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Tue, 12 Jan 2021 11:39:07 +0000 From: "Metzger, Markus T" To: "Bae, Chang Seok" , "Lutomirski, Andy" CC: Borislav Petkov , Andy Lutomirski , "tdevries@suse.com" , x86-ml , lkml Subject: RE: gdbserver + fsgsbase kaputt Thread-Topic: gdbserver + fsgsbase kaputt Thread-Index: AQHW6EXGGSDS0D32IEu+vSvpt9UFe6oizxgAgAAJLICAABKQAIAAmVKAgABFJ3A= Date: Tue, 12 Jan 2021 11:39:07 +0000 Message-ID: References: <20210111200027.GH25645@zn.tnic> <5B5C1F0A-9780-4E42-BC65-742BAEE920BF@intel.com> In-Reply-To: <5B5C1F0A-9780-4E42-BC65-742BAEE920BF@intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-reaction: no-action dlp-version: 11.5.1.3 dlp-product: dlpe-windows authentication-results: intel.com; dkim=none (message not signed) header.d=none;intel.com; dmarc=none action=none header.from=intel.com; x-originating-ip: [91.89.55.195] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: fdcfdd77-3469-408a-9a15-08d8b6eeac16 x-ms-traffictypediagnostic: DM6PR11MB2571: x-ld-processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8882; 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x-ms-exchange-antispam-messagedata: =?us-ascii?Q?imIDZ7nJzqzDJLtsDuLW2nfOzwQ1weJ3SE+kgROPf6ufUkqQmITXq/sjMJEF?= =?us-ascii?Q?bD+v8D03OwlCoTUDdq65xg+vJPo6RKtxwc+f/yULSYVeBRRQIeo1PjsDTyrA?= =?us-ascii?Q?zfIKGLdIDftOSem6TaYZBCAycDcBFoAEKHLKImPFPSl9kGqTOsNJq/NYEO7y?= =?us-ascii?Q?/WG5PoC/z8VSSVCTBE47BNU9LMPNtmq5w/8yQ9UgsmV3GNopWqrEj7kqlacm?= =?us-ascii?Q?6x6xTgIpbqCGctXlClE4Wl0+3R56IpR+peu/4d0WJMpci2p4qYB0LU8QBNOl?= =?us-ascii?Q?THE3r21+mAlvUsQ9MlRnZNJO7NOIYCvE8gxjfoR1TCR5U6QD6X0JkxTL0nY3?= =?us-ascii?Q?aTAwgH0ldtWyYW3+R3QK+m5sxxH8ZCOTOicNJDCS++arWGvQMZZN75s7ecEV?= =?us-ascii?Q?ZdW/OgnB7qEJeQk5pqwJliGZQ8q0UZM3thXkr9lUtpklrF7Twq6KlAdI+QLp?= =?us-ascii?Q?YoOFZwrNGTU/9djUBVbFwdc0TAAqlzlx9DgAbsF2r7FQY/Md45SJUkPXpIsX?= =?us-ascii?Q?CMUw9jDIvk87gVjYL5Bj9MUZFi6bt6kt8tPb4hw1e8U+Qm5U4Xp9P/KiqHeW?= =?us-ascii?Q?rXXGJZN8A8ETHJ6fLiREOON3CxOQGHpCvcwUZvMPmOORvpEd1WDHE4H3ezEu?= =?us-ascii?Q?ayyiO22xTh8k+LPijth0WgUCK/8XL/kqOoFhBYMnCVxB5ti9izTxIZMqya99?= =?us-ascii?Q?l/LiJtQx0k/eE8yejPEKJYEx3uvtZiB4l2j4IT4+f5/ESgBNEia3L7/AE9dx?= =?us-ascii?Q?Obwlbj7NiuvnB3FufjnhfWu+77r0i3xc+GqNJNQXie0Bj3hHZMKeUg9KHYD6?= =?us-ascii?Q?aHFqvR/0Q2dO68TZiECXXl1ZoEfF3CYRjM1jCnDzNhAIW7ruS4JsUC6P6GKQ?= =?us-ascii?Q?7qRsqjKvLgZfmYuQly0NUodc+4DLNnFKaxkBmVA0+g8BTDgqnwyAeUVMePF6?= =?us-ascii?Q?t0K4l2mXGjzP9H2q1S80cVHuO8Knb4Y13CyHVhSxg1w=3D?= Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DM5PR11MB1690.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: fdcfdd77-3469-408a-9a15-08d8b6eeac16 X-MS-Exchange-CrossTenant-originalarrivaltime: 12 Jan 2021 11:39:07.7239 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 7FS2yq8BS8XqUZt3aMtKOKcXT1NJOSyXh54SXK9GtOkFxdBDOB2wX/BzkSVcW6UVBdiDnrqV442Zu2kM2dHv+VaFBDmCVfb4A9EHbKZTytI= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR11MB2571 X-OriginatorOrg: intel.com Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > The GDB behavior looks to be different between the two cases -- with vs > without gdb server, when I checked the GS/GSBASE values on the ptrace fro= nt. 64-bit GDB doesn't support FSGSBASE for 32-bit inferiors and it looks like = gdbserver might not support FSGSBASE, at all. I had added support for the former as part of the tests I wrote about a yea= r ago [1] but never submitted the patch. Was the discussion ever concluded? The general behavior should be that GDB reads a regset, overwrites the regi= sters it knows about, and writes it back again to preserve the original values of re= gisters it doesn't know about. When I log the values that are read and written for FSGSBASE, however, it l= ooks like ptrace is returning a non-zero GS_BASE on a read and gdbserver is writing z= ero on the next write. Chang, is that also what you were seeing? Regards, Markus. [1] https://lkml.org/lkml/2019/11/29/306 Intel Deutschland GmbH Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany Tel: +49 89 99 8853-0, www.intel.de Managing Directors: Christin Eisenschmid, Gary Kershaw Chairperson of the Supervisory Board: Nicole Lau Registered Office: Munich Commercial Register: Amtsgericht Muenchen HRB 186928