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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 23C41C4741F for ; Tue, 29 Sep 2020 14:24:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BD61B206DB for ; Tue, 29 Sep 2020 14:24:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728858AbgI2OYU (ORCPT ); Tue, 29 Sep 2020 10:24:20 -0400 Received: from foss.arm.com ([217.140.110.172]:46102 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727543AbgI2OYT (ORCPT ); Tue, 29 Sep 2020 10:24:19 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C3E5331B; Tue, 29 Sep 2020 07:24:18 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.51.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D59CA3F6CF; Tue, 29 Sep 2020 07:24:13 -0700 (PDT) Date: Tue, 29 Sep 2020 15:24:11 +0100 From: Mark Rutland To: Marco Elver Cc: akpm@linux-foundation.org, glider@google.com, hpa@zytor.com, paulmck@kernel.org, andreyknvl@google.com, aryabinin@virtuozzo.com, luto@kernel.org, bp@alien8.de, catalin.marinas@arm.com, cl@linux.com, dave.hansen@linux.intel.com, rientjes@google.com, dvyukov@google.com, edumazet@google.com, gregkh@linuxfoundation.org, hdanton@sina.com, mingo@redhat.com, jannh@google.com, Jonathan.Cameron@huawei.com, corbet@lwn.net, iamjoonsoo.kim@lge.com, keescook@chromium.org, penberg@kernel.org, peterz@infradead.org, sjpark@amazon.com, tglx@linutronix.de, vbabka@suse.cz, will@kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure Message-ID: <20200929142411.GC53442@C02TD0UTHF1T.local> References: <20200921132611.1700350-1-elver@google.com> <20200921132611.1700350-2-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200921132611.1700350-2-elver@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 21, 2020 at 03:26:02PM +0200, Marco Elver wrote: > From: Alexander Potapenko > > This adds the Kernel Electric-Fence (KFENCE) infrastructure. KFENCE is a > low-overhead sampling-based memory safety error detector of heap > use-after-free, invalid-free, and out-of-bounds access errors. > > KFENCE is designed to be enabled in production kernels, and has near > zero performance overhead. Compared to KASAN, KFENCE trades performance > for precision. The main motivation behind KFENCE's design, is that with > enough total uptime KFENCE will detect bugs in code paths not typically > exercised by non-production test workloads. One way to quickly achieve a > large enough total uptime is when the tool is deployed across a large > fleet of machines. > > KFENCE objects each reside on a dedicated page, at either the left or > right page boundaries. The pages to the left and right of the object > page are "guard pages", whose attributes are changed to a protected > state, and cause page faults on any attempted access to them. Such page > faults are then intercepted by KFENCE, which handles the fault > gracefully by reporting a memory access error. To detect out-of-bounds > writes to memory within the object's page itself, KFENCE also uses > pattern-based redzones. The following figure illustrates the page > layout: > > ---+-----------+-----------+-----------+-----------+-----------+--- > | xxxxxxxxx | O : | xxxxxxxxx | : O | xxxxxxxxx | > | xxxxxxxxx | B : | xxxxxxxxx | : B | xxxxxxxxx | > | x GUARD x | J : RED- | x GUARD x | RED- : J | x GUARD x | > | xxxxxxxxx | E : ZONE | xxxxxxxxx | ZONE : E | xxxxxxxxx | > | xxxxxxxxx | C : | xxxxxxxxx | : C | xxxxxxxxx | > | xxxxxxxxx | T : | xxxxxxxxx | : T | xxxxxxxxx | > ---+-----------+-----------+-----------+-----------+-----------+--- > > Guarded allocations are set up based on a sample interval (can be set > via kfence.sample_interval). After expiration of the sample interval, a > guarded allocation from the KFENCE object pool is returned to the main > allocator (SLAB or SLUB). At this point, the timer is reset, and the > next allocation is set up after the expiration of the interval. >From other sub-threads it sounds like these addresses are not part of the linear/direct map. Having kmalloc return addresses outside of the linear map is going to break anything that relies on virt<->phys conversions, and is liable to make DMA corrupt memory. There were problems of that sort with VMAP_STACK, and this is why kvmalloc() is separate from kmalloc(). Have you tested with CONFIG_DEBUG_VIRTUAL? I'd expect that to scream. I strongly suspect this isn't going to be safe unless you always use an in-place carevout from the linear map (which could be the linear alias of a static carevout). [...] > +static __always_inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) > +{ > + return static_branch_unlikely(&kfence_allocation_key) ? __kfence_alloc(s, size, flags) : > + NULL; > +} Minor (unrelated) nit, but this would be easier to read as: static __always_inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) { if (static_branch_unlikely(&kfence_allocation_key)) return __kfence_alloc(s, size, flags); return NULL; } Thanks, Mark.