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.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
tools/testing/selftests/vm/anon_cow.c | 49 +++++++++++++++++++++++++--
1 file changed, 46 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/vm/anon_cow.c b/tools/testing/selftests/vm/anon_cow.c
index 705bd0b3db11..bbb251eb5025 100644
--- a/tools/testing/selftests/vm/anon_cow.c
+++ b/tools/testing/selftests/vm/anon_cow.c
@@ -190,7 +190,8 @@ static int child_vmsplice_memcmp_fn(char *mem, size_t size,
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 *mem, size_t size, child_fn fn)
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 @@ static void do_test_cow_in_parent(char *mem, size_t size, child_fn fn)
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,
@@ -969,6 +996,14 @@ static const struct test_case test_cases[] = {
"Basic COW after fork()",
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.
@@ -978,6 +1013,14 @@ static const struct test_case test_cases[] = {
"vmsplice() + unmap in child",
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
--
2.38.1
