The patch titled Subject: tools/testing/selftests: add forked (un)/faulted VMA merge tests has been added to the -mm mm-hotfixes-unstable branch. Its filename is tools-testing-selftests-add-forked-un-faulted-vma-merge-tests.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-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: tools/testing/selftests: add forked (un)/faulted VMA merge tests Date: Mon, 5 Jan 2026 20:11:50 +0000

Now we correctly handle forked faulted/unfaulted merge on mremap(), exhaustively assert that we handle this correctly.

Do this in the less duplicative way by adding a new merge_with_fork fixture and forked/unforked variants, and abstract the forking logic as necessary to avoid code duplication with this also.

Link: https://lkml.kernel.org/r/1daf76d89fdb9d96f38a6a0152d8f3c2e9e30ac7.176763827... Fixes: 879bca0a2c4f ("mm/vma: fix incorrectly disallowed anonymous VMA merges") Signed-off-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: David Hildenbrand (Red Hat) david@kernel.org Cc: Jann Horn jannh@google.com Cc: Jeongjun Park aha310510@gmail.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Pedro Falcato pfalcato@suse.de Cc: Rik van Riel riel@surriel.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Yeoreum Yun yeoreum.yun@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

tools/testing/selftests/mm/merge.c | 180 ++++++++++++++++++++------- 1 file changed, 139 insertions(+), 41 deletions(-)

--- a/tools/testing/selftests/mm/merge.c~tools-testing-selftests-add-forked-un-faulted-vma-merge-tests +++ a/tools/testing/selftests/mm/merge.c @@ -22,12 +22,37 @@ FIXTURE(merge) struct procmap_fd procmap; };

+static char *map_carveout(unsigned int page_size) +{ + return mmap(NULL, 30 * page_size, PROT_NONE, + MAP_ANON | MAP_PRIVATE, -1, 0); +} + +static pid_t do_fork(struct procmap_fd *procmap) +{ + pid_t pid = fork(); + + if (pid == -1) + return -1; + if (pid != 0) { + wait(NULL); + return pid; + } + + /* Reopen for child. */ + if (close_procmap(procmap)) + return -1; + if (open_self_procmap(procmap)) + return -1; + + return 0; +} + FIXTURE_SETUP(merge) { self->page_size = psize(); /* Carve out PROT_NONE region to map over. */ - self->carveout = mmap(NULL, 30 * self->page_size, PROT_NONE, - MAP_ANON | MAP_PRIVATE, -1, 0); + self->carveout = map_carveout(self->page_size); ASSERT_NE(self->carveout, MAP_FAILED); /* Setup PROCMAP_QUERY interface. */ ASSERT_EQ(open_self_procmap(&self->procmap), 0); @@ -36,7 +61,8 @@ FIXTURE_SETUP(merge) FIXTURE_TEARDOWN(merge) { ASSERT_EQ(munmap(self->carveout, 30 * self->page_size), 0); - ASSERT_EQ(close_procmap(&self->procmap), 0); + /* May fail for parent of forked process. */ + close_procmap(&self->procmap); /* * Clear unconditionally, as some tests set this. It is no issue if this * fails (KSM may be disabled for instance). @@ -44,6 +70,44 @@ FIXTURE_TEARDOWN(merge) prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0); }

+FIXTURE(merge_with_fork) +{ + unsigned int page_size; + char *carveout; + struct procmap_fd procmap; +}; + +FIXTURE_VARIANT(merge_with_fork) +{ + bool forked; +}; + +FIXTURE_VARIANT_ADD(merge_with_fork, forked) +{ + .forked = true, +}; + +FIXTURE_VARIANT_ADD(merge_with_fork, unforked) +{ + .forked = false, +}; + +FIXTURE_SETUP(merge_with_fork) +{ + self->page_size = psize(); + self->carveout = map_carveout(self->page_size); + ASSERT_NE(self->carveout, MAP_FAILED); + ASSERT_EQ(open_self_procmap(&self->procmap), 0); +} + +FIXTURE_TEARDOWN(merge_with_fork) +{ + ASSERT_EQ(munmap(self->carveout, 30 * self->page_size), 0); + ASSERT_EQ(close_procmap(&self->procmap), 0); + /* See above. */ + prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0); +} + TEST_F(merge, mprotect_unfaulted_left) { unsigned int page_size = self->page_size; @@ -322,8 +386,8 @@ TEST_F(merge, forked_target_vma) unsigned int page_size = self->page_size; char *carveout = self->carveout; struct procmap_fd *procmap = &self->procmap; - pid_t pid; char *ptr, *ptr2; + pid_t pid; int i;

/* @@ -344,19 +408,10 @@ TEST_F(merge, forked_target_vma) */ ptr[0] = 'x';

- pid = fork(); + pid = do_fork(&self->procmap); ASSERT_NE(pid, -1); - - if (pid != 0) { - wait(NULL); + if (pid != 0) return; - } - - /* Child process below: */ - - /* Reopen for child. */ - ASSERT_EQ(close_procmap(&self->procmap), 0); - ASSERT_EQ(open_self_procmap(&self->procmap), 0);

/* unCOWing everything does not cause the AVC to go away. */ for (i = 0; i < 5 * page_size; i += page_size) @@ -386,8 +441,8 @@ TEST_F(merge, forked_source_vma) unsigned int page_size = self->page_size; char *carveout = self->carveout; struct procmap_fd *procmap = &self->procmap; - pid_t pid; char *ptr, *ptr2; + pid_t pid; int i;

/* @@ -408,19 +463,10 @@ TEST_F(merge, forked_source_vma) */ ptr[0] = 'x';

- pid = fork(); + pid = do_fork(&self->procmap); ASSERT_NE(pid, -1); - - if (pid != 0) { - wait(NULL); + if (pid != 0) return; - } - - /* Child process below: */ - - /* Reopen for child. */ - ASSERT_EQ(close_procmap(&self->procmap), 0); - ASSERT_EQ(open_self_procmap(&self->procmap), 0);

/* unCOWing everything does not cause the AVC to go away. */ for (i = 0; i < 5 * page_size; i += page_size) @@ -1171,10 +1217,11 @@ TEST_F(merge, mremap_correct_placed_faul ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 15 * page_size); }

-TEST_F(merge, mremap_faulted_to_unfaulted_prev) +TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev) { struct procmap_fd *procmap = &self->procmap; unsigned int page_size = self->page_size; + unsigned long offset; char *ptr_a, *ptr_b;

/* @@ -1197,6 +1244,14 @@ TEST_F(merge, mremap_faulted_to_unfaulte /* Fault it in. */ ptr_a[0] = 'x';

+ if (variant->forked) { + pid_t pid = do_fork(&self->procmap); + + ASSERT_NE(pid, -1); + if (pid != 0) + return; + } + /* * Now move it out of the way so we can place VMA B in position, * unfaulted. @@ -1220,16 +1275,19 @@ TEST_F(merge, mremap_faulted_to_unfaulte &self->carveout[page_size + 3 * page_size]); ASSERT_NE(ptr_a, MAP_FAILED);

- /* The VMAs should have merged. */ + /* The VMAs should have merged, if not forked. */ 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); + + offset = variant->forked ? 3 * page_size : 6 * page_size; + ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr_b + offset); }

-TEST_F(merge, mremap_faulted_to_unfaulted_next) +TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_next) { struct procmap_fd *procmap = &self->procmap; unsigned int page_size = self->page_size; + unsigned long offset; char *ptr_a, *ptr_b;

/* @@ -1253,6 +1311,14 @@ TEST_F(merge, mremap_faulted_to_unfaulte /* Fault it in. */ ptr_a[0] = 'x';

+ if (variant->forked) { + pid_t pid = do_fork(&self->procmap); + + ASSERT_NE(pid, -1); + if (pid != 0) + return; + } + /* * Now move it out of the way so we can place VMA B in position, * unfaulted. @@ -1276,16 +1342,18 @@ TEST_F(merge, mremap_faulted_to_unfaulte &self->carveout[page_size]); ASSERT_NE(ptr_a, MAP_FAILED);

- /* The VMAs should have merged. */ + /* The VMAs should have merged, if not forked. */ 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); + offset = variant->forked ? 3 * page_size : 6 * page_size; + ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr_a + offset); }

-TEST_F(merge, mremap_faulted_to_unfaulted_prev_unfaulted_next) +TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev_unfaulted_next) { struct procmap_fd *procmap = &self->procmap; unsigned int page_size = self->page_size; + unsigned long offset; char *ptr_a, *ptr_b, *ptr_c;

/* @@ -1307,6 +1375,14 @@ TEST_F(merge, mremap_faulted_to_unfaulte /* Fault it in. */ ptr_b[0] = 'x';

+ if (variant->forked) { + pid_t pid = do_fork(&self->procmap); + + ASSERT_NE(pid, -1); + if (pid != 0) + return; + } + /* * Now move it out of the way so we can place VMAs A, C in position, * unfaulted. @@ -1337,13 +1413,21 @@ TEST_F(merge, mremap_faulted_to_unfaulte &self->carveout[page_size + 3 * page_size]); ASSERT_NE(ptr_b, MAP_FAILED);

- /* The VMAs should have merged. */ + /* The VMAs should have merged, if not forked. */ 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); + offset = variant->forked ? 3 * page_size : 9 * page_size; + ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr_a + offset); + + /* If forked, B and C should also not have merged. */ + if (variant->forked) { + 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 + 3 * page_size); + } }

-TEST_F(merge, mremap_faulted_to_unfaulted_prev_faulted_next) +TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev_faulted_next) { struct procmap_fd *procmap = &self->procmap; unsigned int page_size = self->page_size; @@ -1373,6 +1457,14 @@ TEST_F(merge, mremap_faulted_to_unfaulte /* Fault it in. */ ptr_bc[0] = 'x';

+ if (variant->forked) { + pid_t pid = do_fork(&self->procmap); + + ASSERT_NE(pid, -1); + if (pid != 0) + return; + } + /* * 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 @@ -1397,10 +1489,16 @@ TEST_F(merge, mremap_faulted_to_unfaulte &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); + /* The VMAs should have merged. A,B,C if unforked, B, C if forked. */ + if (variant->forked) { + 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); + } else { + 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 _

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

mm-vma-fix-anon_vma-uaf-on-mremap-faulted-unfaulted-merge.patch tools-testing-selftests-add-tests-for-tgt-src-mremap-merges.patch mm-vma-enforce-vma-fork-limit-on-unfaultedfaulted-mremap-merge-too.patch tools-testing-selftests-add-forked-un-faulted-vma-merge-tests.patch