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=-18.9 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 E51ACC4727E for ; Thu, 1 Oct 2020 18:04:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4883B20848 for ; Thu, 1 Oct 2020 18:04:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="dPA+Od53" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4883B20848 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C11CC900025; Thu, 1 Oct 2020 14:04:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BE8CD900003; Thu, 1 Oct 2020 14:04:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AB18F900025; Thu, 1 Oct 2020 14:04:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0199.hostedemail.com [216.40.44.199]) by kanga.kvack.org (Postfix) with ESMTP id 7DD42900003 for ; Thu, 1 Oct 2020 14:04:06 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 11AFE3631 for ; Thu, 1 Oct 2020 18:04:06 +0000 (UTC) X-FDA: 77324130492.28.kitty24_1102b9a2719d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id E11676C0B for ; Thu, 1 Oct 2020 18:04:05 +0000 (UTC) X-HE-Tag: kitty24_1102b9a2719d X-Filterd-Recvd-Size: 11045 Received: from mail-wr1-f67.google.com (mail-wr1-f67.google.com [209.85.221.67]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Thu, 1 Oct 2020 18:04:05 +0000 (UTC) Received: by mail-wr1-f67.google.com with SMTP id j2so6858474wrx.7 for ; Thu, 01 Oct 2020 11:04:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=0OdyXaVNiyIQMSnkmN1U5DBWCyVDZmuQfjlNhLtDrKs=; b=dPA+Od53q5f/HBtQwvz6tXehIq+teMdNnK314CY3s0ajOt31vt/u/6D54Q/Ix/LC86 VtbYmG/LRaO//ScEveC5LTytEFM1+3pyoHPWuviFMpXhjPErq3Ufy2aSE62Z1E54Jr6x fqWFaqqQi3HGXr9rIfyLZrmvxYUAsZ3HsNF8y8akiDP5oppHmkSq2PJk0baeSBr0X0ou AUH/o1uBlIATCN1Px1ykRaBmK5Mn1QE0VhyzivGl4dPLnU2lDdrakcyrmDF6NyYXkxzN SJIsUNhdD1tp2kvB482PCt/cq9B2r/JGgCl6SNVrMLV76ZijAIXnbqO8oNjGq3WyT6CK Rs/w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=0OdyXaVNiyIQMSnkmN1U5DBWCyVDZmuQfjlNhLtDrKs=; b=OWWMFc6aoJvjSoog3YXiFEzTpDtfaYfI2luW77Iid9oeN6GifEQOJgxKP9YCWRPkvd Iy5471L+OlgxfIXtIpA/dbPFy7L+xRCtp8Iq+1zFDjO4NmkwgtTmOffpI9gWbjDjPWtf Ha4ENUWI6QMzZf41KUPoZFBZ+p1Jusd6F7sJHCu/6jsB95Wx953cTjraRcaUTEdqgzyW 3VyRbNAnSVz+4xA3yXZuxdVv9sCnTF3NmG578W/fAxAlh5EtEx8beonIEYLoAVFhpSyF tRrMmt7iTwzWrNvncdxujW0hXhikUB48Vzz/NSAWjypZk8zWVIi28chh45o77VEBsFOI DyFg== X-Gm-Message-State: AOAM530afZ++bvL5WUjkCuF5J/5RgneYxaMD5zYM7JS6pw0P23ePjk7h LmO20JNN3g3ZNiIvrav7neTlog== X-Google-Smtp-Source: ABdhPJwzl9G8I0FIwZnl+qK3rpBAlZVN5JVj57b7Bi+4u6kcK9IXkcXgdVGaQG1V73bZU6YmgI5YXQ== X-Received: by 2002:adf:e4cf:: with SMTP id v15mr10259531wrm.174.1601575443811; Thu, 01 Oct 2020 11:04:03 -0700 (PDT) Received: from elver.google.com ([100.105.32.75]) by smtp.gmail.com with ESMTPSA id k6sm950946wmf.30.2020.10.01.11.04.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Oct 2020 11:04:03 -0700 (PDT) Date: Thu, 1 Oct 2020 20:03:57 +0200 From: elver@google.com To: Andrey Konovalov Cc: Dmitry Vyukov , Vincenzo Frascino , Catalin Marinas , kasan-dev@googlegroups.com, Andrey Ryabinin , Alexander Potapenko , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 39/39] kasan: add documentation for hardware tag-based mode Message-ID: <20201001180357.GW4162920@elver.google.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.14.5 (2020-06-23) 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 Fri, Sep 25, 2020 at 12:50AM +0200, Andrey Konovalov wrote: > Add documentation for hardware tag-based KASAN mode and also add some > clarifications for software tag-based mode. > > Signed-off-by: Andrey Konovalov > Signed-off-by: Vincenzo Frascino Reviewed-by: Marco Elver > --- > Change-Id: Ib46cb444cfdee44054628940a82f5139e10d0258 > --- > Documentation/dev-tools/kasan.rst | 78 ++++++++++++++++++++++--------- > 1 file changed, 57 insertions(+), 21 deletions(-) > > diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst > index a3030fc6afe5..d2d47c82a7b9 100644 > --- a/Documentation/dev-tools/kasan.rst > +++ b/Documentation/dev-tools/kasan.rst > @@ -5,12 +5,14 @@ Overview > -------- > > KernelAddressSANitizer (KASAN) is a dynamic memory error detector designed to > -find out-of-bound and use-after-free bugs. KASAN has two modes: generic KASAN > -(similar to userspace ASan) and software tag-based KASAN (similar to userspace > -HWASan). > +find out-of-bound and use-after-free bugs. KASAN has three modes: > +1. generic KASAN (similar to userspace ASan), > +2. software tag-based KASAN (similar to userspace HWASan), > +3. hardware tag-based KASAN (based on hardware memory tagging). > > -KASAN uses compile-time instrumentation to insert validity checks before every > -memory access, and therefore requires a compiler version that supports that. > +Software KASAN modes (1 and 2) use compile-time instrumentation to insert > +validity checks before every memory access, and therefore require a compiler > +version that supports that. > > Generic KASAN is supported in both GCC and Clang. With GCC it requires version > 8.3.0 or later. With Clang it requires version 7.0.0 or later, but detection of > @@ -19,7 +21,7 @@ out-of-bounds accesses for global variables is only supported since Clang 11. > Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later. > > Currently generic KASAN is supported for the x86_64, arm64, xtensa, s390 and > -riscv architectures, and tag-based KASAN is supported only for arm64. > +riscv architectures, and tag-based KASAN modes are supported only for arm64. > > Usage > ----- > @@ -28,14 +30,16 @@ To enable KASAN configure kernel with:: > > CONFIG_KASAN = y > > -and choose between CONFIG_KASAN_GENERIC (to enable generic KASAN) and > -CONFIG_KASAN_SW_TAGS (to enable software tag-based KASAN). > +and choose between CONFIG_KASAN_GENERIC (to enable generic KASAN), > +CONFIG_KASAN_SW_TAGS (to enable software tag-based KASAN), and > +CONFIG_KASAN_HW_TAGS (to enable hardware tag-based KASAN). > > -You also need to choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. > -Outline and inline are compiler instrumentation types. The former produces > -smaller binary while the latter is 1.1 - 2 times faster. > +For software modes, you also need to choose between CONFIG_KASAN_OUTLINE and > +CONFIG_KASAN_INLINE. Outline and inline are compiler instrumentation types. > +The former produces smaller binary while the latter is 1.1 - 2 times faster. > > -Both KASAN modes work with both SLUB and SLAB memory allocators. > +Both software KASAN modes work with both SLUB and SLAB memory allocators, > +hardware tag-based KASAN currently only support SLUB. > For better bug detection and nicer reporting, enable CONFIG_STACKTRACE. > > To augment reports with last allocation and freeing stack of the physical page, > @@ -196,17 +200,24 @@ and the second to last. > Software tag-based KASAN > ~~~~~~~~~~~~~~~~~~~~~~~~ > > -Tag-based KASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to > -store a pointer tag in the top byte of kernel pointers. Like generic KASAN it > -uses shadow memory to store memory tags associated with each 16-byte memory > +Software tag-based KASAN requires software memory tagging support in the form > +of HWASan-like compiler instrumentation (see HWASan documentation for details). > + > +Software tag-based KASAN is currently only implemented for arm64 architecture. > + > +Software tag-based KASAN uses the Top Byte Ignore (TBI) feature of arm64 CPUs > +to store a pointer tag in the top byte of kernel pointers. Like generic KASAN > +it uses shadow memory to store memory tags associated with each 16-byte memory > cell (therefore it dedicates 1/16th of the kernel memory for shadow memory). > > -On each memory allocation tag-based KASAN generates a random tag, tags the > -allocated memory with this tag, and embeds this tag into the returned pointer. > +On each memory allocation software tag-based KASAN generates a random tag, tags > +the allocated memory with this tag, and embeds this tag into the returned > +pointer. > + > Software tag-based KASAN uses compile-time instrumentation to insert checks > before each memory access. These checks make sure that tag of the memory that > is being accessed is equal to tag of the pointer that is used to access this > -memory. In case of a tag mismatch tag-based KASAN prints a bug report. > +memory. In case of a tag mismatch software tag-based KASAN prints a bug report. > > Software tag-based KASAN also has two instrumentation modes (outline, that > emits callbacks to check memory accesses; and inline, that performs the shadow > @@ -215,9 +226,34 @@ simply printed from the function that performs the access check. With inline > instrumentation a brk instruction is emitted by the compiler, and a dedicated > brk handler is used to print bug reports. > > -A potential expansion of this mode is a hardware tag-based mode, which would > -use hardware memory tagging support instead of compiler instrumentation and > -manual shadow memory manipulation. > +Software tag-based KASAN uses 0xFF as a match-all pointer tag (accesses through > +pointers with 0xFF pointer tag aren't checked). The value 0xFE is currently > +reserved to tag freed memory regions. > + > +Software tag-based KASAN currently only supports tagging of slab memory. > + > +Hardware tag-based KASAN > +~~~~~~~~~~~~~~~~~~~~~~~~ > + > +Hardware tag-based KASAN is similar to the software mode in concept, but uses > +hardware memory tagging support instead of compiler instrumentation and > +shadow memory. > + > +Hardware tag-based KASAN is currently only implemented for arm64 architecture > +and based on both arm64 Memory Tagging Extension (MTE) introduced in ARMv8.5 > +Instruction Set Architecture, and Top Byte Ignore (TBI). > + > +Special arm64 instructions are used to assign memory tags for each allocation. > +Same tags are assigned to pointers to those allocations. On every memory > +access, hardware makes sure that tag of the memory that is being accessed is > +equal to tag of the pointer that is used to access this memory. In case of a > +tag mismatch a fault is generated and a report is printed. > + > +Hardware tag-based KASAN uses 0xFF as a match-all pointer tag (accesses through > +pointers with 0xFF pointer tag aren't checked). The value 0xFE is currently > +reserved to tag freed memory regions. > + > +Hardware tag-based KASAN currently only supports tagging of slab memory. > > What memory accesses are sanitised by KASAN? > -------------------------------------------- > -- > 2.28.0.681.g6f77f65b4e-goog >