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=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 C05CEC433B4 for ; Mon, 5 Apr 2021 22:43:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9C7986138A for ; Mon, 5 Apr 2021 22:43:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242847AbhDEWno (ORCPT ); Mon, 5 Apr 2021 18:43:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35150 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231375AbhDEWnm (ORCPT ); Mon, 5 Apr 2021 18:43:42 -0400 Received: from mail-ej1-x633.google.com (mail-ej1-x633.google.com [IPv6:2a00:1450:4864:20::633]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 60F5FC06174A for ; Mon, 5 Apr 2021 15:43:34 -0700 (PDT) Received: by mail-ej1-x633.google.com with SMTP id u17so12617495ejk.2 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=N7IbYdxxRgfqrO7LdWOkZ8+lYqXcMvsrCzBiWzRbWAoBHjh2YM5HSH/6Nm2BsWNI7u NfAjMvKNsQ0Vd3BFwHl5ZUUfLGTp/Jm+f5LPrftV0s3etEHiq4SyKJHtDchsZJR9fvB8 lAvG9QWKBym/RGNVu8xZTMRL7tHP92C5QPz1R7jIRoUaJR7/CLG89rzZmlaB8m1XeU9f cPn0UCtgX3N2F53O5sA+O+ktGlWb5gaBdT334ZdYLLjvG54QuChPOeQLPY9Oee/hwxMP TH8oe9LPvDxKwoLKnz+q0aTcm9xEesUkle/H9EJOsEQSjJfefov37vjtWZSciFMtWfYm oWuA== X-Gm-Message-State: AOAM530Lu5Pzbsq89O+n3iZSbGLZh1IbTkyg9CwCCiNqEEO+ZJFy9Jyy NbDmk8WwXTErVpnrY1Mk/w7QMGGy8bKfL2Namp0= 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" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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!