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 bpf-next 2/7] bpf: derive smin/smax from umin/max bounds
Date: Wed, 18 Oct 2023 11:36:20 -0700 [thread overview]
Message-ID: <20231018183625.3952512-3-andrii@kernel.org> (raw)
In-Reply-To: <20231018183625.3952512-1-andrii@kernel.org>
Add smin/smax derivation from appropriate umin/umax values. Previously the
logic was surprisingly asymmetric, trying to derive umin/umax from smin/smax
(if possible), but not trying to do the same in the other direction. A simple
addition to __reg64_deduce_bounds() fixes this.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
kernel/bpf/verifier.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c87144e3c5e8..ee9837463092 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2151,6 +2151,13 @@ static void __reg32_deduce_bounds(struct bpf_reg_state *reg)
static void __reg64_deduce_bounds(struct bpf_reg_state *reg)
{
+ /* u64 range forms a valid s64 range (due to matching sign bit),
+ * so try to learn from that
+ */
+ if ((s64)reg->umin_value <= (s64)reg->umax_value) {
+ reg->smin_value = max_t(s64, reg->smin_value, reg->umin_value);
+ reg->smax_value = min_t(s64, reg->smax_value, reg->umax_value);
+ }
/* Learn sign from signed bounds.
* If we cannot cross the sign boundary, then signed and unsigned bounds
* are the same, so combine. This works even in the negative case, e.g.
--
2.34.1
next prev parent reply other threads:[~2023-10-18 18:36 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-18 18:36 [PATCH bpf-next 0/7] BPF register bounds logic and testing improvements Andrii Nakryiko
2023-10-18 18:36 ` [PATCH bpf-next 1/7] bpf: improve JEQ/JNE branch taken logic Andrii Nakryiko
2023-10-18 18:36 ` Andrii Nakryiko [this message]
2023-10-18 18:36 ` [PATCH bpf-next 3/7] bpf: enhance subregister bounds deduction logic Andrii Nakryiko
2023-10-18 18:36 ` [PATCH bpf-next 4/7] bpf: improve deduction of 64-bit bounds from 32-bit bounds Andrii Nakryiko
2023-10-18 18:36 ` [PATCH bpf-next 5/7] bpf: try harder to deduce register bounds from different numeric domains Andrii Nakryiko
2023-10-18 18:36 ` [PATCH bpf-next 6/7] bpf: drop knowledge-losing __reg_combine_{32,64}_into_{64,32} logic Andrii Nakryiko
2023-10-18 18:36 ` [PATCH bpf-next 7/7] selftests/bpf: BPF register range bounds tester Andrii Nakryiko
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