From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 66E772C21C0 for ; Tue, 13 Jan 2026 15:06:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768316773; cv=none; b=gNvTzCgtlXbYNQ01+wj0tkWployk9Jc+KozLLWdxtO+ydxOmUclDMhE7MXGzKOZpy51QerbhudW+VCQIfR23EJ9ir17rMYlJGIKIn+gkM29sA6SanW3/GAGXpOAekQUbZWi29EwWJ6BGmRqAGVmbYwSWpflTHCPe3HOLzHA5Pzc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768316773; c=relaxed/simple; bh=s+CuNh8nN+c3duGNNJwpTmjqk55xK0VXgzFyC6AyLv0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=n5U6ZrcmPW3QU9SzFMnSUTSGbPdqD9FYgqnr9nh3jQDlmo494x/vZjcPKkaEJJv5KCbPbhvEKxTq0HH60mwbbjnpbBp4A2ZWBl8QVUb9Fv9nrkjhvOXY1grB8C7YtgMtvsfPVhJRFXlcLSA0pbapQo4Yvott9uN8BmCwI7zJye4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=QfLa5wwy; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=aqCr87+z; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QfLa5wwy"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="aqCr87+z" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1768316770; 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=zDwCw69rb94qC+LZlvI4uRVvjhNJWGT4TLlWN2hOUDk=; b=QfLa5wwyjdgveQkQcnLwvBJESnm3VPjQpzyYlI5HhI8X+NnnmBfd+LkYufa5uq5sMvKtJ2 eFbSeMhO1J/Eb953raSf+6REVOQwEC2PTU8JdpwRp9DM4GdYy/aRpLd6m6ImGE1OLckxKZ V4P90qVKCyN5HCtFhyR5v98ukYI/7ZM= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-190-VC9IgKsdNVaBxkTI9c1qlg-1; Tue, 13 Jan 2026 10:06:09 -0500 X-MC-Unique: VC9IgKsdNVaBxkTI9c1qlg-1 X-Mimecast-MFC-AGG-ID: VC9IgKsdNVaBxkTI9c1qlg_1768316768 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-4775e00b16fso59656975e9.2 for ; Tue, 13 Jan 2026 07:06:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1768316768; x=1768921568; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=zDwCw69rb94qC+LZlvI4uRVvjhNJWGT4TLlWN2hOUDk=; b=aqCr87+zwyj2GnwEHpnEbnGq4QhxwM5kFXyv43AoNfNwnVrZElvRjvUBAuzpExUFcF kdy8Fo0sv8HZd+l8wSYA/oH4X/rBhrVBq3oqopvD8vvrJIhFuTjQ/3POhQ0FCyYqET6t j47fTm2/AmzFIjaxpSa6SNNCfOyU7coiGxk/56vLRenPsbv/0HOeER5/ib1raIRLQfak jHnla63HZju/YMvKGCTZpGcr/PeFfMOhKIVhH7gWRbVk77IUfo9EW62nTreW7kadj461 lBsr88h0J7ctmgKoZ4tCxKhLokLSo+ilB6+6rUU8O+BjfN53X5YLlWduAuhWTDWz2Qkg gQpQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768316768; x=1768921568; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=zDwCw69rb94qC+LZlvI4uRVvjhNJWGT4TLlWN2hOUDk=; b=nQhGz9aYKNDT+w8ezZcW3m4JOn0RhZL5xOprt2SdQjwRN5eTARDhbmyyRQ/TnVQHs7 A/tCnKTwchQKN4m/GVXtrFyEYbfyOSm2YhfDsL9m9+X+aG8rCLHCjtlaL+degSIP8+Zs fGm+W1/xms202sa4k1ko9rA0bFMkwjJS0OyoYLi1JgLZMHE3DNXywFtbrfHl4kU01zou LehO0bGIJIWxACEcF5MAZqKUuFl8DBsIAMntT5pkztrQM7KxxPNG+xbZst4wYxn0Nqn8 06u43JKoz6m3IYguRtHOFNBLBOUq43qE/9Aywcd4Z7omJwkx2QvGkBl9KUUHKrpQMryi veRQ== X-Forwarded-Encrypted: i=1; AJvYcCVDfL2mb7b90A3pTU9U6ni031JOiPDdEe1NLGH03VD8grtB5xOwI1UJWJh4y4OFqi/OZ5Nfm8o=@vger.kernel.org X-Gm-Message-State: AOJu0YycZeQBj5OLKAPRRkw7sDNMelNJiq9+kTCaRfhEaw2d1GSqRmvy PrTg7GTQVXHc87MFcKSMM3KWvvP7xFBLbbtuOCHhhFtCT0UiVtjWtVedRjSik0R88xMG4vhEdWh s78qEcx2rW2ZjXMGC0p4zWHV275ZoNknN8VoN1S1FPoE2fACCkySCWbjbaQ== X-Gm-Gg: AY/fxX5Bs4tYrDGqIhUNaP3VarJbxqhUHKy2EHxWR6CzQjjOoKSBTK08a42pqTctr/L wAiIMq2qMHlbNHaC1V9k+nNnIX8e2DilYHJldlrPh/Uon2YPYn/RS4a2d3AMzgegGmyv/SgGLHL vaBaeJSnd5vsAD+DCsXwTuDhaXV36r/fZ+vLSDsiqt1MWUB4fxkoLt9FjcCtBdIcOQ/SwubAEtu xJ5oBgTSqjqyUMXINzohdXEFmiZrVf81MlyjzQP1QrHkccu/j2D05WCHjdAtNlHyxx6J+0IfTbf SXv5ga0aR9apdJIBOkc994pAX4wRVdcNkAiBSjpUj8VpgRY1XYkDQ2tNOlBi0KkMLf5QROcS1Pu b93NABx8g4+aa X-Received: by 2002:a05:600c:3556:b0:479:33be:b23e with SMTP id 5b1f17b1804b1-47d84b3b4eamr286985125e9.17.1768316767873; Tue, 13 Jan 2026 07:06:07 -0800 (PST) X-Google-Smtp-Source: AGHT+IGSrRyHk6thUAyQczy6/cI8N/GQqeafVlq48pG73G8dfSC1NPPmKMlwELspqzYKhAl9nUej4w== X-Received: by 2002:a05:600c:3556:b0:479:33be:b23e with SMTP id 5b1f17b1804b1-47d84b3b4eamr286984645e9.17.1768316767454; Tue, 13 Jan 2026 07:06:07 -0800 (PST) Received: from [192.168.88.32] ([212.105.155.93]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47ee1189f5fsm2255445e9.2.2026.01.13.07.06.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Jan 2026 07:06:06 -0800 (PST) Message-ID: <916a6c1a-681e-4e5e-8d49-75d0de5c46a1@redhat.com> Date: Tue, 13 Jan 2026 16:06:05 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2][next] virtio_net: Fix misalignment bug in struct virtnet_info To: "Michael S. Tsirkin" , Jakub Kicinski Cc: "Gustavo A. R. Silva" , Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Akihiko Odaki , Simon Horman , netdev@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, Kees Cook References: <20260113093839-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20260113093839-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/13/26 3:39 PM, Michael S. Tsirkin wrote: > On Tue, Jan 13, 2026 at 03:30:00PM +0100, Paolo Abeni wrote: >> On 1/10/26 9:07 AM, Gustavo A. R. Silva wrote: >>> Use the new TRAILING_OVERLAP() helper to fix a misalignment bug >>> along with the following warning: >>> >>> drivers/net/virtio_net.c:429:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] >>> >>> This helper creates a union between a flexible-array member (FAM) >>> and a set of members that would otherwise follow it (in this case >>> `u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];`). This >>> overlays the trailing members (rss_hash_key_data) onto the FAM >>> (hash_key_data) while keeping the FAM and the start of MEMBERS aligned. >>> The static_assert() ensures this alignment remains. >>> >>> Notice that due to tail padding in flexible `struct >>> virtio_net_rss_config_trailer`, `rss_trailer.hash_key_data` >>> (at offset 83 in struct virtnet_info) and `rss_hash_key_data` (at >>> offset 84 in struct virtnet_info) are misaligned by one byte. See >>> below: >>> >>> struct virtio_net_rss_config_trailer { >>> __le16 max_tx_vq; /* 0 2 */ >>> __u8 hash_key_length; /* 2 1 */ >>> __u8 hash_key_data[]; /* 3 0 */ >>> >>> /* size: 4, cachelines: 1, members: 3 */ >>> /* padding: 1 */ >>> /* last cacheline: 4 bytes */ >>> }; >>> >>> struct virtnet_info { >>> ... >>> struct virtio_net_rss_config_trailer rss_trailer; /* 80 4 */ >>> >>> /* XXX last struct has 1 byte of padding */ >>> >>> u8 rss_hash_key_data[40]; /* 84 40 */ >>> ... >>> /* size: 832, cachelines: 13, members: 48 */ >>> /* sum members: 801, holes: 8, sum holes: 31 */ >>> /* paddings: 2, sum paddings: 5 */ >>> }; >>> >>> After changes, those members are correctly aligned at offset 795: >>> >>> struct virtnet_info { >>> ... >>> union { >>> struct virtio_net_rss_config_trailer rss_trailer; /* 792 4 */ >>> struct { >>> unsigned char __offset_to_hash_key_data[3]; /* 792 3 */ >>> u8 rss_hash_key_data[40]; /* 795 40 */ >>> }; /* 792 43 */ >>> }; /* 792 44 */ >>> ... >>> /* size: 840, cachelines: 14, members: 47 */ >>> /* sum members: 801, holes: 8, sum holes: 35 */ >>> /* padding: 4 */ >>> /* paddings: 1, sum paddings: 4 */ >>> /* last cacheline: 8 bytes */ >>> }; >>> >>> As a result, the RSS key passed to the device is shifted by 1 >>> byte: the last byte is cut off, and instead a (possibly >>> uninitialized) byte is added at the beginning. >>> >>> As a last note `struct virtio_net_rss_config_hdr *rss_hdr;` is also >>> moved to the end, since it seems those three members should stick >>> around together. :) >>> >>> Cc: stable@vger.kernel.org >>> Fixes: ed3100e90d0d ("virtio_net: Use new RSS config structs") >>> Signed-off-by: Gustavo A. R. Silva >>> --- >>> Changes in v2: >>> - Update subject and changelog text (include feedback from Simon and >>> Michael --thanks folks) >>> - Add Fixes tag and CC -stable. >> >> @Michael, @Jason: This is still apparently targeting 'net-next', but I >> think it should land in the 'net' tree, right? >> >> /P > > Probably but I'm yet to properly review it. The thing that puzzles me at > a first glance is how are things working right now then? Apparently they aren't ?!? rss self-tests for virtio_net are failing: https://netdev-ctrl.bots.linux.dev/logs/vmksft/drv-hw-dbg/results/471521/15-rss-api-py/stdout but the result is into the CI reported as success (no idea why?!?) /P