linux/tools/testing/selftests/powerpc/dexcr/chdexcr.c

// 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 prediction 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;
}