1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (c) 2019 Richard Palethorpe <rpalethorpe@suse.com>
4 * Original byte code was provided by jannh@google.com
5 *
6 * Check for the bug fixed by 95a762e2c8c942780948091f8f2a4f32fce1ac6f
7 * "bpf: fix incorrect sign extension in check_alu_op()"
8 * CVE-2017-16995
9 *
10 * This test is very similar to the reproducer found here:
11 * https://bugs.chromium.org/p/project-zero/issues/detail?id=1454
12 *
13 * However it has been modified to try to corrupt the map struct instead of
14 * writing to a noncanonical pointer. This appears to be more reliable at
15 * producing stack traces and confirms we would be able to overwrite the ops
16 * function pointers, as suggested by Jan.
17 *
18 * If the eBPF code is loaded then this is considered a failure regardless of
19 * whether it is able to cause any visible damage.
20 */
21
22#include <string.h>
23#include <stdio.h>
24#include <inttypes.h>
25
26#include "config.h"
27#include "tst_test.h"
28#include "tst_capability.h"
29#include "bpf_common.h"
30
31#define LOG_SIZE (1024 * 1024)
32
33#define CHECK_BPF_RET(x) ((x) >= 0 || ((x) == -1 && errno != EPERM))
34
35static const char MSG[] = "Ahoj!";
36static char *msg;
37
38static char *log;
39static uint32_t *key;
40static uint64_t *val;
41static union bpf_attr *attr;
42
43static int load_prog(int fd)
44{
45	int ret;
46
47	struct bpf_insn insn[] = {
48		BPF_LD_MAP_FD(BPF_REG_1, fd),
49
50		// fill r0 with pointer to map value
51		BPF_MOV64_REG(BPF_REG_8, BPF_REG_10),
52		BPF_ALU64_IMM(BPF_ADD, BPF_REG_8, -4), // allocate 4 bytes stack
53		BPF_MOV32_IMM(BPF_REG_2, 0),
54		BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_2, 0),
55		BPF_MOV64_REG(BPF_REG_2, BPF_REG_8),
56		BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
57		BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 2),
58		BPF_MOV64_REG(BPF_REG_0, 0), // prepare exit
59		BPF_EXIT_INSN(), // exit
60
61		// r1 = 0xffff'ffff, mistreated as 0xffff'ffff'ffff'ffff
62		BPF_MOV32_IMM(BPF_REG_1, -1),
63		// r1 = 0x1'0000'0000, mistreated as 0
64		BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 1),
65		// r1 = 64, mistreated as 0
66		BPF_ALU64_IMM(BPF_RSH, BPF_REG_1, 26),
67
68		// Write actual value of r1 to map for debugging this test
69		BPF_STX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
70
71		// Corrupt the map meta-data which comes before the map data
72		BPF_MOV64_REG(BPF_REG_2, BPF_REG_0),
73		BPF_ALU64_REG(BPF_SUB, BPF_REG_2, BPF_REG_1),
74
75		BPF_MOV64_IMM(BPF_REG_3, 0xdeadbeef),
76		BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
77		BPF_ALU64_REG(BPF_SUB, BPF_REG_2, BPF_REG_1),
78		BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
79		BPF_ALU64_REG(BPF_SUB, BPF_REG_2, BPF_REG_1),
80		BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
81		BPF_ALU64_REG(BPF_SUB, BPF_REG_2, BPF_REG_1),
82		BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0),
83
84		// terminate to make the verifier happy
85		BPF_MOV32_IMM(BPF_REG_0, 0),
86		BPF_EXIT_INSN()
87	};
88
89	bpf_init_prog_attr(attr, insn, sizeof(insn), log, LOG_SIZE);
90	ret = TST_RETRY_FUNC(bpf(BPF_PROG_LOAD, attr, sizeof(*attr)),
91		CHECK_BPF_RET);
92
93	if (ret < -1)
94		tst_brk(TBROK, "Invalid bpf() return value %d", ret);
95
96	if (ret >= 0) {
97		tst_res(TINFO, "Verification log:");
98		fputs(log, stderr);
99		return ret;
100	}
101
102	if (log[0] == 0)
103		tst_brk(TBROK | TERRNO, "Failed to load program");
104
105	tst_res(TPASS | TERRNO, "Failed verification");
106	return ret;
107}
108
109static void setup(void)
110{
111	rlimit_bump_memlock();
112	memcpy(msg, MSG, sizeof(MSG));
113}
114
115static void run(void)
116{
117	int map_fd, prog_fd;
118
119	map_fd = bpf_map_array_create(32);
120
121	memset(attr, 0, sizeof(*attr));
122	attr->map_fd = map_fd;
123	attr->key = ptr_to_u64(key);
124	attr->value = ptr_to_u64(val);
125	attr->flags = BPF_ANY;
126
127	TEST(bpf(BPF_MAP_UPDATE_ELEM, attr, sizeof(*attr)));
128	if (TST_RET == -1)
129		tst_brk(TBROK | TTERRNO, "Failed to lookup map element");
130
131	prog_fd = load_prog(map_fd);
132	if (prog_fd == -1)
133		goto exit;
134
135	tst_res(TFAIL, "Loaded bad eBPF, now we will run it and maybe crash");
136
137	bpf_run_prog(prog_fd, msg, sizeof(MSG));
138	SAFE_CLOSE(prog_fd);
139
140	*key = 0;
141	bpf_map_array_get(map_fd, key, val);
142	tst_res(TINFO, "Pointer offset was 0x%"PRIx64, *val);
143exit:
144	SAFE_CLOSE(map_fd);
145}
146
147static struct tst_test test = {
148	.setup = setup,
149	.test_all = run,
150	.min_kver = "3.18",
151	.caps = (struct tst_cap []) {
152		TST_CAP(TST_CAP_DROP, CAP_SYS_ADMIN),
153		{}
154	},
155	.bufs = (struct tst_buffers []) {
156		{&key, .size = sizeof(*key)},
157		{&val, .size = sizeof(*val)},
158		{&log, .size = LOG_SIZE},
159		{&attr, .size = sizeof(*attr)},
160		{&msg, .size = sizeof(MSG)},
161		{},
162	},
163	.tags = (const struct tst_tag[]) {
164		{"linux-git", "95a762e2c8c9"},
165		{"CVE", "2017-16995"},
166		{}
167	}
168};
169