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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 A60F0C433DF for ; Mon, 3 Aug 2020 08:08:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E35220678 for ; Mon, 3 Aug 2020 08:08:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726002AbgHCII1 convert rfc822-to-8bit (ORCPT ); Mon, 3 Aug 2020 04:08:27 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:46353 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725948AbgHCII0 (ORCPT ); Mon, 3 Aug 2020 04:08:26 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-111-PHrlPE41MKu5ed8gAMWPYg-1; Mon, 03 Aug 2020 09:08:22 +0100 X-MC-Unique: PHrlPE41MKu5ed8gAMWPYg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 3 Aug 2020 09:08:21 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 3 Aug 2020 09:08:21 +0100 From: David Laight To: 'Pavel Machek' CC: 'Andy Lutomirski' , "madvenka@linux.microsoft.com" , Kernel Hardening , Linux API , linux-arm-kernel , Linux FS Devel , linux-integrity , LKML , "LSM List" , Oleg Nesterov , X86 ML Subject: RE: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor Thread-Topic: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor Thread-Index: AQHWZQT/T+e4gDrzGEmP/30MMvDTCqkgFteggASWI4CAAWJTUA== Date: Mon, 3 Aug 2020 08:08:21 +0000 Message-ID: References: <20200728131050.24443-1-madvenka@linux.microsoft.com> <20200802115600.GB1162@bug> In-Reply-To: <20200802115600.GB1162@bug> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Pavel Machek > Sent: 02 August 2020 12:56 > Hi! > > > > This is quite clever, but now I???m wondering just how much kernel help > > > is really needed. In your series, the trampoline is an non-executable > > > page. I can think of at least two alternative approaches, and I'd > > > like to know the pros and cons. > > > > > > 1. Entirely userspace: a return trampoline would be something like: > > > > > > 1: > > > pushq %rax > > > pushq %rbc > > > pushq %rcx > > > ... > > > pushq %r15 > > > movq %rsp, %rdi # pointer to saved regs > > > leaq 1b(%rip), %rsi # pointer to the trampoline itself > > > callq trampoline_handler # see below > > > > For nested calls (where the trampoline needs to pass the > > original stack frame to the nested function) I think you > > just need a page full of: > > mov $0, scratch_reg; jmp trampoline_handler > > I believe you could do with mov %pc, scratch_reg; jmp ... > > That has advantage of being able to share single physical > page across multiple virtual pages... A lot of architecture don't let you copy %pc that way so you would have to use 'call' - but that trashes the return address cache. It also needs the trampoline handler to know the addresses of the trampolines. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) 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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 9FC72C433DF for ; Mon, 3 Aug 2020 08:10:01 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 691BD2065E for ; Mon, 3 Aug 2020 08:10:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="vEdzvCoT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 691BD2065E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References:Message-ID:Date: Subject:To:From:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=80djtXr/KaObEKuuGjH7Oa4uGFlx+Dnbc60VPFyGhEs=; b=vEdzvCoTnQ7J6nXywvQpqQLjm EO1pTUKFpU9r4BINP4+BIZ+ucxty5C4KKqBFb1r45YC28fEcQy0XRQl+CFjOCxIfOGa0/TQxpxMWQ CcyZH1MmieSV0/Hz7GdpgwdkaPkboFojnheVnbj1t0NNd9XbMbDdlzKyMC2ToyLH7UcUovoy5kawZ B2iKqEECeYJhTpgh5WOWiow2+iPTe1y6mbE44egejUJFWyO0Nb+ytwhcUctauVm3HGE3f+1RzxOIO fcdDosrPyFJmFG1quT93HtXKSHP/sEwPNEbDebOQjH2ZZmkrmWLuOhKdVbkNOxm3TyfPxgpImt4S5 M+wmHDBgQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k2VWK-0005PM-H7; Mon, 03 Aug 2020 08:08:32 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k2VWH-0005Nn-K0 for linux-arm-kernel@lists.infradead.org; Mon, 03 Aug 2020 08:08:30 +0000 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-111-PHrlPE41MKu5ed8gAMWPYg-1; Mon, 03 Aug 2020 09:08:22 +0100 X-MC-Unique: PHrlPE41MKu5ed8gAMWPYg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 3 Aug 2020 09:08:21 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 3 Aug 2020 09:08:21 +0100 From: David Laight To: 'Pavel Machek' Subject: RE: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor Thread-Topic: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor Thread-Index: AQHWZQT/T+e4gDrzGEmP/30MMvDTCqkgFteggASWI4CAAWJTUA== Date: Mon, 3 Aug 2020 08:08:21 +0000 Message-ID: References: <20200728131050.24443-1-madvenka@linux.microsoft.com> <20200802115600.GB1162@bug> In-Reply-To: <20200802115600.GB1162@bug> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200803_040829_852420_0A76BA4D X-CRM114-Status: GOOD ( 15.82 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kernel Hardening , Linux API , X86 ML , LKML , Oleg Nesterov , "madvenka@linux.microsoft.com" , LSM List , 'Andy Lutomirski' , Linux FS Devel , linux-integrity , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Pavel Machek > Sent: 02 August 2020 12:56 > Hi! > > > > This is quite clever, but now I???m wondering just how much kernel help > > > is really needed. In your series, the trampoline is an non-executable > > > page. I can think of at least two alternative approaches, and I'd > > > like to know the pros and cons. > > > > > > 1. Entirely userspace: a return trampoline would be something like: > > > > > > 1: > > > pushq %rax > > > pushq %rbc > > > pushq %rcx > > > ... > > > pushq %r15 > > > movq %rsp, %rdi # pointer to saved regs > > > leaq 1b(%rip), %rsi # pointer to the trampoline itself > > > callq trampoline_handler # see below > > > > For nested calls (where the trampoline needs to pass the > > original stack frame to the nested function) I think you > > just need a page full of: > > mov $0, scratch_reg; jmp trampoline_handler > > I believe you could do with mov %pc, scratch_reg; jmp ... > > That has advantage of being able to share single physical > page across multiple virtual pages... A lot of architecture don't let you copy %pc that way so you would have to use 'call' - but that trashes the return address cache. It also needs the trampoline handler to know the addresses of the trampolines. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel