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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 6349BC1975A for ; Wed, 25 Mar 2020 13:21:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4457A2077D for ; Wed, 25 Mar 2020 13:21:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727394AbgCYNVd (ORCPT ); Wed, 25 Mar 2020 09:21:33 -0400 Received: from foss.arm.com ([217.140.110.172]:48312 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727286AbgCYNVc (ORCPT ); Wed, 25 Mar 2020 09:21:32 -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 E442B31B; Wed, 25 Mar 2020 06:21:31 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E6D813F71F; Wed, 25 Mar 2020 06:21:29 -0700 (PDT) Date: Wed, 25 Mar 2020 13:21:27 +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: <20200325132127.GB12236@lakrids.cambridge.arm.com> References: <20200324203231.64324-1-keescook@chromium.org> <20200324203231.64324-6-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200324203231.64324-6-keescook@chromium.org> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Otherwise, this looks sound to me; I'd jsut like to know whether the overhead is in the same ballpark. Thanks Mark. > --- > arch/arm64/Kconfig | 1 + > arch/arm64/kernel/syscall.c | 10 ++++++++++ > 2 files changed, 11 insertions(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 0b30e884e088..4d5aa4959f72 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -127,6 +127,7 @@ config ARM64 > select HAVE_ARCH_MMAP_RND_BITS > select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT > select HAVE_ARCH_PREL32_RELOCATIONS > + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET > select HAVE_ARCH_SECCOMP_FILTER > select HAVE_ARCH_STACKLEAK > select HAVE_ARCH_THREAD_STRUCT_WHITELIST > diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c > index a12c0c88d345..238dbd753b44 100644 > --- a/arch/arm64/kernel/syscall.c > +++ b/arch/arm64/kernel/syscall.c > @@ -5,6 +5,7 @@ > #include > #include > #include > +#include > #include > > #include > @@ -42,6 +43,8 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, > { > long ret; > > + add_random_kstack_offset(); > + > if (scno < sc_nr) { > syscall_fn_t syscall_fn; > syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)]; > @@ -51,6 +54,13 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, > } > > regs->regs[0] = ret; > + > + /* > + * Since the compiler chooses a 4 bit alignment for the stack, > + * let's save one additional bit (9 total), which gets us up > + * near 5 bits of entropy. > + */ > + choose_random_kstack_offset(get_random_int() & 0x1FF); > } > > static inline bool has_syscall_work(unsigned long flags) > -- > 2.20.1 >