From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Subject: Re: [PATCH -tip v14 03/12] kprobes: checks probe address is instruction boudary on x86 Date: Tue, 18 Aug 2009 20:19:33 -0400 Message-ID: <4A8B4515.3090508@redhat.com> References: <20090813203403.31965.20973.stgit@localhost.localdomain> <20090813203428.31965.21939.stgit@localhost.localdomain> <20090818230340.GF5231@nowhere> <4A8B3693.9000301@redhat.com> <20090818234341.GG5231@nowhere> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Ingo Molnar , Steven Rostedt , lkml , systemtap , kvm , DLE , Ananth N Mavinakayanahalli , Avi Kivity , Andi Kleen , Christoph Hellwig , "Frank Ch. Eigler" , "H. Peter Anvin" , Jason Baron , Jim Keniston , "K.Prasad" , Lai Jiangshan , Li Zefan , =?UTF-8?B?UHJ6ZW15c8WCYXdQYXdlxYJjenlr?= , Roland McGrath , Sam Ravnborg , Srikar Dronamraju Return-path: In-Reply-To: <20090818234341.GG5231@nowhere> List-Unsubscribe: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org List-Id: kvm.vger.kernel.org Frederic Weisbecker wrote: > On Tue, Aug 18, 2009 at 07:17:39PM -0400, Masami Hiramatsu wrote: >> Frederic Weisbecker wrote: >>>> + while (addr < paddr) { >>>> + kernel_insn_init(&insn, (void *)addr); >>>> + insn_get_opcode(&insn); >>>> + >>>> + /* Check if the instruction has been modified. */ >>>> + if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION) { >>>> + ret = recover_probed_instruction(buf, addr); >>> >>> >>> >>> I'm confused about the reason of this recovering. Is it to remove >>> kprobes behind the current setting one in the current function? >> >> No, it recovers just an instruction which is probed by a kprobe, >> because we need to know the first byte of this instruction for >> decoding it. Ah, sorry, it was not accurate. the function recovers an instruction on the buffer(buf), not on the real kernel text. :) >> >> Perhaps we'd better to have more generic interface (text_peek?) >> for it because another subsystem (e.g. kgdb) may want to insert int3... >> >> Thank you, > > > Aah, I see now, it's to keep a sane check of the instructions > boundaries without int 3 artifacts in the middle. > > But in that case, you should re-arm the breakpoint after your > check, right? > > Or may be you could do the check without repatching? Yes, it doesn't modify kernel text, just recover an original instruction from kernel text and backup byte on a buffer. > May be by doing a copy of insn.opcode.bytes and replacing bytes[0] > with what a random kprobe has stolen? Hm, no, this function is protected from other kprobes by kprobe_mutex. Thank you, -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@redhat.com