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,URIBL_BLOCKED,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 C9FE7C433E0 for ; Wed, 20 Jan 2021 16:07:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 89A9A233E2 for ; Wed, 20 Jan 2021 16:07:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731207AbhATQGm (ORCPT ); Wed, 20 Jan 2021 11:06:42 -0500 Received: from mail.kernel.org ([198.145.29.99]:36200 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391192AbhATQFC (ORCPT ); Wed, 20 Jan 2021 11:05:02 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6D8012339E; Wed, 20 Jan 2021 16:04:19 +0000 (UTC) Date: Wed, 20 Jan 2021 16:04:16 +0000 From: Catalin Marinas To: Vincenzo Frascino Cc: Andrey Konovalov , 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: <20210120160416.GF2642@gaia> References: <20210119172607.18400-1-vincenzo.frascino@arm.com> <20210119185206.GA26948@gaia> <418db49b-1412-85ca-909e-9cdcd9fdb089@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <418db49b-1412-85ca-909e-9cdcd9fdb089@arm.com> 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 08:35:49PM +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)); > > > > This seems not working on arm64 because according to virt_addr_valid 0 is a > valid virtual address, in fact: > > __is_lm_address(0) == true && pfn_valid(virt_to_pfn(0)) == true. Ah, so __is_lm_address(0) is true. Maybe we should improve this since virt_to_pfn(0) doesn't make much sense. > An option could be to make an exception for virtual address 0 in > addr_has_metadata() something like: > > static inline bool addr_has_metadata(const void *addr) > { > if ((u64)addr == 0) > return false; > > return (is_vmalloc_addr(addr) || virt_addr_valid(addr)); > } As Andrey replied, passing a non-zero small value would still be incorrectly detected as valid. -- Catalin