Received: by 2002:a05:6a10:eb17:0:0:0:0 with SMTP id hx23csp1333507pxb; Fri, 10 Sep 2021 03:38:46 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyGDZZas+LKSrKyofbEOE1fPjLMzD3LcN0ScR34AIW9ae0/KoIrKU7fHrjH6gGnc5lwQ6BI X-Received: by 2002:a05:6e02:198c:: with SMTP id g12mr5771006ilf.77.1631270326595; Fri, 10 Sep 2021 03:38:46 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1631270326; cv=none; d=google.com; s=arc-20160816; b=tNxzlwICGeE8+xYUTj92dnzGDeTw1UQL/H6AFRSqIrGPeARwD577hGJNNfhi8adnYw RskKXA7ii2g4rQ3gChHqoJqsQ4du4A1HgjAsPwsX6/RxlBjuSiKPzWGTTXN4hDutkIYv g161Zjp9lHSIZilYp/kDq9MsX6oVrZYyxI6qyt/1elEGfswVnxL+ylkbOgqCMpOQylj8 9xZ3/iHtOKj2DrzdUYV/ecN8QhzhmGWm6JG0X3qGzJcp1W5fTW/2xgjBsELbKoh6Ze6G yf0wmx8YMBqhmCugDdrq1DB9V1H97siaOxxkPQIIy5DZfChXJJOTz2okxtQ7ga8+K2a8 eQBA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:in-reply-to:mime-version:user-agent:date :message-id:subject:from:references:cc:to:dkim-signature; bh=H2VnXoHa2A4K95NUzL7qITQw88USxIzmreaA433cCYQ=; b=dzdb4WmnZuIiYWIr5C4/9fIrBI8o3TrYCRSUQb8Yr+LMFv+Dm2MEYV7eT4Go6H1uZN B0FABByqA67D9eW11s3VStADF1oQxB0vCCF7GXfkhnA6nCCVKvBl4wNl4j0ILSoDs5NP uSk7m0G+ydKm93J/VGZ60jjMVmWYY/lb4NlHZcOEKeSAgKiiEhdb41gvhBPiOxMq7+XS YCcrNGn4hC4UZsM3mBJ3TYHIhKA2zI5pSa09jZoX6cUye2nCoWDrEGdkCMBMOCfVFcQk d+Zjj5gOp2WXTgoMS/LuLegCh/BytVJKtoOCVxtyysZ5Qz6KovyytLZpZH7IByz5p0vS pkmw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@suse.com header.s=susede1 header.b=HR548Zw8; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=QUARANTINE sp=NONE dis=NONE) header.from=suse.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id x6si5167740ilv.42.2021.09.10.03.38.34; Fri, 10 Sep 2021 03:38:46 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@suse.com header.s=susede1 header.b=HR548Zw8; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=QUARANTINE sp=NONE dis=NONE) header.from=suse.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232426AbhIJKh7 (ORCPT + 99 others); Fri, 10 Sep 2021 06:37:59 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:52658 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232157AbhIJKh7 (ORCPT ); Fri, 10 Sep 2021 06:37:59 -0400 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 57C2D1FE65; Fri, 10 Sep 2021 10:36:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1631270207; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=H2VnXoHa2A4K95NUzL7qITQw88USxIzmreaA433cCYQ=; b=HR548Zw8DIrBJ/igCxh2VQX2odWSM3fMFY/SXo9k5d2wwRft6NEROE0M2SyIgTThv/c/uc Kafb6F8o2BYzI1gnT6G9xbSF4sFE2rnnOcVK7hUw+wgnQDRJ9lTkw6WSJm5kKY5UoVBaLI I+BHBnDRL6eAh9GcNYYk7x41wJdP2tw= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id EAC4813D29; Fri, 10 Sep 2021 10:36:46 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id qSszNz41O2FOFwAAMHmgww (envelope-from ); Fri, 10 Sep 2021 10:36:46 +0000 To: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= Cc: xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Konrad Rzeszutek Wilk , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Boris Ostrovsky , Stefano Stabellini , Jens Axboe , Jan Beulich References: <20210730103854.12681-1-jgross@suse.com> <20210730103854.12681-3-jgross@suse.com> From: Juergen Gross Subject: Re: [PATCH v3 2/3] xen/blkfront: don't take local copy of a request from the ring page Message-ID: Date: Fri, 10 Sep 2021 12:36:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="YDiXBiNt21aKFiTvqXl3q9RqqBf0BQSSN" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --YDiXBiNt21aKFiTvqXl3q9RqqBf0BQSSN Content-Type: multipart/mixed; boundary="JUVTtvF3oNKhDqHwfJSukXexFi2WlmUoF"; protected-headers="v1" From: Juergen Gross To: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= Cc: xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Konrad Rzeszutek Wilk , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Boris Ostrovsky , Stefano Stabellini , Jens Axboe , Jan Beulich Message-ID: Subject: Re: [PATCH v3 2/3] xen/blkfront: don't take local copy of a request from the ring page References: <20210730103854.12681-1-jgross@suse.com> <20210730103854.12681-3-jgross@suse.com> In-Reply-To: --JUVTtvF3oNKhDqHwfJSukXexFi2WlmUoF Content-Type: multipart/mixed; boundary="------------011F05A4CB9DE931D3CC7582" Content-Language: en-US This is a multi-part message in MIME format. --------------011F05A4CB9DE931D3CC7582 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 10.09.21 12:14, Marek Marczykowski-G=C3=B3recki wrote: > On Fri, Jul 30, 2021 at 12:38:53PM +0200, Juergen Gross wrote: >> In order to avoid a malicious backend being able to influence the loca= l >> copy of a request build the request locally first and then copy it to >> the ring page instead of doing it the other way round as today. >> >> Signed-off-by: Juergen Gross >> Reviewed-by: Jan Beulich >> Acked-by: Roger Pau Monn=C3=A9 >> --- >> V2: >> - init variable to avoid potential compiler warning (Jan Beulich) >> --- >> drivers/block/xen-blkfront.c | 25 +++++++++++++++---------- >> 1 file changed, 15 insertions(+), 10 deletions(-) >> >> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront= =2Ec >> index 15e840287734..b7301006fb28 100644 >=20 > (...) >=20 >> @@ -827,10 +832,10 @@ static int blkif_queue_rw_req(struct request *re= q, struct blkfront_ring_info *ri >> if (setup.segments) >> kunmap_atomic(setup.segments); >> =20 >> - /* Keep a private copy so we can reissue requests when recovering. *= / >> - rinfo->shadow[id].req =3D *ring_req; >> + /* Copy request(s) to the ring page. */ >> + *final_ring_req =3D *ring_req; >=20 > Is this guaranteed to not be optimized by the compiler in an unsafe way= > (like, do the operation the other way around)? I don't think the C standard allows that. AFAIK reordering writes is allowed only between sequence points. And each external function call is a sequence point, making such an optimization in our case illegal. Juergen --------------011F05A4CB9DE931D3CC7582 Content-Type: application/pgp-keys; name="OpenPGP_0xB0DE9DD628BF132F.asc" Content-Transfer-Encoding: quoted-printable Content-Description: OpenPGP public key Content-Disposition: attachment; filename="OpenPGP_0xB0DE9DD628BF132F.asc" -----BEGIN PGP PUBLIC KEY BLOCK----- xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOBy= cWx w3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJvedYm8O= f8Z d621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJNwQpd369y= 9bf IhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvxXP3FAp2pkW0xq= G7/ 377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEBAAHNHEp1ZXJnZW4gR= 3Jv c3MgPGpnQHBmdXBmLm5ldD7CwHkEEwECACMFAlOMcBYCGwMHCwkIBwMCAQYVCAIJCgsEFgIDA= QIe AQIXgAAKCRCw3p3WKL8TL0KdB/93FcIZ3GCNwFU0u3EjNbNjmXBKDY4FUGNQH2lvWAUy+dnyT= hpw dtF/jQ6j9RwE8VP0+NXcYpGJDWlNb9/JmYqLiX2Q3TyevpB0CA3dbBQp0OW0fgCetToGIQrg0= MbD 1C/sEOv8Mr4NAfbauXjZlvTj30H2jO0u+6WGM6nHwbh2l5O8ZiHkH32iaSTfN7Eu5RnNVUJbv= oPH Z8SlM4KWm8rG+lIkGurqqu5gu8q8ZMKdsdGC4bBxdQKDKHEFExLJK/nRPFmAuGlId1E3fe10v= 5QL +qHI3EIPtyfE7i9Hz6rVwi7lWKgh7pe0ZvatAudZ+JNIlBKptb64FaiIOAWDCx1SzR9KdWVyZ= 2Vu IEdyb3NzIDxqZ3Jvc3NAc3VzZS5jb20+wsB5BBMBAgAjBQJTjHCvAhsDBwsJCAcDAgEGFQgCC= QoL BBYCAwECHgECF4AACgkQsN6d1ii/Ey/HmQf/RtI7kv5A2PS4RF7HoZhPVPogNVbC4YA6lW7Dr= Wf0 teC0RR3MzXfy6pJ+7KLgkqMlrAbN/8Dvjoz78X+5vhH/rDLa9BuZQlhFmvcGtCF8eR0T1v0nC= /nu AFVGy+67q2DH8As3KPu0344TBDpAvr2uYM4tSqxK4DURx5INz4ZZ0WNFHcqsfvlGJALDeE0Lh= ITT d9jLzdDad1pQSToCnLl6SBJZjDOX9QQcyUigZFtCXFst4dlsvddrxyqT1f17+2cFSdu7+ynLm= XBK 7abQ3rwJY8SbRO2iRulogc5vr/RLMMlscDAiDkaFQWLoqHHOdfO9rURssHNN8WkMnQfvUewRz= 80h SnVlcmdlbiBHcm9zcyA8amdyb3NzQG5vdmVsbC5jb20+wsB5BBMBAgAjBQJTjHDXAhsDBwsJC= AcD AgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey8PUQf/ehmgCI9jB9hlgexLvgOtf7PJn= FOX gMLdBQgBlVPO3/D9R8LtF9DBAFPNhlrsfIG/SqICoRCqUcJ96Pn3P7UUinFG/I0ECGF4EvTE1= jnD kfJZr6jrbjgyoZHiw/4BNwSTL9rWASyLgqlA8u1mf+c2yUwcGhgkRAd1gOwungxcwzwqgljf0= N51 N5JfVRHRtyfwq/ge+YEkDGcTU6Y0sPOuj4Dyfm8fJzdfHNQsWq3PnczLVELStJNdapwPOoE+l= otu fe3AM2vAEYJ9rTz3Cki4JFUsgLkHFqGZarrPGi1eyQcXeluldO3m91NK/1xMI3/+8jbO0tsn1= tqS EUGIJi7ox80eSnVlcmdlbiBHcm9zcyA8amdyb3NzQHN1c2UuZGU+wsB5BBMBAgAjBQJTjHDrA= hsD BwsJCAcDAgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey+LhQf9GL45eU5vOowA2u5N3= g3O ZUEBmDHVVbqMtzwlmNC4k9Kx39r5s2vcFl4tXqW7g9/ViXYuiDXb0RfUpZiIUW89siKrkzmQ5= dM7 wRqzgJpJwK8Bn2MIxAKArekWpiCKvBOB/Cc+3EXE78XdlxLyOi/NrmSGRIov0karw2RzMNOu5= D+j LRZQd1Sv27AR+IP3I8U4aqnhLpwhK7MEy9oCILlgZ1QZe49kpcumcZKORmzBTNh30FVKK1Evm= V2x AKDoaEOgQB4iFQLhJCdP1I5aSgM5IVFdn7v5YgEYuJYx37IoN1EblHI//x/e2AaIHpzK5h88N= Eaw QsaNRpNSrcfbFmAg987ATQRTjHAWAQgAyzH6AOODMBjgfWE9VeCgsrwH3exNAU32gLq2xvjpW= nHI s98ndPUDpnoxWQugJ6MpMncr0xSwFmHEgnSEjK/PAjppgmyc57BwKII3sV4on+gDVFJR6Y8ZR= wgn BC5mVM6JjQ5xDk8WRXljExRfUX9pNhdE5eBOZJrDRoLUmmjDtKzWaDhIg/+1Hzz93X4fCQkNV= bVF LELU9bMaLPBG/x5q4iYZ2k2ex6d47YE1ZFdMm6YBYMOljGkZKwYde5ldM9mo45mmwe0icXKLk= pEd IXKTZeKDO+Hdv1aqFuAcccTg9RXDQjmwhC3yEmrmcfl0+rPghO0Iv3OOImwTEe4co3c1mwARA= QAB wsBfBBgBAgAJBQJTjHAWAhsMAAoJELDendYovxMvQ/gH/1ha96vm4P/L+bQpJwrZ/dneZcmEw= Tbe 8YFsw2V/Buv6Z4Mysln3nQK5ZadD534CF7TDVft7fC4tU4PONxF5D+/tvgkPfDAfF77zy2AH1= vJz Q1fOU8lYFpZXTXIHb+559UqvIB8AdgR3SAJGHHt4RKA0F7f5ipYBBrC6cyXJyyoprT10EMvU8= VGi wXvTyJz3fjoYsdFzpWPlJEBRMedCot60g5dmbdrZ5DWClAr0yau47zpWj3enf1tLWaqcsuylW= svi uGjKGw7KHQd3bxALOknAp4dN3QwBYCKuZ7AddY9yjynVaD5X7nF9nO5BjR/i1DG86lem3iBDX= zXs ZDn8R38=3D =3D2wuH -----END PGP PUBLIC KEY BLOCK----- --------------011F05A4CB9DE931D3CC7582-- --JUVTtvF3oNKhDqHwfJSukXexFi2WlmUoF-- --YDiXBiNt21aKFiTvqXl3q9RqqBf0BQSSN Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsB5BAABCAAjFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAmE7NT4FAwAAAAAACgkQsN6d1ii/Ey8t 2gf+N+WivElKoy9i6Whxd4rrrfEgFb+GzHmhiPCJfNEpstG02jsb0k43eda74wAcdEVpHl7EIG7i 8gBbJwSxH5ZAm295X5wMia00fFtlyppP5uinCToZsE/sbGx2nOCako4HrVNfCzP16R6tXclaY9ho 0dvWYDCF/owSYAzT5OgDkSxVRRqLbZz1CnjFtVRDgp/UXCPJnehCMZ1nxBh6HNBBLPgrE6YldLqN HzkEqs4n3CBFGOD7BzZ25UbLS7PH+JGDWaEWk1ZLFZFm1unwxM5qn42FQf0f0IvrAGAS3WNiq7Nh Al23xfAoUu3Nulw+cTq3M2avOvoC5C5/y4XeC8aGSg== =Dr55 -----END PGP SIGNATURE----- --YDiXBiNt21aKFiTvqXl3q9RqqBf0BQSSN--