-off-by: Ondrej Mosnacek Acked-by: Peter Xu Acked-by: Christian Brauner (Microsoft) Signed-off-by: Paul Moore Signed-off-by: Sasha Levin

userfaultfd: fix a race between writeprotect and exit_mmap()

2021-10-19T06:22:02+00:00

A race is possible when a process exits, its VMAs are removed by exit_mmap() and at the same time userfaultfd_writeprotect() is called. The race was detected by KASAN on a development kernel, but it appears to be possible on vanilla kernels as well. Use mmget_not_zero() to prevent the race as done in other userfaultfd operations. Link: https://lkml.kernel.org/r/20210921200247.25749-1-namit@vmware.com Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") Signed-off-by: Nadav Amit Tested-by: Li Wang Reviewed-by: Peter Xu Cc: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

userfaultfd: prevent concurrent API initialization

2021-09-03T16:58:16+00:00

userfaultfd assumes that the enabled features are set once and never changed after UFFDIO_API ioctl succeeded. However, currently, UFFDIO_API can be called concurrently from two different threads, succeed on both threads and leave userfaultfd's features in non-deterministic state. Theoretically, other uffd operations (ioctl's and page-faults) can be dispatched while adversely affected by such changes of features. Moreover, the writes to ctx->state and ctx->features are not ordered, which can - theoretically, again - let userfaultfd_ioctl() think that userfaultfd API completed, while the features are still not initialized. To avoid races, it is arguably best to get rid of ctx->state. Since there are only 2 states, record the API initialization in ctx->features as the uppermost bit and remove ctx->state. Link: https://lkml.kernel.org/r/20210808020724.1022515-3-namit@vmware.com Fixes: 9cd75c3cd4c3d ("userfaultfd: non-cooperative: add ability to report non-PF events from uffd descriptor") Signed-off-by: Nadav Amit Cc: Alexander Viro Cc: Andrea Arcangeli Cc: Axel Rasmussen Cc: Jens Axboe Cc: Mike Rapoport Cc: Peter Xu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

userfaultfd: change mmap_changing to atomic

2021-09-03T16:58:16+00:00

Patch series "userfaultfd: minor bug fixes". Three unrelated bug fixes. The first two addresses possible issues (not too theoretical ones), but I did not encounter them in practice. The third patch addresses a test bug that causes the test to fail on my system. It has been sent before as part of a bigger RFC. This patch (of 3): mmap_changing is currently a boolean variable, which is set and cleared without any lock that protects against concurrent modifications. mmap_changing is supposed to mark whether userfaultfd page-faults handling should be retried since mappings are undergoing a change. However, concurrent calls, for instance to madvise(MADV_DONTNEED), might cause mmap_changing to be false, although the remove event was still not read (hence acknowledged) by the user. Change mmap_changing to atomic_t and increase/decrease appropriately. Add a debug assertion to see whether mmap_changing is negative. Link: https://lkml.kernel.org/r/20210808020724.1022515-1-namit@vmware.com Link: https://lkml.kernel.org/r/20210808020724.1022515-2-namit@vmware.com Fixes: df2cc96e77011 ("userfaultfd: prevent non-cooperative events vs mcopy_atomic races") Signed-off-by: Nadav Amit Cc: Mike Rapoport Cc: Peter Xu Cc: Axel Rasmussen Cc: Alexander Viro Cc: Andrea Arcangeli Cc: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

userfaultfd: do not untag user pointers

2021-07-24T00:43:28+00:00

Patch series "userfaultfd: do not untag user pointers", v5. If a user program uses userfaultfd on ranges of heap memory, it may end up passing a tagged pointer to the kernel in the range.start field of the UFFDIO_REGISTER ioctl. This can happen when using an MTE-capable allocator, or on Android if using the Tagged Pointers feature for MTE readiness [1]. When a fault subsequently occurs, the tag is stripped from the fault address returned to the application in the fault.address field of struct uffd_msg. However, from the application's perspective, the tagged address *is* the memory address, so if the application is unaware of memory tags, it may get confused by receiving an address that is, from its point of view, outside of the bounds of the allocation. We observed this behavior in the kselftest for userfaultfd [2] but other applications could have the same problem. Address this by not untagging pointers passed to the userfaultfd ioctls. Instead, let the system call fail. Also change the kselftest to use mmap so that it doesn't encounter this problem. [1] https://source.android.com/devices/tech/debug/tagged-pointers [2] tools/testing/selftests/vm/userfaultfd.c This patch (of 2): Do not untag pointers passed to the userfaultfd ioctls. Instead, let the system call fail. This will provide an early indication of problems with tag-unaware userspace code instead of letting the code get confused later, and is consistent with how we decided to handle brk/mmap/mremap in commit dcde237319e6 ("mm: Avoid creating virtual address aliases in brk()/mmap()/mremap()"), as well as being consistent with the existing tagged address ABI documentation relating to how ioctl arguments are handled. The code change is a revert of commit 7d0325749a6c ("userfaultfd: untag user pointers") plus some fixups to some additional calls to validate_range that have appeared since then. [1] https://source.android.com/devices/tech/debug/tagged-pointers [2] tools/testing/selftests/vm/userfaultfd.c Link: https://lkml.kernel.org/r/20210714195437.118982-1-pcc@google.com Link: https://lkml.kernel.org/r/20210714195437.118982-2-pcc@google.com Link: https://linux-review.googlesource.com/id/I761aa9f0344454c482b83fcfcce547db0a25501b Fixes: 63f0c6037965 ("arm64: Introduce prctl() options to control the tagged user addresses ABI") Signed-off-by: Peter Collingbourne Reviewed-by: Andrey Konovalov Reviewed-by: Catalin Marinas Cc: Alistair Delva Cc: Andrea Arcangeli Cc: Dave Martin Cc: Evgenii Stepanov Cc: Lokesh Gidra Cc: Mitch Phillips Cc: Vincenzo Frascino Cc: Will Deacon Cc: William McVicker Cc: [5.4] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'akpm' (patches from Andrew)

2021-07-02T19:08:10+00:00

Merge more updates from Andrew Morton: "190 patches. Subsystems affected by this patch series: mm (hugetlb, userfaultfd, vmscan, kconfig, proc, z3fold, zbud, ras, mempolicy, memblock, migration, thp, nommu, kconfig, madvise, memory-hotplug, zswap, zsmalloc, zram, cleanups, kfence, and hmm), procfs, sysctl, misc, core-kernel, lib, lz4, checkpatch, init, kprobes, nilfs2, hfs, signals, exec, kcov, selftests, compress/decompress, and ipc" * emailed patches from Andrew Morton : (190 commits) ipc/util.c: use binary search for max_idx ipc/sem.c: use READ_ONCE()/WRITE_ONCE() for use_global_lock ipc: use kmalloc for msg_queue and shmid_kernel ipc sem: use kvmalloc for sem_undo allocation lib/decompressors: remove set but not used variabled 'level' selftests/vm/pkeys: exercise x86 XSAVE init state selftests/vm/pkeys: refill shadow register after implicit kernel write selftests/vm/pkeys: handle negative sys_pkey_alloc() return code selftests/vm/pkeys: fix alloc_random_pkey() to make it really, really random kcov: add __no_sanitize_coverage to fix noinstr for all architectures exec: remove checks in __register_bimfmt() x86: signal: don't do sas_ss_reset() until we are certain that sigframe won't be abandoned hfsplus: report create_date to kstat.btime hfsplus: remove unnecessary oom message nilfs2: remove redundant continue statement in a while-loop kprobes: remove duplicated strong free_insn_page in x86 and s390 init: print out unknown kernel parameters checkpatch: do not complain about positive return values starting with EPOLL checkpatch: improve the indented label test checkpatch: scripts/spdxcheck.py now requires python3 ...

userfaultfd/shmem: advertise shmem minor fault support

2021-07-01T03:47:27+00:00

Now that the feature is fully implemented (the faulting path hooks exist so userspace is notified, and the ioctl to resolve such faults is available), advertise this as a supported feature. Link: https://lkml.kernel.org/r/20210503180737.2487560-6-axelrasmussen@google.com Signed-off-by: Axel Rasmussen Acked-by: Hugh Dickins Acked-by: Peter Xu Cc: Alexander Viro Cc: Andrea Arcangeli Cc: Brian Geffon Cc: "Dr . David Alan Gilbert" Cc: Jerome Glisse Cc: Joe Perches Cc: Kirill A. Shutemov Cc: Lokesh Gidra Cc: Mike Kravetz Cc: Mike Rapoport Cc: Mina Almasry Cc: Oliver Upton Cc: Shaohua Li Cc: Shuah Khan Cc: Stephen Rothwell Cc: Wang Qing Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

userfaultfd/shmem: support minor fault registration for shmem

2021-07-01T03:47:27+00:00

This patch allows shmem-backed VMAs to be registered for minor faults. Minor faults are appropriately relayed to userspace in the fault path, for VMAs with the relevant flag. This commit doesn't hook up the UFFDIO_CONTINUE ioctl for shmem-backed minor faults, though, so userspace doesn't yet have a way to resolve such faults. Because of this, we also don't yet advertise this as a supported feature. That will be done in a separate commit when the feature is fully implemented. Link: https://lkml.kernel.org/r/20210503180737.2487560-4-axelrasmussen@google.com Signed-off-by: Axel Rasmussen Acked-by: Peter Xu Acked-by: Hugh Dickins Cc: Alexander Viro Cc: Andrea Arcangeli Cc: Brian Geffon Cc: "Dr . David Alan Gilbert" Cc: Jerome Glisse Cc: Joe Perches Cc: Kirill A. Shutemov Cc: Lokesh Gidra Cc: Mike Kravetz Cc: Mike Rapoport Cc: Mina Almasry Cc: Oliver Upton Cc: Shaohua Li Cc: Shuah Khan Cc: Stephen Rothwell Cc: Wang Qing Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds