From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f42.google.com (mail-pj1-f42.google.com [209.85.216.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6D24A2C85 for ; Fri, 5 Nov 2021 01:20:26 +0000 (UTC) Received: by mail-pj1-f42.google.com with SMTP id j5-20020a17090a318500b001a6c749e697so1787979pjb.1 for ; Thu, 04 Nov 2021 18:20:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=pKeKaxsMJxim9BgJMliTdTdETDAYX56NckZ9IfvJR64=; b=KDhy/5LPPSH+nl8S4baB/KctuMl4XjcsUbXNlKf9lFoJaCmcmBEzPT+p2Lcv+oDjYl peyz4NNk8uqRizkfw21Suujnc+MR1D+tlPFfyLz3SjqdygDrRJS91HfCeBkExruml+5q 0vRTPn26K5WREyl1Ik6ecmavvqV0XqSEiPHzv0zEa4Ken9ekaK6IRkhI8Vyqqcm6Hpn4 p3dlwOObuVwPAMBdEhKUwcXO3PJKbldgvej/JyLt6rPXxe5gXuOBGNp0Z7gPbCxDm8QC BpZtHatUl+WIBApWnDb5b95glAv5ikscZhI4xW8gWNQMvsj1mlSzCgobzPWrknh75cnK Kg6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=pKeKaxsMJxim9BgJMliTdTdETDAYX56NckZ9IfvJR64=; b=2MXJuiMgcRJ2+sU5SFcx5lD6nMJ72K6ds4W8JNg0B9hFkQ1HRZG3tUWL+/ZmGileHj SgbRNaSdAts6TaIcSRisNBsS4wd1NB1juICC9DE8BOsNM/duH/F3Jc2PaHTgX4ushvxb jymy9Es4IVwZaN3is6KbTJ9zpOo2c5EnWR6aCQTc27La6wYBiW5M+d5D9Otz39P1xuQ7 AjQpuiQmc36ScSc/Stei77WEXoBm0sd9sv0j/cup6vWHiqy3Vk/HHZt1HPuXaKT3Q9ZM WEvo0ckmFExWK4TD008cqooV3vSG4mHdHyIawGHC4is0WxyrszU4zDfYB1drwZXc6OjT NZ0Q== X-Gm-Message-State: AOAM532QvCLJ4yAvuh6QBxNMIX8HgrrRLrdIX/gUvID9RlVzlUjSFvfz dhjUQoUNtNJPcc/ivXIjDVKxplkxJqHGX3Yu7IU= X-Google-Smtp-Source: ABdhPJyjiGQONFgZ8ou0mg68PWXEowJTasGta2KiT8LXfY1ziFzPgwb03LrrQlpOm/veaxWoQvtNhnytcOkox+Vx7gM= X-Received: by 2002:a17:902:f542:b0:141:fa0e:1590 with SMTP id h2-20020a170902f54200b00141fa0e1590mr25245804plf.20.1636075225876; Thu, 04 Nov 2021 18:20:25 -0700 (PDT) Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: In-Reply-To: From: Alexei Starovoitov Date: Thu, 4 Nov 2021 18:20:14 -0700 Message-ID: Subject: Re: Verifier rejects previously accepted program To: Stanislav Fomichev Cc: Lorenz Bauer , Alexei Starovoitov , kernel-team , bpf , regressions@lists.linux.dev, Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau Content-Type: text/plain; charset="UTF-8" On Thu, Nov 4, 2021 at 4:30 PM wrote: > > On 11/04, Alexei Starovoitov wrote: > > On Wed, Nov 3, 2021 at 4:55 AM Lorenz Bauer wrote: > > > > #pragma clang loop unroll(full) > > > for (int b = 1 << 10; b >= 4; b >>= 1) { > > > if (start + b > end) { > > > continue; > > > } > > > > > > // If we do 8 byte reads, we have to handle overflows which is > > > slower than 4 byte reads. > > > for (int i = 0; i < b; i += 4) { > > > csum += *(uint32_t *)(start + i); > > > } > > > > > > start += b; > > > } > > > if (start + 2 <= end) { > > > csum += *(uint16_t *)(start); > > > start += 2; > > > } > > > if (start + 1 <= end) { > > > csum += *(start); > > > } > > > Thanks for flagging! > > Could you craft a test case that we can use a repro and future > > test case? > > > > fp-88=map_value fp-96=mmmmmmmm fp-104=map_value fp-112=inv fp-120=fp > > ... > > > I've bisected the problem to commit 3e8ce29850f1 ("bpf: Prevent > > > pointer mismatch in bpf_timer_init.") The commit seems unrelated to > > > loop processing though (it does touch the verifier however). Either I > > > got the bisection wrong or there is something subtle going on. > > > I stared at that commit and the example asm. > > I suspect the bisect went wrong. > > > Could you try reverting a single > > commit 354e8f1970f8 ("bpf: Support <8-byte scalar spill and refill") > > ? > > The above fp-112=inv means that the verifier is tracking scalar spill. > > That could be the reason for bounded loop logic seeing different > > stack state on every iteration. > > But the asm snippet doesn't have the store to stack at [fp-112] > > location, so it could be a red herring. > > > Are you using the same llvm during bisect? > > The commit 354e8f1970f8 should be harmless > > (when commit f30d4968e9ae ("bpf: Do not reject when the stack read > > size is different from the tracked scalar size")) > > is also applied. That fix is in bpf tree only, so far. > > The tracking of 8-byte spill is the most useful with the latest llvm > > that was taught to use 8-byte aligned stack for such spills. > > > Without being able to repro it's hard to investigate much further. > > Not to derail the conversation, but we do actually see a problem > with commit 354e8f1970f8 ("bpf: Support <8-byte scalar spill and > refill"). Program that passed without it now gets: > > R0=inv(id=0) R1_w=invP0 R2_w=invP0 R5_w=inv0 R6=ctx(id=0,off=0,imm=0) > R7=map_value(id=0,off=0,ks=4,vs=9616,imm=0) R8=inv(id=0) > R9_w=map_value(id=0,off=0,ks=4,vs=9616,imm=0) R10=fp0 fp-8=mmmm???? > fp-16=mmmmmmmm fp-24=00000000 fp-32=inv fp-40=00000000 fp-48=inv > fp-56=mmmmmmmm fp-64=mmmmmmmm > 479: (79) r1 = *(u64 *)(r10 -32) > corrupted spill memory > processed 970 insns (limit 1000000) max_states_per_insn 2 total_states 73 > peak_states 73 mark_read 24 Stan, please read the 2nd part of my sentence above and try again with that patch.