chdexcr.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2
  3#include <errno.h>
  4#include <stddef.h>
  5#include <stdio.h>
  6#include <stdlib.h>
  7#include <string.h>
  8#include <sys/prctl.h>
  9
 10#include "dexcr.h"
 11#include "utils.h"
 12
 13static void die(const char *msg)
 14{
 15	printf("%s\n", msg);
 16	exit(1);
 17}
 18
 19static void help(void)
 20{
 21	printf("Invoke a provided program with a custom DEXCR on-exec reset value\n"
 22	       "\n"
 23	       "usage: chdexcr [CHDEXCR OPTIONS] -- PROGRAM [ARGS...]\n"
 24	       "\n"
 25	       "Each configurable DEXCR aspect is exposed as an option.\n"
 26	       "\n"
 27	       "The normal option sets the aspect in the DEXCR. The --no- variant\n"
 28	       "clears that aspect. For example, --ibrtpd sets the IBRTPD aspect bit,\n"
 29	       "so indirect branch prediction will be disabled in the provided program.\n"
 30	       "Conversely, --no-ibrtpd clears the aspect bit, so indirect branch\n"
 31	       "prediction may occur.\n"
 32	       "\n"
 33	       "CHDEXCR OPTIONS:\n");
 34
 35	for (int i = 0; i < ARRAY_SIZE(aspects); i++) {
 36		const struct dexcr_aspect *aspect = &aspects[i];
 37
 38		if (aspect->prctl == -1)
 39			continue;
 40
 41		printf("  --%-6s / --no-%-6s : %s\n", aspect->opt, aspect->opt, aspect->desc);
 42	}
 43}
 44
 45static const struct dexcr_aspect *opt_to_aspect(const char *opt)
 46{
 47	for (int i = 0; i < ARRAY_SIZE(aspects); i++)
 48		if (aspects[i].prctl != -1 && !strcmp(aspects[i].opt, opt))
 49			return &aspects[i];
 50
 51	return NULL;
 52}
 53
 54static int apply_option(const char *option)
 55{
 56	const struct dexcr_aspect *aspect;
 57	const char *opt = NULL;
 58	const char *set_prefix = "--";
 59	const char *clear_prefix = "--no-";
 60	unsigned long ctrl = 0;
 61	int err;
 62
 63	if (!strcmp(option, "-h") || !strcmp(option, "--help")) {
 64		help();
 65		exit(0);
 66	}
 67
 68	/* Strip out --(no-) prefix and determine ctrl value */
 69	if (!strncmp(option, clear_prefix, strlen(clear_prefix))) {
 70		opt = &option[strlen(clear_prefix)];
 71		ctrl |= PR_PPC_DEXCR_CTRL_CLEAR_ONEXEC;
 72	} else if (!strncmp(option, set_prefix, strlen(set_prefix))) {
 73		opt = &option[strlen(set_prefix)];
 74		ctrl |= PR_PPC_DEXCR_CTRL_SET_ONEXEC;
 75	}
 76
 77	if (!opt || !*opt)
 78		return 1;
 79
 80	aspect = opt_to_aspect(opt);
 81	if (!aspect)
 82		die("unknown aspect");
 83
 84	err = pr_set_dexcr(aspect->prctl, ctrl);
 85	if (err)
 86		die("failed to apply option");
 87
 88	return 0;
 89}
 90
 91int main(int argc, char *const argv[])
 92{
 93	int i;
 94
 95	if (!dexcr_exists())
 96		die("DEXCR not detected on this hardware");
 97
 98	for (i = 1; i < argc; i++)
 99		if (apply_option(argv[i]))
100			break;
101
102	if (i < argc && !strcmp(argv[i], "--"))
103		i++;
104
105	if (i >= argc)
106		die("missing command");
107
108	execvp(argv[i], &argv[i]);
109	perror("execve");
110
111	return errno;
112}