The patch titled
Subject: selftests/vm: anon_cow: add mprotect() optimization tests
has been added to the -mm mm-unstable branch. Its filename is
selftests-vm-anon_cow-add-mprotect-optimization-tests.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-vm-anon_cow-add-mprotect-optimization-tests.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: David Hildenbrand <david@xxxxxxxxxx>
Subject: selftests/vm: anon_cow: add mprotect() optimization tests
Date: Tue, 8 Nov 2022 18:46:52 +0100
Let's extend the test to cover the possible mprotect() optimization when
removing write-protection. mprotect() must not allow write-access to a
COW-shared page by accident.
Link: https://lkml.kernel.org/r/20221108174652.198904-8-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/vm/anon_cow.c | 49 ++++++++++++++++++++++--
1 file changed, 46 insertions(+), 3 deletions(-)
--- a/tools/testing/selftests/vm/anon_cow.c~selftests-vm-anon_cow-add-mprotect-optimization-tests
+++ a/tools/testing/selftests/vm/anon_cow.c
@@ -190,7 +190,8 @@ static int child_vmsplice_memcmp_fn(char
typedef int (*child_fn)(char *mem, size_t size, struct comm_pipes *comm_pipes);
-static void do_test_cow_in_parent(char *mem, size_t size, child_fn fn)
+static void do_test_cow_in_parent(char *mem, size_t size, bool do_mprotect,
+ child_fn fn)
{
struct comm_pipes comm_pipes;
char buf;
@@ -212,6 +213,22 @@ static void do_test_cow_in_parent(char *
while (read(comm_pipes.child_ready[0], &buf, 1) != 1)
;
+
+ if (do_mprotect) {
+ /*
+ * mprotect() optimizations might try avoiding
+ * write-faults by directly mapping pages writable.
+ */
+ ret = mprotect(mem, size, PROT_READ);
+ ret |= mprotect(mem, size, PROT_READ|PROT_WRITE);
+ if (ret) {
+ ksft_test_result_fail("mprotect() failed\n");
+ write(comm_pipes.parent_ready[1], "0", 1);
+ wait(&ret);
+ goto close_comm_pipes;
+ }
+ }
+
/* Modify the page. */
memset(mem, 0xff, size);
write(comm_pipes.parent_ready[1], "0", 1);
@@ -229,12 +246,22 @@ close_comm_pipes:
static void test_cow_in_parent(char *mem, size_t size)
{
- do_test_cow_in_parent(mem, size, child_memcmp_fn);
+ do_test_cow_in_parent(mem, size, false, child_memcmp_fn);
+}
+
+static void test_cow_in_parent_mprotect(char *mem, size_t size)
+{
+ do_test_cow_in_parent(mem, size, true, child_memcmp_fn);
}
static void test_vmsplice_in_child(char *mem, size_t size)
{
- do_test_cow_in_parent(mem, size, child_vmsplice_memcmp_fn);
+ do_test_cow_in_parent(mem, size, false, child_vmsplice_memcmp_fn);
+}
+
+static void test_vmsplice_in_child_mprotect(char *mem, size_t size)
+{
+ do_test_cow_in_parent(mem, size, true, child_vmsplice_memcmp_fn);
}
static void do_test_vmsplice_in_parent(char *mem, size_t size,
@@ -970,6 +997,14 @@ static const struct test_case test_cases
test_cow_in_parent,
},
/*
+ * Basic test, but do an additional mprotect(PROT_READ)+
+ * mprotect(PROT_READ|PROT_WRITE) in the parent before write access.
+ */
+ {
+ "Basic COW after fork() with mprotect() optimization",
+ test_cow_in_parent_mprotect,
+ },
+ /*
* vmsplice() [R/O GUP] + unmap in the child; modify in the parent. If
* we miss to break COW, the child observes modifications by the parent.
* This is CVE-2020-29374 reported by Jann Horn.
@@ -979,6 +1014,14 @@ static const struct test_case test_cases
test_vmsplice_in_child
},
/*
+ * vmsplice() test, but do an additional mprotect(PROT_READ)+
+ * mprotect(PROT_READ|PROT_WRITE) in the parent before write access.
+ */
+ {
+ "vmsplice() + unmap in child with mprotect() optimization",
+ test_vmsplice_in_child_mprotect
+ },
+ /*
* vmsplice() [R/O GUP] in parent before fork(), unmap in parent after
* fork(); modify in the child. If we miss to break COW, the parent
* observes modifications by the child.
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory.patch
selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory-fix.patch
selftests-vm-factor-out-pagemap_is_populated-into-vm_util.patch
selftests-vm-anon_cow-thp-tests.patch
selftests-vm-anon_cow-hugetlb-tests.patch
selftests-vm-anon_cow-add-liburing-test-cases.patch
selftests-vm-anon_cow-add-liburing-test-cases-fix.patch
mm-gup_test-start-stop-read-functionality-for-pin-longterm-test.patch
mm-gup_test-start-stop-read-functionality-for-pin-longterm-test-fix.patch
selftests-vm-anon_cow-add-r-o-longterm-tests-via-gup_test.patch
selftests-vm-add-ksm-unmerge-tests.patch
mm-pagewalk-dont-trigger-test_walk-in-walk_page_vma.patch
selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch
mm-ksm-simplify-break_ksm-to-not-rely-on-vm_fault_write.patch
mm-remove-vm_fault_write.patch
mm-ksm-fix-ksm-cow-breaking-with-userfaultfd-wp-via-fault_flag_unshare.patch
mm-pagewalk-add-walk_page_range_vma.patch
mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch
mm-gup-remove-foll_migration.patch
mm-mprotect-minor-can_change_pte_writable-cleanups.patch
mm-huge_memory-try-avoiding-write-faults-when-changing-pmd-protection.patch
mm-mprotect-factor-out-check-whether-manual-pte-write-upgrades-are-required.patch
mm-autonuma-use-can_change_ptepmd_writable-to-replace-savedwrite.patch
mm-remove-unused-savedwrite-infrastructure.patch
selftests-vm-anon_cow-add-mprotect-optimization-tests.patch
