1// SPDX-License-Identifier: GPL-2.0
2/*
3 * iopl.c - Test case for a Linux on Xen 64-bit bug
4 * Copyright (c) 2015 Andrew Lutomirski
5 */
6
7#define _GNU_SOURCE
8#include <err.h>
9#include <stdio.h>
10#include <stdint.h>
11#include <signal.h>
12#include <setjmp.h>
13#include <stdlib.h>
14#include <string.h>
15#include <errno.h>
16#include <unistd.h>
17#include <sys/types.h>
18#include <sys/wait.h>
19#include <stdbool.h>
20#include <sched.h>
21#include <sys/io.h>
22
23static int nerrs = 0;
24
25static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
26		       int flags)
27{
28	struct sigaction sa;
29	memset(&sa, 0, sizeof(sa));
30	sa.sa_sigaction = handler;
31	sa.sa_flags = SA_SIGINFO | flags;
32	sigemptyset(&sa.sa_mask);
33	if (sigaction(sig, &sa, 0))
34		err(1, "sigaction");
35
36}
37
38static void clearhandler(int sig)
39{
40	struct sigaction sa;
41	memset(&sa, 0, sizeof(sa));
42	sa.sa_handler = SIG_DFL;
43	sigemptyset(&sa.sa_mask);
44	if (sigaction(sig, &sa, 0))
45		err(1, "sigaction");
46}
47
48static jmp_buf jmpbuf;
49
50static void sigsegv(int sig, siginfo_t *si, void *ctx_void)
51{
52	siglongjmp(jmpbuf, 1);
53}
54
55static bool try_outb(unsigned short port)
56{
57	sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
58	if (sigsetjmp(jmpbuf, 1) != 0) {
59		return false;
60	} else {
61		asm volatile ("outb %%al, %w[port]"
62			      : : [port] "Nd" (port), "a" (0));
63		return true;
64	}
65	clearhandler(SIGSEGV);
66}
67
68static void expect_ok_outb(unsigned short port)
69{
70	if (!try_outb(port)) {
71		printf("[FAIL]\toutb to 0x%02hx failed\n", port);
72		exit(1);
73	}
74
75	printf("[OK]\toutb to 0x%02hx worked\n", port);
76}
77
78static void expect_gp_outb(unsigned short port)
79{
80	if (try_outb(port)) {
81		printf("[FAIL]\toutb to 0x%02hx worked\n", port);
82		nerrs++;
83	}
84
85	printf("[OK]\toutb to 0x%02hx failed\n", port);
86}
87
88#define RET_FAULTED	0
89#define RET_FAIL	1
90#define RET_EMUL	2
91
92static int try_cli(void)
93{
94	unsigned long flags;
95
96	sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
97	if (sigsetjmp(jmpbuf, 1) != 0) {
98		return RET_FAULTED;
99	} else {
100		asm volatile("cli; pushf; pop %[flags]"
101				: [flags] "=rm" (flags));
102
103		/* X86_FLAGS_IF */
104		if (!(flags & (1 << 9)))
105			return RET_FAIL;
106		else
107			return RET_EMUL;
108	}
109	clearhandler(SIGSEGV);
110}
111
112static int try_sti(bool irqs_off)
113{
114	unsigned long flags;
115
116	sethandler(SIGSEGV, sigsegv, SA_RESETHAND);
117	if (sigsetjmp(jmpbuf, 1) != 0) {
118		return RET_FAULTED;
119	} else {
120		asm volatile("sti; pushf; pop %[flags]"
121				: [flags] "=rm" (flags));
122
123		/* X86_FLAGS_IF */
124		if (irqs_off && (flags & (1 << 9)))
125			return RET_FAIL;
126		else
127			return RET_EMUL;
128	}
129	clearhandler(SIGSEGV);
130}
131
132static void expect_gp_sti(bool irqs_off)
133{
134	int ret = try_sti(irqs_off);
135
136	switch (ret) {
137	case RET_FAULTED:
138		printf("[OK]\tSTI faulted\n");
139		break;
140	case RET_EMUL:
141		printf("[OK]\tSTI NOPped\n");
142		break;
143	default:
144		printf("[FAIL]\tSTI worked\n");
145		nerrs++;
146	}
147}
148
149/*
150 * Returns whether it managed to disable interrupts.
151 */
152static bool test_cli(void)
153{
154	int ret = try_cli();
155
156	switch (ret) {
157	case RET_FAULTED:
158		printf("[OK]\tCLI faulted\n");
159		break;
160	case RET_EMUL:
161		printf("[OK]\tCLI NOPped\n");
162		break;
163	default:
164		printf("[FAIL]\tCLI worked\n");
165		nerrs++;
166		return true;
167	}
168
169	return false;
170}
171
172int main(void)
173{
174	cpu_set_t cpuset;
175
176	CPU_ZERO(&cpuset);
177	CPU_SET(0, &cpuset);
178	if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
179		err(1, "sched_setaffinity to CPU 0");
180
181	/* Probe for iopl support.  Note that iopl(0) works even as nonroot. */
182	switch(iopl(3)) {
183	case 0:
184		break;
185	case -ENOSYS:
186		printf("[OK]\tiopl() nor supported\n");
187		return 0;
188	default:
189		printf("[OK]\tiopl(3) failed (%d) -- try running as root\n",
190		       errno);
191		return 0;
192	}
193
194	/* Make sure that CLI/STI are blocked even with IOPL level 3 */
195	expect_gp_sti(test_cli());
196	expect_ok_outb(0x80);
197
198	/* Establish an I/O bitmap to test the restore */
199	if (ioperm(0x80, 1, 1) != 0)
200		err(1, "ioperm(0x80, 1, 1) failed\n");
201
202	/* Restore our original state prior to starting the fork test. */
203	if (iopl(0) != 0)
204		err(1, "iopl(0)");
205
206	/*
207	 * Verify that IOPL emulation is disabled and the I/O bitmap still
208	 * works.
209	 */
210	expect_ok_outb(0x80);
211	expect_gp_outb(0xed);
212	/* Drop the I/O bitmap */
213	if (ioperm(0x80, 1, 0) != 0)
214		err(1, "ioperm(0x80, 1, 0) failed\n");
215
216	pid_t child = fork();
217	if (child == -1)
218		err(1, "fork");
219
220	if (child == 0) {
221		printf("\tchild: set IOPL to 3\n");
222		if (iopl(3) != 0)
223			err(1, "iopl");
224
225		printf("[RUN]\tchild: write to 0x80\n");
226		asm volatile ("outb %%al, $0x80" : : "a" (0));
227
228		return 0;
229	} else {
230		int status;
231		if (waitpid(child, &status, 0) != child ||
232		    !WIFEXITED(status)) {
233			printf("[FAIL]\tChild died\n");
234			nerrs++;
235		} else if (WEXITSTATUS(status) != 0) {
236			printf("[FAIL]\tChild failed\n");
237			nerrs++;
238		} else {
239			printf("[OK]\tChild succeeded\n");
240		}
241	}
242
243	printf("[RUN]\tparent: write to 0x80 (should fail)\n");
244
245	expect_gp_outb(0x80);
246	expect_gp_sti(test_cli());
247
248	/* Test the capability checks. */
249	printf("\tiopl(3)\n");
250	if (iopl(3) != 0)
251		err(1, "iopl(3)");
252
253	printf("\tDrop privileges\n");
254	if (setresuid(1, 1, 1) != 0) {
255		printf("[WARN]\tDropping privileges failed\n");
256		goto done;
257	}
258
259	printf("[RUN]\tiopl(3) unprivileged but with IOPL==3\n");
260	if (iopl(3) != 0) {
261		printf("[FAIL]\tiopl(3) should work if iopl is already 3 even if unprivileged\n");
262		nerrs++;
263	}
264
265	printf("[RUN]\tiopl(0) unprivileged\n");
266	if (iopl(0) != 0) {
267		printf("[FAIL]\tiopl(0) should work if iopl is already 3 even if unprivileged\n");
268		nerrs++;
269	}
270
271	printf("[RUN]\tiopl(3) unprivileged\n");
272	if (iopl(3) == 0) {
273		printf("[FAIL]\tiopl(3) should fail if when unprivileged if iopl==0\n");
274		nerrs++;
275	} else {
276		printf("[OK]\tFailed as expected\n");
277	}
278
279done:
280	return nerrs ? 1 : 0;
281}
282