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[PATCH v2 4/5] mm/mseal: Simplify and rename VMA gap check

Lorenzo Stoakes posted 5 patches 6 months, 3 weeks ago
There is a newer version of this series
[PATCH v2 4/5] mm/mseal: Simplify and rename VMA gap check
Posted by Lorenzo Stoakes 6 months, 3 weeks ago 
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.

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>
---
 mm/mseal.c | 56 ++++++++++++++++++++----------------------------------
 1 file changed, 21 insertions(+), 35 deletions(-)

diff --git a/mm/mseal.c b/mm/mseal.c
index adbcc65e9660..794d1043a706 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -37,34 +37,6 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	return ret;
 }

-/*
- * 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.
- */
-static int check_mm_seal(unsigned long start, unsigned long end)
-{
-	struct vm_area_struct *vma;
-	unsigned long nstart = 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_end >= end)
-			return 0;
-
-		nstart = vma->vm_end;
-	}
-
-	return -ENOMEM;
-}
-
 /*
  * Apply sealing.
  */
@@ -102,6 +74,24 @@ static int apply_mm_seal(unsigned long start, unsigned long end)
 	return 0;
 }

+/* Does the [start, end) range contain any unmapped memory? */
+static bool range_contains_unmapped(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
+{
+	struct vm_area_struct *vma;
+	unsigned long prev_end = start;
+	VMA_ITERATOR(vmi, current->mm, start);
+
+	for_each_vma_range(vmi, vma, end) {
+		if (vma->vm_start > prev_end)
+			return true;
+
+		prev_end = vma->vm_end;
+	}
+
+	return prev_end < end;
+}
+
 /*
  * mseal(2) seals the VM's meta data from
  * selected syscalls.
@@ -184,14 +174,10 @@ 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
--
2.50.1
Re: [PATCH v2 4/5] mm/mseal: Simplify and rename VMA gap check
Posted by David Hildenbrand 6 months, 3 weeks ago 
On 15.07.25 15:37, Lorenzo Stoakes wrote:
> 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.
> 
> 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>
> ---
>   mm/mseal.c | 56 ++++++++++++++++++++----------------------------------
>   1 file changed, 21 insertions(+), 35 deletions(-)
> 
> diff --git a/mm/mseal.c b/mm/mseal.c
> index adbcc65e9660..794d1043a706 100644
> --- a/mm/mseal.c
> +++ b/mm/mseal.c
> @@ -37,34 +37,6 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
>   	return ret;
>   }
> 
> -/*
> - * 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.
> - */
> -static int check_mm_seal(unsigned long start, unsigned long end)
> -{
> -	struct vm_area_struct *vma;
> -	unsigned long nstart = 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_end >= end)
> -			return 0;
> -
> -		nstart = vma->vm_end;
> -	}
> -
> -	return -ENOMEM;
> -}
> -
>   /*
>    * Apply sealing.
>    */
> @@ -102,6 +74,24 @@ static int apply_mm_seal(unsigned long start, unsigned long end)
>   	return 0;
>   }
> 
> +/* Does the [start, end) range contain any unmapped memory? */
> +static bool range_contains_unmapped(struct mm_struct *mm,
> +		unsigned long start, unsigned long end)
> +{
> +	struct vm_area_struct *vma;
> +	unsigned long prev_end = start;
> +	VMA_ITERATOR(vmi, current->mm, start);
> +
> +	for_each_vma_range(vmi, vma, end) {
> +		if (vma->vm_start > prev_end)
> +			return true;
> +
> +		prev_end = vma->vm_end;
> +	}
> +
> +	return prev_end < end;
> +}
> +

Probably better to not ... move the function in the same file? Then, we 
can se the actual diff of changes easily.

-- 
Cheers,

David / dhildenb
Re: [PATCH v2 4/5] mm/mseal: Simplify and rename VMA gap check
Posted by Lorenzo Stoakes 6 months, 3 weeks ago 
On Wed, Jul 16, 2025 at 03:38:51PM +0200, David Hildenbrand wrote:
> On 15.07.25 15:37, Lorenzo Stoakes wrote:
> > 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.
> >
> > 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>
> > ---
> >   mm/mseal.c | 56 ++++++++++++++++++++----------------------------------
> >   1 file changed, 21 insertions(+), 35 deletions(-)
> >
> > diff --git a/mm/mseal.c b/mm/mseal.c
> > index adbcc65e9660..794d1043a706 100644
> > --- a/mm/mseal.c
> > +++ b/mm/mseal.c
> > @@ -37,34 +37,6 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >   	return ret;
> >   }
> >
> > -/*
> > - * 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.
> > - */
> > -static int check_mm_seal(unsigned long start, unsigned long end)
> > -{
> > -	struct vm_area_struct *vma;
> > -	unsigned long nstart = 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_end >= end)
> > -			return 0;
> > -
> > -		nstart = vma->vm_end;
> > -	}
> > -
> > -	return -ENOMEM;
> > -}
> > -
> >   /*
> >    * Apply sealing.
> >    */
> > @@ -102,6 +74,24 @@ static int apply_mm_seal(unsigned long start, unsigned long end)
> >   	return 0;
> >   }
> >
> > +/* Does the [start, end) range contain any unmapped memory? */
> > +static bool range_contains_unmapped(struct mm_struct *mm,
> > +		unsigned long start, unsigned long end)
> > +{
> > +	struct vm_area_struct *vma;
> > +	unsigned long prev_end = start;
> > +	VMA_ITERATOR(vmi, current->mm, start);
> > +
> > +	for_each_vma_range(vmi, vma, end) {
> > +		if (vma->vm_start > prev_end)
> > +			return true;
> > +
> > +		prev_end = vma->vm_end;
> > +	}
> > +
> > +	return prev_end < end;
> > +}
> > +
>
> Probably better to not ... move the function in the same file? Then, we can
> se the actual diff of changes easily.

Sure, will respin with that.

>
> --
> Cheers,
>
> David / dhildenb
>

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