diff mbox series

[v4,31/36] kselftest/arm64: Add very basic GCS test program

Message ID 20230807-arm64-gcs-v4-31-68cfa37f9069@kernel.org
State Superseded
Headers show
Series arm64/gcs: Provide support for GCS in userspace | expand

Commit Message

Mark Brown Aug. 7, 2023, 10 p.m. UTC
This test program just covers the basic GCS ABI, covering aspects of the
ABI as standalone features without attempting to integrate things.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/arm64/Makefile        |   2 +-
 tools/testing/selftests/arm64/gcs/.gitignore  |   1 +
 tools/testing/selftests/arm64/gcs/Makefile    |  18 ++
 tools/testing/selftests/arm64/gcs/basic-gcs.c | 356 ++++++++++++++++++++++++++
 tools/testing/selftests/arm64/gcs/gcs-util.h  |  87 +++++++
 5 files changed, 463 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/tools/testing/selftests/arm64/Makefile b/tools/testing/selftests/arm64/Makefile
index 28b93cab8c0d..22029e60eff3 100644
--- a/tools/testing/selftests/arm64/Makefile
+++ b/tools/testing/selftests/arm64/Makefile
@@ -4,7 +4,7 @@ 
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)
 
 ifneq (,$(filter $(ARCH),aarch64 arm64))
-ARM64_SUBTARGETS ?= tags signal pauth fp mte bti abi
+ARM64_SUBTARGETS ?= tags signal pauth fp mte bti abi gcs
 else
 ARM64_SUBTARGETS :=
 endif
diff --git a/tools/testing/selftests/arm64/gcs/.gitignore b/tools/testing/selftests/arm64/gcs/.gitignore
new file mode 100644
index 000000000000..0e5e695ecba5
--- /dev/null
+++ b/tools/testing/selftests/arm64/gcs/.gitignore
@@ -0,0 +1 @@ 
+basic-gcs
diff --git a/tools/testing/selftests/arm64/gcs/Makefile b/tools/testing/selftests/arm64/gcs/Makefile
new file mode 100644
index 000000000000..61a30f483429
--- /dev/null
+++ b/tools/testing/selftests/arm64/gcs/Makefile
@@ -0,0 +1,18 @@ 
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2023 ARM Limited
+#
+# In order to avoid interaction with the toolchain and dynamic linker the
+# portions of these tests that interact with the GCS are implemented using
+# nolibc.
+#
+
+TEST_GEN_PROGS := basic-gcs
+
+include ../../lib.mk
+
+$(OUTPUT)/basic-gcs: basic-gcs.c
+	$(CC) -g -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
+		-static -include ../../../../include/nolibc/nolibc.h \
+		-I../../../../../usr/include \
+		-std=gnu99 -I../.. -g \
+		-ffreestanding -Wall $^ -o $@ -lgcc
diff --git a/tools/testing/selftests/arm64/gcs/basic-gcs.c b/tools/testing/selftests/arm64/gcs/basic-gcs.c
new file mode 100644
index 000000000000..0fac554a3c4d
--- /dev/null
+++ b/tools/testing/selftests/arm64/gcs/basic-gcs.c
@@ -0,0 +1,356 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 ARM Limited.
+ */
+
+#include <limits.h>
+#include <stdbool.h>
+
+#include <linux/prctl.h>
+
+#include <sys/mman.h>
+#include <asm/mman.h>
+
+#include "kselftest.h"
+#include "gcs-util.h"
+
+/* nolibc doesn't have sysconf(), just hard code the maximum */
+static size_t page_size = 65536;
+
+static  __attribute__((noinline)) void valid_gcs_function(void)
+{
+	/* Do something the compiler can't optimise out */
+	my_syscall1(__NR_prctl, PR_SVE_GET_VL);
+}
+
+static inline int gcs_set_status(unsigned long mode)
+{
+	bool enabling = mode & PR_SHADOW_STACK_ENABLE;
+	int ret;
+	unsigned long new_mode;
+
+	/*
+	 * The prctl takes 1 argument but we need to ensure that the
+	 * other 3 values passed in registers to the syscall are zero
+	 * since the kernel validates them.
+	 */
+	ret = my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, mode,
+			  0, 0, 0);
+
+	if (ret == 0) {
+		ret = my_syscall5(__NR_prctl, PR_GET_SHADOW_STACK_STATUS,
+				  &new_mode, 0, 0, 0);
+		if (ret == 0) {
+			if (new_mode != mode) {
+				ksft_print_msg("Mode set to %x not %x\n",
+					       new_mode, mode);
+				ret = -EINVAL;
+			}
+		} else {
+			ksft_print_msg("Failed to validate mode: %d\n", ret);
+		}
+
+		if (enabling != chkfeat_gcs()) {
+			ksft_print_msg("%senabled by prctl but %senabled in CHKFEAT\n",
+				       enabling ? "" : "not ",
+				       chkfeat_gcs() ? "" : "not ");
+			ret = -EINVAL;
+		}
+	}
+
+	return ret;
+}
+
+/* Try to read the status */
+static bool read_status(void)
+{
+	unsigned long state;
+	int ret;
+
+	ret = my_syscall5(__NR_prctl, PR_GET_SHADOW_STACK_STATUS,
+			  &state, 0, 0, 0);
+	if (ret != 0) {
+		ksft_print_msg("Failed to read state: %d\n", ret);
+		return false;
+	}
+
+	return state & PR_SHADOW_STACK_ENABLE;
+}
+
+/* Just a straight enable */
+static bool base_enable(void)
+{
+	int ret;
+
+	ret = gcs_set_status(PR_SHADOW_STACK_ENABLE);
+	if (ret) {
+		ksft_print_msg("PR_SHADOW_STACK_ENABLE failed %d\n", ret);
+		return false;
+	}
+
+	return true;
+}
+
+/* Check we can read GCSPR_EL0 when GCS is enabled */
+static bool read_gcspr_el0(void)
+{
+	unsigned long *gcspr_el0;
+
+	ksft_print_msg("GET GCSPR\n");
+	gcspr_el0 = get_gcspr();
+	ksft_print_msg("GCSPR_EL0 is %p\n", gcspr_el0);
+
+	return true;
+}
+
+/* Also allow writes to stack */
+static bool enable_writeable(void)
+{
+	int ret;
+
+	ret = gcs_set_status(PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE);
+	if (ret) {
+		ksft_print_msg("PR_SHADOW_STACK_ENABLE writeable failed: %d\n", ret);
+		return false;
+	}
+
+	ret = gcs_set_status(PR_SHADOW_STACK_ENABLE);
+	if (ret) {
+		ksft_print_msg("failed to restore plain enable %d\n", ret);
+		return false;
+	}
+
+	return true;
+}
+
+/* Also allow writes to stack */
+static bool enable_push_pop(void)
+{
+	int ret;
+
+	ret = gcs_set_status(PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_PUSH);
+	if (ret) {
+		ksft_print_msg("PR_SHADOW_STACK_ENABLE with push failed: %d\n",
+			       ret);
+		return false;
+	}
+
+	ret = gcs_set_status(PR_SHADOW_STACK_ENABLE);
+	if (ret) {
+		ksft_print_msg("failed to restore plain enable %d\n", ret);
+		return false;
+	}
+
+	return true;
+}
+
+/* Enable GCS and allow everything */
+static bool enable_all(void)
+{
+	int ret;
+
+	ret = gcs_set_status(PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_PUSH |
+			     PR_SHADOW_STACK_WRITE);
+	if (ret) {
+		ksft_print_msg("PR_SHADOW_STACK_ENABLE with everything failed: %d\n",
+			       ret);
+		return false;
+	}
+
+	ret = gcs_set_status(PR_SHADOW_STACK_ENABLE);
+	if (ret) {
+		ksft_print_msg("failed to restore plain enable %d\n", ret);
+		return false;
+	}
+
+	return true;
+}
+
+static bool enable_invalid(void)
+{
+	int ret = gcs_set_status(ULONG_MAX);
+	if (ret == 0) {
+		ksft_print_msg("GCS_SET_STATUS %lx succeeded\n", ULONG_MAX);
+		return false;
+	}
+
+	return true;
+}
+
+/* Map a GCS */
+static bool map_guarded_stack(void)
+{
+	int ret;
+	uint64_t *buf;
+	uint64_t expected_cap;
+	int elem;
+	bool pass = true;
+
+	buf = (void *)my_syscall3(__NR_map_shadow_stack, 0, page_size,
+				  SHADOW_STACK_SET_MARKER |
+				  SHADOW_STACK_SET_TOKEN);
+	if (buf == MAP_FAILED) {
+		ksft_print_msg("Failed to map %d byte GCS: %d\n",
+			       page_size, errno);
+		return false;
+	}
+	ksft_print_msg("Mapped GCS at %p-%p\n", buf,
+		       (uint64_t)buf + page_size);
+
+	/* The top of the newly allocated region should be 0 */
+	elem = (page_size / sizeof(uint64_t)) - 1;
+	if (buf[elem]) {
+		ksft_print_msg("Last entry is 0x%lx not 0x0\n", buf[elem]);
+		pass = false;
+	}
+
+	/* Then a valid cap token */
+	elem--;
+	expected_cap = ((uint64_t)buf + page_size - 16);
+	expected_cap &= GCS_CAP_ADDR_MASK;
+	expected_cap |= GCS_CAP_VALID_TOKEN;
+	if (buf[elem] != expected_cap) {
+		ksft_print_msg("Cap entry is 0x%lx not 0x%lx\n",
+			       buf[elem], expected_cap);
+		pass = false;
+	}
+	ksft_print_msg("cap token is 0x%lx\n", buf[elem]);
+
+	/* The rest should be zeros */
+	for (elem = 0; elem < page_size / sizeof(uint64_t) - 2; elem++) {
+		if (!buf[elem])
+			continue;
+		ksft_print_msg("GCS slot %d is 0x%lx not 0x0\n",
+			       elem, buf[elem]);
+		pass = false;
+	}
+
+	ret = munmap(buf, page_size);
+	if (ret != 0) {
+		ksft_print_msg("Failed to unmap %d byte GCS: %d\n",
+			       page_size, errno);
+		pass = false;
+	}
+
+	return pass;
+}
+
+/* A fork()ed process can run */
+static bool test_fork(void)
+{
+	unsigned long child_mode;
+	int ret, status;
+	pid_t pid;
+	bool pass = true;
+
+	pid = fork();
+	if (pid == -1) {
+		ksft_print_msg("fork() failed: %d\n", errno);
+		pass = false;
+		goto out;
+	}
+	if (pid == 0) {
+		/* In child, make sure we can call a function, read
+		 * the GCS pointer and status and then exit */
+		valid_gcs_function();
+		get_gcspr();
+
+		ret = my_syscall5(__NR_prctl, PR_GET_SHADOW_STACK_STATUS,
+				  &child_mode, 0, 0, 0);
+		if (ret == 0 && !(child_mode & PR_SHADOW_STACK_ENABLE)) {
+			ksft_print_msg("GCS not enabled in child\n");
+			ret = -EINVAL;
+		}
+
+		exit(ret);
+	}
+
+	/*
+	 * In parent, check we can still do function calls then block
+	 * for the child.
+	 */
+	valid_gcs_function();
+
+	ksft_print_msg("Waiting for child %d\n", pid);
+
+	ret = waitpid(pid, &status, 0);
+	if (ret == -1) {
+		ksft_print_msg("Failed to wait for child: %d\n",
+			       errno);
+		return false;
+	}
+
+	if (!WIFEXITED(status)) {
+		ksft_print_msg("Child exited due to signal %d\n",
+			       WTERMSIG(status));
+		pass = false;
+	} else {
+		if (WEXITSTATUS(status)) {
+			ksft_print_msg("Child exited with status %d\n",
+				       WEXITSTATUS(status));
+			pass = false;
+		}
+	}
+
+out:
+
+	return pass;
+}
+
+typedef bool (*gcs_test)(void);
+
+static struct {
+	char *name;
+	gcs_test test;
+	bool needs_enable;
+} tests[] = {
+	{ "read_status", read_status },
+	{ "base_enable", base_enable, true },
+	{ "read_gcspr_el0", read_gcspr_el0 },
+	{ "enable_writeable", enable_writeable, true },
+	{ "enable_push_pop", enable_push_pop, true },
+	{ "enable_all", enable_all, true },
+	{ "enable_invalid", enable_invalid, true },
+	{ "map_guarded_stack", map_guarded_stack },
+	{ "fork", test_fork },
+};
+
+int main(void)
+{
+	int i, ret;
+	unsigned long gcs_mode;
+
+	ksft_print_header();
+
+	/*
+	 * We don't have getauxval() with nolibc so treat a failure to
+	 * read GCS state as a lack of support and skip.
+	 */
+	ret = my_syscall5(__NR_prctl, PR_GET_SHADOW_STACK_STATUS,
+			  &gcs_mode, 0, 0, 0);
+	if (ret != 0)
+		ksft_exit_skip("Failed to read GCS state: %d\n", ret);
+
+	if (!(gcs_mode & PR_SHADOW_STACK_ENABLE)) {
+		gcs_mode = PR_SHADOW_STACK_ENABLE;
+		ret = my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+				  gcs_mode, 0, 0, 0);
+		if (ret != 0)
+			ksft_exit_fail_msg("Failed to enable GCS: %d\n", ret);
+	}
+
+	ksft_set_plan(ARRAY_SIZE(tests));
+
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		ksft_test_result((*tests[i].test)(), "%s\n", tests[i].name);
+	}
+
+	/* One last test: disable GCS, we can do this one time */
+	my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, 0, 0, 0, 0);
+	if (ret != 0)
+		ksft_print_msg("Failed to disable GCS: %d\n", ret);
+
+	ksft_finished();
+
+	return 0;
+}
diff --git a/tools/testing/selftests/arm64/gcs/gcs-util.h b/tools/testing/selftests/arm64/gcs/gcs-util.h
new file mode 100644
index 000000000000..c517f1a710c5
--- /dev/null
+++ b/tools/testing/selftests/arm64/gcs/gcs-util.h
@@ -0,0 +1,87 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023 ARM Limited.
+ */
+
+#ifndef GCS_UTIL_H
+#define GCS_UTIL_H
+
+#include <stdbool.h>
+
+#ifndef __NR_map_shadow_stack
+#define __NR_map_shadow_stack 452
+#endif
+
+#ifndef __NR_prctl
+#define __NR_prctl 167
+#endif
+
+/* Shadow Stack/Guarded Control Stack interface */
+#define PR_GET_SHADOW_STACK_STATUS	71
+#define PR_SET_SHADOW_STACK_STATUS      72
+#define PR_LOCK_SHADOW_STACK_STATUS     73
+
+# define PR_SHADOW_STACK_ENABLE         (1UL << 0)
+# define PR_SHADOW_STACK_WRITE		(1UL << 1)
+# define PR_SHADOW_STACK_PUSH		(1UL << 2)
+
+#define PR_SHADOW_STACK_ALL_MODES \
+	PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE | PR_SHADOW_STACK_PUSH
+
+#define GCS_CAP_ADDR_MASK		(0xfffffffffffff000UL)
+#define GCS_CAP_TOKEN_MASK		(0x0000000000000fffUL)
+#define GCS_CAP_VALID_TOKEN		1
+#define GCS_CAP_IN_PROGRESS_TOKEN	5
+
+#define GCS_CAP(x) (((unsigned long)(x) & GCS_CAP_ADDR_MASK) | \
+		    GCS_CAP_VALID_TOKEN)
+
+static inline unsigned long *get_gcspr(void)
+{
+	unsigned long *gcspr;
+
+	asm volatile(
+		"mrs	%0, S3_3_C2_C5_1"
+	: "=r" (gcspr)
+	:
+	: "cc");
+
+	return gcspr;
+}
+
+static inline void __attribute__((always_inline)) gcsss1(unsigned long *Xt)
+{
+	asm volatile (
+		"sys #3, C7, C7, #2, %0\n"
+		:
+		: "rZ" (Xt)
+		: "memory");
+}
+
+static inline unsigned long __attribute__((always_inline)) *gcsss2(void)
+{
+	unsigned long *Xt;
+
+	asm volatile(
+		"SYSL %0, #3, C7, C7, #3\n"
+		: "=r" (Xt)
+		:
+		: "memory");
+
+	return Xt;
+}
+
+static inline bool chkfeat_gcs(void)
+{
+	register long val __asm__ ("x16") = 1;
+
+	/* CHKFEAT x16 */
+	asm volatile(
+		"hint #0x28\n"
+		: "=r" (val)
+		: "r" (val));
+
+	return val != 1;
+}
+
+#endif