From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Date: Tue, 21 Jun 2016 11:24:18 +0200 Message-ID: <13212319.WrhLzgRA6Z@wuerfel> References: Reply-To: kernel-hardening@lists.openwall.com Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: To: Andy Lutomirski Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Borislav Petkov , Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Josh Poimboeuf , Jann Horn , Heiko Carstens List-Id: linux-arch.vger.kernel.org On Monday, June 20, 2016 4:43:30 PM CEST Andy Lutomirski wrote: >=20 > On my laptop, this adds about 1.5=B5s of overhead to task creation, > which seems to be mainly caused by vmalloc inefficiently allocating > individual pages even when a higher-order page is available on the > freelist. Would it help to have a fixed virtual address for the stack instead and map the current stack to that during a task switch, similar to how we handle fixmap pages? That would of course trade the allocation overhead for a task switch overhead, which may be better or worse. It would also give "current" a constant address, which may give a small performance advantage but may also introduce a new attack vector unless we randomize it again. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.126.131]:54480 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751491AbcFUJaM convert rfc822-to-8bit (ORCPT ); Tue, 21 Jun 2016 05:30:12 -0400 From: Arnd Bergmann Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Date: Tue, 21 Jun 2016 11:24:18 +0200 Message-ID: <13212319.WrhLzgRA6Z@wuerfel> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="iso-8859-1" Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andy Lutomirski Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Borislav Petkov , Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Josh Poimboeuf , Jann Horn , Heiko Carstens Message-ID: <20160621092418._tzFJxAtyygYMD7kbGjeiwOvuOfne2efV-y_T8acFm4@z> On Monday, June 20, 2016 4:43:30 PM CEST Andy Lutomirski wrote: > > On my laptop, this adds about 1.5µs of overhead to task creation, > which seems to be mainly caused by vmalloc inefficiently allocating > individual pages even when a higher-order page is available on the > freelist. Would it help to have a fixed virtual address for the stack instead and map the current stack to that during a task switch, similar to how we handle fixmap pages? That would of course trade the allocation overhead for a task switch overhead, which may be better or worse. It would also give "current" a constant address, which may give a small performance advantage but may also introduce a new attack vector unless we randomize it again. Arnd