From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758012AbcIWEMj (ORCPT ); Fri, 23 Sep 2016 00:12:39 -0400 Received: from mail-yw0-f179.google.com ([209.85.161.179]:36416 "EHLO mail-yw0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757943AbcIWEMg (ORCPT ); Fri, 23 Sep 2016 00:12:36 -0400 Date: Fri, 23 Sep 2016 09:42:30 +0530 From: Pratyush Anand To: Catalin Marinas Cc: Mark Rutland , srikar@linux.vnet.ibm.com, will.deacon@arm.com, oleg@redhat.com, Jungseok Lee , linux@arm.linux.org.uk, vijaya.kumar@caviumnetworks.com, dave.long@linaro.org, Shi Yang , Vladimir Murzin , steve.capper@linaro.org, "Suzuki K. Poulose" , Andre Przywara , Shaokun Zhang , Ashok Kumar , Sandeepa Prabhu , wcohen@redhat.com, linux-arm-kernel@lists.infradead.org, Ard Biesheuvel , linux-kernel@vger.kernel.org, James Morse , Masami Hiramatsu , Robin Murphy , "Kirill A. Shutemov" Subject: Re: [PATCH 5/5] arm64: Add uprobe support Message-ID: <20160923041230.GC29470@localhost.localdomain> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160922165030.GA27704@e104818-lin.cambridge.arm.com> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: > > > On Wed, Sep 21, 2016 at 04:30:47PM +0530, Pratyush Anand wrote: > > > > On 20/09/2016:05:59:46 PM, Catalin Marinas wrote: > > > > > > +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, > > > > > > + unsigned long addr) > > > > > > +{ > > > > > > + probe_opcode_t insn; > > > > > > + > > > > > > + /* TODO: Currently we do not support AARCH32 instruction probing */ > > > > > > > > > > Is there a way to check (not necessarily in this file) that we don't > > > > > probe 32-bit tasks? > > > > > > > > - Well, I do not have complete idea about it that, how it can be done. I think > > > > we can not check that just by looking a single bit in an instruction. > > > > My understanding is that, we can only know about it when we are executing the > > > > instruction, by reading pstate, but that would not be useful for uprobe > > > > instruction analysis. > > > > > > > > I hope, instruction encoding for aarch32 and aarch64 are different, and by > > > > analyzing for all types of aarch32 instructions, we will be able to decide > > > > that whether instruction is 32 bit trace-able or not. Accordingly, we can use > > > > either BRK or BKPT instruction for breakpoint generation. > > > > > > We may have some unrelated instruction encoding overlapping but I > > > haven't checked. I was more thinking about whether we know which task is > > > being probed and check is_compat_task() or maybe using > > > compat_user_mode(regs). > > > > I had thought of this, but problem is that we might not have task in existence > > when we enable uprobes. For example: Lets say we are inserting a trace probe at > > offset 0x690 in a executable binary. > > > > echo "p test:0x690" > /sys/kernel/debug/tracing/uprobe_events > > echo 1 > /sys/kernel/debug/tracing/events/uprobes/enable > > > > In the 'enable' step, it is decided that whether instruction is traceable or > > not. > > > > (1) But at this point 'test' executable might not be running. Let me correct myself first here. When executable is not running, then, arch_uprobe_analyze_insn() is not called while uprobes enabling (ie writing '1' to 'enable'). In that case, it is called when binary is executed and task is created. > > (2) Even if it is running, is_compat_task() or compat_user_mode() might not be > > usable, as they work with 'current' task. > > What I find strange is that uprobes allows you to insert a breakpoint > instruction that's not even compatible with the task (so it would > SIGILL rather than generate a debug exception). > > > What I was thinking that, let it go with 'TODO' as of now. > > Only that I don't have any guarantee that someone is going to fix it ;). > > 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. Thanks for your input. ~Pratyush