[PATCH RFT v4 5/5] kselftest/clone3: Test shadow stack support

[Mark Brown <broonie@kernel.org>]

Add basic test coverage for specifying the shadow stack for a newly
created thread via clone3(), including coverage of the newly extended
argument structure.

In order to facilitate testing on systems without userspace shadow stack
support we manually enable shadow stacks on startup, this is architecture
specific due to the use of an arch_prctl() on x86. Due to interactions with
potential userspace locking of features we actually detect support for
shadow stacks on the running system by attempting to allocate a shadow
stack page during initialisation using map_shadow_stack(), warning if this
succeeds when the enable failed.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/clone3/clone3.c           | 117 ++++++++++++++++++++++
 tools/testing/selftests/clone3/clone3_selftests.h |   7 ++
 2 files changed, 124 insertions(+)

diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index 6adbfd14c841..dbe52582573c 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_enabled;
+static bool shadow_stack_supported;
+static size_t max_supported_args_size;
+
 enum test_mode {
 	CLONE3_ARGS_NO_TEST,
 	CLONE3_ARGS_ALL_0,
@@ -28,6 +33,7 @@ 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,
 };
 
 typedef bool (*filter_function)(void);
@@ -44,6 +50,36 @@ struct test {
 	filter_function filter;
 };
 
+#ifndef __NR_map_shadow_stack
+#define __NR_map_shadow_stack 453
+#endif
+
+/*
+ * We check for shadow stack support by attempting to use
+ * map_shadow_stack() since features may have been locked by the
+ * dynamic linker resulting in spurious errors when we attempt to
+ * enable on startup.  We warn if the enable failed.
+ */
+static void test_shadow_stack_supported(void)
+{
+        long shadow_stack;
+
+	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;
+
+		if (!shadow_stack_enabled)
+			ksft_print_msg("Mapped but did not enable shadow stack\n");
+
+		munmap((void *)shadow_stack, getpagesize());
+	}
+}
+
 static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
 {
 	struct __clone_args args = {
@@ -89,6 +125,9 @@ 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_size = getpagesize();
+		break;
 	}
 
 	memcpy(&args_ext.args, &args, sizeof(struct __clone_args));
@@ -179,6 +218,26 @@ static bool no_timenamespace(void)
 	return true;
 }
 
+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;
@@ -322,16 +381,74 @@ static const struct test tests[] = {
 		.expected = -EINVAL,
 		.test_mode = CLONE3_ARGS_NO_TEST,
 	},
+	{
+		.name = "Shadow stack on system with shadow stack",
+		.flags = CLONE_VM,
+		.size = 0,
+		.expected = 0,
+		.e2big_valid = true,
+		.test_mode = CLONE3_ARGS_SHADOW_STACK,
+		.filter = no_shadow_stack,
+	},
+	{
+		.name = "Shadow stack on system without shadow stack",
+		.flags = CLONE_VM,
+		.size = 0,
+		.expected = -EINVAL,
+		.e2big_valid = true,
+		.test_mode = CLONE3_ARGS_SHADOW_STACK,
+		.filter = have_shadow_stack,
+	},
 };
 
+#ifdef __x86_64__
+#define ARCH_SHSTK_ENABLE	0x5001
+#define ARCH_SHSTK_SHSTK	(1ULL <<  0)
+
+#define ARCH_PRCTL(arg1, arg2)					\
+({								\
+	long _ret;						\
+	register long _num  asm("eax") = __NR_arch_prctl;	\
+	register long _arg1 asm("rdi") = (long)(arg1);		\
+	register long _arg2 asm("rsi") = (long)(arg2);		\
+								\
+	asm volatile (						\
+		"syscall\n"					\
+		: "=a"(_ret)					\
+		: "r"(_arg1), "r"(_arg2),			\
+		  "0"(_num)					\
+		: "rcx", "r11", "memory", "cc"			\
+	);							\
+	_ret;							\
+})
+
+#define ENABLE_SHADOW_STACK
+static inline void enable_shadow_stack(void)
+{
+	int ret = ARCH_PRCTL(ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK);
+	if (ret == 0)
+		shadow_stack_enabled = true;
+}
+
+#endif
+
+#ifndef ENABLE_SHADOW_STACK
+static void enable_shadow_stack(void)
+{
+}
+#endif
+
 int main(int argc, char *argv[])
 {
 	size_t size;
 	int i;
 
+	enable_shadow_stack();
+
 	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 3d2663fe50ba..2e06127091f5 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -31,6 +31,13 @@ struct __clone_args {
 	__aligned_u64 set_tid;
 	__aligned_u64 set_tid_size;
 	__aligned_u64 cgroup;
+#ifndef CLONE_ARGS_SIZE_VER2
+#define CLONE_ARGS_SIZE_VER2 88	/* sizeof third published struct */
+#endif
+	__aligned_u64 shadow_stack_size;
+#ifndef CLONE_ARGS_SIZE_VER3
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
+#endif
 };
 
 static pid_t sys_clone3(struct __clone_args *args, size_t size)

-- 
2.30.2