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=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 060D4C433B4 for ; Mon, 5 Apr 2021 21:53:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 54455613A7 for ; Mon, 5 Apr 2021 21:53:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 54455613A7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9B1776B006E; Mon, 5 Apr 2021 17:53:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9395D6B0073; Mon, 5 Apr 2021 17:53:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 78D746B0075; Mon, 5 Apr 2021 17:53:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0086.hostedemail.com [216.40.44.86]) by kanga.kvack.org (Postfix) with ESMTP id 581AF6B006E for ; Mon, 5 Apr 2021 17:53:05 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 110F38249980 for ; Mon, 5 Apr 2021 21:53:05 +0000 (UTC) X-FDA: 77999664330.06.A110C9E Received: from mail-ed1-f42.google.com (mail-ed1-f42.google.com [209.85.208.42]) by imf18.hostedemail.com (Postfix) with ESMTP id 6D4F92000255 for ; Mon, 5 Apr 2021 21:53:04 +0000 (UTC) Received: by mail-ed1-f42.google.com with SMTP id m3so4261332edv.5 for ; Mon, 05 Apr 2021 14:53:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=5agwQ0zThzc864zDwQsU0D8PGaKGEvgUD6u4hDPScD0=; b=NA7k8+kdwRZCnDG2UOwug4CS0plPPRJreVTt9HdBi+DESBdCmAkiaJANEJacbq09tO HYkXWo50oJApb/05+yZ0XeNQTeVVCYvAf4VVwFH0kmd/My2eExXZBNmVm+n/qb3v5zrK iKbz70/JWKHi7IFRIDxUTXQQ8nHNX7SWv7inM31iiLCN1e/Ycl4PRvG1+UZ9OAyOcxZy ntQiAO1f7mdxSET2eU12Jc1w8N2JfBEr2rpsEoP3a+6TrcXnqD6AuI739k+EUwncMKxd 0AmYCH9vH3qRddtoQ68XVL0fixkOE6Wev2nB/PpFATwdmTrEPeflDr5972/6XVDIR3zE j0bQ== 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=5agwQ0zThzc864zDwQsU0D8PGaKGEvgUD6u4hDPScD0=; b=nsraQvt2UNJlOFeANknc3Y67HRnBIcNpINQ3mzIqVawYn8OqgKkVJGrtAeTO/XWvUW FHmAWPXRrP/AdM1PwAA+Wn3CbAvpbVm1/79XxNxRjfWgWmnF7FEqMqwPMnBB0ZxPmPrR Yfm/EF2YNYaOe+U1a4MKwbfTNIf2Ov28L9faqWGzqN2dxNlOkdfYTb1JrEEhF2FBdxiq lCMeZsdApb8Thc48N/OhHm9t0YftfJGDd0GHzgcufJsM2ueetzW7E6/gentQ0KVkpNRI 9cXzIE8oOsjtQB50HHbmQD0PbEmokwonx+jo1FicktiwwisHR7TCQUW2n+iK0y4aXz7Q sF3A== X-Gm-Message-State: AOAM531pOAyTA1aEhTKNpAjVCEagktq8NzKu1eidOD7saku16l9fu8Dc nq1j2hftpQ0Hy5e5MAmEm+mwpyc9hkwJtdWJqYA= X-Google-Smtp-Source: ABdhPJzLYW8JXD4N1iYvdzWmzlQ7A5bHoQSa+dS5Dt6T6bzAzET4LqVbj+R2p2t0lVUJ+hy7uVz6kMf6qv/5R/ORSmY= X-Received: by 2002:aa7:d541:: with SMTP id u1mr14436442edr.95.1617659583372; Mon, 05 Apr 2021 14:53:03 -0700 (PDT) MIME-Version: 1.0 References: <20210405214321.1953019-1-pcc@google.com> In-Reply-To: <20210405214321.1953019-1-pcc@google.com> From: Andrey Konovalov Date: Mon, 5 Apr 2021 23:52:52 +0200 Message-ID: Subject: Re: [PATCH] kasan: fix kasan_byte_accessible() to be consistent with actual checks To: Peter Collingbourne Cc: Marco Elver , Dmitry Vyukov , Alexander Potapenko , Evgenii Stepanov , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: gfeu8qrghc88abdib1xxu1iz6ifmecah X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6D4F92000255 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf18; identity=mailfrom; envelope-from=""; helo=mail-ed1-f42.google.com; client-ip=209.85.208.42 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617659584-718658 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 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! > > - return (shadow_byte != KASAN_TAG_INVALID) && > - (tag == KASAN_TAG_KERNEL || tag == shadow_byte); > + return untagged_addr >= > + kasan_shadow_to_mem((void *)KASAN_SHADOW_START) && > + (tag == KASAN_TAG_KERNEL || tag == shadow_byte); > } > > #define DEFINE_HWASAN_LOAD_STORE(size) \ > -- > 2.31.0.208.g409f899ff0-goog >