[PATCH v7 5/7] selftests: Add kselftest for syscall user dispatch

Gabriel Krisman Bertazi
2020-11-18T03:29:29Z

Implement functionality tests for syscall user dispatch. In order to
make the test portable, refrain from open coding syscall dispatchers and
calculating glibc memory ranges.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Acked-by: Kees Cook <keescook@chromium.org>

---
Changes since v6:
- Update selftests to reflect {offset,len} api change
Changes since v4:
- Update bad selector test to reflect change in API

Changes since v3:
- Sort entry in Makefile
- Add SPDX header
- Use __NR_syscalls if available
---
tools/testing/selftests/Makefile | 1 +
.../syscall_user_dispatch/.gitignore | 3 +
.../selftests/syscall_user_dispatch/Makefile | 9 +
.../selftests/syscall_user_dispatch/config | 1 +
.../syscall_user_dispatch/sud_test.c | 310 ++++++++++++++++++
5 files changed, 324 insertions(+)
create mode 100644 tools/testing/selftests/syscall_user_dispatch/.gitignore
create mode 100644 tools/testing/selftests/syscall_user_dispatch/Makefile
create mode 100644 tools/testing/selftests/syscall_user_dispatch/config
create mode 100644 tools/testing/selftests/syscall_user_dispatch/sud_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index d9c283503159..96d5682fb9d8 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -56,6 +56,7 @@ TARGETS += sparc64
TARGETS += splice
TARGETS += static_keys
TARGETS += sync
+TARGETS += syscall_user_dispatch
TARGETS += sysctl
TARGETS += tc-testing
TARGETS += timens
diff --git a/tools/testing/selftests/syscall_user_dispatch/.gitignore b/tools/testing/selftests/syscall_user_dispatch/.gitignore
new file mode 100644
index 000000000000..f539615ad5da
--- /dev/null
+++ b/tools/testing/selftests/syscall_user_dispatch/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+sud_test
+sud_benchmark
diff --git a/tools/testing/selftests/syscall_user_dispatch/Makefile b/tools/testing/selftests/syscall_user_dispatch/Makefile
new file mode 100644
index 000000000000..8e15fa42bcda
--- /dev/null
+++ b/tools/testing/selftests/syscall_user_dispatch/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0
+top_srcdir = ../../../..
+INSTALL_HDR_PATH = $(top_srcdir)/usr
+LINUX_HDR_PATH = $(INSTALL_HDR_PATH)/include/
+
+CFLAGS += -Wall -I$(LINUX_HDR_PATH)
+
+TEST_GEN_PROGS := sud_test
+include ../lib.mk
diff --git a/tools/testing/selftests/syscall_user_dispatch/config b/tools/testing/selftests/syscall_user_dispatch/config
new file mode 100644
index 000000000000..039e303e59d7
--- /dev/null
+++ b/tools/testing/selftests/syscall_user_dispatch/config
@@ -0,0 +1 @@
+CONFIG_GENERIC_ENTRY=y
diff --git a/tools/testing/selftests/syscall_user_dispatch/sud_test.c b/tools/testing/selftests/syscall_user_dispatch/sud_test.c
new file mode 100644
index 000000000000..6498b050ef89
--- /dev/null
+++ b/tools/testing/selftests/syscall_user_dispatch/sud_test.c
@@ -0,0 +1,310 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2020 Collabora Ltd.
+ *
+ * Test code for syscall user dispatch
+ */
+
+#define _GNU_SOURCE
+#include <sys/prctl.h>
+#include <sys/sysinfo.h>
+#include <sys/syscall.h>
+#include <signal.h>
+
+#include <asm/unistd.h>
+#include "../kselftest_harness.h"
+
+#ifndef PR_SET_SYSCALL_USER_DISPATCH
+# define PR_SET_SYSCALL_USER_DISPATCH 59
+# define PR_SYS_DISPATCH_OFF 0
+# define PR_SYS_DISPATCH_ON 1
+#endif
+
+#ifndef SYS_USER_DISPATCH
+# define SYS_USER_DISPATCH 2
+#endif
+
+#ifdef __NR_syscalls
+# define MAGIC_SYSCALL_1 (__NR_syscalls + 1) /* Bad Linux syscall number */
+#else
+# define MAGIC_SYSCALL_1 (0xff00) /* Bad Linux syscall number */
+#endif
+
+#define SYSCALL_DISPATCH_ON(x) ((x) = 1)
+#define SYSCALL_DISPATCH_OFF(x) ((x) = 0)
+
+/* Test Summary:
+ *
+ * - dispatch_trigger_sigsys: Verify if PR_SET_SYSCALL_USER_DISPATCH is
+ * able to trigger SIGSYS on a syscall.
+ *
+ * - bad_selector: Test that a bad selector value triggers SIGSYS with
+ * si_errno EINVAL.
+ *
+ * - bad_prctl_param: Test that the API correctly rejects invalid
+ * parameters on prctl
+ *
+ * - dispatch_and_return: Test that a syscall is selectively dispatched
+ * to userspace depending on the value of selector.
+ *
+ * - disable_dispatch: Test that the PR_SYS_DISPATCH_OFF correctly
+ * disables the dispatcher
+ *
+ * - direct_dispatch_range: Test that a syscall within the allowed range
+ * can bypass the dispatcher.
+ */
+
+TEST_SIGNAL(dispatch_trigger_sigsys, SIGSYS)
+{
+ char sel = 0;
+ struct sysinfo info;
+ int ret;
+
+ ret = sysinfo(&info);
+ ASSERT_EQ(0, ret);
+
+ ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &sel);
+ ASSERT_EQ(0, ret) {
+ TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
+ }
+
+ SYSCALL_DISPATCH_ON(sel);
+
+ sysinfo(&info);
+
+ EXPECT_FALSE(true) {
+ TH_LOG("Unreachable!");
+ }
+}
+
+TEST(bad_prctl_param)
+{
+ char sel = 0;
+ int op;
+
+ /* Invalid op */
+ op = -1;
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0, 0, &sel);
+ ASSERT_EQ(EINVAL, errno);
+
+ /* PR_SYS_DISPATCH_OFF */
+ op = PR_SYS_DISPATCH_OFF;
+
+ /* offset != 0 */
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, 0);
+ EXPECT_EQ(EINVAL, errno);
+
+ /* len != 0 */
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0);
+ EXPECT_EQ(EINVAL, errno);
+
+ /* sel != NULL */
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel);
+ EXPECT_EQ(EINVAL, errno);
+
+ /* Valid parameter */
+ errno = 0;
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, 0x0);
+ EXPECT_EQ(0, errno);
+
+ /* PR_SYS_DISPATCH_ON */
+ op = PR_SYS_DISPATCH_ON;
+
+ /* Dispatcher region is bad (offset > 0 && len == 0) */
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, &sel);
+ EXPECT_EQ(EINVAL, errno);
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, -1L, 0x0, &sel);
+ EXPECT_EQ(EINVAL, errno);
+
+ /* Invalid selector */
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x1, (void *) -1);
+ ASSERT_EQ(EFAULT, errno);
+
+ /*
+ * Dispatcher range overflows unsigned long
+ */
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 1, -1L, &sel);
+ ASSERT_EQ(EINVAL, errno) {
+ TH_LOG("Should reject bad syscall range");
+ }
+
+ /*
+ * Allowed range overflows usigned long
+ */
+ prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, -1L, 0x1, &sel);
+ ASSERT_EQ(EINVAL, errno) {
+ TH_LOG("Should reject bad syscall range");
+ }
+}
+
+/*
+ * Use global selector for handle_sigsys tests, to avoid passing
+ * selector to signal handler
+ */
+char glob_sel;
+int nr_syscalls_emulated;
+int si_code;
+int si_errno;
+
+static void handle_sigsys(int sig, siginfo_t *info, void *ucontext)
+{
+ si_code = info->si_code;
+ si_errno = info->si_errno;
+
+ if (info->si_syscall == MAGIC_SYSCALL_1)
+ nr_syscalls_emulated++;
+
+ /* In preparation for sigreturn. */
+ SYSCALL_DISPATCH_OFF(glob_sel);
+}
+
+TEST(dispatch_and_return)
+{
+ long ret;
+ struct sigaction act;
+ sigset_t mask;
+
+ glob_sel = 0;
+ nr_syscalls_emulated = 0;
+ si_code = 0;
+ si_errno = 0;
+
+ memset(&act, 0, sizeof(act));
+ sigemptyset(&mask);
+
+ act.sa_sigaction = handle_sigsys;
+ act.sa_flags = SA_SIGINFO;
+ act.sa_mask = mask;
+
+ ret = sigaction(SIGSYS, &act, NULL);
+ ASSERT_EQ(0, ret);
+
+ /* Make sure selector is good prior to prctl. */
+ SYSCALL_DISPATCH_OFF(glob_sel);
+
+ ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &glob_sel);
+ ASSERT_EQ(0, ret) {
+ TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
+ }
+
+ /* MAGIC_SYSCALL_1 doesn't exist. */
+ SYSCALL_DISPATCH_OFF(glob_sel);
+ ret = syscall(MAGIC_SYSCALL_1);
+ EXPECT_EQ(-1, ret) {
+ TH_LOG("Dispatch triggered unexpectedly");
+ }
+
+ /* MAGIC_SYSCALL_1 should be emulated. */
+ nr_syscalls_emulated = 0;
+ SYSCALL_DISPATCH_ON(glob_sel);
+
+ ret = syscall(MAGIC_SYSCALL_1);
+ EXPECT_EQ(MAGIC_SYSCALL_1, ret) {
+ TH_LOG("Failed to intercept syscall");
+ }
+ EXPECT_EQ(1, nr_syscalls_emulated) {
+ TH_LOG("Failed to emulate syscall");
+ }
+ ASSERT_EQ(SYS_USER_DISPATCH, si_code) {
+ TH_LOG("Bad si_code in SIGSYS");
+ }
+ ASSERT_EQ(0, si_errno) {
+ TH_LOG("Bad si_errno in SIGSYS");
+ }
+}
+
+TEST_SIGNAL(bad_selector, SIGSYS)
+{
+ long ret;
+ struct sigaction act;
+ sigset_t mask;
+ struct sysinfo info;
+
+ glob_sel = 0;
+ nr_syscalls_emulated = 0;
+ si_code = 0;
+ si_errno = 0;
+
+ memset(&act, 0, sizeof(act));
+ sigemptyset(&mask);
+
+ act.sa_sigaction = handle_sigsys;
+ act.sa_flags = SA_SIGINFO;
+ act.sa_mask = mask;
+
+ ret = sigaction(SIGSYS, &act, NULL);
+ ASSERT_EQ(0, ret);
+
+ /* Make sure selector is good prior to prctl. */
+ SYSCALL_DISPATCH_OFF(glob_sel);
+
+ ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &glob_sel);
+ ASSERT_EQ(0, ret) {
+ TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
+ }
+
+ glob_sel = -1;
+
+ sysinfo(&info);
+
+ /* Even though it is ready to catch SIGSYS, the signal is
+ * supposed to be uncatchable.
+ */
+
+ EXPECT_FALSE(true) {
+ TH_LOG("Unreachable!");
+ }
+}
+
+TEST(disable_dispatch)
+{
+ int ret;
+ struct sysinfo info;
+ char sel = 0;
+
+ ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &sel);
+ ASSERT_EQ(0, ret) {
+ TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
+ }
+
+ /* MAGIC_SYSCALL_1 doesn't exist. */
+ SYSCALL_DISPATCH_OFF(glob_sel);
+
+ ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_OFF, 0, 0, 0);
+ EXPECT_EQ(0, ret) {
+ TH_LOG("Failed to unset syscall user dispatch");
+ }
+
+ /* Shouldn't have any effect... */
+ SYSCALL_DISPATCH_ON(glob_sel);
+
+ ret = syscall(__NR_sysinfo, &info);
+ EXPECT_EQ(0, ret) {
+ TH_LOG("Dispatch triggered unexpectedly");
+ }
+}
+
+TEST(direct_dispatch_range)
+{
+ int ret = 0;
+ struct sysinfo info;
+ char sel = 0;
+
+ /*
+ * Instead of calculating libc addresses; allow the entire
+ * memory map and lock the selector.
+ */
+ ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, -1L, &sel);
+ ASSERT_EQ(0, ret) {
+ TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
+ }
+
+ SYSCALL_DISPATCH_ON(sel);
+
+ ret = sysinfo(&info);
+ ASSERT_EQ(0, ret) {
+ TH_LOG("Dispatch triggered unexpectedly");
+ }
+}
+
+TEST_HARNESS_MAIN
--
2.29.2