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=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 4E94BC2D0E8 for ; Thu, 26 Mar 2020 11:15:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0F3BA2073E for ; Thu, 26 Mar 2020 11:15:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F3BA2073E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A18766B0078; Thu, 26 Mar 2020 07:15:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9C9246B007B; Thu, 26 Mar 2020 07:15:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8DECD6B007D; Thu, 26 Mar 2020 07:15:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0200.hostedemail.com [216.40.44.200]) by kanga.kvack.org (Postfix) with ESMTP id 77DB56B0078 for ; Thu, 26 Mar 2020 07:15:41 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 5F9A48248047 for ; Thu, 26 Mar 2020 11:15:41 +0000 (UTC) X-FDA: 76637258082.16.crown07_319e7c95ea32c X-HE-Tag: crown07_319e7c95ea32c X-Filterd-Recvd-Size: 3479 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Thu, 26 Mar 2020 11:15:40 +0000 (UTC) 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 CD1087FA; Thu, 26 Mar 2020 04:15:39 -0700 (PDT) Received: from C02TD0UTHF1T.local (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 531823F71F; Thu, 26 Mar 2020 04:15:36 -0700 (PDT) Date: Thu, 26 Mar 2020 11:15:21 +0000 From: Mark Rutland To: Kees Cook Cc: Thomas Gleixner , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Alexander Potapenko , Ard Biesheuvel , Jann Horn , "Perla, Enrico" , kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 5/5] arm64: entry: Enable random_kstack_offset support Message-ID: <20200326111521.GA72909@C02TD0UTHF1T.local> References: <20200324203231.64324-1-keescook@chromium.org> <20200324203231.64324-6-keescook@chromium.org> <20200325132127.GB12236@lakrids.cambridge.arm.com> <202003251319.AECA788D63@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202003251319.AECA788D63@keescook> 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 Wed, Mar 25, 2020 at 01:22:07PM -0700, Kees Cook wrote: > On Wed, Mar 25, 2020 at 01:21:27PM +0000, Mark Rutland wrote: > > On Tue, Mar 24, 2020 at 01:32:31PM -0700, Kees Cook wrote: > > > Allow for a randomized stack offset on a per-syscall basis, with roughly > > > 5 bits of entropy. > > > > > > Signed-off-by: Kees Cook > > > > Just to check, do you have an idea of the impact on arm64? Patch 3 had > > figures for x86 where it reads the TSC, and it's unclear to me how > > get_random_int() compares to that. > > I didn't do a measurement on arm64 since I don't have a good bare-metal > test environment. I know Andy Lutomirki has plans for making > get_random_get() as fast as possible, so that's why I used it here. Ok. I suspect I also won't get the chance to test that in the next few days, but if I do I'll try to share the results. My concern here was that, get_random_int() has to grab a spinlock and mess with IRQ masking, so has the potential to block for much longer, but that might not be an issue in practice, and I don't think that should block these patches. > I couldn't figure out if there was a comparable instruction like rdtsc > in aarch64 (it seems there's a cycle counter, but I found nothing in > the kernel that seemed to actually use it)? AArch64 doesn't have a direct equivalent. The generic counter (CNTxCT_EL0) is the closest thing, but its nominal frequency is typically much lower than the nominal CPU clock frequency (unlike TSC where they're the same). The cycle counter (PMCCNTR_EL0) is part of the PMU, and can't be relied on in the same way (e.g. as perf reprograms it to generate overflow events, and it can stop for things like WFI/WFE). Thanks, Mark.