From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 64D96C07E99 for ; Thu, 8 Jul 2021 05:47:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 48BCA61CE5 for ; Thu, 8 Jul 2021 05:47:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229593AbhGHFtt (ORCPT ); Thu, 8 Jul 2021 01:49:49 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:48270 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229579AbhGHFtt (ORCPT ); Thu, 8 Jul 2021 01:49:49 -0400 Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (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 0479620131; Thu, 8 Jul 2021 05:47:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1625723227; 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=ip5DNgexySMwzuWqwa7ACJthFTxiFhdfI+wAfyqI2vQ=; b=mtRhjyizl14mUB363xUyJ8hB7aUMyzMYom33vs6fkxmXh8GwkExiFT8QbjKbQGoINv2kte gOjwk1DxWJ93vQZ3gvMeN0i2VIfQ7+bhXGMkeixDvAWNvM/EEzz5AeozWs2btvrqz7US2A 3k5qRk9rE4C8vyovYqa7MoEsauJPO/w= Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (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 imap1.suse-dmz.suse.de (Postfix) with ESMTPS id B37E61340F; Thu, 8 Jul 2021 05:47:06 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id CQAAKlqR5mDNfQAAGKfGzw (envelope-from ); Thu, 08 Jul 2021 05:47:06 +0000 Subject: Re: [PATCH 4/8] xen/blkfront: don't trust the backend response data blindly To: Jan Beulich Cc: Konrad Rzeszutek Wilk , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Boris Ostrovsky , Stefano Stabellini , Jens Axboe , xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210513100302.22027-1-jgross@suse.com> <20210513100302.22027-5-jgross@suse.com> <315ad8b9-8a98-8d3e-f66c-ab32af2731a8@suse.com> <6095c4b9-a9bb-8a38-fb6c-a5483105b802@suse.com> <030ef85e-b5af-f46e-c8dc-88b8d195c4e1@suse.com> <477f01cd-8793-705c-10f9-cf0c0cd6ed84@suse.com> From: Juergen Gross Message-ID: Date: Thu, 8 Jul 2021 07:47:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <477f01cd-8793-705c-10f9-cf0c0cd6ed84@suse.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="65Cl9OH3VxhoDnxdHBagUmL999Yvk5KRj" Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --65Cl9OH3VxhoDnxdHBagUmL999Yvk5KRj Content-Type: multipart/mixed; boundary="TaRSfQAduiJvbDCSd5wNF88LIRKqIxccY"; protected-headers="v1" From: Juergen Gross To: Jan Beulich Cc: Konrad Rzeszutek Wilk , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Boris Ostrovsky , Stefano Stabellini , Jens Axboe , xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: Subject: Re: [PATCH 4/8] xen/blkfront: don't trust the backend response data blindly References: <20210513100302.22027-1-jgross@suse.com> <20210513100302.22027-5-jgross@suse.com> <315ad8b9-8a98-8d3e-f66c-ab32af2731a8@suse.com> <6095c4b9-a9bb-8a38-fb6c-a5483105b802@suse.com> <030ef85e-b5af-f46e-c8dc-88b8d195c4e1@suse.com> <477f01cd-8793-705c-10f9-cf0c0cd6ed84@suse.com> In-Reply-To: <477f01cd-8793-705c-10f9-cf0c0cd6ed84@suse.com> --TaRSfQAduiJvbDCSd5wNF88LIRKqIxccY Content-Type: multipart/mixed; boundary="------------1299B9F7BEB5CBBFFB8C69D9" Content-Language: en-US This is a multi-part message in MIME format. --------------1299B9F7BEB5CBBFFB8C69D9 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 17.05.21 17:33, Jan Beulich wrote: > On 17.05.2021 17:22, Juergen Gross wrote: >> On 17.05.21 17:12, Jan Beulich wrote: >>> On 17.05.2021 16:23, Juergen Gross wrote: >>>> On 17.05.21 16:11, Jan Beulich wrote: >>>>> On 13.05.2021 12:02, Juergen Gross wrote: >>>>>> @@ -1574,10 +1580,16 @@ static irqreturn_t blkif_interrupt(int irq= , void *dev_id) >>>>>> spin_lock_irqsave(&rinfo->ring_lock, flags); >>>>>> again: >>>>>> rp =3D rinfo->ring.sring->rsp_prod; >>>>>> + if (RING_RESPONSE_PROD_OVERFLOW(&rinfo->ring, rp)) { >>>>>> + pr_alert("%s: illegal number of responses %u\n", >>>>>> + info->gd->disk_name, rp - rinfo->ring.rsp_cons); >>>>>> + goto err; >>>>>> + } >>>>>> rmb(); /* Ensure we see queued responses up to 'rp'. */ >>>>> >>>>> I think you want to insert after the barrier. >>>> >>>> Why? The relevant variable which is checked is "rp". The result of t= he >>>> check is in no way depending on the responses themselves. And any ch= ange >>>> of rsp_cons is protected by ring_lock, so there is no possibility of= >>>> reading an old value here. >>> >>> But this is a standard double read situation: You might check a value= >>> and then (via a separate read) use a different one past the barrier. >> >> Yes and no. >> >> rsp_cons should never be written by the other side, and additionally >> it would be read multiple times anyway. >=20 > But I'm talking about rsp_prod, as that's what rp gets loaded from. Oh, now I get your problem. But shouldn't that better be solved by using READ_ONCE() for reading rp instead? Juergen --------------1299B9F7BEB5CBBFFB8C69D9 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----- --------------1299B9F7BEB5CBBFFB8C69D9-- --TaRSfQAduiJvbDCSd5wNF88LIRKqIxccY-- --65Cl9OH3VxhoDnxdHBagUmL999Yvk5KRj Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsB5BAABCAAjFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAmDmkVoFAwAAAAAACgkQsN6d1ii/Ey9d SAf+KLMOHqZAOwV2oMpLnGz6nvcW8YhRf7arZPFHVihB8LPCP/ZMeXdUOOrg4Es9ObCPK3OsCyjO 2ZLyzCQN+5haDXDOJkvUkf6mZ4u/lS44+t0gONnt9mCbH1DAr/8vLPnAGXWbPy1bULNZS58k3j5c Mb/bW0RiqyiAQWP8xXe7EkC4DV5fwQG1QUnOV3ULDUorDihhshR82yfWQ7+HzbzUVg2OZZGU8UlX htMrMbRFoCfAEO98yZ+qbHTE/i54dl7pUAwc1dSqvMrYCGnCf0Q4D8E2xHzOhpDohPxpjPYGXF12 YgTs6YPWhtmHoOKBBACBsPfJWyBa0ZOIFq9oWWbTAQ== =p302 -----END PGP SIGNATURE----- --65Cl9OH3VxhoDnxdHBagUmL999Yvk5KRj--