From 14dad135d68b850f4506d7fc6872f1105dfde3cb Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Fri, 17 Jul 2026 18:27:09 +0100 Subject: [PATCH] mm/mseal: remove superfluous comments, fix confusion around mm Patch series "mm/mseal: further cleanups", v2. The mseal implementation is still rather confusing, so tighten things up a little. The only user of do_mseal() outside of the system call is the MMAP_PAGE_ZERO process personality - retain better control over how mseal is utilised by providing mseal_mmap_page_zero() for this instead. The comments are overly long and confusion, so cut them down so they're a lot clearer. Remove confusing mm_struct params (mseal can not be used on remote mm's) and wrap the actual system call logic into the system call declaration. This patch (of 3): Remove comment blocks that don't add value and eliminate any confusion about whether or not we permit mseal()'ing of remote mm's by not passing through an mm parameter but rather referencing current->mm in each function. Also while we're here, avoid an ugly goto by using an else branch, and move local parameters declarations into reverse xmas tree order. No functional change intended. Link: https://lore.kernel.org/20260717-mseal-fixups-v2-0-0daa0014b813@kernel.org Link: https://lore.kernel.org/20260717-mseal-fixups-v2-1-0daa0014b813@kernel.org Signed-off-by: Lorenzo Stoakes (ARM) Acked-by: David Hildenbrand (Arm) Reviewed-by: Pedro Falcato Cc: Al Viro Cc: Christian Brauner Cc: Jan Kara Cc: Jann Horn Cc: Kees Cook Cc: Liam R. Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/mseal.c | 53 +++++++++++------------------------------------------ 1 file changed, 11 insertions(+), 42 deletions(-) diff --git a/mm/mseal.c b/mm/mseal.c index 9781647483d1..430a252a6da4 100644 --- a/mm/mseal.c +++ b/mm/mseal.c @@ -16,32 +16,11 @@ #include #include "internal.h" -/* - * mseal() disallows an input range which contain unmapped ranges (VMA holes). - * - * It disallows unmapped regions from start to end whether they exist at the - * start, in the middle, or at the end of the range, or any combination thereof. - * - * This is because after sealing a range, there's nothing to stop memory mapping - * of ranges in the remaining gaps later, meaning that the user might then - * wrongly consider the entirety of the mseal()'d range to be sealed when it - * in fact isn't. - */ - -/* - * Does the [start, end) range contain any unmapped memory? - * - * We ensure that: - * - start is part of a valid VMA. - * - end is part of a valid VMA. - * - no gap (unallocated memory) exists between start and end. - */ -static bool range_contains_unmapped(struct mm_struct *mm, - unsigned long start, unsigned long end) +static bool range_contains_unmapped(unsigned long start, unsigned long end) { - struct vm_area_struct *vma; - unsigned long prev_end = start; VMA_ITERATOR(vmi, current->mm, start); + unsigned long prev_end = start; + struct vm_area_struct *vma; for_each_vma_range(vmi, vma, end) { if (vma->vm_start > prev_end) @@ -53,11 +32,10 @@ static bool range_contains_unmapped(struct mm_struct *mm, return prev_end < end; } -static int mseal_apply(struct mm_struct *mm, - unsigned long start, unsigned long end) +static int mseal_apply(unsigned long start, unsigned long end) { + VMA_ITERATOR(vmi, current->mm, start); struct vm_area_struct *vma, *prev; - VMA_ITERATOR(vmi, mm, start); /* We know there are no gaps so this will be non-NULL. */ vma = vma_iter_load(&vmi); @@ -142,10 +120,10 @@ static int mseal_apply(struct mm_struct *mm, */ int do_mseal(unsigned long start, size_t len_in, unsigned long flags) { - size_t len; - int ret = 0; - unsigned long end; struct mm_struct *mm = current->mm; + unsigned long end; + int ret = 0; + size_t len; /* Verify flags not set. */ if (flags) @@ -170,20 +148,11 @@ int do_mseal(unsigned long start, size_t len_in, unsigned long flags) if (mmap_write_lock_killable(mm)) return -EINTR; - if (range_contains_unmapped(mm, start, end)) { + if (range_contains_unmapped(start, end)) ret = -ENOMEM; - goto out; - } + else + ret = mseal_apply(start, end); - /* - * Second pass, this should success, unless there are errors - * from vma_modify_flags, e.g. merge/split error, or process - * reaching the max supported VMAs, however, those cases shall - * be rare. - */ - ret = mseal_apply(mm, start, end); - -out: mmap_write_unlock(mm); return ret; }