Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [Critical] State modification applied to `desc->vma_flags` during action preparation is not propagated back to `map->vma_flags`, resulting in incorrect VMA merging and the silent loss of critical flags like `VM_PFNMAP` and `VM_IO`. --
commit 31f214221abd5db93fe1f46874d29ea3c59a0cc7 Author: Lorenzo Stoakes (ARM) <[email protected]> mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma When a user requests an mmap_action be performed in mmap_prepare, this involves populating the VMA range with data. This patch asserts that no future mmap action is performed on a mergeable VMA upon mmap_prepare validation. > diff --git a/mm/vma.c b/mm/vma.c > index 626a18c08a269..2648fb0e19959 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -2809,6 +2809,15 @@ static int mmap_validate(unsigned long prev_start, > int mmap_prepare_validate(const struct vm_area_desc *prev_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. > + */ > + if (vma_flags_can_merge(&desc->vma_flags) && > + WARN_ON_ONCE(desc->action.type != MMAP_NOTHING)) > + return -EINVAL; > + [Severity: Critical] Does this check actually prevent the merge? Looking at call_mmap_prepare(), map->vma_flags is copied from desc->vma_flags before call_action_prepare() is called: mm/vma.c:call_mmap_prepare() { ... map->vma_flags = desc->vma_flags; ... err = call_action_prepare(map, desc); if (err) return err; err = mmap_prepare_validate(&prev_desc, desc); ... } If call_action_prepare() mutates desc->vma_flags to include action-specific unmergeable flags, vma_flags_can_merge(&desc->vma_flags) will be false here, allowing the validation to pass. However, these changes don't appear to be synchronized back to map->vma_flags. Could this cause the actual VMA operations to operate on the stale and mergeable map->vma_flags? If a VMA lacks VM_PFNMAP or VM_IO but contains PFN-mapped pages, could this lead to memory corruption if kernel mechanisms assume the pages are normal memory and call put_page() on raw PFNs? > return mmap_validate(prev_desc->start, desc->start, > &prev_desc->vma_flags, &desc->vma_flags); > } -- Sashiko AI review ยท https://sashiko.dev/#/patchset/20260914-b4-mmap-prepare-vma-flag-sanify-v2-0-7d9781ed5...@kernel.org?part=5
