From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3522C433E0 for ; Tue, 19 Jan 2021 19:18:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7A6F120706 for ; Tue, 19 Jan 2021 19:18:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391593AbhASTQ4 (ORCPT ); Tue, 19 Jan 2021 14:16:56 -0500 Received: from foss.arm.com ([217.140.110.172]:45962 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727881AbhASTEi (ORCPT ); Tue, 19 Jan 2021 14:04:38 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id F27ADD6E; Tue, 19 Jan 2021 11:03:52 -0800 (PST) Received: from [10.37.8.29] (unknown [10.37.8.29]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 76AB83F719; Tue, 19 Jan 2021 11:03:51 -0800 (PST) Subject: Re: [PATCH] kasan: Add explicit preconditions to kasan_report() To: Catalin Marinas Cc: Andrey Konovalov , LKML , kasan-dev , Leon Romanovsky , Alexander Potapenko , Linux ARM , Andrey Ryabinin , Dmitry Vyukov References: <20210119172607.18400-1-vincenzo.frascino@arm.com> <20210119185206.GA26948@gaia> <20210119190219.GC26948@gaia> From: Vincenzo Frascino Message-ID: <6a5600c0-002a-3e80-0229-494d1c9648ac@arm.com> Date: Tue, 19 Jan 2021 19:07:40 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210119190219.GC26948@gaia> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/19/21 7:02 PM, Catalin Marinas wrote: > On Tue, Jan 19, 2021 at 07:00:57PM +0000, Vincenzo Frascino wrote: >> On 1/19/21 6:52 PM, Catalin Marinas wrote: >>> On Tue, Jan 19, 2021 at 07:27:43PM +0100, Andrey Konovalov wrote: >>>> On Tue, Jan 19, 2021 at 6:26 PM Vincenzo Frascino >>>> wrote: >>>>> >>>>> With the introduction of KASAN_HW_TAGS, kasan_report() dereferences >>>>> the address passed as a parameter. >>>>> >>>>> Add a comment to make sure that the preconditions to the function are >>>>> explicitly clarified. >>>>> >>>>> Note: An invalid address (e.g. NULL pointer address) passed to the >>>>> function when, KASAN_HW_TAGS is enabled, leads to a kernel panic. >>>>> >>>>> Cc: Andrey Ryabinin >>>>> Cc: Alexander Potapenko >>>>> Cc: Dmitry Vyukov >>>>> Cc: Leon Romanovsky >>>>> Cc: Andrey Konovalov >>>>> Signed-off-by: Vincenzo Frascino >>>>> --- >>>>> mm/kasan/report.c | 11 +++++++++++ >>>>> 1 file changed, 11 insertions(+) >>>>> >>>>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c >>>>> index c0fb21797550..2485b585004d 100644 >>>>> --- a/mm/kasan/report.c >>>>> +++ b/mm/kasan/report.c >>>>> @@ -403,6 +403,17 @@ static void __kasan_report(unsigned long addr, size_t size, bool is_write, >>>>> end_report(&flags); >>>>> } >>>>> >>>>> +/** >>>>> + * kasan_report - report kasan fault details >>>>> + * @addr: valid address of the allocation where the tag fault was detected >>>>> + * @size: size of the allocation where the tag fault was detected >>>>> + * @is_write: the instruction that caused the fault was a read or write? >>>>> + * @ip: pointer to the instruction that cause the fault >>>>> + * >>>>> + * Note: When CONFIG_KASAN_HW_TAGS is enabled kasan_report() dereferences >>>>> + * the address to access the tags, hence it must be valid at this point in >>>>> + * order to not cause a kernel panic. >>>>> + */ >>>> >>>> It doesn't dereference the address, it just checks the tags, right? >>>> >>>> Ideally, kasan_report() should survive that with HW_TAGS like with the >>>> other modes. The reason it doesn't is probably because of a blank >>>> addr_has_metadata() definition for HW_TAGS in mm/kasan/kasan.h. I >>>> guess we should somehow check that the memory comes from page_alloc or >>>> kmalloc. Or otherwise make sure that it has tags. Maybe there's an arm >>>> instruction to check whether the memory has tags? >>> >>> There isn't an architected way to probe whether a memory location has a >>> VA->PA mapping. The tags are addressed by PA but you can't reach them if >>> you get a page fault on the VA. So we either document the kasan_report() >>> preconditions or, as you suggest, update addr_has_metadata() for the >>> HW_TAGS case. Something like: >>> >>> return is_vmalloc_addr(virt) || virt_addr_valid(virt)); >> >> Or we could have both ;) > > True. Documentation doesn't hurt (well, only when it's wrong ;)). > Testing the patch now, I will send it in half an hour. -- Regards, Vincenzo