+ mm-mremap-check-remap-conditions-earlier.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/mremap: check remap conditions earlier
has been added to the -mm mm-unstable branch.  Its filename is
     mm-mremap-check-remap-conditions-earlier.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mremap-check-remap-conditions-earlier.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Subject: mm/mremap: check remap conditions earlier
Date: Fri, 11 Jul 2025 12:38:20 +0100

When we expand or move a VMA, this requires a number of additional checks
to be performed.

Make it really obvious under what circumstances these checks must be
performed and aggregate all the checks in one place by invoking this in
check_prep_vma().

We have to adjust the checks to account for shrink + move operations by
checking new_len <= old_len rather than new_len == old_len.

No functional change intended.

Link: https://lkml.kernel.org/r/ffa58050a544e0a8b9077f24d238cbdbba9c1858.1752232673.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mremap.c |   28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

--- a/mm/mremap.c~mm-mremap-check-remap-conditions-earlier
+++ a/mm/mremap.c
@@ -1343,7 +1343,7 @@ static int remap_is_valid(struct vma_rem
 	if (old_len > vma->vm_end - addr)
 		return -EFAULT;
 
-	if (new_len == old_len)
+	if (new_len <= old_len)
 		return 0;
 
 	/* Need to be careful about a growing mapping */
@@ -1443,10 +1443,6 @@ static unsigned long mremap_to(struct vm
 		vrm->old_len = vrm->new_len;
 	}
 
-	err = remap_is_valid(vrm);
-	if (err)
-		return err;
-
 	/* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 	if (vrm->flags & MREMAP_DONTUNMAP) {
 		vm_flags_t vm_flags = vrm->vma->vm_flags;
@@ -1635,10 +1631,6 @@ static unsigned long expand_vma(struct v
 {
 	unsigned long err;
 
-	err = remap_is_valid(vrm);
-	if (err)
-		return err;
-
 	/*
 	 * [addr, old_len) spans precisely to the end of the VMA, so try to
 	 * expand it in-place.
@@ -1705,6 +1697,21 @@ static unsigned long mremap_at(struct vm
 	return -EINVAL;
 }
 
+/*
+ * Will this operation result in the VMA being expanded or moved and thus need
+ * to map a new portion of virtual address space?
+ */
+static bool vrm_will_map_new(struct vma_remap_struct *vrm)
+{
+	if (vrm->remap_type == MREMAP_EXPAND)
+		return true;
+
+	if (vrm_implies_new_addr(vrm))
+		return true;
+
+	return false;
+}
+
 static int check_prep_vma(struct vma_remap_struct *vrm)
 {
 	struct vm_area_struct *vma = vrm->vma;
@@ -1726,6 +1733,9 @@ static int check_prep_vma(struct vma_rem
 	if (!vrm_implies_new_addr(vrm))
 		vrm->new_addr = vrm->addr;
 
+	if (vrm_will_map_new(vrm))
+		return remap_is_valid(vrm);
+
 	return 0;
 }
 
_

Patches currently in -mm which might be from lorenzo.stoakes@oracle.com are

mm-madvise-remove-the-visitor-pattern-and-thread-anon_vma-state.patch
mm-madvise-thread-mm_struct-through-madvise_behavior.patch
mm-madvise-thread-vma-range-state-through-madvise_behavior.patch
mm-madvise-thread-all-madvise-state-through-madv_behavior.patch
mm-madvise-eliminate-very-confusing-manipulation-of-prev-vma.patch
mm-madvise-eliminate-very-confusing-manipulation-of-prev-vma-fix.patch
tools-testing-selftests-add-mremap-unfaulted-faulted-test-cases.patch
mm-mremap-perform-some-simple-cleanups.patch
mm-mremap-refactor-initial-parameter-sanity-checks.patch
mm-mremap-put-vma-check-and-prep-logic-into-helper-function.patch
mm-mremap-cleanup-post-processing-stage-of-mremap.patch
mm-mremap-use-an-explicit-uffd-failure-path-for-mremap.patch
mm-mremap-check-remap-conditions-earlier.patch
mm-mremap-move-remap_is_valid-into-check_prep_vma.patch
mm-mremap-clean-up-mlock-populate-behaviour.patch
mm-mremap-permit-mremap-move-of-multiple-vmas.patch
mm-mremap-permit-mremap-move-of-multiple-vmas-fix.patch
tools-testing-selftests-extend-mremap_test-to-test-multi-vma-mremap.patch