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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 E3462C432C0 for ; Wed, 27 Nov 2019 21:15:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BA63F21771 for ; Wed, 27 Nov 2019 21:15:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574889305; bh=Qug6qxWGhuCnicRV9ATP+BqsY36CKwoLh8gU2NsBJp8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=yBB3XD5FP8BTuDZZ1qlyZ6GZeruq12KQhB09jV/fE7CHwpkr50LWj6lFwkzynWRlB xRwmQialxGqb39sJDBFy7MwS7UUPF0lxCl6Xg3kNjShY7TrplVWi/hKG6AblrcIBuO lXGdyRzNWIB6nH81jpTIrtU7UCYiJrlLFf1RQd7E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387637AbfK0VPE (ORCPT ); Wed, 27 Nov 2019 16:15:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:49770 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387628AbfK0VPB (ORCPT ); Wed, 27 Nov 2019 16:15:01 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 CE8E921771; Wed, 27 Nov 2019 21:14:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574889300; bh=Qug6qxWGhuCnicRV9ATP+BqsY36CKwoLh8gU2NsBJp8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=y7jyq2f9/pgN18C7RrvTGZfAuwizE7WeL1q4H7B43GM4x48OEjqOveW9Hy94M80uT qvrP4OJqvUTB+z5u6ZEwL45OZMw1pNmcadcmaFnL0CoNU5peiHMTFMmESPUvTcciNg 1Z1Wpc/1TYQtlOQoNNPsxuNgmbOfcpodPSfw7N6M= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Michael Ellerman Subject: [PATCH 5.4 66/66] KVM: PPC: Book3S HV: Flush link stack on guest exit to host kernel Date: Wed, 27 Nov 2019 21:33:01 +0100 Message-Id: <20191127202840.697822651@linuxfoundation.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191127202632.536277063@linuxfoundation.org> References: <20191127202632.536277063@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Michael Ellerman commit af2e8c68b9c5403f77096969c516f742f5bb29e0 upstream. On some systems that are vulnerable to Spectre v2, it is up to software to flush the link stack (return address stack), in order to protect against Spectre-RSB. When exiting from a guest we do some house keeping and then potentially exit to C code which is several stack frames deep in the host kernel. We will then execute a series of returns without preceeding calls, opening up the possiblity that the guest could have poisoned the link stack, and direct speculative execution of the host to a gadget of some sort. To prevent this we add a flush of the link stack on exit from a guest. Signed-off-by: Michael Ellerman Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/include/asm/asm-prototypes.h | 2 ++ arch/powerpc/kernel/security.c | 9 +++++++++ arch/powerpc/kvm/book3s_hv_rmhandlers.S | 30 ++++++++++++++++++++++++++++++ 3 files changed, 41 insertions(+) --- a/arch/powerpc/include/asm/asm-prototypes.h +++ b/arch/powerpc/include/asm/asm-prototypes.h @@ -153,9 +153,11 @@ void _kvmppc_save_tm_pr(struct kvm_vcpu extern s32 patch__call_flush_count_cache; extern s32 patch__flush_count_cache_return; extern s32 patch__flush_link_stack_return; +extern s32 patch__call_kvm_flush_link_stack; extern s32 patch__memset_nocache, patch__memcpy_nocache; extern long flush_count_cache; +extern long kvm_flush_link_stack; #ifdef CONFIG_PPC_TRANSACTIONAL_MEM void kvmppc_save_tm_hv(struct kvm_vcpu *vcpu, u64 msr, bool preserve_nv); --- a/arch/powerpc/kernel/security.c +++ b/arch/powerpc/kernel/security.c @@ -400,6 +400,9 @@ static void toggle_count_cache_flush(boo if (!enable) { patch_instruction_site(&patch__call_flush_count_cache, PPC_INST_NOP); +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE + patch_instruction_site(&patch__call_kvm_flush_link_stack, PPC_INST_NOP); +#endif pr_info("link-stack-flush: software flush disabled.\n"); link_stack_flush_enabled = false; no_count_cache_flush(); @@ -410,6 +413,12 @@ static void toggle_count_cache_flush(boo patch_branch_site(&patch__call_flush_count_cache, (u64)&flush_count_cache, BRANCH_SET_LINK); +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE + // This enables the branch from guest_exit_cont to kvm_flush_link_stack + patch_branch_site(&patch__call_kvm_flush_link_stack, + (u64)&kvm_flush_link_stack, BRANCH_SET_LINK); +#endif + pr_info("link-stack-flush: software flush enabled.\n"); link_stack_flush_enabled = true; --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S @@ -11,6 +11,7 @@ */ #include +#include #include #include #include @@ -1487,6 +1488,13 @@ guest_exit_cont: /* r9 = vcpu, r12 = tr 1: #endif /* CONFIG_KVM_XICS */ + /* + * Possibly flush the link stack here, before we do a blr in + * guest_exit_short_path. + */ +1: nop + patch_site 1b patch__call_kvm_flush_link_stack + /* If we came in through the P9 short path, go back out to C now */ lwz r0, STACK_SLOT_SHORT_PATH(r1) cmpwi r0, 0 @@ -1963,6 +1971,28 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300) mtlr r0 blr +.balign 32 +.global kvm_flush_link_stack +kvm_flush_link_stack: + /* Save LR into r0 */ + mflr r0 + + /* Flush the link stack. On Power8 it's up to 32 entries in size. */ + .rept 32 + bl .+4 + .endr + + /* And on Power9 it's up to 64. */ +BEGIN_FTR_SECTION + .rept 32 + bl .+4 + .endr +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300) + + /* Restore LR */ + mtlr r0 + blr + kvmppc_guest_external: /* External interrupt, first check for host_ipi. If this is * set, we know the host wants us out so let's do it now