From patchwork Thu Sep 28 00:19:51 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 727485 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 C122BE7F14F for ; Thu, 28 Sep 2023 00:20:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229493AbjI1AUC (ORCPT ); Wed, 27 Sep 2023 20:20:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34072 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229437AbjI1AUB (ORCPT ); Wed, 27 Sep 2023 20:20:01 -0400 Received: from mail-pl1-x64a.google.com (mail-pl1-x64a.google.com [IPv6:2607:f8b0:4864:20::64a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F2F87BF for ; Wed, 27 Sep 2023 17:19:59 -0700 (PDT) Received: by mail-pl1-x64a.google.com with SMTP id d9443c01a7336-1c6147ea811so87672985ad.2 for ; Wed, 27 Sep 2023 17:19:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1695860399; x=1696465199; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:reply-to:from:to:cc :subject:date:message-id:reply-to; bh=JIhlczPTAFSXJtuz0kr4uNehhoedtrBaBEaYSQ3/D3w=; b=mdqi3CV6ogd+sLjUE0adY1tjTK8dTH8aEdvxS0QxhkeHAFu0CEAbbBC4MFijtqP1Ly sjZTGe4VhUUb/M9MK4TbEOatIHvLNoIhsPHiP350mptcWfo4FF6STM6mL/vMFyLsSZyT X7mnnqlnhUEEmmE4L+2M7AdtXBciHMTjvxlqNP2WFYUccCbdj2AnNTB2KQ+x1ujJZcnr njQZL90vUj2nrWJOTZk4TWrwQ3bo5KBupnlCZ83mzkdvD6qdy+qZcubw71mooKyD+WTp KimIF/iFxfNWmiysn9zEBCwU46D+J9XKcW+HSFh4ADA1egulhRU8BSKJv9NvKUv5n9Gu T7hA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695860399; x=1696465199; h=cc:to:from:subject:message-id:mime-version:date:reply-to :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=JIhlczPTAFSXJtuz0kr4uNehhoedtrBaBEaYSQ3/D3w=; b=ZvZ1gXFfWRIb4RPnRDfuJh8x1V3YAo1jDV19PGfaq4LA6m7FgGqoM9HLzByXqHHsoL D/whyZ4SRywW3LnYBCMmgck7Jwdiuc7zTYAHHsECZ+DAvPcGBPQkZ0tPuorCVtpbyWTI mss/CoOpfnxJK/xzPdh9TwBdbpUY+9J1zKDnuNAgt2i896pqShP09xN8JHqI/IE0y0Q/ rx74SFi8/ieOtk4a8qe79/Tema8uF+GDw/w8DAHCsOeDEJcytFdMys9WiQrLBqyVHakf kcVrgjUgX9rALgOJM/Ix0wkZ4bzwvVJL5Ae5UTBji1+iCZq3uJ/6rHOYYeSbCzIwh/+D Wkng== X-Gm-Message-State: AOJu0YzXFnFVfETMK4WS9h6+AkiB1TV39Jl7sCMIvUN3UXK/7fUuxEoo 0vUqRihlMLSSAw9qjuJACOxa+XSjLdM= X-Google-Smtp-Source: AGHT+IGCbuN35ynl7FnkIb26JwfUSQivcI5ht12Lhq63ANf0P98cgnGB/yAMFxzlpCJU6VRv0zB+soGU8eE= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:903:604:b0:1c0:d418:8806 with SMTP id kg4-20020a170903060400b001c0d4188806mr44172plb.12.1695860399477; Wed, 27 Sep 2023 17:19:59 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 27 Sep 2023 17:19:51 -0700 Mime-Version: 1.0 X-Mailer: git-send-email 2.42.0.582.g8ccd20d70d-goog Message-ID: <20230928001956.924301-1-seanjc@google.com> Subject: [PATCH 0/5] KVM: x86: Fix breakage in KVM_SET_XSAVE's ABI From: Sean Christopherson To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Sean Christopherson , Paolo Bonzini , Shuah Khan , Nathan Chancellor , Nick Desaulniers Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, llvm@lists.linux.dev, Tyler Stachecki , Leonardo Bras Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Rework how KVM limits guest-unsupported xfeatures to effectively hide only when saving state for userspace (KVM_GET_XSAVE), i.e. to let userspace load all host-supported xfeatures (via KVM_SET_XSAVE) irrespective of what features have been exposed to the guest. The effect on KVM_SET_XSAVE was knowingly done by commit ad856280ddea ("x86/kvm/fpu: Limit guest user_xfeatures to supported bits of XCR0"): As a bonus, it will also fail if userspace tries to set fpu features (with the KVM_SET_XSAVE ioctl) that are not compatible to the guest configuration. Such features will never be returned by KVM_GET_XSAVE or KVM_GET_XSAVE2. Peventing userspace from doing stupid things is usually a good idea, but in this case restricting KVM_SET_XSAVE actually exacerbated the problem that commit ad856280ddea was fixing. As reported by Tyler, rejecting KVM_SET_XSAVE for guest-unsupported xfeatures breaks live migration from a kernel without commit ad856280ddea, to a kernel with ad856280ddea. I.e. from a kernel that saves guest-unsupported xfeatures to a kernel that doesn't allow loading guest-unuspported xfeatures. To make matters even worse, QEMU doesn't terminate if KVM_SET_XSAVE fails, and so the end result is that the live migration results (possibly silent) guest data corruption instead of a failed migration. Patch 1 refactors the FPU code to let KVM pass in a mask of which xfeatures to save, patch 2 fixes KVM by passing in guest_supported_xcr0 instead of modifying user_xfeatures directly. Patches 3-5 are regression tests. I have no objection if anyone wants patches 1 and 2 squashed together, I split them purely to make review easier. Note, this doesn't fix the scenario where a guest is migrated from a "bad" to a "good" kernel and the target host doesn't support the over-saved set of xfeatures. I don't see a way to safely handle that in the kernel without an opt-in, which more or less defeats the purpose of handling it in KVM. Sean Christopherson (5): x86/fpu: Allow caller to constrain xfeatures when copying to uabi buffer KVM: x86: Constrain guest-supported xfeatures only at KVM_GET_XSAVE{2} KVM: selftests: Touch relevant XSAVE state in guest for state test KVM: selftests: Load XSAVE state into untouched vCPU during state test KVM: selftests: Force load all supported XSAVE state in state test arch/x86/include/asm/fpu/api.h | 3 +- arch/x86/kernel/fpu/core.c | 5 +- arch/x86/kernel/fpu/xstate.c | 12 +- arch/x86/kernel/fpu/xstate.h | 3 +- arch/x86/kvm/cpuid.c | 8 -- arch/x86/kvm/x86.c | 37 +++--- .../selftests/kvm/include/x86_64/processor.h | 23 ++++ .../testing/selftests/kvm/x86_64/state_test.c | 110 +++++++++++++++++- 8 files changed, 168 insertions(+), 33 deletions(-) base-commit: 5804c19b80bf625c6a9925317f845e497434d6d3