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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 57225C07548 for ; Thu, 10 Sep 2020 19:26:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 14B4121D81 for ; Thu, 10 Sep 2020 19:26:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="rZS11rVG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727773AbgIJTZb (ORCPT ); Thu, 10 Sep 2020 15:25:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731415AbgIJPtc (ORCPT ); Thu, 10 Sep 2020 11:49:32 -0400 Received: from mail-qv1-xf43.google.com (mail-qv1-xf43.google.com [IPv6:2607:f8b0:4864:20::f43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B384EC061796 for ; Thu, 10 Sep 2020 08:48:46 -0700 (PDT) Received: by mail-qv1-xf43.google.com with SMTP id ef16so3553577qvb.8 for ; Thu, 10 Sep 2020 08:48:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mzZ2lLN/xoCXQCadMP3KD01lnN0CJF5729OTiX4TA1k=; b=rZS11rVGYL5ep4IWino2NQi6goYHWye6jCPxILs3Ix3/bXbZEy+oW9dhA3uWl/9kSl OvQfGVC3GCJPLaseAZRCG0qA4mfMcw8hk8EBu8VZ8OFLPZe1Axx64ljgqCtxruwPkZAD Q3vWzxZws/NIoaTu71iD4PPu6sScpp4aytj00Dg/7lyKydCTfnXeY4h4sgEM5ROww+f4 v+N4GT/+MGo71yWSm45kTtU8uEhY8SrLw8ak87gYoy4h1Mq1a8eSEGmMCOJRpdevtoS9 VuZUWtwRqZY8/t5WvHtrRTz1Osj7MVCaplXa1UIZPf3Hm8YvfrB0Uqc6QR+WoN8whxAZ 7Uvg== 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=mzZ2lLN/xoCXQCadMP3KD01lnN0CJF5729OTiX4TA1k=; b=hCEpbj81WkfovS1fiROZJrmqt3LW0yEVlPxn9jsGCsnOaFo6DO9g2qu8pMJ9SBkV2d pN91PV6UE4XEoM8Ez1/uLQ9whrcPev55TbCDeQn6F8bKeu1xELlJ1LE5Eg1GIkW21Jf8 fbOrdn1Rr84j/zjhRIyCCZfBLc73QUxv1DzSqHFlNXhgS0igjnTxbCyAhN2SdzaHRNP9 h6YgKvD/0vSlu34kdSspjdosw7/079mzXxgegZJsQYw+HCSeIJdsUhyNY9NVG2Aq57AP 2gDF87JK8KV1lJEXTLFWvJo6tfd6Hnia0D0qcZ2GhV4R95BBnlR7Rr1YeveUpzm2N26v r+6Q== X-Gm-Message-State: AOAM530TyMyF3dvmJBgzOtxINRIkQyf7pTbrT52lc++12PLY3EW2pRTG sXo2XnWyJ0kFh1bdd6OVxrJMT3xQTPc+qDHO8QPVkw== X-Google-Smtp-Source: ABdhPJxh2XVwiSK5Cy8rwdS2ADng5rr5wnF88amN70Agx8Eq7w/KffAyyLi/G4AzlUPalDqC/TNQ17vsb+5sAfyNH4U= X-Received: by 2002:a0c:e543:: with SMTP id n3mr9296354qvm.11.1599752925133; Thu, 10 Sep 2020 08:48:45 -0700 (PDT) MIME-Version: 1.0 References: <20200907134055.2878499-1-elver@google.com> <20200907134055.2878499-2-elver@google.com> In-Reply-To: From: Dmitry Vyukov Date: Thu, 10 Sep 2020 17:48:34 +0200 Message-ID: Subject: Re: [PATCH RFC 01/10] mm: add Kernel Electric-Fence infrastructure To: Marco Elver Cc: Alexander Potapenko , Andrew Morton , Catalin Marinas , Christoph Lameter , David Rientjes , Joonsoo Kim , Mark Rutland , Pekka Enberg , "H. Peter Anvin" , "Paul E. McKenney" , Andrey Konovalov , Andrey Ryabinin , Andy Lutomirski , Borislav Petkov , Dave Hansen , Eric Dumazet , Greg Kroah-Hartman , Ingo Molnar , Jann Horn , Jonathan Corbet , Kees Cook , Peter Zijlstra , Qian Cai , Thomas Gleixner , Will Deacon , "the arch/x86 maintainers" , "open list:DOCUMENTATION" , LKML , kasan-dev , Linux ARM , Linux-MM Content-Type: text/plain; charset="UTF-8" Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Thu, Sep 10, 2020 at 5:06 PM Marco Elver wrote: > > On Mon, Sep 7, 2020 at 3:41 PM Marco Elver wrote: > > > +config KFENCE_NUM_OBJECTS > > > + int "Number of guarded objects available" > > > + default 255 > > > + range 1 65535 > > > + help > > > + The number of guarded objects available. For each KFENCE object, 2 > > > + pages are required; with one containing the object and two adjacent > > > + ones used as guard pages. > > > > Hi Marco, > > > > Wonder if you tested build/boot with KFENCE_NUM_OBJECTS=65535? Can a > > compiler create such a large object? > > Indeed, I get a "ld: kernel image bigger than KERNEL_IMAGE_SIZE". > Let's lower it to something more reasonable. > > The main reason to have the limit is to constrain random configs and > avoid the inevitable error reports. > > > > +config KFENCE_FAULT_INJECTION > > > + int "Fault injection for stress testing" > > > + default 0 > > > + depends on EXPERT > > > + help > > > + The inverse probability with which to randomly protect KFENCE object > > > + pages, resulting in spurious use-after-frees. The main purpose of > > > + this option is to stress-test KFENCE with concurrent error reports > > > + and allocations/frees. A value of 0 disables fault injection. > > > > I would name this differently. "FAULT_INJECTION" is already taken for > > a different thing, so it's a bit confusing. > > KFENCE_DEBUG_SOMETHING may be a better name. > > It would also be good to make it very clear in the short description > > that this is for testing of KFENCE itself. When I configure syzbot I > > routinely can't figure out if various DEBUG configs detect user > > errors, or enable additional unit tests, or something else. > > Makes sense, we'll change the name. > > > Maybe it should depend on DEBUG_KERNEL as well? > > EXPERT selects DEBUG_KERNEL, so depending on DEBUG_KERNEL doesn't make sense. > > > > +/* > > > + * Get the canary byte pattern for @addr. Use a pattern that varies based on the > > > + * lower 3 bits of the address, to detect memory corruptions with higher > > > + * probability, where similar constants are used. > > > + */ > > > +#define KFENCE_CANARY_PATTERN(addr) ((u8)0xaa ^ (u8)((unsigned long)addr & 0x7)) > > > > (addr) in macro body > > Done for v2. > > > > + seq_con_printf(seq, > > > + "kfence-#%zd [0x" PTR_FMT "-0x" PTR_FMT > > > > PTR_FMT is only used in this file, should it be declared in report.c? > > It's also used by the test. > > > Please post example reports somewhere. It's hard to figure out all > > details of the reporting/formatting. > > They can be seen in Documentation added later in the series (also > viewable here: https://github.com/google/kasan/blob/kfence/Documentation/dev-tools/kfence.rst) Looking at the first report. I got impression we are trying to skip __kfence frames, but this includes it: kfence-#17 [0xffffffffb672f000-0xffffffffb672f01f, size=32, cache=kmalloc-32] allocated in: __kfence_alloc+0x42d/0x4c0 __kmalloc+0x133/0x200 Is it working as intended?