1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
|
From 6c8e098d0324412d4ae9e06c7e611a96b87faf80 Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <daniel@iogearbox.net>
Date: Fri, 22 Dec 2017 16:23:07 +0100
Subject: [PATCH] bpf: fix 32-bit ALU op verification
From: Jann Horn <jannh@google.com>
[ Upstream commit 468f6eafa6c44cb2c5d8aad35e12f06c240a812a ]
32-bit ALU ops operate on 32-bit values and have 32-bit outputs.
Adjust the verifier accordingly.
CVE: CVE-2017-17852
Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=6c8e098d0324412d4ae9e06c7e611a96b87faf80]
Fixes: f1174f77b50c ("bpf/verifier: rework value tracking")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
---
kernel/bpf/verifier.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1e2afb264c31..0c7e4c8a2b8a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1984,6 +1984,10 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
return 0;
}
+/* WARNING: This function does calculations on 64-bit values, but the actual
+ * execution may occur on 32-bit values. Therefore, things like bitshifts
+ * need extra checks in the 32-bit case.
+ */
static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
struct bpf_insn *insn,
struct bpf_reg_state *dst_reg,
@@ -1994,12 +1998,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
bool src_known, dst_known;
s64 smin_val, smax_val;
u64 umin_val, umax_val;
+ u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
- if (BPF_CLASS(insn->code) != BPF_ALU64) {
- /* 32-bit ALU ops are (32,32)->64 */
- coerce_reg_to_size(dst_reg, 4);
- coerce_reg_to_size(&src_reg, 4);
- }
smin_val = src_reg.smin_value;
smax_val = src_reg.smax_value;
umin_val = src_reg.umin_value;
@@ -2135,9 +2135,9 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
__update_reg_bounds(dst_reg);
break;
case BPF_LSH:
- if (umax_val > 63) {
- /* Shifts greater than 63 are undefined. This includes
- * shifts by a negative number.
+ if (umax_val >= insn_bitness) {
+ /* Shifts greater than 31 or 63 are undefined.
+ * This includes shifts by a negative number.
*/
mark_reg_unknown(regs, insn->dst_reg);
break;
@@ -2163,9 +2163,9 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
__update_reg_bounds(dst_reg);
break;
case BPF_RSH:
- if (umax_val > 63) {
- /* Shifts greater than 63 are undefined. This includes
- * shifts by a negative number.
+ if (umax_val >= insn_bitness) {
+ /* Shifts greater than 31 or 63 are undefined.
+ * This includes shifts by a negative number.
*/
mark_reg_unknown(regs, insn->dst_reg);
break;
@@ -2201,6 +2201,12 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
break;
}
+ if (BPF_CLASS(insn->code) != BPF_ALU64) {
+ /* 32-bit ALU ops are (32,32)->32 */
+ coerce_reg_to_size(dst_reg, 4);
+ coerce_reg_to_size(&src_reg, 4);
+ }
+
__reg_deduce_bounds(dst_reg);
__reg_bound_offset(dst_reg);
return 0;
--
2.20.1
|
