Resguardo inicial

linux-7.2.3/tools/testing/selftests/arm64/gcs/.gitignore

@@ -0,0 +1,7 @@
+basic-gcs
+libc-gcs
+gcs-locking
+gcs-stress
+gcs-stress-thread
+gcspushm
+gcsstr

linux-7.2.3/tools/testing/selftests/arm64/gcs/Makefile

@@ -0,0 +1,30 @@
+# 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 libc-gcs gcs-locking gcs-stress gcspushm gcsstr
+TEST_GEN_PROGS_EXTENDED := gcs-stress-thread
+
+LDLIBS+=-lpthread
+
+include ../../lib.mk
+
+$(OUTPUT)/basic-gcs: basic-gcs.c
+	$(CC) $(CFLAGS) -fno-asynchronous-unwind-tables -fno-ident -s -nostdlib -nostdinc \
+		-static -I../../../../include/nolibc -include ../../../../include/nolibc/nolibc.h \
+		-I../../../../../usr/include \
+		-std=gnu99 -I../.. -g \
+		-ffreestanding $^ -o $@ -lgcc
+
+$(OUTPUT)/gcs-stress-thread: gcs-stress-thread.S
+	$(CC) -nostdlib $^ -o $@
+
+$(OUTPUT)/gcspushm: gcspushm.S
+	$(CC) -nostdlib $^ -o $@
+
+$(OUTPUT)/gcsstr: gcsstr.S
+	$(CC) -nostdlib $^ -o $@

linux-7.2.3/tools/testing/selftests/arm64/gcs/basic-gcs.c

@@ -0,0 +1,412 @@
+// 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 <asm/hwcap.h>
+#include <linux/sched.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 */
+	syscall(__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 = syscall(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, mode, 0, 0, 0);
+
+	if (ret == 0) {
+		ret = syscall(__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 %lx not %lx\n",
+					       new_mode, mode);
+				ret = -EINVAL;
+			}
+		} else {
+			ksft_print_msg("Failed to validate mode: %d\n", errno);
+		}
+
+		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 = syscall(__NR_prctl, PR_GET_SHADOW_STACK_STATUS, &state, 0, 0, 0);
+	if (ret != 0) {
+		ksft_print_msg("Failed to read state: %d\n", errno);
+		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 *)syscall(__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 %lu byte GCS: %d\n",
+			       page_size, errno);
+		return false;
+	}
+	ksft_print_msg("Mapped GCS at %p-%p\n", buf,
+		       (void *)((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%llx 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%llx not 0x%llx\n",
+			       buf[elem], expected_cap);
+		pass = false;
+	}
+	ksft_print_msg("cap token is 0x%llx\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%llx not 0x0\n",
+			       elem, buf[elem]);
+		pass = false;
+	}
+
+	ret = munmap(buf, page_size);
+	if (ret != 0) {
+		ksft_print_msg("Failed to unmap %ld 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 = syscall(__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;
+}
+
+/* A vfork()ed process can run and exit */
+static bool test_vfork(void)
+{
+	unsigned long child_mode;
+	int ret, status;
+	pid_t pid;
+	bool pass = true;
+
+	pid = vfork();
+	if (pid == -1) {
+		ksft_print_msg("vfork() 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 = syscall(__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 = EXIT_FAILURE;
+		}
+
+		_exit(ret);
+	}
+
+	/*
+	 * In parent, check we can still do function calls then check
+	 * on 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 },
+	{ "vfork", test_vfork },
+};
+
+int main(void)
+{
+	int i, ret;
+	unsigned long gcs_mode;
+
+	ksft_print_header();
+
+	if (!(getauxval(AT_HWCAP) & HWCAP_GCS))
+		ksft_exit_skip("SKIP GCS not supported\n");
+
+	ret = syscall(__NR_prctl, PR_GET_SHADOW_STACK_STATUS, &gcs_mode, 0, 0, 0);
+	if (ret != 0)
+		ksft_exit_fail_msg("Failed to read GCS state: %d\n", errno);
+
+	if (!(gcs_mode & PR_SHADOW_STACK_ENABLE)) {
+		gcs_mode = PR_SHADOW_STACK_ENABLE;
+		ret = syscall(__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", errno);
+	}
+
+	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 */
+	ret = syscall(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, 0, 0, 0, 0);
+	if (ret != 0)
+		ksft_print_msg("Failed to disable GCS: %d\n", errno);
+
+	ksft_finished();
+
+	return 0;
+}

linux-7.2.3/tools/testing/selftests/arm64/gcs/gcs-locking.c

@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 ARM Limited.
+ *
+ * Tests for GCS mode locking.  These tests rely on both having GCS
+ * unconfigured on entry and on the kselftest harness running each
+ * test in a fork()ed process which will have it's own mode.
+ */
+
+#include <limits.h>
+
+#include <sys/auxv.h>
+#include <sys/prctl.h>
+
+#include <asm/hwcap.h>
+
+#include "kselftest_harness.h"
+
+#include "gcs-util.h"
+
+#define my_syscall2(num, arg1, arg2)                                          \
+({                                                                            \
+	register long _num  __asm__ ("x8") = (num);                           \
+	register long _arg1 __asm__ ("x0") = (long)(arg1);                    \
+	register long _arg2 __asm__ ("x1") = (long)(arg2);                    \
+	register long _arg3 __asm__ ("x2") = 0;                               \
+	register long _arg4 __asm__ ("x3") = 0;                               \
+	register long _arg5 __asm__ ("x4") = 0;                               \
+	                                                                      \
+	__asm__  volatile (                                                   \
+		"svc #0\n"                                                    \
+		: "=r"(_arg1)                                                 \
+		: "r"(_arg1), "r"(_arg2),                                     \
+		  "r"(_arg3), "r"(_arg4),                                     \
+		  "r"(_arg5), "r"(_num)					      \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+/* No mode bits are rejected for locking */
+TEST(lock_all_modes)
+{
+	int ret;
+
+	ret = prctl(PR_LOCK_SHADOW_STACK_STATUS, ULONG_MAX, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+}
+
+FIXTURE(valid_modes)
+{
+};
+
+FIXTURE_VARIANT(valid_modes)
+{
+	unsigned long mode;
+};
+
+FIXTURE_VARIANT_ADD(valid_modes, enable)
+{
+	.mode = PR_SHADOW_STACK_ENABLE,
+};
+
+FIXTURE_VARIANT_ADD(valid_modes, enable_write)
+{
+	.mode = PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE,
+};
+
+FIXTURE_VARIANT_ADD(valid_modes, enable_push)
+{
+	.mode = PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_PUSH,
+};
+
+FIXTURE_VARIANT_ADD(valid_modes, enable_write_push)
+{
+	.mode = PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE |
+		PR_SHADOW_STACK_PUSH,
+};
+
+FIXTURE_SETUP(valid_modes)
+{
+}
+
+FIXTURE_TEARDOWN(valid_modes)
+{
+}
+
+/* We can set the mode at all */
+TEST_F(valid_modes, set)
+{
+	int ret;
+
+	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+			  variant->mode);
+	ASSERT_EQ(ret, 0);
+
+	_exit(0);
+}
+
+/* Enabling, locking then disabling is rejected */
+TEST_F(valid_modes, enable_lock_disable)
+{
+	unsigned long mode;
+	int ret;
+
+	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+			  variant->mode);
+	ASSERT_EQ(ret, 0);
+
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(mode, variant->mode);
+
+	ret = prctl(PR_LOCK_SHADOW_STACK_STATUS, variant->mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, 0);
+	ASSERT_EQ(ret, -EBUSY);
+
+	_exit(0);
+}
+
+/* Locking then enabling is rejected */
+TEST_F(valid_modes, lock_enable)
+{
+	unsigned long mode;
+	int ret;
+
+	ret = prctl(PR_LOCK_SHADOW_STACK_STATUS, variant->mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+			  variant->mode);
+	ASSERT_EQ(ret, -EBUSY);
+
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(mode, 0);
+
+	_exit(0);
+}
+
+/* Locking then changing other modes is fine */
+TEST_F(valid_modes, lock_enable_disable_others)
+{
+	unsigned long mode;
+	int ret;
+
+	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+			  variant->mode);
+	ASSERT_EQ(ret, 0);
+
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(mode, variant->mode);
+
+	ret = prctl(PR_LOCK_SHADOW_STACK_STATUS, variant->mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+
+	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+			  PR_SHADOW_STACK_ALL_MODES);
+	ASSERT_EQ(ret, 0);
+
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(mode, PR_SHADOW_STACK_ALL_MODES);
+
+	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+			  variant->mode);
+	ASSERT_EQ(ret, 0);
+
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(mode, variant->mode);
+
+	_exit(0);
+}
+
+int main(int argc, char **argv)
+{
+	unsigned long mode;
+	int ret;
+
+	if (!(getauxval(AT_HWCAP) & HWCAP_GCS))
+		ksft_exit_skip("SKIP GCS not supported\n");
+
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
+	if (ret) {
+		ksft_print_msg("Failed to read GCS state: %d\n", ret);
+		return EXIT_FAILURE;
+	}
+
+	if (mode & PR_SHADOW_STACK_ENABLE) {
+		ksft_print_msg("GCS was enabled, test unsupported\n");
+		return KSFT_SKIP;
+	}
+
+	return test_harness_run(argc, argv);
+}

linux-7.2.3/tools/testing/selftests/arm64/gcs/gcs-stress-thread.S

@@ -0,0 +1,311 @@
+// Program that loops for ever doing lots of recursions and system calls,
+// intended to be used as part of a stress test for GCS context switching.
+//
+// Copyright 2015-2023 Arm Ltd
+
+#include <asm/unistd.h>
+
+#define sa_sz 32
+#define sa_flags 8
+#define sa_handler 0
+#define sa_mask_sz 8
+
+#define si_code 8
+
+#define SIGINT 2
+#define SIGABRT 6
+#define SIGUSR1 10
+#define SIGSEGV 11
+#define SIGUSR2 12
+#define SIGTERM 15
+#define SEGV_CPERR 10
+
+#define SA_NODEFER 1073741824
+#define SA_SIGINFO 4
+#define ucontext_regs 184
+
+#define PR_SET_SHADOW_STACK_STATUS      75
+# define PR_SHADOW_STACK_ENABLE         (1UL << 0)
+
+#define	GCSPR_EL0 S3_3_C2_C5_1
+
+.macro function name
+	.macro endfunction
+		.type \name, @function
+		.purgem endfunction
+	.endm
+\name:
+.endm
+
+// Print a single character x0 to stdout
+// Clobbers x0-x2,x8
+function putc
+	str	x0, [sp, #-16]!
+
+	mov	x0, #1			// STDOUT_FILENO
+	mov	x1, sp
+	mov	x2, #1
+	mov	x8, #__NR_write
+	svc	#0
+
+	add	sp, sp, #16
+	ret
+endfunction
+.globl	putc
+
+// Print a NUL-terminated string starting at address x0 to stdout
+// Clobbers x0-x3,x8
+function puts
+	mov	x1, x0
+
+	mov	x2, #0
+0:	ldrb	w3, [x0], #1
+	cbz	w3, 1f
+	add	x2, x2, #1
+	b	0b
+
+1:	mov	w0, #1			// STDOUT_FILENO
+	mov	x8, #__NR_write
+	svc	#0
+
+	ret
+endfunction
+.globl	puts
+
+// Utility macro to print a literal string
+// Clobbers x0-x4,x8
+.macro puts string
+	.pushsection .rodata.str1.1, "aMS", @progbits, 1
+.L__puts_literal\@: .string "\string"
+	.popsection
+
+	ldr	x0, =.L__puts_literal\@
+	bl	puts
+.endm
+
+// Print an unsigned decimal number x0 to stdout
+// Clobbers x0-x4,x8
+function putdec
+	mov	x1, sp
+	str	x30, [sp, #-32]!	// Result can't be > 20 digits
+
+	mov	x2, #0
+	strb	w2, [x1, #-1]!		// Write the NUL terminator
+
+	mov	x2, #10
+0:	udiv	x3, x0, x2		// div-mod loop to generate the digits
+	msub	x0, x3, x2, x0
+	add	w0, w0, #'0'
+	strb	w0, [x1, #-1]!
+	mov	x0, x3
+	cbnz	x3, 0b
+
+	ldrb	w0, [x1]
+	cbnz	w0, 1f
+	mov	w0, #'0'		// Print "0" for 0, not ""
+	strb	w0, [x1, #-1]!
+
+1:	mov	x0, x1
+	bl	puts
+
+	ldr	x30, [sp], #32
+	ret
+endfunction
+.globl	putdec
+
+// Print an unsigned decimal number x0 to stdout, followed by a newline
+// Clobbers x0-x5,x8
+function putdecn
+	mov	x5, x30
+
+	bl	putdec
+	mov	x0, #'\n'
+	bl	putc
+
+	ret	x5
+endfunction
+.globl	putdecn
+
+// Fill x1 bytes starting at x0 with 0.
+// Clobbers x1, x2.
+function memclr
+	mov	w2, #0
+endfunction
+.globl	memclr
+	// fall through to memfill
+
+// Trivial memory fill: fill x1 bytes starting at address x0 with byte w2
+// Clobbers x1
+function memfill
+	cmp	x1, #0
+	b.eq	1f
+
+0:	strb	w2, [x0], #1
+	subs	x1, x1, #1
+	b.ne	0b
+
+1:	ret
+endfunction
+.globl	memfill
+
+// w0: signal number
+// x1: sa_action
+// w2: sa_flags
+// Clobbers x0-x6,x8
+function setsignal
+	str	x30, [sp, #-((sa_sz + 15) / 16 * 16 + 16)]!
+
+	mov	w4, w0
+	mov	x5, x1
+	mov	w6, w2
+
+	add	x0, sp, #16
+	mov	x1, #sa_sz
+	bl	memclr
+
+	mov	w0, w4
+	add	x1, sp, #16
+	str	w6, [x1, #sa_flags]
+	str	x5, [x1, #sa_handler]
+	mov	x2, #0
+	mov	x3, #sa_mask_sz
+	mov	x8, #__NR_rt_sigaction
+	svc	#0
+
+	cbz	w0, 1f
+
+	puts	"sigaction failure\n"
+	b	abort
+
+1:	ldr	x30, [sp], #((sa_sz + 15) / 16 * 16 + 16)
+	ret
+endfunction
+
+
+function tickle_handler
+	// Perhaps collect GCSPR_EL0 here in future?
+	ret
+endfunction
+
+function terminate_handler
+	mov	w21, w0
+	mov	x20, x2
+
+	puts	"Terminated by signal "
+	mov	w0, w21
+	bl	putdec
+	puts	", no error\n"
+
+	mov	x0, #0
+	mov	x8, #__NR_exit
+	svc	#0
+endfunction
+
+function segv_handler
+	// stash the siginfo_t *
+	mov	x20, x1
+
+	// Disable GCS, we don't want additional faults logging things
+	mov	x0, PR_SET_SHADOW_STACK_STATUS
+	mov	x1, xzr
+	mov	x2, xzr
+	mov	x3, xzr
+	mov	x4, xzr
+	mov	x5, xzr
+	mov	x8, #__NR_prctl
+	svc	#0
+
+	puts	"Got SIGSEGV code "
+
+	ldr	x21, [x20, #si_code]
+	mov	x0, x21
+	bl	putdec
+
+	// GCS faults should have si_code SEGV_CPERR
+	cmp	x21, #SEGV_CPERR
+	bne	1f
+
+	puts	" (GCS violation)"
+1:
+	mov	x0, '\n'
+	bl	putc
+	b	abort
+endfunction
+
+// Recurse x20 times
+.macro recurse id
+function recurse\id
+	stp	x29, x30, [sp, #-16]!
+	mov	x29, sp
+
+	cmp	x20, 0
+	beq	1f
+	sub	x20, x20, 1
+	bl	recurse\id
+
+1:
+	ldp	x29, x30, [sp], #16
+
+	// Do a syscall immediately prior to returning to try to provoke
+	// scheduling and migration at a point where coherency issues
+	// might trigger.
+	mov	x8, #__NR_getpid
+	svc	#0
+
+	ret
+endfunction
+.endm
+
+// Generate and use two copies so we're changing the GCS contents
+recurse 1
+recurse 2
+
+.globl _start
+function _start
+	// Run with GCS
+	mov	x0, PR_SET_SHADOW_STACK_STATUS
+	mov	x1, PR_SHADOW_STACK_ENABLE
+	mov	x2, xzr
+	mov	x3, xzr
+	mov	x4, xzr
+	mov	x5, xzr
+	mov	x8, #__NR_prctl
+	svc	#0
+	cbz	x0, 1f
+	puts	"Failed to enable GCS\n"
+	b	abort
+1:
+
+	mov	w0, #SIGTERM
+	adr	x1, terminate_handler
+	mov	w2, #SA_SIGINFO
+	bl	setsignal
+
+	mov	w0, #SIGUSR1
+	adr	x1, tickle_handler
+	mov	w2, #SA_SIGINFO
+	orr	w2, w2, #SA_NODEFER
+	bl	setsignal
+
+	mov	w0, #SIGSEGV
+	adr	x1, segv_handler
+	mov	w2, #SA_SIGINFO
+	orr	w2, w2, #SA_NODEFER
+	bl	setsignal
+
+	puts	"Running\n"
+
+loop:
+	// Small recursion depth so we're frequently flipping between
+	// the two recursors and changing what's on the stack
+	mov	x20, #5
+	bl	recurse1
+	mov	x20, #5
+	bl	recurse2
+	b	loop
+endfunction
+
+abort:
+	mov	x0, #255
+	mov	x8, #__NR_exit
+	svc	#0

linux-7.2.3/tools/testing/selftests/arm64/gcs/gcs-stress.c

@@ -0,0 +1,530 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2022-3 ARM Limited.
+ */
+
+#define _GNU_SOURCE
+#define _POSIX_C_SOURCE 199309L
+
+#include <errno.h>
+#include <getopt.h>
+#include <poll.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/auxv.h>
+#include <sys/epoll.h>
+#include <sys/prctl.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/wait.h>
+#include <asm/hwcap.h>
+
+#include "kselftest.h"
+
+struct child_data {
+	char *name, *output;
+	pid_t pid;
+	int stdout;
+	bool output_seen;
+	bool exited;
+	int exit_status;
+	int exit_signal;
+};
+
+static int epoll_fd;
+static struct child_data *children;
+static struct epoll_event *evs;
+static int tests;
+static int num_children;
+static bool terminate;
+
+static int startup_pipe[2];
+
+static int num_processors(void)
+{
+	long nproc = sysconf(_SC_NPROCESSORS_CONF);
+	if (nproc < 0) {
+		perror("Unable to read number of processors\n");
+		exit(EXIT_FAILURE);
+	}
+
+	return nproc;
+}
+
+static void start_thread(struct child_data *child, int id)
+{
+	int ret, pipefd[2], i;
+	struct epoll_event ev;
+
+	ret = pipe(pipefd);
+	if (ret != 0)
+		ksft_exit_fail_msg("Failed to create stdout pipe: %s (%d)\n",
+				   strerror(errno), errno);
+
+	child->pid = fork();
+	if (child->pid == -1)
+		ksft_exit_fail_msg("fork() failed: %s (%d)\n",
+				   strerror(errno), errno);
+
+	if (!child->pid) {
+		/*
+		 * In child, replace stdout with the pipe, errors to
+		 * stderr from here as kselftest prints to stdout.
+		 */
+		ret = dup2(pipefd[1], 1);
+		if (ret == -1) {
+			fprintf(stderr, "dup2() %d\n", errno);
+			exit(EXIT_FAILURE);
+		}
+
+		/*
+		 * Duplicate the read side of the startup pipe to
+		 * FD 3 so we can close everything else.
+		 */
+		ret = dup2(startup_pipe[0], 3);
+		if (ret == -1) {
+			fprintf(stderr, "dup2() %d\n", errno);
+			exit(EXIT_FAILURE);
+		}
+
+		/*
+		 * Very dumb mechanism to clean open FDs other than
+		 * stdio. We don't want O_CLOEXEC for the pipes...
+		 */
+		for (i = 4; i < 8192; i++)
+			close(i);
+
+		/*
+		 * Read from the startup pipe, there should be no data
+		 * and we should block until it is closed.  We just
+		 * carry on on error since this isn't super critical.
+		 */
+		ret = read(3, &i, sizeof(i));
+		if (ret < 0)
+			fprintf(stderr, "read(startp pipe) failed: %s (%d)\n",
+				strerror(errno), errno);
+		if (ret > 0)
+			fprintf(stderr, "%d bytes of data on startup pipe\n",
+				ret);
+		close(3);
+
+		ret = execl("gcs-stress-thread", "gcs-stress-thread", NULL);
+		fprintf(stderr, "execl(gcs-stress-thread) failed: %d (%s)\n",
+			errno, strerror(errno));
+
+		exit(EXIT_FAILURE);
+	} else {
+		/*
+		 * In parent, remember the child and close our copy of the
+		 * write side of stdout.
+		 */
+		close(pipefd[1]);
+		child->stdout = pipefd[0];
+		child->output = NULL;
+		child->exited = false;
+		child->output_seen = false;
+
+		ev.events = EPOLLIN | EPOLLHUP;
+		ev.data.ptr = child;
+
+		ret = asprintf(&child->name, "Thread-%d", id);
+		if (ret == -1)
+			ksft_exit_fail_msg("asprintf() failed\n");
+
+		ret = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, child->stdout, &ev);
+		if (ret < 0) {
+			ksft_exit_fail_msg("%s EPOLL_CTL_ADD failed: %s (%d)\n",
+					   child->name, strerror(errno), errno);
+		}
+	}
+
+	ksft_print_msg("Started %s\n", child->name);
+	num_children++;
+}
+
+static bool child_output_read(struct child_data *child)
+{
+	char read_data[1024];
+	char work[1024];
+	int ret, len, cur_work, cur_read;
+
+	ret = read(child->stdout, read_data, sizeof(read_data));
+	if (ret < 0) {
+		if (errno == EINTR)
+			return true;
+
+		ksft_print_msg("%s: read() failed: %s (%d)\n",
+			       child->name, strerror(errno),
+			       errno);
+		return false;
+	}
+	len = ret;
+
+	child->output_seen = true;
+
+	/* Pick up any partial read */
+	if (child->output) {
+		strncpy(work, child->output, sizeof(work) - 1);
+		cur_work = strnlen(work, sizeof(work));
+		free(child->output);
+		child->output = NULL;
+	} else {
+		cur_work = 0;
+	}
+
+	cur_read = 0;
+	while (cur_read < len) {
+		work[cur_work] = read_data[cur_read++];
+
+		if (work[cur_work] == '\n') {
+			work[cur_work] = '\0';
+			ksft_print_msg("%s: %s\n", child->name, work);
+			cur_work = 0;
+		} else {
+			cur_work++;
+		}
+	}
+
+	if (cur_work) {
+		work[cur_work] = '\0';
+		ret = asprintf(&child->output, "%s", work);
+		if (ret == -1)
+			ksft_exit_fail_msg("Out of memory\n");
+	}
+
+	return false;
+}
+
+static void child_output(struct child_data *child, uint32_t events,
+			 bool flush)
+{
+	bool read_more;
+
+	if (events & EPOLLIN) {
+		do {
+			read_more = child_output_read(child);
+		} while (read_more);
+	}
+
+	if (events & EPOLLHUP) {
+		close(child->stdout);
+		child->stdout = -1;
+		flush = true;
+	}
+
+	if (flush && child->output) {
+		ksft_print_msg("%s: %s<EOF>\n", child->name, child->output);
+		free(child->output);
+		child->output = NULL;
+	}
+}
+
+static void child_tickle(struct child_data *child)
+{
+	if (child->output_seen && !child->exited)
+		kill(child->pid, SIGUSR1);
+}
+
+static void child_stop(struct child_data *child)
+{
+	if (!child->exited)
+		kill(child->pid, SIGTERM);
+}
+
+static void child_cleanup(struct child_data *child)
+{
+	pid_t ret;
+	int status;
+	bool fail = false;
+
+	if (!child->exited) {
+		do {
+			ret = waitpid(child->pid, &status, 0);
+			if (ret == -1 && errno == EINTR)
+				continue;
+
+			if (ret == -1) {
+				ksft_print_msg("waitpid(%d) failed: %s (%d)\n",
+					       child->pid, strerror(errno),
+					       errno);
+				fail = true;
+				break;
+			}
+
+			if (WIFEXITED(status)) {
+				child->exit_status = WEXITSTATUS(status);
+				child->exited = true;
+			}
+
+			if (WIFSIGNALED(status)) {
+				child->exit_signal = WTERMSIG(status);
+				ksft_print_msg("%s: Exited due to signal %d\n",
+					       child->name, child->exit_signal);
+				fail = true;
+				child->exited = true;
+			}
+		} while (!child->exited);
+	}
+
+	if (!child->output_seen) {
+		ksft_print_msg("%s no output seen\n", child->name);
+		fail = true;
+	}
+
+	if (child->exit_status != 0) {
+		ksft_print_msg("%s exited with error code %d\n",
+			       child->name, child->exit_status);
+		fail = true;
+	}
+
+	ksft_test_result(!fail, "%s\n", child->name);
+}
+
+static void handle_child_signal(int sig, siginfo_t *info, void *context)
+{
+	int i;
+	bool found = false;
+
+	for (i = 0; i < num_children; i++) {
+		if (children[i].pid == info->si_pid) {
+			children[i].exited = true;
+			children[i].exit_status = info->si_status;
+			found = true;
+			break;
+		}
+	}
+
+	if (!found)
+		ksft_print_msg("SIGCHLD for unknown PID %d with status %d\n",
+			       info->si_pid, info->si_status);
+}
+
+static void handle_exit_signal(int sig, siginfo_t *info, void *context)
+{
+	int i;
+
+	/* If we're already exiting then don't signal again */
+	if (terminate)
+		return;
+
+	ksft_print_msg("Got signal, exiting...\n");
+
+	terminate = true;
+
+	/*
+	 * This should be redundant, the main loop should clean up
+	 * after us, but for safety stop everything we can here.
+	 */
+	for (i = 0; i < num_children; i++)
+		child_stop(&children[i]);
+}
+
+/* Handle any pending output without blocking */
+static void drain_output(bool flush)
+{
+	int ret = 1;
+	int i;
+
+	while (ret > 0) {
+		ret = epoll_wait(epoll_fd, evs, tests, 0);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			ksft_print_msg("epoll_wait() failed: %s (%d)\n",
+				       strerror(errno), errno);
+		}
+
+		for (i = 0; i < ret; i++)
+			child_output(evs[i].data.ptr, evs[i].events, flush);
+	}
+}
+
+static const struct option options[] = {
+	{ "timeout",	required_argument, NULL, 't' },
+	{ }
+};
+
+int main(int argc, char **argv)
+{
+	int seen_children;
+	bool all_children_started = false;
+	int gcs_threads;
+	int timeout = 10;
+	int ret, cpus, i, c;
+	struct sigaction sa;
+
+	while ((c = getopt_long(argc, argv, "t:", options, NULL)) != -1) {
+		switch (c) {
+		case 't':
+			ret = sscanf(optarg, "%d", &timeout);
+			if (ret != 1)
+				ksft_exit_fail_msg("Failed to parse timeout %s\n",
+						   optarg);
+			break;
+		default:
+			ksft_exit_fail_msg("Unknown argument\n");
+		}
+	}
+
+	cpus = num_processors();
+	tests = 0;
+
+	if (getauxval(AT_HWCAP) & HWCAP_GCS) {
+		/* One extra thread, trying to trigger migrations */
+		gcs_threads = cpus + 1;
+		tests += gcs_threads;
+	} else {
+		gcs_threads = 0;
+	}
+
+	ksft_print_header();
+	ksft_set_plan(tests);
+
+	ksft_print_msg("%d CPUs, %d GCS threads\n",
+		       cpus, gcs_threads);
+
+	if (!tests)
+		ksft_exit_skip("No tests scheduled\n");
+
+	if (timeout > 0)
+		ksft_print_msg("Will run for %ds\n", timeout);
+	else
+		ksft_print_msg("Will run until terminated\n");
+
+	children = calloc(sizeof(*children), tests);
+	if (!children)
+		ksft_exit_fail_msg("Unable to allocate child data\n");
+
+	ret = epoll_create1(EPOLL_CLOEXEC);
+	if (ret < 0)
+		ksft_exit_fail_msg("epoll_create1() failed: %s (%d)\n",
+				   strerror(errno), ret);
+	epoll_fd = ret;
+
+	/* Create a pipe which children will block on before execing */
+	ret = pipe(startup_pipe);
+	if (ret != 0)
+		ksft_exit_fail_msg("Failed to create startup pipe: %s (%d)\n",
+				   strerror(errno), errno);
+
+	/* Get signal handers ready before we start any children */
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_sigaction = handle_exit_signal;
+	sa.sa_flags = SA_RESTART | SA_SIGINFO;
+	sigemptyset(&sa.sa_mask);
+	ret = sigaction(SIGINT, &sa, NULL);
+	if (ret < 0)
+		ksft_print_msg("Failed to install SIGINT handler: %s (%d)\n",
+			       strerror(errno), errno);
+	ret = sigaction(SIGTERM, &sa, NULL);
+	if (ret < 0)
+		ksft_print_msg("Failed to install SIGTERM handler: %s (%d)\n",
+			       strerror(errno), errno);
+	sa.sa_sigaction = handle_child_signal;
+	ret = sigaction(SIGCHLD, &sa, NULL);
+	if (ret < 0)
+		ksft_print_msg("Failed to install SIGCHLD handler: %s (%d)\n",
+			       strerror(errno), errno);
+
+	evs = calloc(tests, sizeof(*evs));
+	if (!evs)
+		ksft_exit_fail_msg("Failed to allocate %d epoll events\n",
+				   tests);
+
+	for (i = 0; i < gcs_threads; i++)
+		start_thread(&children[i], i);
+
+	/*
+	 * All children started, close the startup pipe and let them
+	 * run.
+	 */
+	close(startup_pipe[0]);
+	close(startup_pipe[1]);
+
+	timeout *= 10;
+	for (;;) {
+		/* Did we get a signal asking us to exit? */
+		if (terminate)
+			break;
+
+		/*
+		 * Timeout is counted in 100ms with no output, the
+		 * tests print during startup then are silent when
+		 * running so this should ensure they all ran enough
+		 * to install the signal handler, this is especially
+		 * useful in emulation where we will both be slow and
+		 * likely to have a large set of VLs.
+		 */
+		ret = epoll_wait(epoll_fd, evs, tests, 100);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			ksft_exit_fail_msg("epoll_wait() failed: %s (%d)\n",
+					   strerror(errno), errno);
+		}
+
+		/* Output? */
+		if (ret > 0) {
+			for (i = 0; i < ret; i++) {
+				child_output(evs[i].data.ptr, evs[i].events,
+					     false);
+			}
+			continue;
+		}
+
+		/* Otherwise epoll_wait() timed out */
+
+		/*
+		 * If the child processes have not produced output they
+		 * aren't actually running the tests yet.
+		 */
+		if (!all_children_started) {
+			seen_children = 0;
+
+			for (i = 0; i < num_children; i++)
+				if (children[i].output_seen ||
+				    children[i].exited)
+					seen_children++;
+
+			if (seen_children != num_children) {
+				ksft_print_msg("Waiting for %d children\n",
+					       num_children - seen_children);
+				continue;
+			}
+
+			all_children_started = true;
+		}
+
+		ksft_print_msg("Sending signals, timeout remaining: %d00ms\n",
+			       timeout);
+
+		for (i = 0; i < num_children; i++)
+			child_tickle(&children[i]);
+
+		/* Negative timeout means run indefinitely */
+		if (timeout < 0)
+			continue;
+		if (--timeout == 0)
+			break;
+	}
+
+	ksft_print_msg("Finishing up...\n");
+	terminate = true;
+
+	for (i = 0; i < tests; i++)
+		child_stop(&children[i]);
+
+	drain_output(false);
+
+	for (i = 0; i < tests; i++)
+		child_cleanup(&children[i]);
+
+	drain_output(true);
+
+	ksft_finished();
+}

linux-7.2.3/tools/testing/selftests/arm64/gcs/gcs-util.h

@@ -0,0 +1,94 @@
+/* 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 453
+#endif
+
+#ifndef __NR_prctl
+#define __NR_prctl 167
+#endif
+
+#ifndef NT_ARM_GCS
+#define NT_ARM_GCS 0x410
+#endif
+
+/* Shadow Stack/Guarded Control Stack interface */
+#define PR_GET_SHADOW_STACK_STATUS	74
+#define PR_SET_SHADOW_STACK_STATUS      75
+#define PR_LOCK_SHADOW_STACK_STATUS     76
+
+# 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 SHADOW_STACK_SET_TOKEN (1ULL << 0)     /* Set up a restore token in the shadow stack */
+#define SHADOW_STACK_SET_MARKER (1ULL << 1)     /* Set up a top of stack merker in the shadow stack */
+
+#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

linux-7.2.3/tools/testing/selftests/arm64/gcs/gcspushm.S

@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// Copyright 2024 Arm Limited
+//
+// Give ourselves GCS push permissions then use them
+
+#include <asm/unistd.h>
+
+/* Shadow Stack/Guarded Control Stack interface */
+#define PR_GET_SHADOW_STACK_STATUS	74
+#define PR_SET_SHADOW_STACK_STATUS      75
+#define PR_LOCK_SHADOW_STACK_STATUS     76
+
+# define PR_SHADOW_STACK_ENABLE         (1UL << 0)
+# define PR_SHADOW_STACK_WRITE		(1UL << 1)
+# define PR_SHADOW_STACK_PUSH		(1UL << 2)
+
+#define KSFT_SKIP 4
+
+.macro function name
+	.macro endfunction
+		.type \name, @function
+		.purgem endfunction
+	.endm
+\name:
+.endm
+
+// Print a single character x0 to stdout
+// Clobbers x0-x2,x8
+function putc
+	str	x0, [sp, #-16]!
+
+	mov	x0, #1			// STDOUT_FILENO
+	mov	x1, sp
+	mov	x2, #1
+	mov	x8, #__NR_write
+	svc	#0
+
+	add	sp, sp, #16
+	ret
+endfunction
+.globl	putc
+
+// Print a NUL-terminated string starting at address x0 to stdout
+// Clobbers x0-x3,x8
+function puts
+	mov	x1, x0
+
+	mov	x2, #0
+0:	ldrb	w3, [x0], #1
+	cbz	w3, 1f
+	add	x2, x2, #1
+	b	0b
+
+1:	mov	w0, #1			// STDOUT_FILENO
+	mov	x8, #__NR_write
+	svc	#0
+
+	ret
+endfunction
+.globl	puts
+
+// Utility macro to print a literal string
+// Clobbers x0-x4,x8
+.macro puts string
+	.pushsection .rodata.str1.1, "aMS", @progbits, 1
+.L__puts_literal\@: .string "\string"
+	.popsection
+
+	ldr	x0, =.L__puts_literal\@
+	bl	puts
+.endm
+
+.globl _start
+function _start
+	// Run with GCS
+	mov	x0, PR_SET_SHADOW_STACK_STATUS
+	mov	x1, PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_PUSH
+	mov	x2, xzr
+	mov	x3, xzr
+	mov	x4, xzr
+	mov	x5, xzr
+	mov	x8, #__NR_prctl
+	svc	#0
+	cbz	x0, 1f
+	puts	"Failed to enable GCS with push permission\n"
+	mov	x0, #KSFT_SKIP
+	b	2f
+1:
+	sys	#3, c7, c7, #0, x0	// GCSPUSHM
+	sysl	x0, #3, c7, c7, #1	// GCSPOPM
+
+	mov	x0, #0
+2:
+	mov	x8, #__NR_exit
+	svc	#0

linux-7.2.3/tools/testing/selftests/arm64/gcs/gcsstr.S

@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// Copyright 2024 Arm Limited
+//
+// Give ourselves GCS write permissions then use them
+
+#include <asm/unistd.h>
+
+/* Shadow Stack/Guarded Control Stack interface */
+#define PR_GET_SHADOW_STACK_STATUS	74
+#define PR_SET_SHADOW_STACK_STATUS      75
+#define PR_LOCK_SHADOW_STACK_STATUS     76
+
+# define PR_SHADOW_STACK_ENABLE         (1UL << 0)
+# define PR_SHADOW_STACK_WRITE		(1UL << 1)
+# define PR_SHADOW_STACK_PUSH		(1UL << 2)
+
+#define	GCSPR_EL0 S3_3_C2_C5_1
+
+#define KSFT_SKIP 4
+
+.macro function name
+	.macro endfunction
+		.type \name, @function
+		.purgem endfunction
+	.endm
+\name:
+.endm
+
+// Print a single character x0 to stdout
+// Clobbers x0-x2,x8
+function putc
+	str	x0, [sp, #-16]!
+
+	mov	x0, #1			// STDOUT_FILENO
+	mov	x1, sp
+	mov	x2, #1
+	mov	x8, #__NR_write
+	svc	#0
+
+	add	sp, sp, #16
+	ret
+endfunction
+.globl	putc
+
+// Print a NUL-terminated string starting at address x0 to stdout
+// Clobbers x0-x3,x8
+function puts
+	mov	x1, x0
+
+	mov	x2, #0
+0:	ldrb	w3, [x0], #1
+	cbz	w3, 1f
+	add	x2, x2, #1
+	b	0b
+
+1:	mov	w0, #1			// STDOUT_FILENO
+	mov	x8, #__NR_write
+	svc	#0
+
+	ret
+endfunction
+.globl	puts
+
+// Utility macro to print a literal string
+// Clobbers x0-x4,x8
+.macro puts string
+	.pushsection .rodata.str1.1, "aMS", @progbits, 1
+.L__puts_literal\@: .string "\string"
+	.popsection
+
+	ldr	x0, =.L__puts_literal\@
+	bl	puts
+.endm
+
+.globl _start
+function _start
+	// Run with GCS
+	mov	x0, PR_SET_SHADOW_STACK_STATUS
+	mov	x1, PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE
+	mov	x2, xzr
+	mov	x3, xzr
+	mov	x4, xzr
+	mov	x5, xzr
+	mov	x8, #__NR_prctl
+	svc	#0
+	cbz	x0, 1f
+	puts	"Failed to enable GCS with write permission\n"
+	mov	x0, #KSFT_SKIP
+	b	2f
+1:
+	mrs	x0, GCSPR_EL0
+	sub	x0, x0, #8
+	.inst	0xd91f1c01	// GCSSTR x1, x0
+
+	mov	x0, #0
+2:
+	mov	x8, #__NR_exit
+	svc	#0

linux-7.2.3/tools/testing/selftests/arm64/gcs/libc-gcs.c

@@ -0,0 +1,729 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 ARM Limited.
+ */
+
+#define _GNU_SOURCE
+
+#include <pthread.h>
+#include <stdbool.h>
+
+#include <sys/auxv.h>
+#include <sys/mman.h>
+#include <sys/prctl.h>
+#include <sys/ptrace.h>
+#include <sys/uio.h>
+
+#include <asm/hwcap.h>
+#include <asm/mman.h>
+#include <asm/ptrace.h>
+
+#include <linux/compiler.h>
+
+#include "kselftest_harness.h"
+
+#include "gcs-util.h"
+
+#define my_syscall2(num, arg1, arg2)                                          \
+({                                                                            \
+	register long _num  __asm__ ("x8") = (num);                           \
+	register long _arg1 __asm__ ("x0") = (long)(arg1);                    \
+	register long _arg2 __asm__ ("x1") = (long)(arg2);                    \
+	register long _arg3 __asm__ ("x2") = 0;                               \
+	register long _arg4 __asm__ ("x3") = 0;                               \
+	register long _arg5 __asm__ ("x4") = 0;                               \
+	                                                                      \
+	__asm__  volatile (                                                   \
+		"svc #0\n"                                                    \
+		: "=r"(_arg1)                                                 \
+		: "r"(_arg1), "r"(_arg2),                                     \
+		  "r"(_arg3), "r"(_arg4),                                     \
+		  "r"(_arg5), "r"(_num)					      \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+static noinline void gcs_recurse(int depth)
+{
+	if (depth)
+		gcs_recurse(depth - 1);
+
+	/* Prevent tail call optimization so we actually recurse */
+	asm volatile("dsb sy" : : : "memory");
+}
+
+/* Smoke test that a function call and return works*/
+TEST(can_call_function)
+{
+	gcs_recurse(0);
+}
+
+static void *gcs_test_thread(void *arg)
+{
+	int ret;
+	unsigned long mode;
+
+	/*
+	 * Some libcs don't seem to fill unused arguments with 0 but
+	 * the kernel validates this so we supply all 5 arguments.
+	 */
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
+	if (ret != 0) {
+		ksft_print_msg("PR_GET_SHADOW_STACK_STATUS failed: %d\n", ret);
+		return NULL;
+	}
+
+	if (!(mode & PR_SHADOW_STACK_ENABLE)) {
+		ksft_print_msg("GCS not enabled in thread, mode is %lu\n",
+			       mode);
+		return NULL;
+	}
+
+	/* Just in case... */
+	gcs_recurse(0);
+
+	/* Use a non-NULL value to indicate a pass */
+	return &gcs_test_thread;
+}
+
+/* Verify that if we start a new thread it has GCS enabled */
+TEST(gcs_enabled_thread)
+{
+	pthread_t thread;
+	void *thread_ret;
+	int ret;
+
+	ret = pthread_create(&thread, NULL, gcs_test_thread, NULL);
+	ASSERT_TRUE(ret == 0);
+	if (ret != 0)
+		return;
+
+	ret = pthread_join(thread, &thread_ret);
+	ASSERT_TRUE(ret == 0);
+	if (ret != 0)
+		return;
+
+	ASSERT_TRUE(thread_ret != NULL);
+}
+
+/* Read the GCS until we find the terminator */
+TEST(gcs_find_terminator)
+{
+	unsigned long *gcs, *cur;
+
+	gcs = get_gcspr();
+	cur = gcs;
+	while (*cur)
+		cur++;
+
+	ksft_print_msg("GCS in use from %p-%p\n", gcs, cur);
+
+	/*
+	 * We should have at least whatever called into this test so
+	 * the two pointer should differ.
+	 */
+	ASSERT_TRUE(gcs != cur);
+}
+
+/*
+ * We can access a GCS via ptrace
+ *
+ * This could usefully have a fixture but note that each test is
+ * fork()ed into a new child which causes issues.  Might be better to
+ * lift at least some of this out into a separate, non-harness, test
+ * program.
+ */
+TEST(ptrace_read_write)
+{
+	pid_t child, pid;
+	int ret, status;
+	siginfo_t si;
+	uint64_t val, rval, gcspr;
+	struct user_gcs child_gcs;
+	struct iovec iov, local_iov, remote_iov;
+
+	child = fork();
+	if (child == -1) {
+		ksft_print_msg("fork() failed: %d (%s)\n",
+			       errno, strerror(errno));
+		ASSERT_NE(child, -1);
+	}
+
+	if (child == 0) {
+		/*
+		 * In child, make sure there's something on the stack and
+		 * ask to be traced.
+		 */
+		gcs_recurse(0);
+		if (ptrace(PTRACE_TRACEME, -1, NULL, NULL))
+			ksft_exit_fail_msg("PTRACE_TRACEME %s",
+					   strerror(errno));
+
+		if (raise(SIGSTOP))
+			ksft_exit_fail_msg("raise(SIGSTOP) %s",
+					   strerror(errno));
+
+		return;
+	}
+
+	ksft_print_msg("Child: %d\n", child);
+
+	/* Attach to the child */
+	while (1) {
+		int sig;
+
+		pid = wait(&status);
+		if (pid == -1) {
+			ksft_print_msg("wait() failed: %s",
+				       strerror(errno));
+			goto error;
+		}
+
+		/*
+		 * This should never happen but it's hard to flag in
+		 * the framework.
+		 */
+		if (pid != child)
+			continue;
+
+		if (WIFEXITED(status) || WIFSIGNALED(status))
+			ksft_exit_fail_msg("Child died unexpectedly\n");
+
+		if (!WIFSTOPPED(status))
+			goto error;
+
+		sig = WSTOPSIG(status);
+
+		if (ptrace(PTRACE_GETSIGINFO, pid, NULL, &si)) {
+			if (errno == ESRCH) {
+				ASSERT_NE(errno, ESRCH);
+				return;
+			}
+
+			if (errno == EINVAL) {
+				sig = 0; /* bust group-stop */
+				goto cont;
+			}
+
+			ksft_print_msg("PTRACE_GETSIGINFO: %s\n",
+				       strerror(errno));
+			goto error;
+		}
+
+		if (sig == SIGSTOP && si.si_code == SI_TKILL &&
+		    si.si_pid == pid)
+			break;
+
+	cont:
+		if (ptrace(PTRACE_CONT, pid, NULL, sig)) {
+			if (errno == ESRCH) {
+				ASSERT_NE(errno, ESRCH);
+				return;
+			}
+
+			ksft_print_msg("PTRACE_CONT: %s\n", strerror(errno));
+			goto error;
+		}
+	}
+
+	/* Where is the child GCS? */
+	iov.iov_base = &child_gcs;
+	iov.iov_len = sizeof(child_gcs);
+	ret = ptrace(PTRACE_GETREGSET, child, NT_ARM_GCS, &iov);
+	if (ret != 0) {
+		ksft_print_msg("Failed to read child GCS state: %s (%d)\n",
+			       strerror(errno), errno);
+		goto error;
+	}
+
+	/* We should have inherited GCS over fork(), confirm */
+	if (!(child_gcs.features_enabled & PR_SHADOW_STACK_ENABLE)) {
+		ASSERT_TRUE(child_gcs.features_enabled &
+			    PR_SHADOW_STACK_ENABLE);
+		goto error;
+	}
+
+	gcspr = child_gcs.gcspr_el0;
+	ksft_print_msg("Child GCSPR 0x%lx, flags %llx, locked %llx\n",
+		       gcspr, child_gcs.features_enabled,
+		       child_gcs.features_locked);
+
+	/* Ideally we'd cross check with the child memory map */
+
+	errno = 0;
+	val = ptrace(PTRACE_PEEKDATA, child, (void *)gcspr, NULL);
+	ret = errno;
+	if (ret != 0)
+		ksft_print_msg("PTRACE_PEEKDATA failed: %s (%d)\n",
+			       strerror(ret), ret);
+	EXPECT_EQ(ret, 0);
+
+	/* The child should be in a function, the GCSPR shouldn't be 0 */
+	EXPECT_NE(val, 0);
+
+	/* Same thing via process_vm_readv() */
+	local_iov.iov_base = &rval;
+	local_iov.iov_len = sizeof(rval);
+	remote_iov.iov_base = (void *)gcspr;
+	remote_iov.iov_len = sizeof(rval);
+	ret = process_vm_readv(child, &local_iov, 1, &remote_iov, 1, 0);
+	if (ret == -1)
+		ksft_print_msg("process_vm_readv() failed: %s (%d)\n",
+			       strerror(errno), errno);
+	EXPECT_EQ(ret, sizeof(rval));
+	EXPECT_EQ(val, rval);
+
+	/* Write data via a peek */
+	ret = ptrace(PTRACE_POKEDATA, child, (void *)gcspr, NULL);
+	if (ret == -1)
+		ksft_print_msg("PTRACE_POKEDATA failed: %s (%d)\n",
+			       strerror(errno), errno);
+	EXPECT_EQ(ret, 0);
+	EXPECT_EQ(0, ptrace(PTRACE_PEEKDATA, child, (void *)gcspr, NULL));
+
+	/* Restore what we had before */
+	ret = ptrace(PTRACE_POKEDATA, child, (void *)gcspr, val);
+	if (ret == -1)
+		ksft_print_msg("PTRACE_POKEDATA failed: %s (%d)\n",
+			       strerror(errno), errno);
+	EXPECT_EQ(ret, 0);
+	EXPECT_EQ(val, ptrace(PTRACE_PEEKDATA, child, (void *)gcspr, NULL));
+
+	/* That's all, folks */
+	kill(child, SIGKILL);
+	return;
+
+error:
+	kill(child, SIGKILL);
+	ASSERT_FALSE(true);
+}
+
+FIXTURE(map_gcs)
+{
+	unsigned long *stack;
+};
+
+FIXTURE_VARIANT(map_gcs)
+{
+	size_t stack_size;
+	unsigned long flags;
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s2k_cap_marker)
+{
+	.stack_size = 2 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s2k_cap)
+{
+	.stack_size = 2 * 1024,
+	.flags = SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s2k_marker)
+{
+	.stack_size = 2 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s2k)
+{
+	.stack_size = 2 * 1024,
+	.flags = 0,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s4k_cap_marker)
+{
+	.stack_size = 4 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s4k_cap)
+{
+	.stack_size = 4 * 1024,
+	.flags = SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s3k_marker)
+{
+	.stack_size = 4 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s4k)
+{
+	.stack_size = 4 * 1024,
+	.flags = 0,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s16k_cap_marker)
+{
+	.stack_size = 16 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s16k_cap)
+{
+	.stack_size = 16 * 1024,
+	.flags = SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s16k_marker)
+{
+	.stack_size = 16 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s16k)
+{
+	.stack_size = 16 * 1024,
+	.flags = 0,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s64k_cap_marker)
+{
+	.stack_size = 64 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s64k_cap)
+{
+	.stack_size = 64 * 1024,
+	.flags = SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s64k_marker)
+{
+	.stack_size = 64 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s64k)
+{
+	.stack_size = 64 * 1024,
+	.flags = 0,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s128k_cap_marker)
+{
+	.stack_size = 128 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s128k_cap)
+{
+	.stack_size = 128 * 1024,
+	.flags = SHADOW_STACK_SET_TOKEN,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s128k_marker)
+{
+	.stack_size = 128 * 1024,
+	.flags = SHADOW_STACK_SET_MARKER,
+};
+
+FIXTURE_VARIANT_ADD(map_gcs, s128k)
+{
+	.stack_size = 128 * 1024,
+	.flags = 0,
+};
+
+FIXTURE_SETUP(map_gcs)
+{
+	self->stack = (void *)syscall(__NR_map_shadow_stack, 0,
+				      variant->stack_size, 
+				      variant->flags);
+	ASSERT_FALSE(self->stack == MAP_FAILED);
+	ksft_print_msg("Allocated stack from %p-%p\n", self->stack,
+		       self->stack + variant->stack_size);
+}
+
+FIXTURE_TEARDOWN(map_gcs)
+{
+	int ret;
+
+	if (self->stack != MAP_FAILED) {
+		ret = munmap(self->stack, variant->stack_size);
+		ASSERT_EQ(ret, 0);
+	}
+}
+
+/* The stack has a cap token */
+TEST_F(map_gcs, stack_capped)
+{
+	unsigned long *stack = self->stack;
+	size_t cap_index;
+
+	cap_index = (variant->stack_size / sizeof(unsigned long));
+
+	switch (variant->flags & (SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN)) {
+	case SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN:
+		cap_index -= 2;
+		break;
+	case SHADOW_STACK_SET_TOKEN:
+		cap_index -= 1;
+		break;
+	case SHADOW_STACK_SET_MARKER:
+	case 0:
+		/* No cap, no test */
+		return;
+	}
+
+	ASSERT_EQ(stack[cap_index], GCS_CAP(&stack[cap_index]));
+}
+
+/* The top of the stack is 0 */
+TEST_F(map_gcs, stack_terminated)
+{
+	unsigned long *stack = self->stack;
+	size_t term_index;
+
+	if (!(variant->flags & SHADOW_STACK_SET_MARKER))
+		return;
+
+	term_index = (variant->stack_size / sizeof(unsigned long)) - 1;
+
+	ASSERT_EQ(stack[term_index], 0);
+}
+
+/* Writes should fault */
+TEST_F_SIGNAL(map_gcs, not_writeable, SIGSEGV)
+{
+	self->stack[0] = 0;
+}
+
+/* Put it all together, we can safely switch to and from the stack */
+TEST_F(map_gcs, stack_switch)
+{
+	size_t cap_index;
+	cap_index = (variant->stack_size / sizeof(unsigned long));
+	unsigned long *orig_gcspr_el0, *pivot_gcspr_el0;
+
+	/* Skip over the stack terminator and point at the cap */
+	switch (variant->flags & (SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN)) {
+	case SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN:
+		cap_index -= 2;
+		break;
+	case SHADOW_STACK_SET_TOKEN:
+		cap_index -= 1;
+		break;
+	case SHADOW_STACK_SET_MARKER:
+	case 0:
+		/* No cap, no test */
+		return;
+	}
+	pivot_gcspr_el0 = &self->stack[cap_index];
+
+	/* Pivot to the new GCS */
+	ksft_print_msg("Pivoting to %p from %p, target has value 0x%lx\n",
+		       pivot_gcspr_el0, get_gcspr(),
+		       *pivot_gcspr_el0);
+	gcsss1(pivot_gcspr_el0);
+	orig_gcspr_el0 = gcsss2();
+	ksft_print_msg("Pivoted to %p from %p, target has value 0x%lx\n",
+		       get_gcspr(), orig_gcspr_el0,
+		       *pivot_gcspr_el0);
+
+	ksft_print_msg("Pivoted, GCSPR_EL0 now %p\n", get_gcspr());
+
+	/* New GCS must be in the new buffer */
+	ASSERT_TRUE((unsigned long)get_gcspr() > (unsigned long)self->stack);
+	ASSERT_TRUE((unsigned long)get_gcspr() <=
+		    (unsigned long)self->stack + variant->stack_size);
+
+	/* We should be able to use all but 2 slots of the new stack */
+	ksft_print_msg("Recursing %zu levels\n", cap_index - 1);
+	gcs_recurse(cap_index - 1);
+
+	/* Pivot back to the original GCS */
+	gcsss1(orig_gcspr_el0);
+	pivot_gcspr_el0 = gcsss2();
+
+	gcs_recurse(0);
+	ksft_print_msg("Pivoted back to GCSPR_EL0 0x%p\n", get_gcspr());
+}
+
+/* We fault if we try to go beyond the end of the stack */
+TEST_F_SIGNAL(map_gcs, stack_overflow, SIGSEGV)
+{
+	size_t cap_index;
+	cap_index = (variant->stack_size / sizeof(unsigned long));
+	unsigned long *orig_gcspr_el0, *pivot_gcspr_el0;
+
+	/* Skip over the stack terminator and point at the cap */
+	switch (variant->flags & (SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN)) {
+	case SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN:
+		cap_index -= 2;
+		break;
+	case SHADOW_STACK_SET_TOKEN:
+		cap_index -= 1;
+		break;
+	case SHADOW_STACK_SET_MARKER:
+	case 0:
+		/* No cap, no test but we need to SEGV to avoid a false fail */
+		orig_gcspr_el0 = get_gcspr();
+		*orig_gcspr_el0 = 0;
+		return;
+	}
+	pivot_gcspr_el0 = &self->stack[cap_index];
+
+	/* Pivot to the new GCS */
+	ksft_print_msg("Pivoting to %p from %p, target has value 0x%lx\n",
+		       pivot_gcspr_el0, get_gcspr(),
+		       *pivot_gcspr_el0);
+	gcsss1(pivot_gcspr_el0);
+	orig_gcspr_el0 = gcsss2();
+	ksft_print_msg("Pivoted to %p from %p, target has value 0x%lx\n",
+		       pivot_gcspr_el0, orig_gcspr_el0,
+		       *pivot_gcspr_el0);
+
+	ksft_print_msg("Pivoted, GCSPR_EL0 now %p\n", get_gcspr());
+
+	/* New GCS must be in the new buffer */
+	ASSERT_TRUE((unsigned long)get_gcspr() > (unsigned long)self->stack);
+	ASSERT_TRUE((unsigned long)get_gcspr() <=
+		    (unsigned long)self->stack + variant->stack_size);
+
+	/* Now try to recurse, we should fault doing this. */
+	ksft_print_msg("Recursing %zu levels...\n", cap_index + 1);
+	gcs_recurse(cap_index + 1);
+	ksft_print_msg("...done\n");
+
+	/* Clean up properly to try to guard against spurious passes. */
+	gcsss1(orig_gcspr_el0);
+	pivot_gcspr_el0 = gcsss2();
+	ksft_print_msg("Pivoted back to GCSPR_EL0 0x%p\n", get_gcspr());
+}
+
+FIXTURE(map_invalid_gcs)
+{
+};
+
+FIXTURE_VARIANT(map_invalid_gcs)
+{
+	size_t stack_size;
+};
+
+FIXTURE_SETUP(map_invalid_gcs)
+{
+}
+
+FIXTURE_TEARDOWN(map_invalid_gcs)
+{
+}
+
+/* GCS must be larger than 16 bytes */
+FIXTURE_VARIANT_ADD(map_invalid_gcs, too_small)
+{
+	.stack_size = 8,
+};
+
+/* GCS size must be 16 byte aligned */
+FIXTURE_VARIANT_ADD(map_invalid_gcs, unligned_1)  { .stack_size = 1024 + 1  };
+FIXTURE_VARIANT_ADD(map_invalid_gcs, unligned_2)  { .stack_size = 1024 + 2  };
+FIXTURE_VARIANT_ADD(map_invalid_gcs, unligned_3)  { .stack_size = 1024 + 3  };
+FIXTURE_VARIANT_ADD(map_invalid_gcs, unligned_4)  { .stack_size = 1024 + 4  };
+FIXTURE_VARIANT_ADD(map_invalid_gcs, unligned_5)  { .stack_size = 1024 + 5  };
+FIXTURE_VARIANT_ADD(map_invalid_gcs, unligned_6)  { .stack_size = 1024 + 6  };
+FIXTURE_VARIANT_ADD(map_invalid_gcs, unligned_7)  { .stack_size = 1024 + 7  };
+
+TEST_F(map_invalid_gcs, do_map)
+{
+	void *stack;
+
+	stack = (void *)syscall(__NR_map_shadow_stack, 0,
+				variant->stack_size, 0);
+	ASSERT_TRUE(stack == MAP_FAILED);
+	if (stack != MAP_FAILED)
+		munmap(stack, variant->stack_size);
+}
+
+FIXTURE(invalid_mprotect)
+{
+	unsigned long *stack;
+	size_t stack_size;
+};
+
+FIXTURE_VARIANT(invalid_mprotect)
+{
+	unsigned long flags;
+};
+
+FIXTURE_SETUP(invalid_mprotect)
+{
+	self->stack_size = sysconf(_SC_PAGE_SIZE);
+	self->stack = (void *)syscall(__NR_map_shadow_stack, 0,
+				      self->stack_size, 0);
+	ASSERT_FALSE(self->stack == MAP_FAILED);
+	ksft_print_msg("Allocated stack from %p-%p\n", self->stack,
+		       self->stack + self->stack_size);
+}
+
+FIXTURE_TEARDOWN(invalid_mprotect)
+{
+	int ret;
+
+	if (self->stack != MAP_FAILED) {
+		ret = munmap(self->stack, self->stack_size);
+		ASSERT_EQ(ret, 0);
+	}
+}
+
+FIXTURE_VARIANT_ADD(invalid_mprotect, exec)
+{
+	.flags = PROT_EXEC,
+};
+
+TEST_F(invalid_mprotect, do_map)
+{
+	int ret;
+
+	ret = mprotect(self->stack, self->stack_size, variant->flags);
+	ASSERT_EQ(ret, -1);
+}
+
+TEST_F(invalid_mprotect, do_map_read)
+{
+	int ret;
+
+	ret = mprotect(self->stack, self->stack_size,
+		       variant->flags | PROT_READ);
+	ASSERT_EQ(ret, -1);
+}
+
+int main(int argc, char **argv)
+{
+	unsigned long gcs_mode;
+	int ret;
+
+	if (!(getauxval(AT_HWCAP) & HWCAP_GCS))
+		ksft_exit_skip("SKIP GCS not supported\n");
+
+	/* 
+	 * Force shadow stacks on, our tests *should* be fine with or
+	 * without libc support and with or without this having ended
+	 * up tagged for GCS and enabled by the dynamic linker.  We
+	 * can't use the libc prctl() function since we can't return
+	 * from enabling the stack.
+	 */
+	ret = my_syscall2(__NR_prctl, PR_GET_SHADOW_STACK_STATUS, &gcs_mode);
+	if (ret) {
+		ksft_print_msg("Failed to read GCS state: %d\n", ret);
+		return EXIT_FAILURE;
+	}
+	
+	if (!(gcs_mode & PR_SHADOW_STACK_ENABLE)) {
+		gcs_mode = PR_SHADOW_STACK_ENABLE;
+		ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+				  gcs_mode);
+		if (ret) {
+			ksft_print_msg("Failed to configure GCS: %d\n", ret);
+			return EXIT_FAILURE;
+		}
+	}
+
+	/* Avoid returning in case libc doesn't understand GCS */
+	exit(test_harness_run(argc, argv));
+}