From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756900AbcCROnd (ORCPT ); Fri, 18 Mar 2016 10:43:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40585 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755247AbcCROn2 (ORCPT ); Fri, 18 Mar 2016 10:43:28 -0400 Date: Fri, 18 Mar 2016 20:13:25 +0530 From: Pratyush Anand To: James Morse Cc: David Long , Will Deacon , Catalin Marinas , Sandeepa Prabhu , William Cohen , Steve Capper , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Marc Zyngier , Dave P Martin , Mark Rutland , Robin Murphy , Ard Biesheuvel , Jens Wiklander , Christoffer Dall , Alex =?iso-8859-1?Q?Benn=E9e?= , Yang Shi , Greg Kroah-Hartman , Viresh Kumar , "Suzuki K. Poulose" , Kees Cook , Zi Shen Lim , John Blackwood , Feng Kan , Balamurugan Shanmugam , Vladimir Murzin , Mark Salyzyn , Petr Mladek , Andrew Morton , Mark Brown Subject: Re: [PATCH v11 3/9] arm64: add copy_to/from_user to kprobes blacklist Message-ID: <20160318144325.GB29225@dhcppc6.redhat.com> References: <1457501543-24197-1-git-send-email-dave.long@linaro.org> <1457501543-24197-4-git-send-email-dave.long@linaro.org> <56E858D8.8030300@arm.com> <20160316054329.GC28915@dhcppc6.redhat.com> <56E9350A.7010909@arm.com> <20160317075726.GA16882@dhcppc6.redhat.com> <20160318132902.GA29225@dhcppc6.redhat.com> <56EC0A89.3030606@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56EC0A89.3030606@arm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi James, On 18/03/2016:02:02:49 PM, James Morse wrote: > Hi Pratyush, > > On 18/03/16 13:29, Pratyush Anand wrote: > > Probably, I can see why does not it work. So, when we are single stepping an > > instruction and page fault occurs, we will come to el1_da in entry.S. Here, we > > do enable_dbg. As soon as we will do this, we will start receiving single step > > exception after each instruction (not sure, probably for each alternate > > instruction). Since, there will not be any matching single step handler for > > these instructions, so we will see warning "Unexpected kernel single-step > > exception at EL1". > > > > So, I think, we should > > > > (1) may be do not enable debug for el1_da, or > > (2) enable_dbg only when single stepping is not enabled, or > > (3) or disable single stepping during el1_da execution. > > > > (1) will solve the issue for sure, but not sure if it could be the best choice. > > A variation on (3): > > In kernel/entry.S when entered from EL0 we test for TIF_SINGLESTEP in the > thread_info flags, and use disable_step_tsk/enable_step_tsk to save/restore the > single-step state. > > Could we do this regardless of which EL we came from? Thanks for another idea. I think, we can not do this as it is, because TIF_SINGLESTEP will not be set for kprobe events. But, we can introduce a variant disable_step_kernel and enable_step_kernel, which can be called in el1_da. I will write a test case to reproduce the issue without this patch, and then will do test with a patch based on something like above. ~Pratyush From mboxrd@z Thu Jan 1 00:00:00 1970 From: panand@redhat.com (Pratyush Anand) Date: Fri, 18 Mar 2016 20:13:25 +0530 Subject: [PATCH v11 3/9] arm64: add copy_to/from_user to kprobes blacklist In-Reply-To: <56EC0A89.3030606@arm.com> References: <1457501543-24197-1-git-send-email-dave.long@linaro.org> <1457501543-24197-4-git-send-email-dave.long@linaro.org> <56E858D8.8030300@arm.com> <20160316054329.GC28915@dhcppc6.redhat.com> <56E9350A.7010909@arm.com> <20160317075726.GA16882@dhcppc6.redhat.com> <20160318132902.GA29225@dhcppc6.redhat.com> <56EC0A89.3030606@arm.com> Message-ID: <20160318144325.GB29225@dhcppc6.redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi James, On 18/03/2016:02:02:49 PM, James Morse wrote: > Hi Pratyush, > > On 18/03/16 13:29, Pratyush Anand wrote: > > Probably, I can see why does not it work. So, when we are single stepping an > > instruction and page fault occurs, we will come to el1_da in entry.S. Here, we > > do enable_dbg. As soon as we will do this, we will start receiving single step > > exception after each instruction (not sure, probably for each alternate > > instruction). Since, there will not be any matching single step handler for > > these instructions, so we will see warning "Unexpected kernel single-step > > exception at EL1". > > > > So, I think, we should > > > > (1) may be do not enable debug for el1_da, or > > (2) enable_dbg only when single stepping is not enabled, or > > (3) or disable single stepping during el1_da execution. > > > > (1) will solve the issue for sure, but not sure if it could be the best choice. > > A variation on (3): > > In kernel/entry.S when entered from EL0 we test for TIF_SINGLESTEP in the > thread_info flags, and use disable_step_tsk/enable_step_tsk to save/restore the > single-step state. > > Could we do this regardless of which EL we came from? Thanks for another idea. I think, we can not do this as it is, because TIF_SINGLESTEP will not be set for kprobe events. But, we can introduce a variant disable_step_kernel and enable_step_kernel, which can be called in el1_da. I will write a test case to reproduce the issue without this patch, and then will do test with a patch based on something like above. ~Pratyush