From mboxrd@z Thu Jan 1 00:00:00 1970 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 B2E8DC04AA5 for ; Thu, 25 Aug 2022 06:19:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234909AbiHYGTo (ORCPT ); Thu, 25 Aug 2022 02:19:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58404 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232970AbiHYGTm (ORCPT ); Thu, 25 Aug 2022 02:19:42 -0400 Received: from mail-pg1-x52b.google.com (mail-pg1-x52b.google.com [IPv6:2607:f8b0:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 19417A0241 for ; Wed, 24 Aug 2022 23:19:42 -0700 (PDT) Received: by mail-pg1-x52b.google.com with SMTP id g189so2966714pgc.0 for ; Wed, 24 Aug 2022 23:19:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:to:from:date:from:to:cc; bh=fkbcSf2QvoM1v7ga7p3BoCyFgPv97LPNk8LIaDWElhw=; b=I1JcOCvbPo289ue9TzwzKwcpIp/sdUMrn3Vg/zg+zOXqRJ/cC3avo5Gvz/idU4KwVU lorXTjGxNqOOvLlADm7CIbXftZ+bpos5A0enGg3uJd80aW5WcHF3Tbe/s5cH2fAPcpv2 tQbALWmyvRqA3AWfc1zrEiuDHbVsX5AvA6NH02akud1jelm7S5CZa/S7tKSN0Uu874kw op3VAT2taNi9XhKDAmFNQYBzAyCfiFT5S78sMYsnMdLrEKpXFTuwczx/yql1gkLpcvXp LfMtTXCk8zEP3xGgykzzo+oZy5meyMlKZjS5UFEWyUZWyRxkqvi9lkenH1ZNMd9KOp2D RYCw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:to:from:date:x-gm-message-state:from:to:cc; bh=fkbcSf2QvoM1v7ga7p3BoCyFgPv97LPNk8LIaDWElhw=; b=NcTcna18Z8W/0eiqe7y2ogH/cJ3goCUL3dMt7zMfME9qiq2L3rrGTx/+oQCDAHEz9D UkLY3xo50CAWbg3i84fVRTWgRsKb27pppn9oZqTRZoV31F3cC+wSns9AUHNTRYFK7ciI lVR03LkcomW+k4oqJ6XIOmrYbVLE+M5LWKTqugnxpqoSwc5VcU5TPJ5JMbhC2z5JRqkw BWHQ6f+UDfY0hrRZRGXPCiUINQiZ1WDbe13kY7jqg/yZ/IymvBKJr5/uUHnvRPo070xR 8JhfzSZ4CWxQGiKsV4rCk7UVOL4iU/ga8bpDuKO9FUqHhWuwE8FlhkgXvP68TSKOPIEk eMOw== X-Gm-Message-State: ACgBeo3TO+EEWU9w4acHbWhgtHR/Ow3xkjcceNe3/WF1gNb1cEnEXGjo wU2+8Qjx4+mwB93RD9AmrzGMMYt9USU= X-Google-Smtp-Source: AA6agR75VHZT33VfNiVGIxvOaYf2thFZuOSLgesUQJfI97z/n4nRvHcivzVLifQjXbKgCNUh7lkDrg== X-Received: by 2002:a63:834a:0:b0:42b:358f:640d with SMTP id h71-20020a63834a000000b0042b358f640dmr2077971pge.235.1661408381588; Wed, 24 Aug 2022 23:19:41 -0700 (PDT) Received: from localhost ([98.97.36.33]) by smtp.gmail.com with ESMTPSA id n12-20020a170902e54c00b0016d773aae60sm13863766plf.19.2022.08.24.23.19.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Aug 2022 23:19:40 -0700 (PDT) Date: Wed, 24 Aug 2022 23:19:39 -0700 From: John Fastabend To: Yonghong Song , John Fastabend , Eduard Zingerman , bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, kernel-team@fb.com Message-ID: <6307147b5c97b_e1c39208d6@john.notmuch> In-Reply-To: References: <20220822094312.175448-1-eddyz87@gmail.com> <20220822094312.175448-2-eddyz87@gmail.com> <63055fa5a080e_292a8208db@john.notmuch> Subject: Re: [PATCH RFC bpf-next 1/2] bpf: propagate nullness information for reg to reg comparisons Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Yonghong Song wrote: > > > On 8/23/22 4:15 PM, John Fastabend wrote: > > Eduard Zingerman wrote: > >> 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). > > > > I think the idea makes sense. Perhaps Yonhong can comment seeing he was active > > on the LLVM thread. I just scanned the LLVM side for now will take a look > > in more detail in a bit. > > The issue is discovered when making some changes in llvm compiler. > I think it is good to add support in verifier so in the future > if compiler generates such code patterns, user won't get > surprised verification failure. > I agree. Read the LLVM thread as well.