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=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 3ACCCC433E0 for ; Fri, 15 Jan 2021 16:57:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 14FF223128 for ; Fri, 15 Jan 2021 16:57:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728274AbhAOQ4q (ORCPT ); Fri, 15 Jan 2021 11:56:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:42708 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725818AbhAOQ4o (ORCPT ); Fri, 15 Jan 2021 11:56:44 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7DA3F20738; Fri, 15 Jan 2021 16:56:01 +0000 (UTC) Date: Fri, 15 Jan 2021 16:55:59 +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: <20210115165558.GF16707@gaia> References: <1965508bcbec62699715d32bef91628ef55b4b44.1610553774.git.andreyknvl@google.com> <20210113165441.GC27045@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) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Catalin