From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966359AbcIZLCJ (ORCPT ); Mon, 26 Sep 2016 07:02:09 -0400 Received: from foss.arm.com ([217.140.101.70]:58464 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933204AbcIZLCH (ORCPT ); Mon, 26 Sep 2016 07:02:07 -0400 Date: Mon, 26 Sep 2016 12:01:59 +0100 From: Catalin Marinas To: Pratyush Anand Cc: Mark Rutland , srikar@linux.vnet.ibm.com, Will Deacon , Oleg Nesterov , Jungseok Lee , Russell King - ARM Linux , vijaya.kumar@caviumnetworks.com, Dave Long , Shi Yang , Vladimir Murzin , Steve Capper , "Suzuki K. Poulose" , Andre Przywara , Shaokun Zhang , Ashok Kumar , Sandeepa Prabhu , Will Cohen , linux-arm-kernel , Ard Biesheuvel , open list , James Morse , Masami Hiramatsu , Robin Murphy , "Kirill A. Shutemov" Subject: Re: [PATCH 5/5] arm64: Add uprobe support Message-ID: <20160926110159.GB27498@e104818-lin.cambridge.arm.com> References: <20160920165946.GA19353@e104818-lin.cambridge.arm.com> <20160921110047.GA29470@localhost.localdomain> <20160921170403.GE12180@e104818-lin.cambridge.arm.com> <20160922032328.GB29470@localhost.localdomain> <20160922165030.GA27704@e104818-lin.cambridge.arm.com> <20160923041230.GC29470@localhost.localdomain> <20160923130528.GE2161@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 25, 2016 at 10:32:28PM +0530, Pratyush Anand wrote: > On Fri, Sep 23, 2016 at 6:35 PM, Catalin Marinas > wrote: > > On Fri, Sep 23, 2016 at 09:42:30AM +0530, Pratyush Anand wrote: > >> On 22/09/2016:05:50:30 PM, Catalin Marinas wrote: > >> > On Thu, Sep 22, 2016 at 08:53:28AM +0530, Pratyush Anand wrote: > >> > > On 21/09/2016:06:04:04 PM, Catalin Marinas wrote: > > >> > As a quick workaround you could check mm->task_size > TASK_SIZE_32 in > >> > the arch_uprobe_analyze_insn() function. > >> > >> It would be doable. TASK_SIZE_32 is defined only for COMPAT. So, may be I can > >> return -EINVAL when mm->task_size < TASK_SIZE_64. > > > > That's just a temporary workaround. If we ever merge ILP32, this test > > would no longer be enough (as the ISA is AArch64 but with TASK_SIZE_32). > > OK.. So what about doing something similar what x86 is doing. > We can have a flag for task Type in arch specific mm_context_t. We > also set this flag in COMPAT_SET_PERSONALITY() along with setting > thread_info flag, and we clear them in SET_PERSONALITY(). This looks like a better approach. > > Looking at prepare_uprobe(), we have a weak is_trap_insn() function. > > This check is meaningless without knowing which instruction set we > > target. A false positive here, however, is not that bad as we wouldn't > > end up inserting the wrong breakpoint in the executable. But it looks to > > me like the core uprobe code needs to pass some additional information > > like the type of task or ELF format to the arch code to make a useful > > choice of breakpoint type. > > It seems that 'strtle r0, [r0], #160' would have the closest matching > aarch32 instruction wrt BRK64_OPCODE_UPROBES(0xd42000A0). But that too > seems a bad instruction. So, may be we can use still weak > is_trap_insn(). Even if the is_trap_insn() check passes, we would reject the probe in arch_uprobe_analyze_insn() immediately after based on the mm type check, so not too bad. If we add support for probing 32-bit tasks, I would rather have is_trap_insn() take the mm_struct as argument so that a non-weak implementation can check for the correct encoding. -- Catalin