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Wed, 12 May 2021 18:48:11 +0000 From: "Bae, Chang Seok" To: Borislav Petkov CC: Andy Lutomirski , "bp@suse.de" , "tglx@linutronix.de" , "mingo@kernel.org" , "x86@kernel.org" , "Brown, Len" , "Hansen, Dave" , "hjl.tools@gmail.com" , "Dave.Martin@arm.com" , "jannh@google.com" , "mpe@ellerman.id.au" , "carlos@redhat.com" , "Luck, Tony" , "Shankar, Ravi V" , "libc-alpha@sourceware.org" , "linux-arch@vger.kernel.org" , "linux-api@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v8 5/6] x86/signal: Detect and prevent an alternate signal stack overflow Thread-Topic: [PATCH v8 5/6] x86/signal: Detect and prevent an alternate signal stack overflow Thread-Index: AQHXNzOQXxUM6Mub30elxTKCBjQG3areurqAgAGVlAA= Date: Wed, 12 May 2021 18:48:11 +0000 Message-ID: References: <20210422044856.27250-1-chang.seok.bae@intel.com> <20210422044856.27250-6-chang.seok.bae@intel.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.120.23.2.4) x-originating-ip: [73.189.248.82] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 3579f252-742c-4aed-692b-08d915767dee x-ms-traffictypediagnostic: PH0PR11MB4821: 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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charset="us-ascii" Content-ID: <672E4078839CC64EAB2AA2A497300EC0@namprd11.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: PH0PR11MB4855.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3579f252-742c-4aed-692b-08d915767dee X-MS-Exchange-CrossTenant-originalarrivaltime: 12 May 2021 18:48:11.1422 (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: RQ+fF4DLGNg+NEA42yedtwQjJ/6ieLYemjQzrr22t1/WjO6tz2vkJuS6/3j2t19a1D9wPICDuhXJMOOCISlqajw5PVCRq/c9THHXMXcRCHc= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB4821 X-OriginatorOrg: intel.com X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 12 May 2021 18:48:20 -0000 On May 11, 2021, at 11:36, Borislav Petkov wrote: >=20 > I clumsily tried to register a SIGSEGV handler with >=20 > act.sa_sigaction =3D my_sigsegv; > sigaction(SIGSEGV, &act, NULL); >=20 > but that doesn't fire - task gets killed. Maybe I'm doing it wrong. Since the altstack is already overflowed, perhaps set the flag like this --= not using it to get the handler: act.sa_sigaction =3D my_sigsegv; + act.sa_flags =3D SA_SIGINFO; sigaction(SIGSEGV, &act, NULL); FWIW, I think this is just a workaround for this case; in practice, altstac= k is rather a backup for normal stack corruption. Thanks, Chang