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,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 BA7B0C433E0 for ; Tue, 19 Jan 2021 20:22:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C77C23104 for ; Tue, 19 Jan 2021 20:22:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729057AbhASUWA (ORCPT ); Tue, 19 Jan 2021 15:22:00 -0500 Received: from mail.kernel.org ([198.145.29.99]:36678 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727816AbhASSww (ORCPT ); Tue, 19 Jan 2021 13:52:52 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8A55820776; Tue, 19 Jan 2021 18:52:09 +0000 (UTC) Date: Tue, 19 Jan 2021 18:52:07 +0000 From: Catalin Marinas To: Andrey Konovalov Cc: Vincenzo Frascino , LKML , kasan-dev , Leon Romanovsky , Alexander Potapenko , Linux ARM , Andrey Ryabinin , Dmitry Vyukov Subject: Re: [PATCH] kasan: Add explicit preconditions to kasan_report() Message-ID: <20210119185206.GA26948@gaia> References: <20210119172607.18400-1-vincenzo.frascino@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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)); -- Catalin