From: Andrii Nakryiko <andrii@kernel.org>
To: <bpf@vger.kernel.org>, <ast@kernel.org>, <daniel@iogearbox.net>,
<martin.lau@kernel.org>
Cc: <andrii@kernel.org>, <kernel-team@meta.com>
Subject: [PATCH v5 bpf-next 20/23] bpf: enhance BPF_JEQ/BPF_JNE is_branch_taken logic
Date: Fri, 27 Oct 2023 11:13:43 -0700 [thread overview]
Message-ID: <20231027181346.4019398-21-andrii@kernel.org> (raw)
In-Reply-To: <20231027181346.4019398-1-andrii@kernel.org>
Use 32-bit subranges to prune some 64-bit BPF_JEQ/BPF_JNE conditions
that otherwise would be "inconclusive" (i.e., is_branch_taken() would
return -1). This can happen, for example, when registers are initialized
as 64-bit u64/s64, then compared for inequality as 32-bit subregisters,
and then followed by 64-bit equality/inequality check. That 32-bit
inequality can establish some pattern for lower 32 bits of a register
(e.g., s< 0 condition determines whether the bit #31 is zero or not),
while overall 64-bit value could be anything (according to a value range
representation).
This is not a fancy quirky special case, but actually a handling that's
necessary to prevent correctness issue with BPF verifier's range
tracking: set_range_min_max() assumes that register ranges are
non-overlapping, and if that condition is not guaranteed by
is_branch_taken() we can end up with invalid ranges, where min > max.
[0] https://lore.kernel.org/bpf/CACkBjsY2q1_fUohD7hRmKGqv1MV=eP2f6XK8kjkYNw7BaiF8iQ@mail.gmail.com/
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
kernel/bpf/verifier.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f18a8247e5e2..cf5bf7ab4410 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14214,6 +14214,18 @@ static int is_scalar_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_sta
return 0;
if (smin1 > smax2 || smax1 < smin2)
return 0;
+ if (!is_jmp32) {
+ /* if 64-bit ranges are inconclusive, see if we can
+ * utilize 32-bit subrange knowledge to eliminate
+ * branches that can't be taken a priori
+ */
+ if (reg1->u32_min_value > reg2->u32_max_value ||
+ reg1->u32_max_value < reg2->u32_min_value)
+ return 0;
+ if (reg1->s32_min_value > reg2->s32_max_value ||
+ reg1->s32_max_value < reg2->s32_min_value)
+ return 0;
+ }
break;
case BPF_JNE:
/* const tnums */
@@ -14229,6 +14241,18 @@ static int is_scalar_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_sta
return 1;
if (smin1 > smax2 || smax1 < smin2)
return 1;
+ if (!is_jmp32) {
+ /* if 64-bit ranges are inconclusive, see if we can
+ * utilize 32-bit subrange knowledge to eliminate
+ * branches that can't be taken a priori
+ */
+ if (reg1->u32_min_value > reg2->u32_max_value ||
+ reg1->u32_max_value < reg2->u32_min_value)
+ return 1;
+ if (reg1->s32_min_value > reg2->s32_max_value ||
+ reg1->s32_max_value < reg2->s32_min_value)
+ return 1;
+ }
break;
case BPF_JSET:
if (!is_reg_const(reg2, is_jmp32)) {
--
2.34.1
next prev parent reply other threads:[~2023-10-27 18:16 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-27 18:13 [PATCH v5 bpf-next 00/23] BPF register bounds logic and testing improvements Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 01/23] selftests/bpf: fix RELEASE=1 build for tc_opts Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 02/23] selftests/bpf: satisfy compiler by having explicit return in btf test Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 03/23] bpf: derive smin/smax from umin/max bounds Andrii Nakryiko
2023-10-31 15:37 ` Eduard Zingerman
2023-10-31 17:30 ` Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 04/23] bpf: derive smin32/smax32 from umin32/umax32 bounds Andrii Nakryiko
2023-10-31 15:37 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 05/23] bpf: derive subreg bounds from full bounds when upper 32 bits are constant Andrii Nakryiko
2023-10-31 15:37 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 06/23] bpf: add special smin32/smax32 derivation from 64-bit bounds Andrii Nakryiko
2023-10-31 15:37 ` Eduard Zingerman
2023-10-31 17:39 ` Andrii Nakryiko
2023-10-31 18:41 ` Alexei Starovoitov
2023-10-31 18:49 ` Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 07/23] bpf: improve deduction of 64-bit bounds from 32-bit bounds Andrii Nakryiko
2023-10-31 15:37 ` Eduard Zingerman
2023-10-31 20:26 ` Alexei Starovoitov
2023-10-31 20:33 ` Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 08/23] bpf: try harder to deduce register bounds from different numeric domains Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 09/23] bpf: drop knowledge-losing __reg_combine_{32,64}_into_{64,32} logic Andrii Nakryiko
2023-10-31 15:38 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 10/23] selftests/bpf: BPF register range bounds tester Andrii Nakryiko
2023-11-08 22:08 ` Eduard Zingerman
2023-11-08 23:23 ` Andrii Nakryiko
2023-11-09 0:30 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 11/23] bpf: rename is_branch_taken reg arguments to prepare for the second one Andrii Nakryiko
2023-10-30 19:39 ` Alexei Starovoitov
2023-10-31 5:19 ` Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 12/23] bpf: generalize is_branch_taken() to work with two registers Andrii Nakryiko
2023-10-31 15:38 ` Eduard Zingerman
2023-10-31 17:41 ` Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 13/23] bpf: move is_branch_taken() down Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 14/23] bpf: generalize is_branch_taken to handle all conditional jumps in one place Andrii Nakryiko
2023-10-31 15:38 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 15/23] bpf: unify 32-bit and 64-bit is_branch_taken logic Andrii Nakryiko
2023-10-30 19:52 ` Alexei Starovoitov
2023-10-31 5:28 ` Andrii Nakryiko
2023-10-31 17:35 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 16/23] bpf: prepare reg_set_min_max for second set of registers Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 17/23] bpf: generalize reg_set_min_max() to handle two sets of two registers Andrii Nakryiko
2023-10-31 2:02 ` Alexei Starovoitov
2023-10-31 6:03 ` Andrii Nakryiko
2023-10-31 16:23 ` Alexei Starovoitov
2023-10-31 17:50 ` Andrii Nakryiko
2023-10-31 17:56 ` Andrii Nakryiko
2023-10-31 18:04 ` Alexei Starovoitov
2023-10-31 18:06 ` Andrii Nakryiko
2023-10-31 18:14 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 18/23] bpf: generalize reg_set_min_max() to handle non-const register comparisons Andrii Nakryiko
2023-10-31 23:25 ` Eduard Zingerman
2023-11-01 16:35 ` Andrii Nakryiko
2023-11-01 17:12 ` Eduard Zingerman
2023-10-27 18:13 ` [PATCH v5 bpf-next 19/23] bpf: generalize is_scalar_branch_taken() logic Andrii Nakryiko
2023-10-31 2:12 ` Alexei Starovoitov
2023-10-31 6:12 ` Andrii Nakryiko
2023-10-31 16:34 ` Alexei Starovoitov
2023-10-31 18:01 ` Andrii Nakryiko
2023-10-31 20:53 ` Andrii Nakryiko
2023-10-31 20:55 ` Andrii Nakryiko
2023-10-27 18:13 ` Andrii Nakryiko [this message]
2023-10-31 2:20 ` [PATCH v5 bpf-next 20/23] bpf: enhance BPF_JEQ/BPF_JNE is_branch_taken logic Alexei Starovoitov
2023-10-31 6:16 ` Andrii Nakryiko
2023-10-31 16:36 ` Alexei Starovoitov
2023-10-31 18:04 ` Andrii Nakryiko
2023-10-31 18:06 ` Alexei Starovoitov
2023-10-27 18:13 ` [PATCH v5 bpf-next 21/23] selftests/bpf: adjust OP_EQ/OP_NE handling to use subranges for branch taken Andrii Nakryiko
2023-11-08 18:22 ` Eduard Zingerman
2023-11-08 19:59 ` Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 22/23] selftests/bpf: add range x range test to reg_bounds Andrii Nakryiko
2023-10-27 18:13 ` [PATCH v5 bpf-next 23/23] selftests/bpf: add iter test requiring range x range logic Andrii Nakryiko
2023-10-30 17:55 ` [PATCH v5 bpf-next 00/23] BPF register bounds logic and testing improvements Alexei Starovoitov
2023-10-31 5:19 ` Andrii Nakryiko
2023-11-01 12:37 ` Paul Chaignon
2023-11-01 17:13 ` Andrii Nakryiko
2023-11-07 6:37 ` Harishankar Vishwanathan
2023-11-07 16:38 ` Paul Chaignon
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