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Message-ID: <f903af2930c7c2c6e0948c886b58d0f42d8e8ba3.1767638272.git.lorenzo.stoakes@oracle.com>
Date: Mon, 5 Jan 2026 20:11:48 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
Pedro Falcato <pfalcato@...e.de>, Yeoreum Yun <yeoreum.yun@....com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
David Hildenbrand <david@...nel.org>,
Jeongjun Park <aha310510@...il.com>, Rik van Riel <riel@...riel.com>,
Harry Yoo <harry.yoo@...cle.com>
Subject: [PATCH v2 2/4] tools/testing/selftests: add tests for !tgt, src mremap() merges
Test that mremap()'ing a VMA into a position such that the target VMA on
merge is unfaulted and the source faulted is correctly performed.
We cover 4 cases:
1. Previous VMA unfaulted:
copied -----|
v
|-----------|.............|
| unfaulted |(faulted VMA)|
|-----------|.............|
prev
target = prev, expand prev to cover.
2. Next VMA unfaulted:
copied -----|
v
|.............|-----------|
|(faulted VMA)| unfaulted |
|.............|-----------|
next
target = next, expand next to cover.
3. Both adjacent VMAs unfaulted:
copied -----|
v
|-----------|.............|-----------|
| unfaulted |(faulted VMA)| unfaulted |
|-----------|.............|-----------|
prev next
target = prev, expand prev to cover.
4. prev unfaulted, next faulted:
copied -----|
v
|-----------|.............|-----------|
| unfaulted |(faulted VMA)| faulted |
|-----------|.............|-----------|
prev next
target = prev, expand prev to cover. Essentially equivalent to 3, but
with additional requirement that next's anon_vma is the same as the
copied VMA's.
Each of these are performed with MREMAP_DONTUNMAP set, which will cause a
KASAN assert for UAF or an assert on zero refcount anon_vma if a bug exists
with correctly propagating anon_vma state in each scenario.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Fixes: 879bca0a2c4f ("mm/vma: fix incorrectly disallowed anonymous VMA merges")
Cc: stable@...nel.org
---
tools/testing/selftests/mm/merge.c | 232 +++++++++++++++++++++++++++++
1 file changed, 232 insertions(+)
diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c
index 363c1033cc7d..22be149f7109 100644
--- a/tools/testing/selftests/mm/merge.c
+++ b/tools/testing/selftests/mm/merge.c
@@ -1171,4 +1171,236 @@ TEST_F(merge, mremap_correct_placed_faulted)
ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 15 * page_size);
}
+TEST_F(merge, mremap_faulted_to_unfaulted_prev)
+{
+ struct procmap_fd *procmap = &self->procmap;
+ unsigned int page_size = self->page_size;
+ char *ptr_a, *ptr_b;
+
+ /*
+ * mremap() such that A and B merge:
+ *
+ * |------------|
+ * | \ |
+ * |-----------| | / |---------|
+ * | unfaulted | v \ | faulted |
+ * |-----------| / |---------|
+ * B \ A
+ */
+
+ /* Map VMA A into place. */
+ ptr_a = mmap(&self->carveout[page_size + 3 * page_size],
+ 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+ /* Fault it in. */
+ ptr_a[0] = 'x';
+
+ /*
+ * Now move it out of the way so we can place VMA B in position,
+ * unfaulted.
+ */
+ ptr_a = mremap(ptr_a, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE, &self->carveout[20 * page_size]);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+
+ /* Map VMA B into place. */
+ ptr_b = mmap(&self->carveout[page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_b, MAP_FAILED);
+
+ /*
+ * Now move VMA A into position with MREMAP_DONTUNMAP to catch incorrect
+ * anon_vma propagation.
+ */
+ ptr_a = mremap(ptr_a, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+ &self->carveout[page_size + 3 * page_size]);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+
+ /* The VMAs should have merged. */
+ ASSERT_TRUE(find_vma_procmap(procmap, ptr_b));
+ ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr_b);
+ ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr_b + 6 * page_size);
+}
+
+TEST_F(merge, mremap_faulted_to_unfaulted_next)
+{
+ struct procmap_fd *procmap = &self->procmap;
+ unsigned int page_size = self->page_size;
+ char *ptr_a, *ptr_b;
+
+ /*
+ * mremap() such that A and B merge:
+ *
+ * |---------------------------|
+ * | \ |
+ * | |-----------| / |---------|
+ * v | unfaulted | \ | faulted |
+ * |-----------| / |---------|
+ * B \ A
+ *
+ * Then unmap VMA A to trigger the bug.
+ */
+
+ /* Map VMA A into place. */
+ ptr_a = mmap(&self->carveout[page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+ /* Fault it in. */
+ ptr_a[0] = 'x';
+
+ /*
+ * Now move it out of the way so we can place VMA B in position,
+ * unfaulted.
+ */
+ ptr_a = mremap(ptr_a, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE, &self->carveout[20 * page_size]);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+
+ /* Map VMA B into place. */
+ ptr_b = mmap(&self->carveout[page_size + 3 * page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_b, MAP_FAILED);
+
+ /*
+ * Now move VMA A into position with MREMAP_DONTUNMAP to catch incorrect
+ * anon_vma propagation.
+ */
+ ptr_a = mremap(ptr_a, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+ &self->carveout[page_size]);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+
+ /* The VMAs should have merged. */
+ ASSERT_TRUE(find_vma_procmap(procmap, ptr_a));
+ ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr_a);
+ ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr_a + 6 * page_size);
+}
+
+TEST_F(merge, mremap_faulted_to_unfaulted_prev_unfaulted_next)
+{
+ struct procmap_fd *procmap = &self->procmap;
+ unsigned int page_size = self->page_size;
+ char *ptr_a, *ptr_b, *ptr_c;
+
+ /*
+ * mremap() with MREMAP_DONTUNMAP such that A, B and C merge:
+ *
+ * |---------------------------|
+ * | \ |
+ * |-----------| | |-----------| / |---------|
+ * | unfaulted | v | unfaulted | \ | faulted |
+ * |-----------| |-----------| / |---------|
+ * A C \ B
+ */
+
+ /* Map VMA B into place. */
+ ptr_b = mmap(&self->carveout[page_size + 3 * page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_b, MAP_FAILED);
+ /* Fault it in. */
+ ptr_b[0] = 'x';
+
+ /*
+ * Now move it out of the way so we can place VMAs A, C in position,
+ * unfaulted.
+ */
+ ptr_b = mremap(ptr_b, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE, &self->carveout[20 * page_size]);
+ ASSERT_NE(ptr_b, MAP_FAILED);
+
+ /* Map VMA A into place. */
+
+ ptr_a = mmap(&self->carveout[page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+
+ /* Map VMA C into place. */
+ ptr_c = mmap(&self->carveout[page_size + 3 * page_size + 3 * page_size],
+ 3 * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_c, MAP_FAILED);
+
+ /*
+ * Now move VMA B into position with MREMAP_DONTUNMAP to catch incorrect
+ * anon_vma propagation.
+ */
+ ptr_b = mremap(ptr_b, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+ &self->carveout[page_size + 3 * page_size]);
+ ASSERT_NE(ptr_b, MAP_FAILED);
+
+ /* The VMAs should have merged. */
+ ASSERT_TRUE(find_vma_procmap(procmap, ptr_a));
+ ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr_a);
+ ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr_a + 9 * page_size);
+}
+
+TEST_F(merge, mremap_faulted_to_unfaulted_prev_faulted_next)
+{
+ struct procmap_fd *procmap = &self->procmap;
+ unsigned int page_size = self->page_size;
+ char *ptr_a, *ptr_b, *ptr_bc;
+
+ /*
+ * mremap() with MREMAP_DONTUNMAP such that A, B and C merge:
+ *
+ * |---------------------------|
+ * | \ |
+ * |-----------| | |-----------| / |---------|
+ * | unfaulted | v | faulted | \ | faulted |
+ * |-----------| |-----------| / |---------|
+ * A C \ B
+ */
+
+ /*
+ * Map VMA B and C into place. We have to map them together so their
+ * anon_vma is the same and the vma->vm_pgoff's are correctly aligned.
+ */
+ ptr_bc = mmap(&self->carveout[page_size + 3 * page_size],
+ 3 * page_size + 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_bc, MAP_FAILED);
+
+ /* Fault it in. */
+ ptr_bc[0] = 'x';
+
+ /*
+ * Now move VMA B out the way (splitting VMA BC) so we can place VMA A
+ * in position, unfaulted, and leave the remainder of the VMA we just
+ * moved in place, faulted, as VMA C.
+ */
+ ptr_b = mremap(ptr_bc, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE, &self->carveout[20 * page_size]);
+ ASSERT_NE(ptr_b, MAP_FAILED);
+
+ /* Map VMA A into place. */
+ ptr_a = mmap(&self->carveout[page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
+ ASSERT_NE(ptr_a, MAP_FAILED);
+
+ /*
+ * Now move VMA B into position with MREMAP_DONTUNMAP to catch incorrect
+ * anon_vma propagation.
+ */
+ ptr_b = mremap(ptr_b, 3 * page_size, 3 * page_size,
+ MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+ &self->carveout[page_size + 3 * page_size]);
+ ASSERT_NE(ptr_b, MAP_FAILED);
+
+ /* The VMAs should have merged. */
+ ASSERT_TRUE(find_vma_procmap(procmap, ptr_a));
+ ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr_a);
+ ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr_a + 9 * page_size);
+}
+
TEST_HARNESS_MAIN
--
2.52.0
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