kselftest/arm64: Add simple test for MTE prctl

The current tests use the prctls for various things but there's no
coverage of the edges of the interface so add some basics. This isn't
hugely useful as it is (it originally had some coverage for the
combinations with asymmetric mode but we removed the prctl() for that)
but it might be a helpful starting point for future work, for example
covering error handling.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220419103243.24774-5-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/mte/.gitignore

@@ -3,5 +3,6 @@ check_gcr_el1_cswitch
 check_tags_inclusion
 check_child_memory
 check_mmap_options
+check_prctl
 check_ksm_options
 check_user_mem

tools/testing/selftests/arm64/mte/check_prctl.c

@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2022 ARM Limited
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <sys/auxv.h>
+#include <sys/prctl.h>
+
+#include <asm/hwcap.h>
+
+#include "kselftest.h"
+
+static int set_tagged_addr_ctrl(int val)
+{
+	int ret;
+
+	ret = prctl(PR_SET_TAGGED_ADDR_CTRL, val, 0, 0, 0);
+	if (ret < 0)
+		ksft_print_msg("PR_SET_TAGGED_ADDR_CTRL: failed %d %d (%s)\n",
+			       ret, errno, strerror(errno));
+	return ret;
+}
+
+static int get_tagged_addr_ctrl(void)
+{
+	int ret;
+
+	ret = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+	if (ret < 0)
+		ksft_print_msg("PR_GET_TAGGED_ADDR_CTRL failed: %d %d (%s)\n",
+			       ret, errno, strerror(errno));
+	return ret;
+}
+
+/*
+ * Read the current mode without having done any configuration, should
+ * run first.
+ */
+void check_basic_read(void)
+{
+	int ret;
+
+	ret = get_tagged_addr_ctrl();
+	if (ret < 0) {
+		ksft_test_result_fail("check_basic_read\n");
+		return;
+	}
+
+	if (ret & PR_MTE_TCF_SYNC)
+		ksft_print_msg("SYNC enabled\n");
+	if (ret & PR_MTE_TCF_ASYNC)
+		ksft_print_msg("ASYNC enabled\n");
+
+	/* Any configuration is valid */
+	ksft_test_result_pass("check_basic_read\n");
+}
+
+/*
+ * Attempt to set a specified combination of modes.
+ */
+void set_mode_test(const char *name, int hwcap2, int mask)
+{
+	int ret;
+
+	if ((getauxval(AT_HWCAP2) & hwcap2) != hwcap2) {
+		ksft_test_result_skip("%s\n", name);
+		return;
+	}
+
+	ret = set_tagged_addr_ctrl(mask);
+	if (ret < 0) {
+		ksft_test_result_fail("%s\n", name);
+		return;
+	}
+
+	ret = get_tagged_addr_ctrl();
+	if (ret < 0) {
+		ksft_test_result_fail("%s\n", name);
+		return;
+	}
+
+	if ((ret & PR_MTE_TCF_MASK) == mask) {
+		ksft_test_result_pass("%s\n", name);
+	} else {
+		ksft_print_msg("Got %x, expected %x\n",
+			       (ret & PR_MTE_TCF_MASK), mask);
+		ksft_test_result_fail("%s\n", name);
+	}
+}
+
+struct mte_mode {
+	int mask;
+	int hwcap2;
+	const char *name;
+} mte_modes[] = {
+	{ PR_MTE_TCF_NONE,  0,          "NONE"  },
+	{ PR_MTE_TCF_SYNC,  HWCAP2_MTE, "SYNC"  },
+	{ PR_MTE_TCF_ASYNC, HWCAP2_MTE, "ASYNC" },
+	{ PR_MTE_TCF_SYNC | PR_MTE_TCF_ASYNC,  HWCAP2_MTE, "SYNC+ASYNC"  },
+};
+
+int main(void)
+{
+	int i;
+
+	ksft_print_header();
+	ksft_set_plan(5);
+
+	check_basic_read();
+	for (i = 0; i < ARRAY_SIZE(mte_modes); i++)
+		set_mode_test(mte_modes[i].name, mte_modes[i].hwcap2,
+			      mte_modes[i].mask);
+
+	ksft_print_cnts();
+
+	return 0;
+}