Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754422AbcCRSNz (ORCPT ); Fri, 18 Mar 2016 14:13:55 -0400 Received: from foss.arm.com ([217.140.101.70]:56149 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751016AbcCRSNw (ORCPT ); Fri, 18 Mar 2016 14:13:52 -0400 Message-ID: <56EC4504.6060702@arm.com> Date: Fri, 18 Mar 2016 18:12:20 +0000 From: James Morse User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Pratyush Anand 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 , =?windows-1252?Q?Alex_?= =?windows-1252?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 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> <20160318144325.GB29225@dhcppc6.redhat.com> In-Reply-To: <20160318144325.GB29225@dhcppc6.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1344 Lines: 39 Hi Pratyush, On 18/03/16 14:43, Pratyush Anand wrote: > On 18/03/2016:02:02:49 PM, James Morse wrote: >> 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. Hmmm, I see kernel_enable_single_step() doesn't set it, but setup_singlestep() in patch 5 could... There is probably a good reason its never set for a kernel thread, I will have a look at where else it is used. > But, we can introduce a > variant disable_step_kernel and enable_step_kernel, which can be called in > el1_da. What about sp/pc misalignment, or undefined instructions? Or worse... an irq occurs during your el1_da call (el1_da may re-enable irqs). el1_irq doesn't know you were careful not to unmask debug exceptions, it blindly turns them back on. The problem is the 'single step me' bit is still set, save/restoring it will save us having to consider every interaction, (and then missing some!). It would also mean you don't have to disable interrupts while single stepping in patch 5 (comment above kprobes_save_local_irqflag()). Thanks, James