From patchwork Mon Feb 24 16:54:41 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 13988468 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 08955263F21 for ; Mon, 24 Feb 2025 16:54:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740416088; cv=none; b=LRO8QYxh8KxqyQxC6WtthCl+bFJfAetUMqgMs5teNogd3PybQfARAi08611/Wn59umqBCHobYR/xtZ7nJjn9aviSsKCkum+qLZVeFnR6/eisY2oX8OIEyAdr/mMK4fzVnF62jhJEKRj3yZnNoqZNTRdJcgJnIuwq6zhRwinMBCM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740416088; c=relaxed/simple; bh=l6+UgceNnntZd11WS3K/VkPrhV4bTFxROks7VDhHDt4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ud5HF/gb2bu4xARzVvLr/oC8jpdG+am20U0cC8RxHSHvcIZ5raItDJj3o+1AsVD6Q+S2mTIRF8E2hbyiccAeklKUKpFlmcUYtQoSYi8Lm9Kl/eHihX4/XtWodlrFYe8C49qDMgYSWqNdufAoK2fUTvmtIjCWlcz8ZvsxmvGpIk4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=rHko1+FC; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="rHko1+FC" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2fc1c7c8396so9562014a91.0 for ; Mon, 24 Feb 2025 08:54:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1740416086; x=1741020886; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=FdhSq59XhU0FyUWTPTJyf9MJm43UgRUBo6YYKsIpDDY=; b=rHko1+FCbxIDa+I+dAipTsXiGoWo4jNsScjxf7jmcgyb8GggeMn9hKnBXv3IagRHpm 8KeZbNMWKyolmSQjRoSaloS48mOXBanFH3TeOuaNft/USHrFR05gu4WOyVk8Z/wARD5J GzisB+E630P7Txx9GdfVRf73fJAhc4OGh419qKXv137S+p5F5DmyvLtYND+2W7NY0G4M QlWOtEsSpe/yOc9yNk7DvfkpLYtE2VBXUHe2NUxdfy2x4SPafYO/vqhpD22Yy3WE5SHk Rqix70MgA1xt1qWAk5zu6/0+0ffgelsnQ1MyiGEjG0PwUWzzWqMcY5erQhQWbEr0NH7v r7hg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740416086; x=1741020886; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=FdhSq59XhU0FyUWTPTJyf9MJm43UgRUBo6YYKsIpDDY=; b=Srun38+OuosdI4Ddb7Ct3eeGJHop6pgifDX8Z4hv10xPDqPTU5tFTzRhdpQ0h32r16 LaG99PLhADzzDldcpv7u9UakuvXRU1DvZVJCCrMNA8rKsZJAwjxyzJVfB0n/ff45Ct6X zfZCZJZ8Anael+LrSd1mZyUzq8QhGangvdmItpSR80umoXrahDenyLmybj23ovvWNvOk UHxHkCtw4mwJ4SsMluZFU0cfBW+A8QfBnK1mW+babVrW3RzD+3JDCgu8woo88TZf8QOj ALM9habEj2Iq+vpVO7/p/nTc0o7LsHQpfEjHhBHSa2AyAk7viARUmwMcfNHm8nxKi9/u uljA== X-Gm-Message-State: AOJu0Yx2zcH1+EhU3AGduy+lEcO7TjkwdmXRcJrEUjJGjEMrtPKF10Pq EKQmWhacrbpfQrTtTuhJRwBOwEwMhrcC1s0R7Hsex6flUl+gUrQBA+8j1VUelp8ZnalrsrLB9BX ohg== X-Google-Smtp-Source: AGHT+IFSrtAKmj8Gq/INI+PFQV3lvbZ1NNr6PG1+wrG9VH16gYz3Az2kA6DLNGmb/eanLpAY4R2Dm5bmv6U= X-Received: from pjbsx15.prod.google.com ([2002:a17:90b:2ccf:b0:2fb:fa62:d40]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4d0d:b0:2ee:8430:b831 with SMTP id 98e67ed59e1d1-2fce868c84cmr23717052a91.2.1740416086342; Mon, 24 Feb 2025 08:54:46 -0800 (PST) Reply-To: Sean Christopherson Date: Mon, 24 Feb 2025 08:54:41 -0800 In-Reply-To: <20250224165442.2338294-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250224165442.2338294-1-seanjc@google.com> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog Message-ID: <20250224165442.2338294-2-seanjc@google.com> Subject: [PATCH v2 1/2] KVM: SVM: Set RFLAGS.IF=1 in C code, to get VMRUN out of the STI shadow From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Doug Covelli Enable/disable local IRQs, i.e. set/clear RFLAGS.IF, in the common svm_vcpu_enter_exit() just after/before guest_state_{enter,exit}_irqoff() so that VMRUN is not executed in an STI shadow. AMD CPUs have a quirk (some would say "bug"), where the STI shadow bleeds into the guest's intr_state field if a #VMEXIT occurs during injection of an event, i.e. if the VMRUN doesn't complete before the subsequent #VMEXIT. The spurious "interrupts masked" state is relatively benign, as it only occurs during event injection and is transient. Because KVM is already injecting an event, the guest can't be in HLT, and if KVM is querying IRQ blocking for injection, then KVM would need to force an immediate exit anyways since injecting multiple events is impossible. However, because KVM copies int_state verbatim from vmcb02 to vmcb12, the spurious STI shadow is visible to L1 when running a nested VM, which can trip sanity checks, e.g. in VMware's VMM. Hoist the STI+CLI all the way to C code, as the aforementioned calls to guest_state_{enter,exit}_irqoff() already inform lockdep that IRQs are enabled/disabled, and taking a fault on VMRUN with RFLAGS.IF=1 is already possible. I.e. if there's kernel code that is confused by running with RFLAGS.IF=1, then it's already a problem. In practice, since GIF=0 also blocks NMIs, the only change in exposure to non-KVM code (relative to surrounding VMRUN with STI+CLI) is exception handling code, and except for the kvm_rebooting=1 case, all exception in the core VM-Enter/VM-Exit path are fatal. Use the "raw" variants to enable/disable IRQs to avoid tracing in the "no instrumentation" code; the guest state helpers also take care of tracing IRQ state. Oppurtunstically document why KVM needs to do STI in the first place. Reported-by: Doug Covelli Closes: https://lore.kernel.org/all/CADH9ctBs1YPmE4aCfGPNBwA10cA8RuAk2gO7542DjMZgs4uzJQ@mail.gmail.com Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Reviewed-by: Jim Mattson --- arch/x86/kvm/svm/svm.c | 14 ++++++++++++++ arch/x86/kvm/svm/vmenter.S | 10 +--------- 2 files changed, 15 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index b8aa0f36850f..df5c23613b95 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4189,6 +4189,18 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_in guest_state_enter_irqoff(); + /* + * Set RFLAGS.IF prior to VMRUN, as the host's RFLAGS.IF at the time of + * VMRUN controls whether or not physical IRQs are masked (KVM always + * runs with V_INTR_MASKING_MASK). Toggle RFLAGS.IF here to avoid the + * temptation to do STI+VMRUN+CLI, as AMD CPUs bleed the STI shadow + * into guest state if delivery of an event during VMRUN triggers a + * #VMEXIT, and the guest_state transitions already tell lockdep that + * IRQs are being enabled/disabled. Note! GIF=0 for the entirety of + * this path, so IRQs aren't actually unmasked while running host code. + */ + raw_local_irq_enable(); + amd_clear_divider(); if (sev_es_guest(vcpu->kvm)) @@ -4197,6 +4209,8 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_in else __svm_vcpu_run(svm, spec_ctrl_intercepted); + raw_local_irq_disable(); + guest_state_exit_irqoff(); } diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S index 2ed80aea3bb1..0c61153b275f 100644 --- a/arch/x86/kvm/svm/vmenter.S +++ b/arch/x86/kvm/svm/vmenter.S @@ -170,12 +170,8 @@ SYM_FUNC_START(__svm_vcpu_run) mov VCPU_RDI(%_ASM_DI), %_ASM_DI /* Enter guest mode */ - sti - 3: vmrun %_ASM_AX 4: - cli - /* Pop @svm to RAX while it's the only available register. */ pop %_ASM_AX @@ -340,12 +336,8 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run) mov KVM_VMCB_pa(%rax), %rax /* Enter guest mode */ - sti - 1: vmrun %rax - -2: cli - +2: /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */ FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT