[PATCH v4 04/38] mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma
flat view
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Date: 2026-10-03 16:34:31
Also in:
bpf, fuse-devel, kvm, kvm-riscv, kvmarm, linux-arch, linux-doc, linux-fbdev, linux-fsdevel, linux-mm, linux-perf-users, linux-rdma, linux-riscv, linux-s390, linux-scsi, linux-sound, linux-usb, linuxppc-dev, lkml, selinux, sparclinux
Subsystem:
memory management, memory mapping, the rest · Maintainers:
Andrew Morton, Liam R. Howlett, Lorenzo Stoakes, Linus Torvalds
4 review trailers; queued in linux-next as 216caeeb2b8b on 2026-10-07.
When a user requests an mmap_action be performed in mmap_prepare, this involves populating the VMA range with data. However, if the VMA is mergeable, it might then mistakenly be merged with another VMA without having populated the range. Every mmap action currently available sets VMA flags such that the VMA cannot be merged. However, to ensure that no future mmap action falls foul of this, assert that this is the case upon mmap_prepare validation. Reviewed-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Gregory Price (Meta) <gourry@gourry.net> Acked-by: David Hildenbrand (Arm) <david@kernel.org> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> --- mm/vma.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/mm/vma.c b/mm/vma.c
index 159fd3ff8560..a9532bbd4ee2 100644
--- a/mm/vma.c
+++ b/mm/vma.c@@ -2812,6 +2812,18 @@ static int mmap_validate(unsigned long orig_start, unsigned long orig_end, int mmap_prepare_validate(const struct vm_area_desc *orig_desc, const struct vm_area_desc *desc) { + /* + * It is not valid to execute mmap actions for VMAs which can be merged, + * as any such merge would leave portions of the mapping incorrectly + * unmapped. + * + * This is checked after mmap_action_prepare(), as it may update the VMA + * flags and therefore whether the VMA can be merged. + */ + if (vma_flags_can_merge(&desc->vma_flags) && + WARN_ON_ONCE(desc->action.type != MMAP_NOTHING)) + return -EINVAL; + return mmap_validate(orig_desc->start, orig_desc->end, desc->start, desc->end, &orig_desc->vma_flags, &desc->vma_flags);
--
2.55.0