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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 ADA55C352A5 for ; Mon, 10 Feb 2020 17:19:23 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 143F220715 for ; Mon, 10 Feb 2020 17:19:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 143F220715 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-17751-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 25742 invoked by uid 550); 10 Feb 2020 17:19:16 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 25717 invoked from network); 10 Feb 2020 17:19:15 -0000 From: James Morse Subject: Re: [PATCH v7 09/11] arm64: disable SCS for hypervisor code To: Sami Tolvanen Cc: Will Deacon , Catalin Marinas , Steven Rostedt , Masami Hiramatsu , Ard Biesheuvel , Mark Rutland , 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 References: <20191018161033.261971-1-samitolvanen@google.com> <20200128184934.77625-1-samitolvanen@google.com> <20200128184934.77625-10-samitolvanen@google.com> Message-ID: <6f62b3c0-e796-e91c-f53b-23bd80fcb065@arm.com> Date: Mon, 10 Feb 2020 17:18:58 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200128184934.77625-10-samitolvanen@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Hi Sami, On 28/01/2020 18:49, Sami Tolvanen wrote: > Filter out CC_FLAGS_SCS and -ffixed-x18 for code that runs at a > different exception level. Hmmm, there are two things being disabled here. Stashing the lr in memory pointed to by VA won't work transparently at EL2 ... but shouldn't KVM's C code still treat x18 as a fixed register? As you have an __attribute__((no_sanitize("shadow-call-stack"))), could we add that to __hyp_text instead? (its a smaller hammer!) All of KVM's EL2 code is marked __hyp_text, but that isn't everything in these files. Doing it like this would leave KVM's VHE-only paths covered. As an example, with VHE the kernel and KVM both run at EL2, and KVM behaves differently: kvm_vcpu_put_sysregs() in kvm/hyp/sysreg-sr.c is called from a preempt notifier as the EL2 registers are always accessible. Thanks, James > diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile > index ea710f674cb6..5843adef9ef6 100644 > --- a/arch/arm64/kvm/hyp/Makefile > +++ b/arch/arm64/kvm/hyp/Makefile > @@ -28,3 +28,6 @@ GCOV_PROFILE := n > KASAN_SANITIZE := n > UBSAN_SANITIZE := n > KCOV_INSTRUMENT := n > + > +# remove the SCS flags from all objects in this directory > +KBUILD_CFLAGS := $(filter-out -ffixed-x18 $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))