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, 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 02380CA9EB5 for ; Mon, 4 Nov 2019 17:05:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C80542080F for ; Mon, 4 Nov 2019 17:05:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728641AbfKDRFD (ORCPT ); Mon, 4 Nov 2019 12:05:03 -0500 Received: from foss.arm.com ([217.140.110.172]:47476 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727861AbfKDRFD (ORCPT ); Mon, 4 Nov 2019 12:05:03 -0500 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 9992D1F1; Mon, 4 Nov 2019 09:05:02 -0800 (PST) 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 605073F71A; Mon, 4 Nov 2019 09:05:00 -0800 (PST) Date: Mon, 4 Nov 2019 17:04:54 +0000 From: Mark Rutland To: Sami Tolvanen Cc: Will Deacon , Catalin Marinas , Steven Rostedt , Masami Hiramatsu , Ard Biesheuvel , Dave Martin , Kees Cook , Laura Abbott , Marc Zyngier , Nick Desaulniers , Jann Horn , Miguel Ojeda , Masahiro Yamada , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 10/17] arm64: disable kretprobes with SCS Message-ID: <20191104170454.GA2024@lakrids.cambridge.arm.com> References: <20191018161033.261971-1-samitolvanen@google.com> <20191101221150.116536-1-samitolvanen@google.com> <20191101221150.116536-11-samitolvanen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191101221150.116536-11-samitolvanen@google.com> 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 Fri, Nov 01, 2019 at 03:11:43PM -0700, Sami Tolvanen wrote: > With CONFIG_KRETPROBES, function return addresses are modified to > redirect control flow to kretprobe_trampoline. This is incompatible > with SCS. I'm a bit confused as to why that's the case -- could you please elaborate on how this is incompatible? IIUC kretrobes works by patching the function entry point with a BRK, so that it can modify the LR _before_ it is saved to the stack. I don't see how SCS affects that. When the instrumented function returns, it'll balance its SCS state, then "return" to kretprobe_trampoline. Since kretprobe_trampoline is plain assembly, it doesn't have SCS, and can modify the LR live, as it does. So functionally, that appears to work. What am I missing? Thanks, Mark. > Signed-off-by: Sami Tolvanen > Reviewed-by: Kees Cook > --- > arch/arm64/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 3f047afb982c..e7b57a8a5531 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -165,7 +165,7 @@ config ARM64 > select HAVE_STACKPROTECTOR > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES > - select HAVE_KRETPROBES > + select HAVE_KRETPROBES if !SHADOW_CALL_STACK > select HAVE_GENERIC_VDSO > select IOMMU_DMA if IOMMU_SUPPORT > select IRQ_DOMAIN > -- > 2.24.0.rc1.363.gb1bccd3e3d-goog >