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mm/mseal: simplify and rename VMA gap check

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The check_mm_seal() function is doing something general - checking whether
a range contains only VMAs (or rather that it does NOT contain any
unmapped regions).

So rename this function to range_contains_unmapped().

Additionally simplify the logic, we are simply checking whether the last
vma->vm_end has either a VMA starting after it or ends before the end
parameter.

This check is rather dubious, so it is sensible to keep it local to
mm/mseal.c as at a later stage it may be removed, and we don't want any
other mm code to perform such a check.

No functional change intended.

[lorenzo.stoakes@oracle.com: add comment explaining why we disallow gaps on mseal()]
  Link: https://lkml.kernel.org/r/d85b3d55-09dc-43ba-8204-b48267a96751@lucifer.local
Link: https://lkml.kernel.org/r/dd50984eff1e242b5f7f0f070a3360ef760e06b8.1753431105.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Jeff Xu <jeffxu@chromium.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Cc: Jann Horn <jannh@google.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes
2025-07-25 09:29:44 +01:00
committed by Andrew Morton
parent 8b2914162a
commit 530e090964
1 changed files with 28 additions and 23 deletions
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51
mm/mseal.c
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@@ -38,31 +38,40 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
}
/*
* Check for do_mseal:
* 1> start is part of a valid vma.
* 2> end is part of a valid vma.
* 3> No gap (unallocated address) between start and end.
* 4> map is sealable.
* 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 sealng 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.
*/
static int check_mm_seal(unsigned long start, unsigned long end)
/*
* 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)
{
struct vm_area_struct *vma;
unsigned long nstart = start;
unsigned long prev_end = start;
VMA_ITERATOR(vmi, current->mm, start);
/* going through each vma to check. */
for_each_vma_range(vmi, vma, end) {
if (vma->vm_start > nstart)
/* unallocated memory found. */
return -ENOMEM;
if (vma->vm_start > prev_end)
return true;
if (vma->vm_end >= end)
return 0;
nstart = vma->vm_end;
prev_end = vma->vm_end;
}
return -ENOMEM;
return prev_end < end;
}
/*
@@ -184,14 +193,10 @@ int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
if (mmap_write_lock_killable(mm))
return -EINTR;
/*
* First pass, this helps to avoid
* partial sealing in case of error in input address range,
* e.g. ENOMEM error.
*/
ret = check_mm_seal(start, end);
if (ret)
if (range_contains_unmapped(mm, start, end)) {
ret = -ENOMEM;
goto out;
}
/*
* Second pass, this should success, unless there are errors