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}
113