From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?windows-1252?Q?Andr=E9_Hentschel?= Subject: Re: [PATCH] arm64: Preserve the user r/w register tpidr_el0 on context switch and fork in compat mode Date: Tue, 05 May 2015 19:09:57 +0200 Message-ID: <5548F965.9070302@dawncrow.de> References: <55464BB2.7030401@dawncrow.de> <20150505105111.GB1550@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20150505105111.GB1550@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Will Deacon Cc: "linux-arch@vger.kernel.org" , Russell King - ARM Linux , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "gregkh@linuxfoundation.org" , Jonathan Austin , Nathan Lynch , Catalin Marinas List-Id: linux-arch.vger.kernel.org Am 05.05.2015 um 12:51 schrieb Will Deacon: > On Sun, May 03, 2015 at 05:24:18PM +0100, Andr=E9 Hentschel wrote: >> From: Andr=E9 Hentschel >> >> Since commit a4780adeefd042482f624f5e0d577bf9cdcbb760 the user write= able TLS >> register on ARM is preserved per thread. >> >> This patch does it analogous to the ARM patch, but for compat mode o= n ARM64. >> >> Signed-off-by: Andr=E9 Hentschel >> Cc: Will Deacon >> Cc: Jonathan Austin =20 >> >> --- >> This patch is against Linux 4.1-rc1 (b787f68c36d49bb1d9236f403813641= efa74a031) >=20 > Curious, but why do you need this? iirc, we added this for arch/arm/ = because > of some windows rt (?) emulation in wine. Is that still the case here= and is > anybody actually using that? Yes, Windows ARM binaries are the well known use case, but also the com= pat mode should do what the arm kernel is doing I=92d think and the code wasn't adjusted y= et. What i'm curious about is why the main TLS register on arm64 is the use= r writeable, I'm not an security expert but this looks odd. I could easily provoke a= crash by writing to it... CCing Catalin Marinas From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mo4-p00-ob.smtp.rzone.de ([81.169.146.161]:62818 "EHLO mo4-p00-ob.smtp.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965729AbbEERKh (ORCPT ); Tue, 5 May 2015 13:10:37 -0400 Message-ID: <5548F965.9070302@dawncrow.de> Date: Tue, 05 May 2015 19:09:57 +0200 From: =?windows-1252?Q?Andr=E9_Hentschel?= MIME-Version: 1.0 Subject: Re: [PATCH] arm64: Preserve the user r/w register tpidr_el0 on context switch and fork in compat mode References: <55464BB2.7030401@dawncrow.de> <20150505105111.GB1550@arm.com> In-Reply-To: <20150505105111.GB1550@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Will Deacon Cc: "linux-arch@vger.kernel.org" , Russell King - ARM Linux , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "gregkh@linuxfoundation.org" , Jonathan Austin , Nathan Lynch , Catalin Marinas Message-ID: <20150505170957.5qghiPMmmYQT4KYvHhvuZVOmBKar7UuCvW9fv1kHE_c@z> Am 05.05.2015 um 12:51 schrieb Will Deacon: > On Sun, May 03, 2015 at 05:24:18PM +0100, André Hentschel wrote: >> From: André Hentschel >> >> Since commit a4780adeefd042482f624f5e0d577bf9cdcbb760 the user writeable TLS >> register on ARM is preserved per thread. >> >> This patch does it analogous to the ARM patch, but for compat mode on ARM64. >> >> Signed-off-by: André Hentschel >> Cc: Will Deacon >> Cc: Jonathan Austin >> >> --- >> This patch is against Linux 4.1-rc1 (b787f68c36d49bb1d9236f403813641efa74a031) > > Curious, but why do you need this? iirc, we added this for arch/arm/ because > of some windows rt (?) emulation in wine. Is that still the case here and is > anybody actually using that? Yes, Windows ARM binaries are the well known use case, but also the compat mode should do what the arm kernel is doing I’d think and the code wasn't adjusted yet. What i'm curious about is why the main TLS register on arm64 is the user writeable, I'm not an security expert but this looks odd. I could easily provoke a crash by writing to it... CCing Catalin Marinas