From patchwork Mon Jun 28 12:48:14 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: stsp X-Patchwork-Id: 12347961 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=-13.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 8C7AAC49361 for ; Mon, 28 Jun 2021 12:48:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74C1361C43 for ; Mon, 28 Jun 2021 12:48:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233046AbhF1Muq (ORCPT ); Mon, 28 Jun 2021 08:50:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232889AbhF1Muo (ORCPT ); Mon, 28 Jun 2021 08:50:44 -0400 Received: from forward104o.mail.yandex.net (forward104o.mail.yandex.net [IPv6:2a02:6b8:0:1a2d::607]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2703AC061574 for ; Mon, 28 Jun 2021 05:48:19 -0700 (PDT) Received: from myt6-61e9e731de9c.qloud-c.yandex.net (myt6-61e9e731de9c.qloud-c.yandex.net [IPv6:2a02:6b8:c12:4ca0:0:640:61e9:e731]) by forward104o.mail.yandex.net (Yandex) with ESMTP id 5B5289417FB; Mon, 28 Jun 2021 15:48:16 +0300 (MSK) Received: from myt6-efff10c3476a.qloud-c.yandex.net (myt6-efff10c3476a.qloud-c.yandex.net [2a02:6b8:c12:13a3:0:640:efff:10c3]) by myt6-61e9e731de9c.qloud-c.yandex.net (mxback/Yandex) with ESMTP id YKmTjDflVM-mGH4vt5d; Mon, 28 Jun 2021 15:48:16 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex.ru; s=mail; t=1624884496; bh=MXNIktVnLvg3iLfiytyT0Mz6xWZ11yPrq2AeNMBm0q0=; h=Subject:To:From:Message-Id:Cc:Date; b=jTUleteRy+KgIYcY6o8OLpp9EcxHIy9RcykHn5yIrPicVPVzipQRrJWvbchTuAilm qINn4hevNZX4nhzIEY63LCbSTgdod+Mjs+I/M9EmpCq4yg0/Bkv8GJEq+f28pfMzqd dAu2rivY1Wo1oW8CfOqmaaqrnhZ2aOJ1irBBDsjA= Authentication-Results: myt6-61e9e731de9c.qloud-c.yandex.net; dkim=pass header.i=@yandex.ru Received: by myt6-efff10c3476a.qloud-c.yandex.net (smtp/Yandex) with ESMTPSA id DVoVBENo2Z-mF28pnua; Mon, 28 Jun 2021 15:48:15 +0300 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client certificate not present) From: Stas Sergeev Cc: Stas Sergeev , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Jan Kiszka , x86@kernel.org, "H. Peter Anvin" , kvm@vger.kernel.org Subject: [PATCH v2] KVM: X86: Fix exception untrigger on ret to user Date: Mon, 28 Jun 2021 15:48:14 +0300 Message-Id: <20210628124814.1001507-1-stsp2@yandex.ru> X-Mailer: git-send-email 2.32.0 MIME-Version: 1.0 To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org When returning to user, the special care is taken about the exception that was already injected to VMCS but not yet to guest. cancel_injection removes such exception from VMCS. It is set as pending, and if the user does KVM_SET_REGS, it gets completely canceled. This didn't happen though, because the vcpu->arch.exception.injected and vcpu->arch.exception.pending were forgotten to update in cancel_injection. As the result, KVM_SET_REGS didn't cancel out anything, and the exception was re-injected on the next KVM_RUN, even though the guest registers (like EIP) were already modified. This was leading to an exception coming from the "wrong place". This patch makes sure the vcpu->arch.exception.injected and vcpu->arch.exception.pending are in sync with the reality (and with VMCS). Also it adds clearing of pending exception to __set_sregs() the same way it is in __set_regs(). See patch b4f14abd9 that added it to __set_regs(). How to trigger the buggy scenario (that is, without this patch): - Make sure you have the old CPU where shadow page tables are used. Core2 family should be fine for the task. In this case, all PF exceptions produce the exit to monitor. - You need the _TIF_SIGPENDING flag set at the right moment to get kvm_vcpu_exit_request() to return true when the PF exception was just injected. In that case the cancel_injection path is executed. - You need the "unlucky" user-space that executes KVM_SET_REGS at the right moment. This leads to KVM_SET_REGS not clearing the exception, but instead corrupting its context. v2 changes: - do not add WARN_ON_ONCE() to __set_regs(). As explained by Vitaly Kuznetsov, it can be user-triggerable. - clear pending exception also in __set_sregs(). - update description with the bug-triggering scenario. Signed-off-by: Stas Sergeev CC: Paolo Bonzini CC: Sean Christopherson CC: Vitaly Kuznetsov CC: Jim Mattson CC: Joerg Roedel CC: Thomas Gleixner CC: Ingo Molnar CC: Borislav Petkov CC: Jan Kiszka CC: x86@kernel.org CC: "H. Peter Anvin" CC: kvm@vger.kernel.org --- arch/x86/kvm/x86.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index e0f4a46649d7..d1026e9216e4 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9450,7 +9450,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) cancel_injection: if (req_immediate_exit) kvm_make_request(KVM_REQ_EVENT, vcpu); - static_call(kvm_x86_cancel_injection)(vcpu); + if (vcpu->arch.exception.injected) { + static_call(kvm_x86_cancel_injection)(vcpu); + vcpu->arch.exception.injected = false; + vcpu->arch.exception.pending = true; + } if (unlikely(vcpu->arch.apic_attention)) kvm_lapic_sync_from_vapic(vcpu); out: @@ -10077,6 +10081,8 @@ static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs) pr_debug("Set back pending irq %d\n", pending_vec); } + vcpu->arch.exception.pending = false; + kvm_make_request(KVM_REQ_EVENT, vcpu); ret = 0;