From patchwork Thu Feb 17 05:30:29 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Leonardo Bras X-Patchwork-Id: 12749378 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D51C6C433EF for ; Thu, 17 Feb 2022 05:31:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234294AbiBQFbf (ORCPT ); Thu, 17 Feb 2022 00:31:35 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:42484 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234231AbiBQFbe (ORCPT ); Thu, 17 Feb 2022 00:31:34 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 19B0C2A4158 for ; Wed, 16 Feb 2022 21:31:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645075879; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+S8NFXssddbsAeetjWyXbDGSuT3B6JkqWWn56zJM37k=; b=XMF/vt6ya7t3HVTRyWP3d181G/CGpEX4xHDkZMc/DgDYy5cWDauTTPd7jYQF5FX144NkJA KSUoVCX/eJylVYwTSJ79XDwGi/5j+Y/WkaeVLd8etA29TadrnnCTrlDpTqI9/SYNjKDuVH Thes7J/k9Xp3gKnPRxJLbJJCxjdBz7o= Received: from mail-ot1-f71.google.com (mail-ot1-f71.google.com [209.85.210.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-519-4W6xcaymOm6jF6rMEYy3Yw-1; Thu, 17 Feb 2022 00:31:17 -0500 X-MC-Unique: 4W6xcaymOm6jF6rMEYy3Yw-1 Received: by mail-ot1-f71.google.com with SMTP id n99-20020a9d206c000000b00590dde2cca8so2532543ota.9 for ; Wed, 16 Feb 2022 21:31:17 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=+S8NFXssddbsAeetjWyXbDGSuT3B6JkqWWn56zJM37k=; b=LYROUODoFdQBPT2zo1OcOJLdIKBIqeOF99ncgc6Yi4+AkUHZQL4UG1hOwmi3rLj2Xh fVhUEWOzVP+cRbZOXRbCeFltRMeVrj3WYkC+2o8hSLdGjRc39tjrEF6AYlhG/3PnOmke hicxMsfRN8BxZlkoF8GyoKKn3VwXWS5xT2P8OE9PKzwsO3fcQjX0ByVNNA80KcIdGIig uUxJG0cQo9wMhmxC4hTkkk3BQ14dLmcR+hN01Ekr2PjgjFaOLH3TfxL2J40IMfpdADGy 7DMZCvXIKGK8N1knvdvLkeGe6z3WaaIv0Nem2EKIL8VE36DZK2EcL+sAm6CWh9NDKUOw A7ag== X-Gm-Message-State: AOAM530lXZh3shXaeGXcoEb+mBXx4RQ4JmRyNRJvcWl7oioBEWNYKmTb qw5eS51CotzpvhWQzbDCyetd729a9aWXs4f5Li3fpzX0B4wuA6nIrylRqhb69cAHyB4HDTm0xSr mv46cEC2Z9YcT X-Received: by 2002:a05:6808:2208:b0:2d3:5181:44a7 with SMTP id bd8-20020a056808220800b002d3518144a7mr2049004oib.201.1645075877047; Wed, 16 Feb 2022 21:31:17 -0800 (PST) X-Google-Smtp-Source: ABdhPJypATkApCAZFKg7P+NajSA5dJuQsvGJ0jKhojrg7tL8lVsKiiizKsfuEgaVzuav2Mw5l075hg== X-Received: by 2002:a05:6808:2208:b0:2d3:5181:44a7 with SMTP id bd8-20020a056808220800b002d3518144a7mr2048996oib.201.1645075876797; Wed, 16 Feb 2022 21:31:16 -0800 (PST) Received: from LeoBras.redhat.com ([2804:431:c7f1:c12c:38a3:24a6:f679:3afd]) by smtp.gmail.com with ESMTPSA id cm18sm8571688oab.7.2022.02.16.21.31.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Feb 2022 21:31:15 -0800 (PST) From: Leonardo Bras To: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , "Chang S. Bae" , Andy Lutomirski , David Gilbert , Peter Xu Cc: Leonardo Bras , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 1/2] x86/kvm/fpu: Mask guest fpstate->xfeatures with guest_supported_xcr0 Date: Thu, 17 Feb 2022 02:30:29 -0300 Message-Id: <20220217053028.96432-2-leobras@redhat.com> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220217053028.96432-1-leobras@redhat.com> References: <20220217053028.96432-1-leobras@redhat.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org During host/guest switch (like in kvm_arch_vcpu_ioctl_run()), the kernel swaps the fpu between host/guest contexts, by using fpu_swap_kvm_fpstate(). When xsave feature is available, the fpu swap is done by: - xsave(s) instruction, with guest's fpstate->xfeatures as mask, is used to store the current state of the fpu registers to a buffer. - xrstor(s) instruction, with (fpu_kernel_cfg.max_features & XFEATURE_MASK_FPSTATE) as mask, is used to put the buffer into fpu regs. For xsave(s) the mask is used to limit what parts of the fpu regs will be copied to the buffer. Likewise on xrstor(s), the mask is used to limit what parts of the fpu regs will be changed. The mask for xsave(s), the guest's fpstate->xfeatures, is defined on kvm_arch_vcpu_create(), which (in summary) sets it to all features supported by the cpu which are enabled on kernel config. This means that xsave(s) will save to guest buffer all the fpu regs contents the cpu has enabled when the guest is paused, even if they are not used. This would not be an issue, if xrstor(s) would also do that. xrstor(s)'s mask for host/guest swap is basically every valid feature contained in kernel config, except XFEATURE_MASK_PKRU. Accordingto kernel src, it is instead switched in switch_to() and flush_thread(). Then, the following happens with a host supporting PKRU starts a guest that does not support it: 1 - Host has XFEATURE_MASK_PKRU set. 1st switch to guest, 2 - xsave(s) fpu regs to host fpustate (buffer has XFEATURE_MASK_PKRU) 3 - xrstor(s) guest fpustate to fpu regs (fpu regs have XFEATURE_MASK_PKRU) 4 - guest runs, then switch back to host, 5 - xsave(s) fpu regs to guest fpstate (buffer now have XFEATURE_MASK_PKRU) 6 - xrstor(s) host fpstate to fpu regs. 7 - kvm_vcpu_ioctl_x86_get_xsave() copy guest fpstate to userspace (with XFEATURE_MASK_PKRU, which should not be supported by guest vcpu) On 5, even though the guest does not support PKRU, it does have the flag set on guest fpstate, which is transferred to userspace via vcpu ioctl KVM_GET_XSAVE. This becomes a problem when the user decides on migrating the above guest to another machine that does not support PKRU: The new host restores guest's fpu regs to as they were before (xrstor(s)), but since the new host don't support PKRU, a general-protection exception ocurs in xrstor(s) and that crashes the guest. This can be solved by making the guest's fpstate->user_xfeatures hold a copy of guest_supported_xcr0. This way, on 7 the only flags copied to userspace will be the ones compatible to guest requirements, and thus there will be no issue during migration. As a bonus, it will also fail if userspace tries to set fpu features that are not compatible to the guest configuration. (KVM_SET_XSAVE ioctl) Also, since kvm_vcpu_after_set_cpuid() now sets fpstate->user_xfeatures, there is not need to set it in kvm_check_cpuid(). So, change fpstate_realloc() so it does not touch fpstate->user_xfeatures if a non-NULL guest_fpu is passed, which is the case when kvm_check_cpuid() calls it. Signed-off-by: Leonardo Bras --- arch/x86/kernel/fpu/xstate.c | 5 ++++- arch/x86/kvm/cpuid.c | 2 ++ 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 02b3ddaf4f75..7c7824ae7862 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -1558,7 +1558,10 @@ static int fpstate_realloc(u64 xfeatures, unsigned int ksize, fpregs_restore_userregs(); newfps->xfeatures = curfps->xfeatures | xfeatures; - newfps->user_xfeatures = curfps->user_xfeatures | xfeatures; + + if (!guest_fpu) + newfps->user_xfeatures = curfps->user_xfeatures | xfeatures; + newfps->xfd = curfps->xfd & ~xfeatures; /* Do the final updates within the locked region */ diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 494d4d351859..71125291c578 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -296,6 +296,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) vcpu->arch.guest_supported_xcr0 = cpuid_get_supported_xcr0(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent); + vcpu->arch.guest_fpu.fpstate->user_xfeatures = vcpu->arch.guest_supported_xcr0; + kvm_update_pv_runtime(vcpu); vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);