[PATCH v2 2/8] selftests/mm: Skip sysmap_is_sealed when system mappings aren't sealed

[Chris Down <chris@chrisdown.name>]

Now that sysmap_is_sealed runs with the other mm tests, it also runs on
kernels built without CONFIG_MSEAL_SYSTEM_MAPPINGS, where it fails.
Userspace can't tell whether the option is enabled, but a sealed [vdso]
in a new process means that it is.

So let's use [vdso] as the reference: skip if it isn't sealed, and
otherwise expect the other system mappings to be sealed too, and [stack]
not to be.

Signed-off-by: Chris Down <chris@chrisdown.name>
---
 tools/testing/selftests/mm/run_vmtests.sh     |  7 +++++-
 tools/testing/selftests/mm/sysmap_is_sealed.c | 22 +++++++++++++++++++
 tools/testing/selftests/mm/vm_util.c          |  5 +++++
 tools/testing/selftests/mm/vm_util.h          |  1 +
 4 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 573da5006268..1134a2e82610 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -307,7 +307,12 @@ fi
 
 CATEGORY="mmap" run_test ./map_populate
 CATEGORY="mmap" run_test ./droppable
-CATEGORY="mmap" run_test ./sysmap_is_sealed
+if gzip -dcfq /proc/config.gz "/boot/config-$(uname -r)" 2>/dev/null |
+		grep -q "^CONFIG_MSEAL_SYSTEM_MAPPINGS=y"; then
+	CATEGORY="mmap" run_test ./sysmap_is_sealed
+else
+	CATEGORY="mmap" run_test ./sysmap_is_sealed -T expect_sealed
+fi
 
 CATEGORY="mlock" run_test ./mlock-random-test
 
diff --git a/tools/testing/selftests/mm/sysmap_is_sealed.c b/tools/testing/selftests/mm/sysmap_is_sealed.c
index cb0ca6ed7ebe..d5ab2b0d8ca7 100644
--- a/tools/testing/selftests/mm/sysmap_is_sealed.c
+++ b/tools/testing/selftests/mm/sysmap_is_sealed.c
@@ -10,9 +10,11 @@
 #include <unistd.h>
 #include <string.h>
 #include <stdbool.h>
+#include <sys/auxv.h>
 
 #include "kselftest.h"
 #include "kselftest_harness.h"
+#include "vm_util.h"
 
 #define VMFLAGS "VmFlags:"
 #define MSEAL_FLAGS "sl"
@@ -46,6 +48,23 @@ bool mapping_is_sealed(char *name, FILE *maps)
 	return false;
 }
 
+static bool sysmaps_sealed(void)
+{
+	void *vdso = (void *)getauxval(AT_SYSINFO_EHDR);
+
+	return vdso && check_vmflag_sealed(vdso);
+}
+
+/*
+ * Kernels built without CONFIG_MSEAL_SYSTEM_MAPPINGS don't seal system
+ * mappings either, so check_sealed skips if they aren't sealed. This fails
+ * instead, so run_vmtests.sh only runs it when that's set.
+ */
+TEST(expect_sealed)
+{
+	EXPECT_TRUE(sysmaps_sealed());
+}
+
 FIXTURE(basic) {
 	FILE *maps;
 };
@@ -107,6 +126,9 @@ FIXTURE_VARIANT_ADD(basic, stack) {
 
 TEST_F(basic, check_sealed)
 {
+	if (!sysmaps_sealed())
+		SKIP(return, "system mappings are not sealed");
+
 	if (!has_mapping(variant->name, self->maps)) {
 		SKIP(return, "could not find the mapping, %s",
 			variant->name);
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 8ef226107d78..6732f76b7e61 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -785,6 +785,11 @@ bool check_vmflag_guard(void *addr)
 	return check_vmflag(addr, "gu");
 }
 
+bool check_vmflag_sealed(void *addr)
+{
+	return check_vmflag(addr, "sl");
+}
+
 bool softdirty_supported(void)
 {
 	char *addr;
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index d32cb79d9905..0e94793b0d21 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -117,6 +117,7 @@ int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 bool check_vmflag_io(void *addr);
 bool check_vmflag_pfnmap(void *addr);
 bool check_vmflag_guard(void *addr);
+bool check_vmflag_sealed(void *addr);
 int open_procmap(pid_t pid, struct procmap_fd *procmap_out);
 int query_procmap(struct procmap_fd *procmap);
 bool find_vma_procmap(struct procmap_fd *procmap, void *address);
-- 
2.54.0