From patchwork Fri Jun 19 14:30:38 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 223769 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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT 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 20A05C433E1 for ; Fri, 19 Jun 2020 16:28:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 009CA217A0 for ; Fri, 19 Jun 2020 16:28:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592584094; bh=We1j8t3ry/5aeI/mTNzvMj2rnXXr23+3mHuJif/Bsew=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=IHZEHa47DF36VcF6GYgQS3QKJNMd9pfyx5+MU5791CgCIRwn6n7sl/mQi5Iul7oXJ ZwXYPhD8D5HfKVIoNW3RUD6G6HwxaBwnVAHDSSMmrXq4N1pb/QkirLvSFroXFJH6oC o48kwcuc/3c3vF3sJbJ1g8WwenkzkrnvXpI9CHNA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394798AbgFSQ1r (ORCPT ); Fri, 19 Jun 2020 12:27:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:50546 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389989AbgFSOzj (ORCPT ); Fri, 19 Jun 2020 10:55:39 -0400 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 7F0E62158C; Fri, 19 Jun 2020 14:55:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592578539; bh=We1j8t3ry/5aeI/mTNzvMj2rnXXr23+3mHuJif/Bsew=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=U27KDNV+7peOZ98HU11ZDyrouwFEjGxvnDdZCGD3iTWheCxmBw3mVeOIXs4Hm5TUu 3VKQhQMcqVe1nO/CxmVBECEROy5ys7ugKrtN6+zPdp3s2+PCBDGZe9PG+yfEi2FExY 7Qo7OTH8sA0srfq4xn0u3oylnXtfBDlXapuLzIwY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Paolo Bonzini , Sasha Levin Subject: [PATCH 4.19 053/267] KVM: x86: only do L1TF workaround on affected processors Date: Fri, 19 Jun 2020 16:30:38 +0200 Message-Id: <20200619141651.428799275@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200619141648.840376470@linuxfoundation.org> References: <20200619141648.840376470@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Paolo Bonzini [ Upstream commit d43e2675e96fc6ae1a633b6a69d296394448cc32 ] KVM stores the gfn in MMIO SPTEs as a caching optimization. These are split in two parts, as in "[high 11111 low]", to thwart any attempt to use these bits in an L1TF attack. This works as long as there are 5 free bits between MAXPHYADDR and bit 50 (inclusive), leaving bit 51 free so that the MMIO access triggers a reserved-bit-set page fault. The bit positions however were computed wrongly for AMD processors that have encryption support. In this case, x86_phys_bits is reduced (for example from 48 to 43, to account for the C bit at position 47 and four bits used internally to store the SEV ASID and other stuff) while x86_cache_bits in would remain set to 48, and _all_ bits between the reduced MAXPHYADDR and bit 51 are set. Then low_phys_bits would also cover some of the bits that are set in the shadow_mmio_value, terribly confusing the gfn caching mechanism. To fix this, avoid splitting gfns as long as the processor does not have the L1TF bug (which includes all AMD processors). When there is no splitting, low_phys_bits can be set to the reduced MAXPHYADDR removing the overlap. This fixes "npt=0" operation on EPYC processors. Thanks to Maxim Levitsky for bisecting this bug. Cc: stable@vger.kernel.org Fixes: 52918ed5fcf0 ("KVM: SVM: Override default MMIO mask if memory encryption is enabled") Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin --- arch/x86/kvm/mmu.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index ac0a794267d4..18632f15b29f 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -294,6 +294,8 @@ kvm_mmu_calc_root_page_role(struct kvm_vcpu *vcpu); void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask, u64 mmio_value) { BUG_ON((mmio_mask & mmio_value) != mmio_value); + WARN_ON(mmio_value & (shadow_nonpresent_or_rsvd_mask << shadow_nonpresent_or_rsvd_mask_len)); + WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask); shadow_mmio_value = mmio_value | SPTE_SPECIAL_MASK; shadow_mmio_mask = mmio_mask | SPTE_SPECIAL_MASK; } @@ -486,16 +488,15 @@ static void kvm_mmu_reset_all_pte_masks(void) * the most significant bits of legal physical address space. */ shadow_nonpresent_or_rsvd_mask = 0; - low_phys_bits = boot_cpu_data.x86_cache_bits; - if (boot_cpu_data.x86_cache_bits < - 52 - shadow_nonpresent_or_rsvd_mask_len) { + low_phys_bits = boot_cpu_data.x86_phys_bits; + if (boot_cpu_has_bug(X86_BUG_L1TF) && + !WARN_ON_ONCE(boot_cpu_data.x86_cache_bits >= + 52 - shadow_nonpresent_or_rsvd_mask_len)) { + low_phys_bits = boot_cpu_data.x86_cache_bits + - shadow_nonpresent_or_rsvd_mask_len; shadow_nonpresent_or_rsvd_mask = - rsvd_bits(boot_cpu_data.x86_cache_bits - - shadow_nonpresent_or_rsvd_mask_len, - boot_cpu_data.x86_cache_bits - 1); - low_phys_bits -= shadow_nonpresent_or_rsvd_mask_len; - } else - WARN_ON_ONCE(boot_cpu_has_bug(X86_BUG_L1TF)); + rsvd_bits(low_phys_bits, boot_cpu_data.x86_cache_bits - 1); + } shadow_nonpresent_or_rsvd_lower_gfn_mask = GENMASK_ULL(low_phys_bits - 1, PAGE_SHIFT);