We currently disallow the installation of lightweight guard regions in VMAs whose flags intersect VMA_SPECIAL_FLAGS or VMA_HUGETLB_BIT, or VMA_LOCKED_BIT unless allow_locked is set.
hugetlb VMAs set VMA_DONTEXPAND_BIT so this was already redundant, VMA_SPECIAL_FLAGS already sufficed. However, now that VMA_IO_BIT is only set if VMA_PFNMAP or VMA_MIXEDMAP_BIT is set, this check collapses to being the equivalent of !vma_can_merge(). Update is_valid_guard_vma() to reflect this. No functional change intended. Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]> --- mm/madvise.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 467601a8525b..0922d5f07a12 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1221,19 +1221,25 @@ static long madvise_remove(struct madvise_behavior *madv_behavior) return error; } -static bool is_valid_guard_vma(struct vm_area_struct *vma, bool allow_locked) +static bool is_valid_guard_vma(const struct vm_area_struct *vma, + bool allow_locked) { - vm_flags_t disallowed = VM_SPECIAL | VM_HUGETLB; - /* - * A user could lock after setting a guard range but that's fine, as + * A user could lock after setting a guard range but that's fine as * they'd not be able to fault in. The issue arises when we try to zap * existing locked VMAs. We don't want to do that. */ - if (!allow_locked) - disallowed |= VM_LOCKED; + if (!allow_locked && vma_test(vma, VMA_LOCKED_BIT)) + return false; + /* + * Guard regions require a VMA whose page tables are managed solely by + * the core, which is also what merging requires, so disallow any flags + * that would prevent a merge. + */ + if (!vma_can_merge(vma)) + return false; - return !(vma->vm_flags & disallowed); + return true; } static bool is_guard_pte_marker(pte_t ptent) -- 2.55.0
