From f88723a609787254f7645eb6ac261b8363e8a5bc Mon Sep 17 00:00:00 2001
From: Benjamin Gray <bgray@linux.ibm.com>
Date: Wed, 17 Apr 2024 21:23:24 +1000
Subject: selftests/powerpc/dexcr: Add chdexcr utility

Adds a utility to exercise the prctl DEXCR inheritance in the shell.
Supports setting and clearing each aspect.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
[mpe: Use correct SPDX license, use execvp() for usability, print errors]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240417112325.728010-9-bgray@linux.ibm.com
---
 tools/testing/selftests/powerpc/dexcr/chdexcr.c | 112 ++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 tools/testing/selftests/powerpc/dexcr/chdexcr.c

(limited to 'tools/testing/selftests/powerpc/dexcr/chdexcr.c')

diff --git a/tools/testing/selftests/powerpc/dexcr/chdexcr.c b/tools/testing/selftests/powerpc/dexcr/chdexcr.c
new file mode 100644
index 000000000000..bda44630cada
--- /dev/null
+++ b/tools/testing/selftests/powerpc/dexcr/chdexcr.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/prctl.h>
+
+#include "dexcr.h"
+#include "utils.h"
+
+static void die(const char *msg)
+{
+	printf("%s\n", msg);
+	exit(1);
+}
+
+static void help(void)
+{
+	printf("Invoke a provided program with a custom DEXCR on-exec reset value\n"
+	       "\n"
+	       "usage: chdexcr [CHDEXCR OPTIONS] -- PROGRAM [ARGS...]\n"
+	       "\n"
+	       "Each configurable DEXCR aspect is exposed as an option.\n"
+	       "\n"
+	       "The normal option sets the aspect in the DEXCR. The --no- variant\n"
+	       "clears that aspect. For example, --ibrtpd sets the IBRTPD aspect bit,\n"
+	       "so indirect branch predicition will be disabled in the provided program.\n"
+	       "Conversely, --no-ibrtpd clears the aspect bit, so indirect branch\n"
+	       "prediction may occur.\n"
+	       "\n"
+	       "CHDEXCR OPTIONS:\n");
+
+	for (int i = 0; i < ARRAY_SIZE(aspects); i++) {
+		const struct dexcr_aspect *aspect = &aspects[i];
+
+		if (aspect->prctl == -1)
+			continue;
+
+		printf("  --%-6s / --no-%-6s : %s\n", aspect->opt, aspect->opt, aspect->desc);
+	}
+}
+
+static const struct dexcr_aspect *opt_to_aspect(const char *opt)
+{
+	for (int i = 0; i < ARRAY_SIZE(aspects); i++)
+		if (aspects[i].prctl != -1 && !strcmp(aspects[i].opt, opt))
+			return &aspects[i];
+
+	return NULL;
+}
+
+static int apply_option(const char *option)
+{
+	const struct dexcr_aspect *aspect;
+	const char *opt = NULL;
+	const char *set_prefix = "--";
+	const char *clear_prefix = "--no-";
+	unsigned long ctrl = 0;
+	int err;
+
+	if (!strcmp(option, "-h") || !strcmp(option, "--help")) {
+		help();
+		exit(0);
+	}
+
+	/* Strip out --(no-) prefix and determine ctrl value */
+	if (!strncmp(option, clear_prefix, strlen(clear_prefix))) {
+		opt = &option[strlen(clear_prefix)];
+		ctrl |= PR_PPC_DEXCR_CTRL_CLEAR_ONEXEC;
+	} else if (!strncmp(option, set_prefix, strlen(set_prefix))) {
+		opt = &option[strlen(set_prefix)];
+		ctrl |= PR_PPC_DEXCR_CTRL_SET_ONEXEC;
+	}
+
+	if (!opt || !*opt)
+		return 1;
+
+	aspect = opt_to_aspect(opt);
+	if (!aspect)
+		die("unknown aspect");
+
+	err = pr_set_dexcr(aspect->prctl, ctrl);
+	if (err)
+		die("failed to apply option");
+
+	return 0;
+}
+
+int main(int argc, char *const argv[])
+{
+	int i;
+
+	if (!dexcr_exists())
+		die("DEXCR not detected on this hardware");
+
+	for (i = 1; i < argc; i++)
+		if (apply_option(argv[i]))
+			break;
+
+	if (i < argc && !strcmp(argv[i], "--"))
+		i++;
+
+	if (i >= argc)
+		die("missing command");
+
+	execvp(argv[i], &argv[i]);
+	perror("execve");
+
+	return errno;
+}
-- 
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