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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 86083C35254 for ; Mon, 10 Feb 2020 17:52:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5E30420842 for ; Mon, 10 Feb 2020 17:52:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581357144; bh=w4QaI4rwl8xDK0pPvWLaHd5U0Rdh0Tn4UR8oOFoh5Pg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=fJHj1UMxg0smQsl+CWFr+p3323Wx0dL+M9ABDcv5/+iqa22NzOcX4uBsKr03jF5Pw 465MdWZdeF5a6T174QUibwBVjdxlDE+T+8zVlzWNsiLojDLycfoGY/J3ttX/x3DHlT 0SCdWsDdE95thb8oNCi+L0WAVFhxLHX7QRFIRaU8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726563AbgBJRwX (ORCPT ); Mon, 10 Feb 2020 12:52:23 -0500 Received: from mail.kernel.org ([198.145.29.99]:37690 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726961AbgBJRwX (ORCPT ); Mon, 10 Feb 2020 12:52:23 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1B5BB20715; Mon, 10 Feb 2020 17:52:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581357142; bh=w4QaI4rwl8xDK0pPvWLaHd5U0Rdh0Tn4UR8oOFoh5Pg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SwvUPgIlRB37NIGfkknNFZdWlQ7zdhhxoI9oOpxIjAVtbw5kEW46Z3Xua3ED9FVVz Qe5ek2fpczwxrW3E2Q2bxRjmv2GVXM5HzJ/+ZCQ75nikohMXSsDTxFneXJ9W328+oF NUm3yhGlentzJM3zl1Cd+UZ7gCE75VqB9vrOyToY= Date: Mon, 10 Feb 2020 17:52:15 +0000 From: Will Deacon To: James Morse Cc: Sami Tolvanen , 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 Subject: Re: [PATCH v7 09/11] arm64: disable SCS for hypervisor code Message-ID: <20200210175214.GA23318@willie-the-truck> References: <20191018161033.261971-1-samitolvanen@google.com> <20200128184934.77625-1-samitolvanen@google.com> <20200128184934.77625-10-samitolvanen@google.com> <6f62b3c0-e796-e91c-f53b-23bd80fcb065@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6f62b3c0-e796-e91c-f53b-23bd80fcb065@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 10, 2020 at 05:18:58PM +0000, James Morse wrote: > 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? My review of v6 suggested dropping the -ffixed-x18 as well, since it's only introduced by SCS (in patch 5) and so isn't required by anything else. Why do you think it's needed? > 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. That's a good point, and I agree that it would be nice to have SCS covering the VHE paths. If you do that as a function attribute (which feels pretty fragile to me), then I guess we'll have to keep the -ffixed-x18 for the non-VHE code after all because GCC at least doesn't like having the register saving ABI specified on a per-function basis. Will 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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A0B4AC35254 for ; Mon, 10 Feb 2020 17:52:27 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 769AC2080C for ; Mon, 10 Feb 2020 17:52:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="PACS18Zx"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="SwvUPgIl" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 769AC2080C Authentication-Results: mail.kernel.org; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Feb 10, 2020 at 05:18:58PM +0000, James Morse wrote: > 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? My review of v6 suggested dropping the -ffixed-x18 as well, since it's only introduced by SCS (in patch 5) and so isn't required by anything else. Why do you think it's needed? > 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. That's a good point, and I agree that it would be nice to have SCS covering the VHE paths. If you do that as a function attribute (which feels pretty fragile to me), then I guess we'll have to keep the -ffixed-x18 for the non-VHE code after all because GCC at least doesn't like having the register saving ABI specified on a per-function basis. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel