From patchwork Thu Sep 16 18:15:34 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Oliver Upton X-Patchwork-Id: 12500027 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=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 D9BE6C433F5 for ; Thu, 16 Sep 2021 18:56:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C649060E52 for ; Thu, 16 Sep 2021 18:56:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344712AbhIPS55 (ORCPT ); Thu, 16 Sep 2021 14:57:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51652 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245110AbhIPS5a (ORCPT ); Thu, 16 Sep 2021 14:57:30 -0400 Received: from mail-oo1-xc49.google.com (mail-oo1-xc49.google.com [IPv6:2607:f8b0:4864:20::c49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C1854C04A157 for ; Thu, 16 Sep 2021 11:15:45 -0700 (PDT) Received: by mail-oo1-xc49.google.com with SMTP id e17-20020a056820061100b002910b1828a0so34384119oow.16 for ; Thu, 16 Sep 2021 11:15:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=/xw1HPEE3yg6hDZiSRSN4mqpJW+LQ6wXxySnmKRFyJ8=; b=aeIy+Fj9Ddx5QaJjlHoSsG2pqbF8w2bOPA1NUF6/sz/meu/pc2y7XH5Frw9KOhU9jX /kH/TSaeEzKpU3E9F4mu2P4UwMb8CA8hVkOuGgpkMxluodvQx0JB40MGxrC/28jBzSpS tOcue5Y0S/zW65/M/S+fci0vMm5hJ5aXdp3cKtcIkEKR27UTz5eqwFNzBMVkFzM01TOD rlmCukD6+Sq5NdvlmiFK9SoTsk9V7CF9hxsEpXwf31yhlcLh4USsTGsziVGOqmjspN8o 0Ky6X+cH1ZOM4CgbuHJIjBmRAlEsdJzbNTWMO+pHL8eK5LJOZ0KcX4fxKffaaQujOn7V WyoQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=/xw1HPEE3yg6hDZiSRSN4mqpJW+LQ6wXxySnmKRFyJ8=; b=uie8DFHgysaFaBZtacoOObCeASNNw+M6I4+cWgOqSu7ve7EucI4yn/7M/xhPgHauxG KnmA/oIj4FAoHYbJjIy/J6KttA8WStPLVL0B15KXlSYihMotCscNIPPPHlmJZZKU1S4/ UmFynFfBeDyHAq71083WC5HN1BgIfIXKeXfRsM3KiiwBcuQfoawGNcHzQIeEWPvLGhbB ZMkodpf5LILHVTrzyE4zEFjK6/z8qwhnGGMOZl2gxxGlV3D1pt1IyAs29JQFbUP38YTV gXuq1oKi+6UPQrCUteq9DsB+RaekmpZa0RSSEQPKpAtdb327hNRFCZLHxM3m19s9Oxsh ajyg== X-Gm-Message-State: AOAM531/rrlpX+YoXYLvr5Uh55qGiaO41gedVe1RWmwZ3SS8SV3QcUIQ qnEboZJ3SDB+21mzMz+Ne21wI3jAzYgwmfe2GUmRAdj9/iSsOYOID7dkPPUrGheHexN2Cr1uZN6 eGtghMWzkHBZ0UQG7/wWclvXGxATYBs5PGbGcA0XAdbQFhmj8Y0rkA9+/2Q== X-Google-Smtp-Source: ABdhPJwhSdiutQtzePdJzjaNwKrgENSZ7USY45/SDq1qTsydz5Pm4qLqm2IgqkpSSQFsIfTfuENKHUrRnnM= X-Received: from oupton.c.googlers.com ([fda3:e722:ac3:cc00:2b:ff92:c0a8:404]) (user=oupton job=sendgmr) by 2002:a9d:7f07:: with SMTP id j7mr5952745otq.84.1631816144992; Thu, 16 Sep 2021 11:15:44 -0700 (PDT) Date: Thu, 16 Sep 2021 18:15:34 +0000 In-Reply-To: <20210916181538.968978-1-oupton@google.com> Message-Id: <20210916181538.968978-4-oupton@google.com> Mime-Version: 1.0 References: <20210916181538.968978-1-oupton@google.com> X-Mailer: git-send-email 2.33.0.464.g1972c5931b-goog Subject: [PATCH v8 3/7] KVM: x86: Fix potential race in KVM_GET_CLOCK From: Oliver Upton To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu Cc: Paolo Bonzini , Sean Christopherson , Marc Zyngier , Peter Shier , Jim Mattson , David Matlack , Ricardo Koller , Jing Zhang , Raghavendra Rao Anata , James Morse , Alexandru Elisei , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, Andrew Jones , Will Deacon , Catalin Marinas , Oliver Upton Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean noticed that KVM_GET_CLOCK was checking kvm_arch.use_master_clock outside of the pvclock sync lock. This is problematic, as the clock value written to the user may or may not actually correspond to a stable TSC. Fix the race by populating the entire kvm_clock_data structure behind the pvclock_gtod_sync_lock. Suggested-by: Sean Christopherson Signed-off-by: Oliver Upton --- arch/x86/kvm/x86.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c910cf31958f..523c4e5c109f 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2793,19 +2793,20 @@ static void kvm_update_masterclock(struct kvm *kvm) kvm_end_pvclock_update(kvm); } -u64 get_kvmclock_ns(struct kvm *kvm) +static void get_kvmclock(struct kvm *kvm, struct kvm_clock_data *data) { struct kvm_arch *ka = &kvm->arch; struct pvclock_vcpu_time_info hv_clock; unsigned long flags; - u64 ret; spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags); if (!ka->use_master_clock) { spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags); - return get_kvmclock_base_ns() + ka->kvmclock_offset; + data->clock = get_kvmclock_base_ns() + ka->kvmclock_offset; + return; } + data->flags |= KVM_CLOCK_TSC_STABLE; hv_clock.tsc_timestamp = ka->master_cycle_now; hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset; spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags); @@ -2817,13 +2818,26 @@ u64 get_kvmclock_ns(struct kvm *kvm) kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL, &hv_clock.tsc_shift, &hv_clock.tsc_to_system_mul); - ret = __pvclock_read_cycles(&hv_clock, rdtsc()); - } else - ret = get_kvmclock_base_ns() + ka->kvmclock_offset; + data->clock = __pvclock_read_cycles(&hv_clock, rdtsc()); + } else { + data->clock = get_kvmclock_base_ns() + ka->kvmclock_offset; + } put_cpu(); +} - return ret; +u64 get_kvmclock_ns(struct kvm *kvm) +{ + struct kvm_clock_data data; + + /* + * Zero flags as it's accessed RMW, leave everything else uninitialized + * as clock is always written and no other fields are consumed. + */ + data.flags = 0; + + get_kvmclock(kvm, &data); + return data.clock; } static void kvm_setup_pvclock_page(struct kvm_vcpu *v, @@ -5832,13 +5846,9 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned long state) static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp) { struct kvm_clock_data data; - u64 now_ns; - - now_ns = get_kvmclock_ns(kvm); - user_ns.clock = now_ns; - user_ns.flags = kvm->arch.use_master_clock ? KVM_CLOCK_TSC_STABLE : 0; - memset(&user_ns.pad, 0, sizeof(user_ns.pad)); + memset(&data, 0, sizeof(data)); + get_kvmclock(kvm, &data); if (copy_to_user(argp, &data, sizeof(data))) return -EFAULT;