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[23.128.96.18]) by mx.google.com with ESMTP id a14si556465edv.4.2021.05.05.14.57.24; Wed, 05 May 2021 14:57:48 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@linux.microsoft.com header.s=default header.b=C52y7+v8; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linux.microsoft.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234844AbhEERxK (ORCPT + 99 others); Wed, 5 May 2021 13:53:10 -0400 Received: from linux.microsoft.com ([13.77.154.182]:41146 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234090AbhEERwl (ORCPT ); Wed, 5 May 2021 13:52:41 -0400 Received: from [192.168.254.32] (unknown [47.187.223.33]) by linux.microsoft.com (Postfix) with ESMTPSA id 24BC220B7178; Wed, 5 May 2021 10:51:43 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 24BC220B7178 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1620237103; bh=sdd8ZMJAgH8gVKupmR0QjAVLyv9Ta+9CM3nIhnT4w4E=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=C52y7+v8ilF8BexdEy/Wkqfza8Rzms0fSCvyQ9ulzKSjekGM8BRm9cRpZqNzS5W9h EIcCsR2tBclzDi/ycQ5EEVUUYIt84oU3VROjxUcutquknWLFcHsZ5NCbFIkhPnVtuD Bvn1ceilFKmtswxjkUzyiFqKarfVpHCBGPQ7kCwM= Subject: Re: [RFC PATCH v3 2/4] arm64: Check the return PC against unreliable code sections To: Mark Brown Cc: jpoimboe@redhat.com, mark.rutland@arm.com, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <65cf4dfbc439b010b50a0c46ec500432acde86d6> <20210503173615.21576-1-madvenka@linux.microsoft.com> <20210503173615.21576-3-madvenka@linux.microsoft.com> <20210504160508.GC7094@sirena.org.uk> <1bd2b177-509a-21d9-e349-9b2388db45eb@linux.microsoft.com> <20210505163406.GB4541@sirena.org.uk> From: "Madhavan T. Venkataraman" Message-ID: <64373047-1029-df65-e7aa-b8058850fbde@linux.microsoft.com> Date: Wed, 5 May 2021 12:51:42 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210505163406.GB4541@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/5/21 11:34 AM, Mark Brown wrote: > On Tue, May 04, 2021 at 02:03:14PM -0500, Madhavan T. Venkataraman wrote: >> On 5/4/21 11:05 AM, Mark Brown wrote: > >>>> @@ -118,9 +160,21 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) >>>> return -EINVAL; >>>> frame->pc = ret_stack->ret; >>>> frame->pc = ptrauth_strip_insn_pac(frame->pc); >>>> + return 0; >>>> } > >>> Do we not need to look up the range of the restored pc and validate >>> what's being pointed to here? It's not immediately obvious why we do >>> the lookup before handling the function graph tracer, especially given >>> that we never look at the result and there's now a return added skipping >>> further reliability checks. At the very least I think this needs some >>> additional comments so the code is more obvious. > >> I want sym_code_ranges[] to contain both unwindable and non-unwindable ranges. >> Unwindable ranges will be special ranges such as the return_to_handler() and >> kretprobe_trampoline() functions for which the unwinder has (or will have) >> special code to unwind. So, the lookup_range() has to happen before the >> function graph code. Please look at the last patch in the series for >> the fix for the above function graph code. > > That sounds reasonable but like I say should probably be called out in > the code so it's clear to people working with it. > OK. To make this better, I will do the lookup_range() after the function graph code to begin with. Then, in the last patch for the function graph code, I will move it up. This way, the code is clear and your comment is addressed. >> On the question of "should the original return address be checked against >> sym_code_ranges[]?" - I assumed that if there is a function graph trace on a >> function, it had to be an ftraceable function. It would not be a part >> of sym_code_ranges[]. Is that a wrong assumption on my part? > > I can't think of any cases where it wouldn't be right now, but it seems > easier to just do a redundant check than to have the assumption in the > code and have to think about if it's missing. > Agreed. Will do the check. Madhavan