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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3EE7AC433F5 for ; Sun, 20 Mar 2022 21:09:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4479C6B0072; Sun, 20 Mar 2022 17:09:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3F67C6B0073; Sun, 20 Mar 2022 17:09:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2971F6B0074; Sun, 20 Mar 2022 17:09:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 1813B6B0072 for ; Sun, 20 Mar 2022 17:09:45 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id CF43822AB4 for ; Sun, 20 Mar 2022 21:09:44 +0000 (UTC) X-FDA: 79266006288.05.651C938 Received: from mail-io1-f49.google.com (mail-io1-f49.google.com [209.85.166.49]) by imf12.hostedemail.com (Postfix) with ESMTP id D902E40018 for ; Sun, 20 Mar 2022 21:09:43 +0000 (UTC) Received: by mail-io1-f49.google.com with SMTP id l18so14885345ioj.2 for ; Sun, 20 Mar 2022 14:09:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Uu3NPXS3YIK/joqnoO2dCxxZrdruyUVh70Rwb4NqWi8=; b=peCpeuakEvX6D9DkWAvoxRIedMD/39lVZWCnWMzXtri03y9r62H6zmrugVSd2V6Hnl yNgQlrRrkY5LOSfKIyB0mcQWaLclmNYbtS7Df8eBRfi86fUcUomspIvZeeMvSeYnj0in nDF7eZNpiFFCY/pjp6ygoxeX9KEC7hglQY1MN7LvMqX7SUur4xKzkWFvSSHIcgKt5CKK v6+ptK9uDU0LA9ECsg46r4NCs/Gxy4hQQtQ3XG5NJvScH196cq0hbQ7SE4TQYIBumZBV Vk/MJcmAZlhdSbuXePQoJqG7CWuQiogqYCmhdv574+F3DX+e+JE5bixYQtJtbH/UaKF1 nvyA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Uu3NPXS3YIK/joqnoO2dCxxZrdruyUVh70Rwb4NqWi8=; b=RecKFz22ArQpdjDLTYGziXgotgfjfLlmQM6YSkPECm6pe6Jyk5/bDgtxtwrziUSETG 5K1+WCoLiHod6dkIgVsV7jzdeIubF0BOXnD6crr35HsiUPJSkK/XfJttTwYpTIbJ8Tht ZHWey08+WJAvi5tsmGVcwhhQ6GfjzJ5E4FBE1ZU/PlBOZciQB17kNePDrbzJ4vPmAM+c Ylvh6LQrYKU4/m4W+maw2mxXpZo47TDcxKddeJaHJb3nhoY/5ZOU0jSYYW6eYcgAQu/v ShHltNCmfXGL+bgPSlIOSouK9YqkRnpBt8R8UvT+5uDuwW499bfr2ZqUiyS+UbdwfBEA ll7A== X-Gm-Message-State: AOAM531kn/0NCmvcyPRWtBRSAhOQ879huEsl6MlXVKING4PBZtHCnACc FSpMdwFzMzGxNQdQ1Nc9FjGRRR1OaR88t+aSARM= X-Google-Smtp-Source: ABdhPJxtnQc5xK7BNvEj8B3gFxPHw3v/vJyiqBQB12KNZ11hRyLBynaAARBpB1/R7HnY+wIoLY5Ba/RGVkuYmR9jHi8= X-Received: by 2002:a05:6638:210a:b0:31a:536e:4714 with SMTP id n10-20020a056638210a00b0031a536e4714mr10058666jaj.71.1647810583809; Sun, 20 Mar 2022 14:09:43 -0700 (PDT) MIME-Version: 1.0 References: <57133fafc4d74377a4a08d98e276d58fe4a127dc.1647115974.git.andreyknvl@google.com> In-Reply-To: From: Andrey Konovalov Date: Sun, 20 Mar 2022 22:09:33 +0100 Message-ID: Subject: Re: [PATCH] kasan, scs: collect stack traces from shadow stack To: Marco Elver Cc: andrey.konovalov@linux.dev, Alexander Potapenko , Andrew Morton , Dmitry Vyukov , Andrey Ryabinin , kasan-dev , Vincenzo Frascino , Catalin Marinas , Will Deacon , Mark Rutland , Sami Tolvanen , Peter Collingbourne , Evgenii Stepanov , Linux Memory Management List , LKML , Andrey Konovalov Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D902E40018 X-Stat-Signature: owpndbhmbrdtnwb7oj7yj8zn6fbf7t47 Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=peCpeuak; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf12.hostedemail.com: domain of andreyknvl@gmail.com designates 209.85.166.49 as permitted sender) smtp.mailfrom=andreyknvl@gmail.com X-Rspam-User: X-HE-Tag: 1647810583-867897 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 Mon, Mar 14, 2022 at 8:01 AM Marco Elver wrote: > > > Instead of invoking the unwinder, collect the stack trace by copying > > frames from the Shadow Call Stack whenever it is enabled. This reduces > > boot time by 30% for all KASAN modes when Shadow Call Stack is enabled. > > This is impressive. I was surprised too. > > We could integrate shadow stack trace collection into kernel/stacktrace.c > > as e.g. stack_trace_save_shadow(). However, using stack_trace_consume_fn > > leads to invoking a callback on each saved from, which is undesirable. > > The plain copy loop is faster. > > Why is stack_trace_consume_fn required? This is an internal detail of > arch_stack_walk(), but to implement stack_trace_save_shadow() that's > not used at all. > > I think having stack_trace_save_shadow() as you have implemented in > kernel/stacktrace.c or simply in kernel/scs.c itself would be > appropriate. The other stack trace routines consistently use on stack_trace_consume_fn. But I think you're right, we don't need it. Will do in v2. > > We could add a command line flag to switch between stack trace collection > > modes. I noticed that Shadow Call Stack might be missing certain frames > > in stacks originating from a fault that happens in the middle of a > > function. I am not sure if this case is important to handle though. > > I think SCS should just work - and if it doesn't, can we fix it? It is > unclear to me what would be a deciding factor to choose between stack > trace collection modes, since it is hard to quantify when and if SCS > doesn't work as intended. So I fear it'd just be an option that's > never used because we don't understand when it's required to be used. Let's just rely on SCS for now and reconsider in case any significant limitations are discovered. > > +#ifdef CONFIG_SHADOW_CALL_STACK > > + > > +#ifdef CONFIG_ARM64_PTR_AUTH > > +#define PAC_TAG_RESET(x) (x | GENMASK(63, CONFIG_ARM64_VA_BITS)) > > This should go into arch/arm64/include/asm/kasan.h, and here it should > then just do > > #ifndef PAC_TAG_RESET > #define ... > > > > +#else > > +#define PAC_TAG_RESET(x) (x) > > +#endif > > But perhaps there's a better, more generic location for this macro? Will move in v2. Thanks!