kernel/linux.git/fs/userfaultfd.c, branch v6.1.168

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

2025-06-27T10:07:04+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 [acsjakub: contextual change - keep call to mas_next()] Cc: Signed-off-by: Jakub Acs Signed-off-by: Greg Kroah-Hartman

Fix userfaultfd_api to return EINVAL as expected

2024-07-18T11:18:41+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

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

2023-04-26T12:28:37+00:00

commit 2ff559f31a5d50c31a3f9d849f8af90dc36c7105 upstream. 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 Signed-off-by: Greg Kroah-Hartman

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

2023-01-24T06:24:36+00:00

commit 51d3d5eb74ff53b92dcff48b30ae2ed8edd85a32 upstream. 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 Signed-off-by: Greg Kroah-Hartman

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 ...

Merge tag 'lsm-pr-20221003' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/lsm

2022-10-04T00:51:52+00:00

Pull LSM updates from Paul Moore: "Seven patches for the LSM layer and we've got a mix of trivial and significant patches. Highlights below, starting with the smaller bits first so they don't get lost in the discussion of the larger items: - Remove some redundant NULL pointer checks in the common LSM audit code. - Ratelimit the lockdown LSM's access denial messages. With this change there is a chance that the last visible lockdown message on the console is outdated/old, but it does help preserve the initial series of lockdown denials that started the denial message flood and my gut feeling is that these might be the more valuable messages. - Open userfaultfds as readonly instead of read/write. While this code obviously lives outside the LSM, it does have a noticeable impact on the LSMs with Ondrej explaining the situation in the commit description. It is worth noting that this patch languished on the VFS list for over a year without any comments (objections or otherwise) so I took the liberty of pulling it into the LSM tree after giving fair notice. It has been in linux-next since the end of August without any noticeable problems. - Add a LSM hook for user namespace creation, with implementations for both the BPF LSM and SELinux. Even though the changes are fairly small, this is the bulk of the diffstat as we are also including BPF LSM selftests for the new hook. It's also the most contentious of the changes in this pull request with Eric Biederman NACK'ing the LSM hook multiple times during its development and discussion upstream. While I've never taken NACK's lightly, I'm sending these patches to you because it is my belief that they are of good quality, satisfy a long-standing need of users and distros, and are in keeping with the existing nature of the LSM layer and the Linux Kernel as a whole. The patches in implement a LSM hook for user namespace creation that allows for a granular approach, configurable at runtime, which enables both monitoring and control of user namespaces. The general consensus has been that this is far preferable to the other solutions that have been adopted downstream including outright removal from the kernel, disabling via system wide sysctls, or various other out-of-tree mechanisms that users have been forced to adopt since we haven't been able to provide them an upstream solution for their requests. Eric has been steadfast in his objections to this LSM hook, explaining that any restrictions on the user namespace could have significant impact on userspace. While there is the possibility of impacting userspace, it is important to note that this solution only impacts userspace when it is requested based on the runtime configuration supplied by the distro/admin/user. Frederick (the pathset author), the LSM/security community, and myself have tried to work with Eric during development of this patchset to find a mutually acceptable solution, but Eric's approach and unwillingness to engage in a meaningful way have made this impossible. I have CC'd Eric directly on this pull request so he has a chance to provide his side of the story; there have been no objections outside of Eric's" * tag 'lsm-pr-20221003' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/lsm: lockdown: ratelimit denial messages userfaultfd: open userfaultfds with O_RDONLY selinux: Implement userns_create hook selftests/bpf: Add tests verifying bpf lsm userns_create hook bpf-lsm: Make bpf_lsm_userns_create() sleepable security, lsm: Introduce security_create_user_ns() lsm: clean up redundant NULL pointer check

userfaultfd: use maple tree iterator to iterate VMAs

2022-09-27T02:46:21+00:00

Don't use the mm_struct linked list or the vma->vm_next in prep for removal. Link: https://lkml.kernel.org/r/20220906194824.2110408-45-Liam.Howlett@oracle.com Signed-off-by: Liam R. Howlett Tested-by: Yu Zhao Cc: Catalin Marinas Cc: David Hildenbrand Cc: David Howells Cc: Davidlohr Bueso Cc: "Matthew Wilcox (Oracle)" Cc: SeongJae Park Cc: Sven Schnelle Cc: Vlastimil Babka Cc: Will Deacon Signed-off-by: Andrew Morton

userfaultfd: add /dev/userfaultfd for fine grained access control

2022-09-12T03:25:48+00:00

Historically, it has been shown that intercepting kernel faults with userfaultfd (thereby forcing the kernel to wait for an arbitrary amount of time) can be exploited, or at least can make some kinds of exploits easier. So, in 37cd0575b8 "userfaultfd: add UFFD_USER_MODE_ONLY" we changed things so, in order for kernel faults to be handled by userfaultfd, either the process needs CAP_SYS_PTRACE, or this sysctl must be configured so that any unprivileged user can do it. In a typical implementation of a hypervisor with live migration (take QEMU/KVM as one such example), we do indeed need to be able to handle kernel faults. But, both options above are less than ideal: - Toggling the sysctl increases attack surface by allowing any unprivileged user to do it. - Granting the live migration process CAP_SYS_PTRACE gives it this ability, but *also* the ability to "observe and control the execution of another process [...], and examine and change [its] memory and registers" (from ptrace(2)). This isn't something we need or want to be able to do, so granting this permission violates the "principle of least privilege". This is all a long winded way to say: we want a more fine-grained way to grant access to userfaultfd, without granting other additional permissions at the same time. To achieve this, add a /dev/userfaultfd misc device. This device provides an alternative to the userfaultfd(2) syscall for the creation of new userfaultfds. The idea is, any userfaultfds created this way will be able to handle kernel faults, without the caller having any special capabilities. Access to this mechanism is instead restricted using e.g. standard filesystem permissions. [axelrasmussen@google.com: Handle misc_register() failure properly] Link: https://lkml.kernel.org/r/20220819205201.658693-3-axelrasmussen@google.com Link: https://lkml.kernel.org/r/20220808175614.3885028-3-axelrasmussen@google.com Signed-off-by: Axel Rasmussen Acked-by: Nadav Amit Acked-by: Peter Xu Acked-by: Mike Rapoport Cc: Al Viro Cc: Dave Hansen Cc: Dmitry V. Levin Cc: Gleb Fotengauer-Malinovskiy Cc: Hugh Dickins Cc: Jan Kara Cc: Jonathan Corbet Cc: Mel Gorman Cc: Mike Kravetz Cc: Shuah Khan Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Zhang Yi Cc: Mike Rapoport Signed-off-by: Andrew Morton

userfaultfd: open userfaultfds with O_RDONLY

2022-08-30T20:04:31+00:00

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