From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BB58CC13B; Sat, 2 Aug 2025 18:52:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754160764; cv=none; b=DZneWyR/iBqCx7RiemHOP7y1wGNNZAwLifrPDfY6iX6rRo8Xyufo4LiXLdIczMdC7j4jxPe4W0788KXqEdMewRug1OMsUfDX/N8AJhEiJ1YcouC1eGZHUd4n+ZrHw3jPFEoKrGV0O/ngI+jtnjJKkeRmyW0012tp6J4VzZ9tEQM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754160764; c=relaxed/simple; bh=oKJ4o+84X2gZrWbVCPsj5JL/+cPPXG/1i+v6w3VXMC4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G4OVXseBCKejkVH/nMIVkwDrc4kejYYddfQ9deF1SV3NevZSjkBa5UvP2ah7crOnyR3ZLsG/GRg+RXilQpSELqC4kzW/YiTGpr36yZMJrtmibtn0/tB8Dd/MOrfodA7LZfgRAePRMUSvHZSwHVKsdhNPh36g8BS3rSEDj8Z9IN0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IYBwfnNt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IYBwfnNt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 482AEC4CEEF; Sat, 2 Aug 2025 18:52:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754160764; bh=oKJ4o+84X2gZrWbVCPsj5JL/+cPPXG/1i+v6w3VXMC4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IYBwfnNtT4MqM4tAxSAR/QjCr7jN/hWRSOJgtIEv0cqySxNbaTHzmL9697+/+clTy 0lXodjB2ALTL7KFhGrf+dOPaEl9UbiFS54b7fa4RPCFJKSLnMw3+lHXIhVFcfql4tk EreD2tbkCoyLDzoRzkgqjrUMwcRQvCio3Ls6fBtqgVXJztGW2LWZASS2RrIBIkD7AT c0zVOsLH8KRoGneQL/KaueDbzCGBKwbg6bdBvo/bGvF4O2p2+F2sWmwdT4Kdop5vt5 HrEf3c+GE+zleyRAtl8EMibSGfp7N92FZFvklyyggz/EWUz2WkS9klmheE01e7SxVA eneqE0XK/GfVg== Date: Sat, 2 Aug 2025 11:52:44 -0700 From: Kees Cook To: Alexander Lobakin Cc: Simon Horman , intel-wired-lan@lists.osuosl.org, Michal Kubiak , Maciej Fijalkowski , Tony Nguyen , Przemek Kitszel , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , nxne.cnse.osdt.itp.upstreaming@intel.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH iwl-next v3 16/18] idpf: add support for XDP on Rx Message-ID: <202508021152.AD1850CD2@keescook> References: <20250730160717.28976-1-aleksander.lobakin@intel.com> <20250730160717.28976-17-aleksander.lobakin@intel.com> <20250731123734.GA8494@horms.kernel.org> <202507310955.03E47CFA4@keescook> <8c085ba0-29a3-492a-b9f1-e7d02b5fb558@intel.com> Precedence: bulk X-Mailing-List: netdev@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: On Fri, Aug 01, 2025 at 03:17:42PM +0200, Alexander Lobakin wrote: > From: Alexander Lobakin > Date: Fri, 1 Aug 2025 15:12:43 +0200 > > > From: Kees Cook > > Date: Thu, 31 Jul 2025 10:05:47 -0700 > > > >> On Thu, Jul 31, 2025 at 01:37:34PM +0100, Simon Horman wrote: > >>> While I appreciate the desire for improved performance and nicer code > >>> generation. I think the idea of writing 64 bits of data to the > >>> address of a 32 bit member of a structure goes against the direction > >>> of hardening work by Kees and others. > >> > >> Agreed: it's better to avoid obscuring these details from the compiler > >> so it can have an "actual" view of the object sizes involved. > >> > >>> Indeed, it seems to me this is the kind of thing that struct_group() > >>> aims to avoid. > >>> > >>> In this case struct group() doesn't seem like the best option, > >>> because it would provide a 64-bit buffer that we can memcpy into. > >>> But it seems altogether better to simply assign u64 value to a u64 member. > >> > >> Agreed: with struct_group you get a sized pointer, and while you can > >> provide a struct tag to make it an assignable object, it doesn't make > >> too much sense here. > >> > >>> So I'm wondering if an approach along the following lines is appropriate > >>> (Very lightly compile tested only!). > >>> > >>> And yes, there is room for improvement of the wording of the comment > >>> I included below. > >>> > >>> diff --git a/include/net/libeth/xdp.h b/include/net/libeth/xdp.h > >>> index f4880b50e804..a7d3d8e44aa6 100644 > >>> --- a/include/net/libeth/xdp.h > >>> +++ b/include/net/libeth/xdp.h > >>> @@ -1283,11 +1283,7 @@ static inline void libeth_xdp_prepare_buff(struct libeth_xdp_buff *xdp, > >>> const struct page *page = __netmem_to_page(fqe->netmem); > >>> > >>> #ifdef __LIBETH_WORD_ACCESS > >>> - static_assert(offsetofend(typeof(xdp->base), flags) - > >>> - offsetof(typeof(xdp->base), frame_sz) == > >>> - sizeof(u64)); > >>> - > >>> - *(u64 *)&xdp->base.frame_sz = fqe->truesize; > >>> + xdp->base.frame_sz_le_qword = fqe->truesize; > >>> #else > >>> xdp_init_buff(&xdp->base, fqe->truesize, xdp->base.rxq); > >>> #endif > >>> diff --git a/include/net/xdp.h b/include/net/xdp.h > >>> index b40f1f96cb11..b5eedeb82c9b 100644 > >>> --- a/include/net/xdp.h > >>> +++ b/include/net/xdp.h > >>> @@ -85,8 +85,19 @@ struct xdp_buff { > >>> void *data_hard_start; > >>> struct xdp_rxq_info *rxq; > >>> struct xdp_txq_info *txq; > >>> - u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/ > >>> - u32 flags; /* supported values defined in xdp_buff_flags */ > >>> + union { > >>> + /* Allow setting frame_sz and flags as a single u64 on > >>> + * little endian systems. This may may give optimal > >>> + * performance. */ > >>> + u64 frame_sz_le_qword; > >>> + struct { > >>> + /* Frame size to deduce data_hard_end/reserved > >>> + * tailroom. */ > >>> + u32 frame_sz; > >>> + /* Supported values defined in xdp_buff_flags. */ > >>> + u32 flags; > >>> + }; > >>> + }; > >>> }; > >> > >> Yeah, this looks like a nice way to express this, and is way more > >> descriptive than "(u64 *)&xdp->base.frame_sz" :) > > > > Sounds good to me! > > > > Let me send v4 where I'll fix this. > > Note: would it be okay if I send v4 with this fix when the window opens, > while our validation will retest v3 from Tony's tree in meantine? It's a > cosmetic change anyway and does not involve any functional changes. If this is directed at me, yeah, I don't see any high urgency here. -- Kees Cook