From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 97A31382 for ; Sun, 22 Oct 2023 20:58:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from mx0b-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1D237E9 for ; Sun, 22 Oct 2023 13:58:05 -0700 (PDT) Received: from pps.filterd (m0109331.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 39MHGEJZ022358 for ; Sun, 22 Oct 2023 13:58:04 -0700 Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3tvcfyw2gx-2 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Sun, 22 Oct 2023 13:58:04 -0700 Received: from twshared44805.48.prn1.facebook.com (2620:10d:c0a8:1c::11) by mail.thefacebook.com (2620:10d:c0a8:82::b) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Sun, 22 Oct 2023 13:58:02 -0700 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id 0E4E03A33D296; Sun, 22 Oct 2023 13:57:48 -0700 (PDT) From: Andrii Nakryiko To: , , , CC: , Subject: [PATCH v4 bpf-next 1/7] bpf: improve JEQ/JNE branch taken logic Date: Sun, 22 Oct 2023 13:57:37 -0700 Message-ID: <20231022205743.72352-2-andrii@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231022205743.72352-1-andrii@kernel.org> References: <20231022205743.72352-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-GUID: EQhTxQxnxF8CvhTFO0MVBiacjwWwig7s X-Proofpoint-ORIG-GUID: EQhTxQxnxF8CvhTFO0MVBiacjwWwig7s X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-10-22_19,2023-10-19_01,2023-05-22_02 When determining if if/else branch will always or never be taken, use signed range knowledge in addition to currently used unsigned range knowl= edge. If either signed or unsigned range suggests that condition is always/never taken, return corresponding branch_taken verdict. Current use of unsigned range for this seems arbitrary and unnecessarily incomplete. It is possible for *signed* operations to be performed on register, which could "invalidate" unsigned range for that register. In such case branch_taken will be artificially useless, even if we can still tell that some constant is outside of register value range based on its signed bounds. veristat-based validation shows zero differences across selftests, Cilium, and Meta-internal BPF object files. Signed-off-by: Andrii Nakryiko --- kernel/bpf/verifier.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e9bc5d4a25a1..f8fca3fbe20f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13725,12 +13725,16 @@ static int is_branch32_taken(struct bpf_reg_sta= te *reg, u32 val, u8 opcode) return !!tnum_equals_const(subreg, val); else if (val < reg->u32_min_value || val > reg->u32_max_value) return 0; + else if (sval < reg->s32_min_value || sval > reg->s32_max_value) + return 0; break; case BPF_JNE: if (tnum_is_const(subreg)) return !tnum_equals_const(subreg, val); else if (val < reg->u32_min_value || val > reg->u32_max_value) return 1; + else if (sval < reg->s32_min_value || sval > reg->s32_max_value) + return 1; break; case BPF_JSET: if ((~subreg.mask & subreg.value) & val) @@ -13802,12 +13806,16 @@ static int is_branch64_taken(struct bpf_reg_sta= te *reg, u64 val, u8 opcode) return !!tnum_equals_const(reg->var_off, val); else if (val < reg->umin_value || val > reg->umax_value) return 0; + else if (sval < reg->smin_value || sval > reg->smax_value) + return 0; break; case BPF_JNE: if (tnum_is_const(reg->var_off)) return !tnum_equals_const(reg->var_off, val); else if (val < reg->umin_value || val > reg->umax_value) return 1; + else if (sval < reg->smin_value || sval > reg->smax_value) + return 1; break; case BPF_JSET: if ((~reg->var_off.mask & reg->var_off.value) & val) --=20 2.34.1