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=-23.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 E9205C433ED for ; Mon, 5 Apr 2021 22:07:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A0D9C613C3 for ; Mon, 5 Apr 2021 22:07:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241314AbhDEWHq (ORCPT ); Mon, 5 Apr 2021 18:07:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55540 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232628AbhDEWHn (ORCPT ); Mon, 5 Apr 2021 18:07:43 -0400 Received: from mail-il1-x130.google.com (mail-il1-x130.google.com [IPv6:2607:f8b0:4864:20::130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 13EE0C061756 for ; Mon, 5 Apr 2021 15:07:37 -0700 (PDT) Received: by mail-il1-x130.google.com with SMTP id z9so11354853ilb.4 for ; Mon, 05 Apr 2021 15:07:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=SqNqwPugUsFfYIOn9Xnz7sTj2i1Lh+cPdEqfufLvtro=; b=JRQibDUJOCYRONPO7/h68qgaO3C6iu2PnWJt+gHkMCRmDiy4Zn4RuSVnnovi01VLOU 8/vLuLjBl+bjDflkeEwSk7dMXgbmkSkAmUa029IQ7BykuUJrzF/myQS8OvhISfp5FAoU /RlQ9l8LFSJLr1HxmnkONyyd/dhj0UG5mUd3mv+4lQLeNELujEdOzzUpsSoA0EKTkoMP 7+YuQVlKRkBOu8LpNCl8h7G8rehzSxJvGKATdwGzd49UrY++QgImsTz8vuBsEPz26TC5 QKvrsl5H5amsC9hQEgRJnPOrT7VisfIMSuV1lFHXyP5a8DoJfJ6T+3SJctJ3/gptyXIY 1sAQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=SqNqwPugUsFfYIOn9Xnz7sTj2i1Lh+cPdEqfufLvtro=; b=Y2CfPBzt/KnwUGxq8TuLKjuI+ourT7bXpZEbXxTMtbP3SsRnjsj/DsGgdPixI3Wfz7 cvTasKyiUv+arELfuC2bxUcJzUk6/XrrfjNgBlHb4I/+8zZnOoQRPW3nDC4vlsvxUi0I ZFJA/vArl/j/yKYEcEv5hN5fsKC5ESZXbxPmYEJYCD9kHR9y749DBtqZ3xd22BanXNZg vRtguFAUg2gn572l49EMiQUvmK1n1pxYkXNNBjAVRksm1Zfg8T99nIzLxfzCqnhPTbsB jfIHcwQnHidIwTSD7efOVLqzjYe9Q0CqQqNRxBdxL+PGi658uDwr3ylwi1/IX16A+WqW eibA== X-Gm-Message-State: AOAM531eR88XxWe5atCUAooND+UcL1cQchjdxK/putaqmojOvOIBFnnI w9OsnHAdthrxFf38qgkcGyx6idfKKXRltCKrhchX9g== X-Google-Smtp-Source: ABdhPJzXT3hYr0/Y0T/iwf8Bj0YfhD8CFEMSzs//a1D3pDq4ig8lGJ+3N4iT/Fd6bJz2XE2Sb8bIQBH38nlPI9/vj+8= X-Received: by 2002:a92:de42:: with SMTP id e2mr20795355ilr.278.1617660456342; Mon, 05 Apr 2021 15:07:36 -0700 (PDT) MIME-Version: 1.0 References: <20210405214321.1953019-1-pcc@google.com> In-Reply-To: From: Peter Collingbourne Date: Mon, 5 Apr 2021 15:07:25 -0700 Message-ID: Subject: Re: [PATCH] kasan: fix kasan_byte_accessible() to be consistent with actual checks To: Andrey Konovalov Cc: Marco Elver , Dmitry Vyukov , Alexander Potapenko , Evgenii Stepanov , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 5, 2021 at 2:53 PM Andrey Konovalov wrote: > > On Mon, Apr 5, 2021 at 11:43 PM Peter Collingbourne wrote: > > > > We can sometimes end up with kasan_byte_accessible() being called > > on non-slab memory. For example ksize() and krealloc() may end up > > calling it on KFENCE allocated memory. In this case the memory will > > be tagged with KASAN_SHADOW_INIT, which a subsequent patch ("kasan: > > initialize shadow to TAG_INVALID for SW_TAGS") will set to the same > > value as KASAN_TAG_INVALID, causing kasan_byte_accessible() to fail > > when called on non-slab memory. > > > > This highlighted the fact that the check in kasan_byte_accessible() > > was inconsistent with checks as implemented for loads and stores > > (kasan_check_range() in SW tags mode and hardware-implemented > > checks in HW tags mode). kasan_check_range() does not have a > > check for KASAN_TAG_INVALID, and instead has a comparison against > > KASAN_SHADOW_START. In HW tags mode, we do not have either, but we > > do set TCR_EL1.TCMA which corresponds with the comparison against > > KASAN_TAG_KERNEL. > > > > Therefore, update kasan_byte_accessible() for both SW and HW tags > > modes to correspond with the respective checks on loads and stores. > > > > Link: https://linux-review.googlesource.com/id/Ic6d40803c57dcc6331bd97fbb9a60b0d38a65a36 > > Signed-off-by: Peter Collingbourne > > --- > > mm/kasan/kasan.h | 3 +-- > > mm/kasan/sw_tags.c | 8 +++++--- > > 2 files changed, 6 insertions(+), 5 deletions(-) > > > > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > > index 8c55634d6edd..e18e8da35255 100644 > > --- a/mm/kasan/kasan.h > > +++ b/mm/kasan/kasan.h > > @@ -368,8 +368,7 @@ static inline bool kasan_byte_accessible(const void *addr) > > u8 ptr_tag = get_tag(addr); > > u8 mem_tag = hw_get_mem_tag((void *)addr); > > > > - return (mem_tag != KASAN_TAG_INVALID) && > > - (ptr_tag == KASAN_TAG_KERNEL || ptr_tag == mem_tag); > > + return ptr_tag == KASAN_TAG_KERNEL || ptr_tag == mem_tag; > > } > > > > #else /* CONFIG_KASAN_HW_TAGS */ > > diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c > > index 94c2d33be333..914225eeda99 100644 > > --- a/mm/kasan/sw_tags.c > > +++ b/mm/kasan/sw_tags.c > > @@ -121,10 +121,12 @@ bool kasan_check_range(unsigned long addr, size_t size, bool write, > > bool kasan_byte_accessible(const void *addr) > > { > > u8 tag = get_tag(addr); > > - u8 shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(kasan_reset_tag(addr))); > > + void *untagged_addr = kasan_reset_tag(addr); > > + u8 shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(untagged_addr)); > > Hi Peter, > > Let's move dereferencing shadow memory past the KASAN_SHADOW_START > check. Otherwise, in case the check is to fail, accessing shadow will > likely crash the kernel. > > Thanks! Makes sense, fixed in v2. Peter