[PATCH RFC RFT 5/5] kselftest/clone3: Test shadow stack support

[Mark Brown]

Add basic test coverage for specifying the shadow stack for a newly
created thread via clone3(), including coverage of the newly extended
argument structure. We detect support for shadow stacks on the running
system by attempting to allocate a shadow stack page during initialisation
using map_shadow_stack().

Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 tools/testing/selftests/clone3/clone3.c           | 97 +++++++++++++++++++++++
 tools/testing/selftests/clone3/clone3_selftests.h |  5 ++
 2 files changed, 102 insertions(+)

diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index f1802db82e4e..33c35fdfcdfc 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -11,6 +11,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <sys/mman.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
 #include <sys/un.h>
@@ -21,6 +22,10 @@
 #include "../kselftest.h"
 #include "clone3_selftests.h"
 
+static bool shadow_stack_supported;
+static __u64 shadow_stack;
+static size_t max_supported_args_size;
+
 enum test_mode {
 	CLONE3_ARGS_NO_TEST,
 	CLONE3_ARGS_ALL_0,
@@ -28,6 +33,9 @@ enum test_mode {
 	CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG,
 	CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG,
 	CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
+	CLONE3_ARGS_SHADOW_STACK,
+	CLONE3_ARGS_SHADOW_STACK_SIZE_ONLY,
+	CLONE3_ARGS_SHADOW_STACK_POINTER_ONLY,
 };
 
 typedef bool (*filter_function)(void);
@@ -44,6 +52,28 @@ struct test {
 	filter_function filter;
 };
 
+#ifndef __NR_map_shadow_stack
+#define __NR_map_shadow_stack 453
+#endif
+
+static void test_shadow_stack_supported(void)
+{
+	shadow_stack = syscall(__NR_map_shadow_stack, 0, getpagesize(), 0);
+	if (shadow_stack == -1) {
+		ksft_print_msg("map_shadow_stack() not supported\n");
+	} else if ((void *)shadow_stack == MAP_FAILED) {
+		ksft_print_msg("Failed to map shadow stack\n");
+	} else {
+		ksft_print_msg("Shadow stack supportd\n");
+		shadow_stack_supported = true;
+	}
+
+	/* Dummy stack to use for validating error checks */
+	if (!shadow_stack_supported) {
+		shadow_stack = (__u64)malloc(getpagesize());
+	}
+}
+
 static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
 {
 	struct __clone_args args = {
@@ -89,6 +119,16 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
 	case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG:
 		args.exit_signal = 0x00000000000000f0ULL;
 		break;
+	case CLONE3_ARGS_SHADOW_STACK:
+		args.shadow_stack = shadow_stack;
+		args.shadow_stack_size = getpagesize();
+		break;
+	case CLONE3_ARGS_SHADOW_STACK_SIZE_ONLY:
+		args.shadow_stack_size = getpagesize();
+		break;
+	case CLONE3_ARGS_SHADOW_STACK_POINTER_ONLY:
+		args.shadow_stack = shadow_stack;
+		break;
 	}
 
 	memcpy(&args_ext.args, &args, sizeof(struct __clone_args));
@@ -167,6 +207,26 @@ static bool not_root(void)
 	return false;
 }
 
+static bool have_shadow_stack(void)
+{
+	if (shadow_stack_supported) {
+		ksft_print_msg("Shadow stack supported\n");
+		return true;
+	}
+
+	return false;
+}
+
+static bool no_shadow_stack(void)
+{
+	if (!shadow_stack_supported) {
+		ksft_print_msg("Shadow stack not supported\n");
+		return true;
+	}
+
+	return false;
+}
+
 static size_t page_size_plus_8(void)
 {
 	return getpagesize() + 8;
@@ -309,6 +369,42 @@ static const struct test tests[] = {
 		.expected = -EINVAL,
 		.test_mode = CLONE3_ARGS_NO_TEST,
 	},
+	{
+		.name = "Shadow stack on system with shadow stack",
+		.flags = 0,
+		.size = 0,
+		.expected = 0,
+		.e2big_valid = true,
+		.test_mode = CLONE3_ARGS_SHADOW_STACK,
+		.filter = no_shadow_stack,
+	},
+	{
+		.name = "Shadow stack with only size specified",
+		.flags = 0,
+		.size = 0,
+		.expected = -EINVAL,
+		.e2big_valid = true,
+		.test_mode = CLONE3_ARGS_SHADOW_STACK_SIZE_ONLY,
+		.filter = no_shadow_stack,
+	},
+	{
+		.name = "Shadow stack with only pointer specified",
+		.flags = 0,
+		.size = 0,
+		.expected = -EINVAL,
+		.e2big_valid = true,
+		.test_mode = CLONE3_ARGS_SHADOW_STACK_POINTER_ONLY,
+		.filter = no_shadow_stack,
+	},
+	{
+		.name = "Shadow stack on system without shadow stack",
+		.flags = 0,
+		.size = 0,
+		.expected = -EINVAL,
+		.e2big_valid = true,
+		.test_mode = CLONE3_ARGS_SHADOW_STACK,
+		.filter = have_shadow_stack,
+	},
 };
 
 int main(int argc, char *argv[])
@@ -319,6 +415,7 @@ int main(int argc, char *argv[])
 	ksft_print_header();
 	ksft_set_plan(ARRAY_SIZE(tests));
 	test_clone3_supported();
+	test_shadow_stack_supported();
 
 	for (i = 0; i < ARRAY_SIZE(tests); i++)
 		test_clone3(&tests[i]);
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
index e81ffaaee02b..a77db460211b 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -43,6 +43,11 @@ struct __clone_args {
 	__aligned_u64 cgroup;
 #ifndef CLONE_ARGS_SIZE_VER2
 #define CLONE_ARGS_SIZE_VER2 88	/* sizeof third published struct */
+#endif
+	__aligned_u64 shadow_stack;
+	__aligned_u64 shadow_stack_size;
+#ifndef CLONE_ARGS_SIZE_VER3
+#define CLONE_ARGS_SIZE_VER3 104 /* sizeof fourth published struct */
 #endif
 };
 

-- 
2.30.2