From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed1-f47.google.com (mail-ed1-f47.google.com [209.85.208.47]) (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 7D7763033B for ; Sat, 16 Dec 2023 15:13:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Q/8flqvL" Received: by mail-ed1-f47.google.com with SMTP id 4fb4d7f45d1cf-54cb4fa667bso1949851a12.3 for ; Sat, 16 Dec 2023 07:13:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1702739617; x=1703344417; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=iCCWJFiw8zJ8aKdFkgzDNpEm1k74RVBn3QtHjndJQ/s=; b=Q/8flqvL2JlGC+ZWp9EINVrnd5nWQFvyBs8yGY4C27eUcHQFSlD32T/yZtuO0HLrxT SgKcg/qcYVp7+Y8X3Aann4C2XTEtv/fZA+USfqxmLr7gvBc7MyXMtNjeJXK8uMzoPqO7 X7ZIXnSEh0TPVDJUCMOjcoHWwEw1sb3tGB5WVxUuWFKhmeIfh6aLrYO9iJ6ZgQyRV1FU CN6aRVmncUiPjpR9nrUHQG7iLRalXoNHpqW2G2JZ4vCS4mv0RLDWoQZPgh1NZsJhWETb WtOQ8S3hacEmSxo5GAlhHayESg+2O6g6WtPoj87+Z9iD8AelNt5rOaW4VU6d5fzbSIqZ ekOw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702739617; x=1703344417; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=iCCWJFiw8zJ8aKdFkgzDNpEm1k74RVBn3QtHjndJQ/s=; b=XAO52lF6SIa5kqbR7ZFJFLTlfAm5C4bNMOV/7AuW/ckEOiec9VPWce+BNDd8zNk27d LTIaLhIygaUL62l6Gk8deOt9A84HwNebHsmrb3Tu7al5+rR3VlPVx45B1eEtjKzxGpSG A0LvDfcVqduCH5kzh+j1jnh7hzhKFrqCwP+W24rT75PRcQFRZX/Ct6NOo8H8V0IHZUtK sdXRFFgBkdxms9c85lYT7gWnnK+P42JIJAdcPxlty8rF7i1P7iAf4+0oAqAmEmjWLZm6 pFz2myhmhTaoLt4+wvmQ4xInHFxvzQYm7gZ1xWrJ/07Mvirn4ejXDAEB0n5eXGmEWGGC WTdA== X-Gm-Message-State: AOJu0Yx0SCYk4Jgn6Io8DfMCxXYqaK/ZXyHdhbOBBb5BBlSpRMMusAhx +71ljLmsPfYxWrkKPo8nWho= X-Google-Smtp-Source: AGHT+IHMNyQtDCdKaTIvsbZtJKHyQ/oQf1kKTu0jF3q6q/IJC23ejOFk3VS0SSxqqMQnYeqziZ5KAg== X-Received: by 2002:a17:906:2cc:b0:a23:2eed:8117 with SMTP id 12-20020a17090602cc00b00a232eed8117mr239253ejk.152.1702739616479; Sat, 16 Dec 2023 07:13:36 -0800 (PST) Received: from localhost ([185.220.101.137]) by smtp.gmail.com with ESMTPSA id vo9-20020a170907a80900b00a1d450d6f8esm12165367ejc.17.2023.12.16.07.13.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 16 Dec 2023 07:13:36 -0800 (PST) Date: Sat, 16 Dec 2023 17:13:32 +0200 From: Maxim Mikityanskiy To: Andrii Nakryiko Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, martin.lau@kernel.org, kernel-team@meta.com Subject: Re: [PATCH bpf-next] bpf: ensure precise is reset to false in __mark_reg_const_zero() Message-ID: References: <20231215235822.908223-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231215235822.908223-1-andrii@kernel.org> On Fri, 15 Dec 2023 at 15:58:22 -0800, Andrii Nakryiko wrote: > It is safe to always start with imprecise SCALAR_VALUE register. > Previously __mark_reg_const_zero() relied on caller to reset precise > mark, but it's very error prone and we already missed it in a few > places. So instead make __mark_reg_const_zero() reset precision always, > as it's a safe default for SCALAR_VALUE. Explanation is basically the > same as for why we are resetting (or rather not setting) precision in > current state. If necessary, precision propagation will set it to > precise correctly. > > As such, also remove a big comment about forward precision propagation > in mark_reg_stack_read() and avoid unnecessarily setting precision to > true after reading from STACK_ZERO stack. Again, precision propagation > will correctly handle this, if that SCALAR_VALUE register will ever be > needed to be precise. > > Reported-by: Maxim Mikityanskiy > Signed-off-by: Andrii Nakryiko > --- > kernel/bpf/verifier.c | 16 +++------------- > .../selftests/bpf/progs/verifier_spill_fill.c | 10 ++++++++-- > 2 files changed, 11 insertions(+), 15 deletions(-) Thanks for the prompt fix! Acked-by: Maxim Mikityanskiy