From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 8C22B1B78F3; Mon, 2 Feb 2026 05:54:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770011677; cv=none; b=MVzx/6k2rwoGDvqz2ZGp30QEWok3Ve+PHH1pa/h/psDP2EwTNOct5C6yifuac4Kr2RmTGvPSxCCJqEkTyrW4clNWXMj49U+sstaqhKHmSJgbXrA8uknXxG59McWfh51BbeMSboK9KVt00v9Ka9v2/UyYdAQT49CGlWV8/MPChog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770011677; c=relaxed/simple; bh=lywCEDPlyt3OiiQXvf51QMlsZ5pzc1imtu/yowAFg8o=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=kqfRdouoMFXQ7rtRqe9yl6GcM8tXDbmsR5WyQR2Q8hO8u22aDweQRSe2EqNTrT1dWRfnud0kK4MLcZMfVByy3XvSvBe+P3t27n4BZXYMD1r5uyxr91B4WBxXXug7/gxwK0JUfVEpUzKTltmIuY9lZ6cpvRZykCD3Oqu9BMIF50Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lOa+etln; arc=none smtp.client-ip=95.215.58.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lOa+etln" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770011663; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Puxak2G+sBfL8q+PoNUkwncDertRMCGcIIZgmn1JsYo=; b=lOa+etlnIqi57X6jQidrane+sY2vEBUct3hUX9jhq/pDN7i9y9CBmfGpuMRoviBZrnK8jj NYxK4nwYjGYDuqFfozx45SODW/+fzOAe0fRyHOd5ut4eMbLhhTiD9PSxZ22Yx4eM+JGRv9 zW5JnF8thNlnZh8Hsjqe7M1ceGoOtz4= Date: Mon, 2 Feb 2026 13:54:14 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v2 1/2] bpf: Disallow BPF_F_LOCK with mixed special fields and centralize flag checks Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang To: Martin KaFai Lau , Kumar Kartikeya Dwivedi Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-patches-bot@fb.com References: <20260123055658.372869-1-leon.hwang@linux.dev> <20260123055658.372869-2-leon.hwang@linux.dev> <2a351923-5918-4735-8072-f21379e598c4@linux.dev> In-Reply-To: <2a351923-5918-4735-8072-f21379e598c4@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 28/1/26 23:22, Leon Hwang wrote: > > > On 2026/1/28 10:27, Kumar Kartikeya Dwivedi wrote: >> On Fri, 23 Jan 2026 at 06:58, Leon Hwang wrote: >>> >>> Disallow combining BPF_F_LOCK with map values that contain special BTF >>> fields other than bpf_spin_lock (e.g. kptr or uptr). Such mixing may lead >>> to subtle or undefined behavior in map value handling. Reject these >>> combinations early by returning -EOPNOTSUPP. >> >> The commit log is really suboptimal in giving context on why you're doing this. >> You should summarize the discussion from [0], otherwise unless people >> go dig that thread they'd have no clue. >> >> Also, I would remove the 'undefined behavior' wording. It's just >> semantically different, in that the update doesn't free fields, >> but there's no undefined behavior. >> >> [0]: https://lore.kernel.org/bpf/CAADnVQLib8ebe8cmGRj98YZiArendX8u=dSKNUrUFz6NGq7LRg@mail.gmail.com >> Hi Martin, Do you recall the original reasoning for disallowing BPF_F_LOCK together with BPF_UPTR in 'bpf_task_storage.c::bpf_pid_task_storage_update_elem()'? I didn’t find an explicit explanation in the commit message of ba512b00e5ef (“bpf: Add uptr support in the map_value of the task local storage”), and I’m trying to better understand the underlying concern. This is in the context of addressing Alexei’s comment in the linked discussion: I’d like to clearly articulate the risks of mixing BPF_F_LOCK with other special fields, rather than relying on vague phrasing. Thanks, Leon