Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <7e075c90-5adb-856a-36fb-73a8d424cd0b@oracle.com>
Date:   Mon, 18 Jul 2022 09:36:26 -0400
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.11.0
Subject: Re: Build warnings in Xen 5.15.y and 5.10.y with retbleed backports
Content-Language: en-US
To:     Juergen Gross <jgross@suse.com>, Nicolai Stange <nstange@suse.de>,
        Greg KH <gregkh@linuxfoundation.org>
Cc:     Stefano Stabellini <sstabellini@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, jpoimboe@redhat.com,
        Ben Hutchings <ben@decadent.org.uk>
References: <Ys2jlGMqAe6+h1SX@kroah.com>
 <ddcdd531-fc33-39df-a69f-5352d7a1c8af@oracle.com>
 <Ys3MI7cv2yKj9RFc@kroah.com>
 <1b8fee7f-5af2-332e-d2c9-ceecd6ff487b@oracle.com>
 <875yjxrp66.fsf@linux.fritz.box>
 <ed82e54e-ccc4-f514-7018-8410d0f5bb82@oracle.com>
 <6eea38ab-17d2-7bdc-1277-9964a3828a9e@suse.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
In-Reply-To: <6eea38ab-17d2-7bdc-1277-9964a3828a9e@suse.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?YmxiY2s1Z1dXQXl1TlpjVjR0MVltc3A0TVRNRnlsSDFxdzdLcGhEZHp1cnZX?=
 =?utf-8?B?UEpOUUFiWnZEU0o2d0VVWG1PeklVeEZkd1NqR083SWR1bEZFMTV0RHY0Z3ZG?=
 =?utf-8?B?OVpndFBXcCtJK3pWUTBSbHVDbDBybnREQXRPL1l2WnZPekJHQVo1dW5TbzVs?=
 =?utf-8?B?eFJvSDV6NW4zNHpmWGlialdvSUNoUTk3VFM4Sy93WFNWN2lLTWdLcWJMZVpp?=
 =?utf-8?B?RXMwNFl0a2cyVDNVNGRzdS9ibXZMUXE0akpmZWkzd1U5Wlk3ZnpiZTQraU5y?=
 =?utf-8?B?RUliY25tZ2syUWkwK0E4WGI5TDk0QndnQjFKcHREckhPMnJQSmlxUmgxMWEw?=
 =?utf-8?B?cmRNMndJcWRzUityelZnQmhhblFtNE5kNEc5Wk5PRnhHMitFTXEwaE8vOFFp?=
 =?utf-8?B?cXJZdGs5amN6NFhqZGhsWXFZbnc0c0RPS2ZkUUZHNEpiNkd5TUZCckdtU2dU?=
 =?utf-8?B?V2VDcFZpM1habjRKMkl3QWR0OTN6OWVHdXd2YlFLQ2pqaWZtNGRScmJnNDly?=
 =?utf-8?B?OWdmeHlFanptMHBTS3g0cWFXQlN5TTJRNDY4ZEV5UEVBZFRObFJ3TjdHL2Ns?=
 =?utf-8?B?OEdxOTZpbFJ1clk1OTFMSjg4ZU11REVSM1JvWCtvck11MWdNT1VJbDBja2FS?=
 =?utf-8?B?RHhDSytXRGV0bFo5UGZPZ0RnM2E2SHhZbGx5V21HSTNGMEJUbE9zMHFkaC95?=
 =?utf-8?B?RytYRVpDdmR3Nkd2WkNHTUE1S2NtRFhRQnZZdHNQRkVrdVVtOXRKYit4VGZM?=
 =?utf-8?B?UWZuMlI1S0JmWlR0YU5CVWFmdDgwcVEvVVBGdHp2OEVoT3hldlhSbGhHcWFM?=
 =?utf-8?B?NVg2czhQSkplRERJeHpBRm8zYVprTnpoWllwTkh1WGhGcG52czlhbkhqbC9l?=
 =?utf-8?B?OUxWeERyUFVFUE1yclg1Tzk4NmgyS1VJaVlCUExCQzlnNEwwaHprZFdSMks1?=
 =?utf-8?B?QVI0L052YmpIWWZJNVJkeDhFUTkrWFpMakNvYU5zNTJ3U0VzVXhtTExUaVB5?=
 =?utf-8?B?UUYyb3U3RmlzZDVUZGJuU3l4VWU0NkJINURScXJqYy9TcmlTY3Y3NU1KVEdw?=
 =?utf-8?B?RFk0UnF2SlFWeXJ5L0hEVWsxU3docjhuWm9XZEU4eFpnV1VwWGdtK1A2VXIr?=
 =?utf-8?B?ZktlRkpKeDZBS0YzaUdHdzZJdWVPZmlCYldBa3gxaVNPUXpIREJocnVka3dx?=
 =?utf-8?B?cG9xOWVmVStFemIwS3JpRlRrRWhYQnliUUh6L3BMOUFLOVlKcWpmZEtIbzVY?=
 =?utf-8?B?ZFhWUWxMYVptU1loWHJOdzNydy9HNzBXM0Z3TUtFZTByd2kwbU1md29NRlF6?=
 =?utf-8?B?aUltSG9oeXlLTGJHQWI1dWxmUDBXSWY5b0VmY25kOVFtdUduNVVkOEpZbzNK?=
 =?utf-8?B?SFFHcEVCVGdYRXZrck5mcWs3cTg4emh0aVU5RkxWVk1EZzZlaUJTZWNmQ0Vm?=
 =?utf-8?B?akdSSkN4WkxTR2dTZEY1TEtrY2UrVytVbkJpS01HMmhIZllNWExOTUhYcXFn?=
 =?utf-8?B?cHRqQTRVa0tFVGdFVVBkaS9pOUgvVmtpcTZmd3hDRTNGUWV2dDNuNzBhUnhj?=
 =?utf-8?B?eGk4TW93T014cDk5aDU3dXUwZ0VxK281aW1RZjZyS1pwUTYrb2hnbWNuS0kw?=
 =?utf-8?B?ai9ndTkzcHdGT1BsSlVXK25LMGM2VDMzdlpmalYwQ1I4d3ZiN0lRNmRjV21a?=
 =?utf-8?B?MFN2Uzd1cUozRHE4d0tOclBsallJbFpZazFROXY2b1M5Y0kxaExXbFROb2Ni?=
 =?utf-8?B?WkN5WnpmQ1E5RTZjTGNZNnFIdWo1S2ovQjd2eC8vdnFLTWRXdEFqUElqMVNw?=
 =?utf-8?B?Z2NlbVJLbDNpd3ZlNkhWTFYrSkY3VXYySWRNUDRXZGMrck9NUk5UTXBVbEFP?=
 =?utf-8?B?NS91cll1VTV1RW5CTUlwWjMxb2lmWXZsSVM3ZkdLRmIxV01YVGRGa004WENL?=
 =?utf-8?B?ZndaSjhjZ1JjQW9tNTZDR3N4TDN2ZXRzbm5MYnpNVHRORUxZV1g5MXRPRjNW?=
 =?utf-8?B?UFhVcmNYalpyMWE0VXNPU2c4K2N6Rk85OHFoUlFzcm9tb2oxQ0VSRHVxVVhl?=
 =?utf-8?B?Q0h6NDRKSWMxSjd4K3Q4NEtkU0ZJVDZHNXl6Y3lRVXFSdU43bGo3Qk9YMitw?=
 =?utf-8?B?NzRRdkhZc2lDbG1JeGU4TUVRT0VaUkQ1YmtEMGQwV0pvUVh5OWpWeHBlY212?=
 =?utf-8?B?aVE9PQ==?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 956a61a8-131d-4a9e-29b5-08da68c28798
X-MS-Exchange-CrossTenant-AuthSource: BLAPR10MB5009.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jul 2022 13:36:33.5763
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: lK1AIdeIt6/RrX1Le4u1OKvHjz6bemHp05CeGLE9xU9mkPEjYSk5KDPx+X8Qu53WGyTWBCuwTZeUuxji5aZTIanhIgKsmCVqAyiSRkgE9/g=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR10MB2712
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.122.1
 definitions=2022-07-18_12,2022-07-18_01,2022-06-22_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 bulkscore=0 phishscore=0
 suspectscore=0 mlxlogscore=990 adultscore=0 spamscore=0 mlxscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2206140000
 definitions=main-2207180058
X-Proofpoint-ORIG-GUID: b5XY6G6y847g1fD1OvOY8nCptARhD_t4
X-Proofpoint-GUID: b5XY6G6y847g1fD1OvOY8nCptARhD_t4
X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_LOW,
        RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 7/17/22 1:20 AM, Juergen Gross wrote:
>
> What about filling the complete hypercall page just with "int 3" or "ud2"?
>
> Any try to do a hypercall before the hypercall page has been initialized
> is a bug anyway. What good can come from calling a function which will
> return a basically random value instead of doing a privileged operation?
>

This is all about objtool, that's why 'ret' was added there originally by f4b4bc10b0b8 ("x86/xen: Support objtool vmlinux.o validation in xen-head.S").


Before that it was all 'nop' which is similar to what you are suggesting ('int3' or 'ud2' would of course be better)


-boris