1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (c) 2021 SUSE LLC <[email protected]>
4 */
5
6 /*\
7 * [Description]
8 *
9 * Compare the effects of 32-bit div/mod by zero with the "expected"
10 * behaviour.
11 *
12 * The commit "bpf: fix subprog verifier bypass by div/mod by 0
13 * exception", changed div/mod by zero from exiting the current
14 * program to setting the destination register to zero (div) or
15 * leaving it untouched (mod).
16 *
17 * This solved one verfier bug which allowed dodgy pointer values, but
18 * it turned out that the source register was being 32-bit truncated
19 * when it should not be. Also the destination register for mod was
20 * not being truncated when it should be.
21 *
22 * So then we have the following two fixes:
23 * "bpf: Fix 32 bit src register truncation on div/mod"
24 * "bpf: Fix truncation handling for mod32 dst reg wrt zero"
25 *
26 * Testing for all of these issues is a problem. Not least because
27 * division by zero is undefined, so in theory any result is
28 * acceptable so long as the verifier and runtime behaviour
29 * match.
30 *
31 * However to keep things simple we just check if the source and
32 * destination register runtime values match the current upstream
33 * behaviour at the time of writing.
34 *
35 * If the test fails you may have one or more of the above patches
36 * missing. In this case it is possible that you are not vulnerable
37 * depending on what other backports and fixes have been applied. If
38 * upstream changes the behaviour of division by zero, then the test
39 * will need updating.
40 *
41 * Note that we use r6 as the src register and r7 as the dst. w6 and
42 * w7 are the same registers treated as 32bit.
43 */
44
45 #include <stdio.h>
46 #include <string.h>
47 #include <inttypes.h>
48
49 #include "config.h"
50 #include "tst_test.h"
51 #include "tst_taint.h"
52 #include "tst_capability.h"
53 #include "bpf_common.h"
54
55 static const char MSG[] = "Ahoj!";
56 static char *msg;
57
58 static int map_fd;
59 static uint32_t *key;
60 static uint64_t *val;
61 static char *log;
62 static union bpf_attr *attr;
63
ensure_ptr_arithmetic(void)64 static void ensure_ptr_arithmetic(void)
65 {
66 const struct bpf_insn prog_insn[] = {
67 /* r2 = r10
68 * r3 = -1
69 * r2 += r3
70 * *(char *)r2 = 0
71 */
72 BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
73 BPF_MOV64_IMM(BPF_REG_3, -1),
74 BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3),
75 BPF_ST_MEM(BPF_B, BPF_REG_2, 0, 0),
76
77 /* exit(0) */
78 BPF_MOV64_IMM(BPF_REG_0, 0),
79 BPF_EXIT_INSN()
80 };
81 int ret;
82
83 bpf_init_prog_attr(attr, prog_insn, sizeof(prog_insn), log, BUFSIZE);
84
85 ret = TST_RETRY_FUNC(bpf(BPF_PROG_LOAD, attr, sizeof(*attr)),
86 TST_RETVAL_GE0);
87
88 if (ret >= 0) {
89 tst_res(TINFO, "Have pointer arithmetic");
90 SAFE_CLOSE(ret);
91 return;
92 }
93
94 if (ret != -1)
95 tst_brk(TBROK, "Invalid bpf() return value: %d", ret);
96
97 if (log[0] != 0)
98 tst_brk(TCONF | TERRNO, "No pointer arithmetic:\n %s", log);
99
100 tst_brk(TBROK | TERRNO, "Failed to load program");
101 }
102
load_prog(void)103 static int load_prog(void)
104 {
105 const struct bpf_insn prog_insn[] = {
106 /* r6 = 1 << 32
107 * r7 = -1
108 */
109 BPF_LD_IMM64(BPF_REG_6, 1ULL << 32),
110 BPF_MOV64_IMM(BPF_REG_7, -1LL),
111
112 /* w7 /= w6 */
113 BPF_ALU32_REG(BPF_DIV, BPF_REG_7, BPF_REG_6),
114
115 /* map[1] = r6
116 * map[2] = r7
117 */
118 BPF_MAP_ARRAY_STX(map_fd, 0, BPF_REG_6),
119 BPF_MAP_ARRAY_STX(map_fd, 1, BPF_REG_7),
120
121 /* r6 = 1 << 32
122 * r7 = -1
123 */
124 BPF_LD_IMM64(BPF_REG_6, 1ULL << 32),
125 BPF_MOV64_IMM(BPF_REG_7, -1LL),
126
127 /* w7 %= w6 */
128 BPF_ALU32_REG(BPF_MOD, BPF_REG_7, BPF_REG_6),
129
130 /* map[3] = r6
131 * map[4] = r7
132 */
133 BPF_MAP_ARRAY_STX(map_fd, 2, BPF_REG_6),
134 BPF_MAP_ARRAY_STX(map_fd, 3, BPF_REG_7),
135
136 /* exit(0) */
137 BPF_MOV64_IMM(BPF_REG_0, 0),
138 BPF_EXIT_INSN()
139 };
140
141 bpf_init_prog_attr(attr, prog_insn, sizeof(prog_insn), log, BUFSIZE);
142
143 return bpf_load_prog(attr, log);
144 }
145
expect_reg_val(const char * const reg_name,const uint64_t expected_val)146 static void expect_reg_val(const char *const reg_name,
147 const uint64_t expected_val)
148 {
149 bpf_map_array_get(map_fd, key, val);
150
151 (*key)++;
152
153 if (*val != expected_val) {
154 tst_res(TFAIL,
155 "%s = %"PRIu64", but should be %"PRIu64,
156 reg_name, *val, expected_val);
157 } else {
158 tst_res(TPASS, "%s = %"PRIu64, reg_name, *val);
159 }
160 }
161
setup(void)162 static void setup(void)
163 {
164 rlimit_bump_memlock();
165 memcpy(msg, MSG, sizeof(MSG));
166 }
167
run(void)168 static void run(void)
169 {
170 int prog_fd;
171
172 map_fd = bpf_map_array_create(8);
173
174 ensure_ptr_arithmetic();
175 prog_fd = load_prog();
176 bpf_run_prog(prog_fd, msg, sizeof(MSG));
177 SAFE_CLOSE(prog_fd);
178
179 *key = 0;
180
181 tst_res(TINFO, "Check w7(-1) /= w6(0) [r7 = -1, r6 = 1 << 32]");
182 expect_reg_val("src(r6)", 1ULL << 32);
183 expect_reg_val("dst(r7)", 0);
184
185 tst_res(TINFO, "Check w7(-1) %%= w6(0) [r7 = -1, r6 = 1 << 32]");
186 expect_reg_val("src(r6)", 1ULL << 32);
187 expect_reg_val("dst(r7)", (uint32_t)-1);
188
189 SAFE_CLOSE(map_fd);
190 }
191
192 static struct tst_test test = {
193 .setup = setup,
194 .test_all = run,
195 .min_kver = "3.18",
196 .taint_check = TST_TAINT_W | TST_TAINT_D,
197 .caps = (struct tst_cap []) {
198 TST_CAP(TST_CAP_DROP, CAP_SYS_ADMIN),
199 TST_CAP(TST_CAP_DROP, CAP_BPF),
200 {}
201 },
202 .bufs = (struct tst_buffers []) {
203 {&key, .size = sizeof(*key)},
204 {&val, .size = sizeof(*val)},
205 {&log, .size = BUFSIZE},
206 {&attr, .size = sizeof(*attr)},
207 {&msg, .size = sizeof(MSG)},
208 {}
209 },
210 .tags = (const struct tst_tag[]) {
211 {"linux-git", "f6b1b3bf0d5f"},
212 {"linux-git", "468f6eafa6c4"},
213 {"linux-git", "e88b2c6e5a4d"},
214 {"linux-git", "9b00f1b78809"},
215 {"CVE", "CVE-2021-3444"},
216 {}
217 }
218 };
219