From patchwork Fri Aug 26 17:29:14 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eduard Zingerman X-Patchwork-Id: 12956350 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D983CECAAA3 for ; Fri, 26 Aug 2022 17:30:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245656AbiHZRaG (ORCPT ); Fri, 26 Aug 2022 13:30:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58804 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234955AbiHZRaF (ORCPT ); Fri, 26 Aug 2022 13:30:05 -0400 Received: from mail-ej1-x630.google.com (mail-ej1-x630.google.com [IPv6:2a00:1450:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A26566E8B1 for ; Fri, 26 Aug 2022 10:30:03 -0700 (PDT) Received: by mail-ej1-x630.google.com with SMTP id y3so4443367ejc.1 for ; Fri, 26 Aug 2022 10:30:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc; bh=gZPHolGeQ9kHWgDJvA3e7p1d0KYEdfpTn+cIOF7RCvU=; b=kDEm7srz61odMfDTnsdWgJ25tcG2YXqLxSSXXezCqW4RHVbwCQOVGHvrIMDIvG/Sq/ 2CN73uTowt0CtfjhO0RGeW5Fkpk6RwffiadCD8ALMnMpSSxpMOzFOetm8UIcmKgyLXhx jfEqUHVpXW8u7ka1o5yOEtVlOPiVfRRmlgZ3QNOeVwRjANuinSXWXADL0DKbNZTIaA0s o7qSFLxkonxQ6S/qoRa0BQs4jHedGkywuqCykRCtu1fdEv53hIluPjPwq8KXZK29GHIR ECELyd3libAY3vGezzOnWdEgoUxL/5QWA6w2zYce+roXf8zmz6wECTwyCBC+KwmBm5Np N51g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc; bh=gZPHolGeQ9kHWgDJvA3e7p1d0KYEdfpTn+cIOF7RCvU=; b=QUvGpE64xTXFmbtqFOjGxaX6zetUPKULsZ7mbad2vyowaQ5didwZySxjAWgXdI2PUs 5FKv52uMzqdO2bnc2rsXl9arj+c6UottnhsV9sq7P1xKi45eJKWgQYWo2e5tNGkm06FZ tNmKFlXoXM09E85SF93N88Pmwti9YXemvniPQ/QSwZwfk+0So28nVFzTjd8WdB1aAMHt rynOstqvRsfwZEDblvNRyrmuzl/OToxh1ZkXmbNDvgf+oyyUMXl4i/2eJKZm+bMXlUrv jnsI77JtywUOxiAGZ6u5oLiBaCBX110mdIoxUdBkq+zJJCGLMDobJQuHmhCc90Ei6iIu L/cA== X-Gm-Message-State: ACgBeo3MsYiVXc+mSpwhTuCJURG7Ble0YItN+/7EXOj0wc6h3TzA5Er4 m+ImMdZXPpSYoGnhYkfRvmj28jLlPA/iK7v3 X-Google-Smtp-Source: AA6agR6NTQ1dpfJV1JKVFmo1x0EGe+lv5S87/Jhta1sx65cKG3Tk6AxP0ervUsks3vyHKwIn0Bt5Dg== X-Received: by 2002:a17:907:60c7:b0:731:4b42:4e3e with SMTP id hv7-20020a17090760c700b007314b424e3emr6076553ejc.236.1661535001698; Fri, 26 Aug 2022 10:30:01 -0700 (PDT) Received: from badger.. (boundsly.muster.volia.net. [93.72.16.93]) by smtp.gmail.com with ESMTPSA id l13-20020a170906a40d00b0073d79d0c9c7sm1119896ejz.127.2022.08.26.10.30.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Aug 2022 10:30:01 -0700 (PDT) From: Eduard Zingerman To: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, kernel-team@fb.com, yhs@fb.com, john.fastabend@gmail.com Cc: Eduard Zingerman Subject: [PATCH bpf-next 1/2] bpf: propagate nullness information for reg to reg comparisons Date: Fri, 26 Aug 2022 20:29:14 +0300 Message-Id: <20220826172915.1536914-2-eddyz87@gmail.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220826172915.1536914-1-eddyz87@gmail.com> References: <20220826172915.1536914-1-eddyz87@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Propagate nullness information for branches of register to register equality compare instructions. The following rules are used: - suppose register A maybe null - suppose register B is not null - for JNE A, B, ... - A is not null in the false branch - for JEQ A, B, ... - A is not null in the true branch E.g. for program like below: r6 = skb->sk; r7 = sk_fullsock(r6); r0 = sk_fullsock(r6); if (r0 == 0) return 0; (a) if (r0 != r7) return 0; (b) *r7->type; (c) return 0; It is safe to dereference r7 at point (c), because of (a) and (b). Signed-off-by: Eduard Zingerman Acked-by: Yonghong Song --- kernel/bpf/verifier.c | 41 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 39 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 0194a36d0b36..7585288e035b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -472,6 +472,11 @@ static bool type_may_be_null(u32 type) return type & PTR_MAYBE_NULL; } +static bool type_is_pointer(enum bpf_reg_type type) +{ + return type != NOT_INIT && type != SCALAR_VALUE; +} + static bool is_acquire_function(enum bpf_func_id func_id, const struct bpf_map *map) { @@ -10064,6 +10069,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, struct bpf_verifier_state *other_branch; struct bpf_reg_state *regs = this_branch->frame[this_branch->curframe]->regs; struct bpf_reg_state *dst_reg, *other_branch_regs, *src_reg = NULL; + struct bpf_reg_state *eq_branch_regs; u8 opcode = BPF_OP(insn->code); bool is_jmp32; int pred = -1; @@ -10173,8 +10179,8 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, /* detect if we are comparing against a constant value so we can adjust * our min/max values for our dst register. * this is only legit if both are scalars (or pointers to the same - * object, I suppose, but we don't support that right now), because - * otherwise the different base pointers mean the offsets aren't + * object, I suppose, see the PTR_MAYBE_NULL related if block below), + * because otherwise the different base pointers mean the offsets aren't * comparable. */ if (BPF_SRC(insn->code) == BPF_X) { @@ -10223,6 +10229,37 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, find_equal_scalars(other_branch, &other_branch_regs[insn->dst_reg]); } + /* if one pointer register is compared to another pointer + * register check if PTR_MAYBE_NULL could be lifted. + * E.g. register A - maybe null + * register B - not null + * for JNE A, B, ... - A is not null in the false branch; + * for JEQ A, B, ... - A is not null in the true branch. + */ + if (!is_jmp32 && + BPF_SRC(insn->code) == BPF_X && + type_is_pointer(src_reg->type) && type_is_pointer(dst_reg->type) && + type_may_be_null(src_reg->type) != type_may_be_null(dst_reg->type)) { + eq_branch_regs = NULL; + switch (opcode) { + case BPF_JEQ: + eq_branch_regs = other_branch_regs; + break; + case BPF_JNE: + eq_branch_regs = regs; + break; + default: + /* do nothing */ + break; + } + if (eq_branch_regs) { + if (type_may_be_null(src_reg->type)) + mark_ptr_not_null_reg(&eq_branch_regs[insn->src_reg]); + else + mark_ptr_not_null_reg(&eq_branch_regs[insn->dst_reg]); + } + } + /* detect if R == 0 where R is returned from bpf_map_lookup_elem(). * NOTE: these optimizations below are related with pointer comparison * which will never be JMP32.