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=-15.2 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=ham 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 0B16DC433E0 for ; Fri, 15 Jan 2021 17:06:13 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AFD5F2313E for ; Fri, 15 Jan 2021 17:06:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AFD5F2313E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id CDDBC8D0199; Fri, 15 Jan 2021 12:06:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C66DD8D016A; Fri, 15 Jan 2021 12:06:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B2F108D0199; Fri, 15 Jan 2021 12:06:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0052.hostedemail.com [216.40.44.52]) by kanga.kvack.org (Postfix) with ESMTP id 99A158D016A for ; Fri, 15 Jan 2021 12:06:11 -0500 (EST) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 561CF18201289 for ; Fri, 15 Jan 2021 17:06:11 +0000 (UTC) X-FDA: 77708637342.01.pot86_181094027531 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin01.hostedemail.com (Postfix) with ESMTP id 10A8A10053A25 for ; Fri, 15 Jan 2021 17:06:03 +0000 (UTC) X-HE-Tag: pot86_181094027531 X-Filterd-Recvd-Size: 5331 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf26.hostedemail.com (Postfix) with ESMTP for ; Fri, 15 Jan 2021 17:06:02 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 2CB0E222B3; Fri, 15 Jan 2021 17:05:59 +0000 (UTC) Date: Fri, 15 Jan 2021 17:05:56 +0000 From: Catalin Marinas To: Andrey Konovalov Cc: Vincenzo Frascino , Dmitry Vyukov , Alexander Potapenko , Marco Elver , Andrew Morton , Will Deacon , Andrey Ryabinin , Peter Collingbourne , Evgenii Stepanov , Branislav Rankov , Kevin Brodsky , kasan-dev , Linux ARM , Linux Memory Management List , LKML Subject: Re: [PATCH 2/2] kasan, arm64: fix pointer tags in KASAN reports Message-ID: <20210115170556.GG16707@gaia> References: <1965508bcbec62699715d32bef91628ef55b4b44.1610553774.git.andreyknvl@google.com> <20210113165441.GC27045@gaia> <20210115165558.GF16707@gaia> 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jan 15, 2021 at 06:00:36PM +0100, Andrey Konovalov wrote: > On Fri, Jan 15, 2021 at 5:56 PM Catalin Marinas wrote: > > > > On Fri, Jan 15, 2021 at 05:30:40PM +0100, Andrey Konovalov wrote: > > > On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas wrote: > > > > On Wed, Jan 13, 2021 at 05:03:30PM +0100, Andrey Konovalov wrote: > > > > > As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address > > > > > that is passed to report_tag_fault has pointer tags in the format of 0x0X, > > > > > while KASAN uses 0xFX format (note the difference in the top 4 bits). > > > > > > > > > > Fix up the pointer tag before calling kasan_report. > > > > > > > > > > Link: https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649 > > > > > Fixes: dceec3ff7807 ("arm64: expose FAR_EL1 tag bits in siginfo") > > > > > Fixes: 4291e9ee6189 ("kasan, arm64: print report from tag fault handler") > > > > > Signed-off-by: Andrey Konovalov > > > > > --- > > > > > arch/arm64/mm/fault.c | 2 ++ > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > > > > index 3c40da479899..a218f6f2fdc8 100644 > > > > > --- a/arch/arm64/mm/fault.c > > > > > +++ b/arch/arm64/mm/fault.c > > > > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr, > > > > > { > > > > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0; > > > > > > > > > > + /* The format of KASAN tags is 0xF. */ > > > > > + addr |= (0xF0UL << MTE_TAG_SHIFT); > > > > > > > > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this > > > > was added, the only tag faults were generated for user addresses. > > > > > > > > Anyway, I'd rather fix it in there based on bit 55, something like (only > > > > compile-tested): > > > > > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > > > index 3c40da479899..2b71079d2d32 100644 > > > > --- a/arch/arm64/mm/fault.c > > > > +++ b/arch/arm64/mm/fault.c > > > > @@ -709,10 +709,11 @@ static int do_tag_check_fault(unsigned long far, unsigned int esr, > > > > struct pt_regs *regs) > > > > { > > > > /* > > > > - * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag > > > > - * check faults. Mask them out now so that userspace doesn't see them. > > > > + * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN > > > > + * for tag check faults. Set them to the corresponding bits in the > > > > + * untagged address. > > > > */ > > > > - far &= (1UL << 60) - 1; > > > > + far = (untagged_addr(far) & ~MTE_TAG_MASK) | (far & MTE_TAG_MASK) ; > > > > do_bad_area(far, esr, regs); > > > > return 0; > > > > } > > > > > > BTW, we can do "untagged_addr(far) | (far & MTE_TAG_MASK)" here, as > > > untagged_addr() doesn't change kernel pointers. > > > > untagged_addr() does change tagged kernel pointers, it sign-extends from > > bit 55. So the top byte becomes 0xff and you can no longer or the tag > > bits in. > > That's __untagged_addr(), untagged_addr() keeps the bits for kernel > pointers as of 597399d0cb91. Ah, you are right. In this case I think we should use __untagged_addr() above. Even if the tag check fault happened on a kernel address, bits 63:60 are still unknown. -- Catalin