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 33852C433B4 for ; Mon, 5 Apr 2021 22:43:36 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B2392613D6 for ; Mon, 5 Apr 2021 22:43:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2392613D6 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 35CF66B0071; Mon, 5 Apr 2021 18:43:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 334EC6B0073; Mon, 5 Apr 2021 18:43:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1D6976B0075; Mon, 5 Apr 2021 18:43:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0050.hostedemail.com [216.40.44.50]) by kanga.kvack.org (Postfix) with ESMTP id 03BFF6B0071 for ; Mon, 5 Apr 2021 18:43:34 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id B01E8812C for ; Mon, 5 Apr 2021 22:43:34 +0000 (UTC) X-FDA: 77999791548.20.64A4F40 Received: from mail-ej1-f50.google.com (mail-ej1-f50.google.com [209.85.218.50]) by imf06.hostedemail.com (Postfix) with ESMTP id 369C4C0007CF for ; Mon, 5 Apr 2021 22:43:35 +0000 (UTC) Received: by mail-ej1-f50.google.com with SMTP id u5so18905380ejn.8 for ; Mon, 05 Apr 2021 15:43:34 -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=yo52b4J16syd/qfNeKjfg1qCC8mR8uBgoSHsQDF+zy8=; b=hwD7BLAc9IN7zVKm9X1tRpL0lk2t4cFOw4vHEPOS36yFjYpHpOOn3/O4nHZHyOzuye EVyw7NL8OztU4tehz0MzJZfB7pZSCnUK4Ckvfh0vrpOU/XQb3Cp9NFiHAML/xAaLzd75 BX8nrk2MQmvxKk9Eb9HERskM/ze/Ol68W6wlwsCEQg9hBIkD9AodO/fLyda0CRJi3ljo houat1mIpC8vvPhMT3PZEXZSxojvQP07XAWZ8hNnDeyjx5CWCf+bq58DL76LM8JiuKqB Fpz9Tj/mHNxKkdKyskQK1z99GL3PIt4yFe2C/Ybg2FR0u87WTNqvkRD2l0Ec1hgOTHk+ K1Gw== 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=yo52b4J16syd/qfNeKjfg1qCC8mR8uBgoSHsQDF+zy8=; b=tGwOHv1lA09u7dYIl0ZIi8qKoRw5zglh4MwJPIg5iYYq2RDCL1QRMVOSHeo54cLPfQ 57zU22mh4u75heiy11G5GwQQB3N1BSbGB+c9hzoQ5OuBt8yyTFuEbMpNbtwjE0qGoW6y p88UsMz7Y4b6fJRZA3tE0xRydSGS2wbXkJarn+vm0GK4YXC6lX1cW8nB4iHVkEAxZTgG Nt6hNokVxHmnbnBbbYY08XcV5ddgYEst7As23ZNgHCklRcsIaPSA1s/dMSVMMn+uH7m6 sNtHYD2Qifrm0OgsSPE3cZlVAPMU1ehDyXJiHzDJmAQQ7KX0c5vDZajnVvZ0PuiZIkPv SMtw== X-Gm-Message-State: AOAM531Zwjy4Wh/EJrVcwqjB/nq/AqgcGjdv5Nyf5FwPBTfs2TKc47/b wK0ECB2jV+xeWOjl7+C0rhAlRM0khAy6sum0dupX33ImHpY= X-Google-Smtp-Source: ABdhPJwKlSaCOul8s/f4tEbscuCbIAZgiL/leovnNzFPGSauV6kH5prdShdudT7OVnZq0CVtP6h77utCNn/TicH9uD8= X-Received: by 2002:a17:906:4e17:: with SMTP id z23mr30869445eju.439.1617662613103; Mon, 05 Apr 2021 15:43:33 -0700 (PDT) MIME-Version: 1.0 References: <20210405220647.1965262-1-pcc@google.com> In-Reply-To: <20210405220647.1965262-1-pcc@google.com> From: Andrey Konovalov Date: Tue, 6 Apr 2021 00:43:22 +0200 Message-ID: Subject: Re: [PATCH v2] 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: jpxw5jb1xa6i6qxcu4c86qdpjqxu5a9x X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 369C4C0007CF Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf06; identity=mailfrom; envelope-from=""; helo=mail-ej1-f50.google.com; client-ip=209.85.218.50 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617662615-973107 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 Tue, Apr 6, 2021 at 12:07 AM 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 | 10 +++++++--- > 2 files changed, 8 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..00ae8913fc74 100644 > --- a/mm/kasan/sw_tags.c > +++ b/mm/kasan/sw_tags.c > @@ -121,10 +121,14 @@ 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; > > - return (shadow_byte != KASAN_TAG_INVALID) && > - (tag == KASAN_TAG_KERNEL || tag == shadow_byte); > + if (untagged_addr < kasan_shadow_to_mem((void *)KASAN_SHADOW_START)) > + return false; > + > + shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(untagged_addr)); > + return tag == KASAN_TAG_KERNEL || tag == shadow_byte; > } > > #define DEFINE_HWASAN_LOAD_STORE(size) \ > -- > 2.31.0.208.g409f899ff0-goog > Reviewed-by: Andrey Konovalov Thank you, Peter!