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=-16.5 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,DKIM_INVALID,DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,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 BBA58C432BE for ; Mon, 16 Aug 2021 00:11:45 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 5AC46613A2 for ; Mon, 16 Aug 2021 00:11:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5AC46613A2 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 0ED6A4B0E6; Sun, 15 Aug 2021 20:11:45 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Authentication-Results: mm01.cs.columbia.edu (amavisd-new); dkim=softfail (fail, message has been altered) header.i=@google.com Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 0wnqw2cbMbIX; Sun, 15 Aug 2021 20:11:41 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 4C1284B0ED; Sun, 15 Aug 2021 20:11:38 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id E15894B0CC for ; Sun, 15 Aug 2021 20:11:36 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 0Eeo3x5rb2zk for ; Sun, 15 Aug 2021 20:11:35 -0400 (EDT) Received: from mail-il1-f202.google.com (mail-il1-f202.google.com [209.85.166.202]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id CB9B04B0B6 for ; Sun, 15 Aug 2021 20:11:35 -0400 (EDT) Received: by mail-il1-f202.google.com with SMTP id c16-20020a92cf500000b02902243aec7e27so5601551ilr.22 for ; Sun, 15 Aug 2021 17:11:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=J0lJJJkW+NmZlpb6fpFofwzCF2N0YPn/fE7VW8sEN0E=; b=onMRm+c0TmbvvH91s8krImCv1CKEk4b274WYjrqgKk7gKLOUw9VrXJClkZ1DmSna/8 3tepivV3mzLKvagWxhpO+/WQdfkPceIPNKfBb2bGq51hsXJu/WQCIkjs874UB7dk0W9W oXAUvi79qPx6l8QqPRpDusbWhyXuCw7E1AogPxUA0fgJz83AKxK+/O+IR3aKYsxFeqZM JjNSmzkGS23X+RekEHj1AacWn1arDI/RxjwhBttOKfWKf9+zoiG8nYGaSZvEuGaZs74t Vs8UyftyhM2f38KfhifByPOjskfYoVIv781b+80yLp+3M+udeuw+Zi4uFZAtu/XHAmkx u6/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=J0lJJJkW+NmZlpb6fpFofwzCF2N0YPn/fE7VW8sEN0E=; b=XPeIZgZUdBXqZZMg8Ly+dxbObwsWiF9UcW1kT2XcCV+DRX4IgZPran1BCayHcmXPEm M4CZPmWOu6JffaakVoZX/MBfg4xOM0SLDXqCMGgrk1R2R/O6LXJ/pvQxcSmttx3LlHwU +uI1weSIslYh206G4Wdlz2+JYzLfwwAj1DCFbCuzFqswHer9LHyUUk/4O59q/sErIkhy HQhFhZjQWYpVohl8Cn4qpC3Kv0t8OPF2Mf8MwLVE64PI+dOdW8e0hEz9QgOaADnbG1xk Z1OeS3Pl42/jZ9pQYzzfr+ytqmrF28IgKr31F8oeEd5yjJYMgEzJv2it2X5KouYCYXxZ owmQ== X-Gm-Message-State: AOAM531IMSHEbB1wm5O/Ik+ZnbGE6x0twfS/nLj5OopbHcIncu4gMv7h E1gAZo76kM5z54w0oKMQM3CVYHLNDDs= X-Google-Smtp-Source: ABdhPJw09eGgNy3EXbjdqGFxxJgFJV5YrUuGjNKkF5zMC9eqOSxrLDgPkbJpMCJxluIG+Ci2XveMUkYVc70= X-Received: from oupton.c.googlers.com ([fda3:e722:ac3:cc00:2b:ff92:c0a8:404]) (user=oupton job=sendgmr) by 2002:a02:cd09:: with SMTP id g9mr12684753jaq.87.1629072695306; Sun, 15 Aug 2021 17:11:35 -0700 (PDT) Date: Mon, 16 Aug 2021 00:11:25 +0000 In-Reply-To: <20210816001130.3059564-1-oupton@google.com> Message-Id: <20210816001130.3059564-2-oupton@google.com> Mime-Version: 1.0 References: <20210816001130.3059564-1-oupton@google.com> X-Mailer: git-send-email 2.33.0.rc1.237.g0d66db33f3-goog Subject: [PATCH v7 1/6] KVM: x86: Fix potential race in KVM_GET_CLOCK From: Oliver Upton To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu Cc: Catalin Marinas , Will Deacon , Marc Zyngier , Raghavendra Rao Anata , Peter Shier , Sean Christopherson , David Matlack , Paolo Bonzini , linux-arm-kernel@lists.infradead.org, Jim Mattson X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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 | 39 ++++++++++++++++++++++++++++----------- 1 file changed, 28 insertions(+), 11 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index fdc0c18339fb..2f3929bd5f58 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2787,19 +2787,20 @@ 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); @@ -2811,13 +2812,26 @@ 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, @@ -6098,11 +6112,14 @@ long kvm_arch_vm_ioctl(struct file *filp, } case KVM_GET_CLOCK: { struct kvm_clock_data user_ns; - 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; + /* + * Zero flags as it is accessed RMW, leave everything else + * uninitialized as clock is always written and no other fields + * are consumed. + */ + user_ns.flags = 0; + get_kvmclock(kvm, &user_ns); memset(&user_ns.pad, 0, sizeof(user_ns.pad)); r = -EFAULT; -- 2.33.0.rc1.237.g0d66db33f3-goog _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm