From nobody Mon Feb 9 12:09:06 2026 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 6721436E371 for ; Thu, 30 Oct 2025 18:58:09 +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=1761850690; cv=none; b=t7Zm3KSCgguAdu/eiSm1q8zOxLOSNwfCeKBX4Gch5mJOhhkJPPxghwAvlnl9+S6ubQ4WowYelw+XnagsvnfxdRYMMfAHqhCQpAYKtRk7+SByfG6dqo1a8ykUjyiDD1+9MQSi5cYslJRpSwfHq2u6Mj+/H31zIu0V9ZbWFsxn+B4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761850690; c=relaxed/simple; bh=gBhNaafHCGkv+teWASnFAg94iaqRXR4iTaEf314TGQw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=SlrA0mcnyAycBxLnkD8c2dr7F0bFg5AeswSExs1QRSHI/bH477wgKgEhdtQ2c4Rt8NDRp1lFKYXtufPsnDNmykuy8bRqrTM8aZHStKMQZvscqsKwRBi7FGuSnnZl1m+wN6qcFTCO9eRLKva0+kvsPmSyJf9F9nXSEEg/zd1i47c= 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=HWs9Lyz5; 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="HWs9Lyz5" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-3405e02ff45so1077305a91.3 for ; Thu, 30 Oct 2025 11:58:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1761850688; x=1762455488; 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=qjjFGFuC/i6bzqqoHJlMMUDjmHoXRQt84ZbrHXQbM7E=; b=HWs9Lyz5OCyyh3garUoE71nuAbQkfTfhXvZxE767LyOADb6ZHldXCl+V+Lka5Itmqn DkHc0lw6yju9GQUcXOPOhw9n5hvcCVaehr6+LDcrd7X4UrcKQV0Jn5tTmSGVwLtQbclf cy28DxlQ3ztPcxk7LEXKbpjGkyiXMPEG6z1rPXMEP8Ft3Z/DmJkZnazha0T4nJYl5bto lPkibCei09hYZHBXBg5jLPAPQB6LMPliJmEM8O9ODYYYCHXirSNQ3h6EPd1Xrjln6BCj 1wQgAfLQwnpGmPMJi0v8drOuvSxvN9ulSsiR0DxGkugLmCyg55RVZulHHddjlz6dKQ/7 Bq8Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761850688; x=1762455488; 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=qjjFGFuC/i6bzqqoHJlMMUDjmHoXRQt84ZbrHXQbM7E=; b=fqGTnffKGmxvvEhVqWVvrmRxzXtb/zlR+W6AddS7cjgzGTsDx7wzTU/akAzw37EIH2 gTDLoOs7P0qIHm/YkD2wKyYW3pEbHoteMAlmZkjQf0iT6VtsY/W4BaMNn1XVh5+QH0c8 vZjDKFZkbp7KW3dF2tz5BbfLF/qrgkDQ/UNhzoH+CaK5+CeOeCr2TktD5texdA7JspEy h8W06GvxIHXcvzDZ8zo4eqizfJ5Xi8aHlk9v5XmXIh1x11l5Py2PsL3TGGb1QR+CpWGB gGAExcQZ8elTvPPTRX01k6amYsX25TqaAJu4VpUc0YozC2ccYk3hel970nt9mDpgLXyT 023Q== X-Forwarded-Encrypted: i=1; AJvYcCViUJuHuftU+w8uj1GPogRBlOF+M+vpsPca4MqCZGcTjHu78AZjaWGN2mXWS7BbUNtDBJAWFyWRqLyw1d0=@vger.kernel.org X-Gm-Message-State: AOJu0YxecXdiez5Rc5AMFRYDxb44CcHfmVdmioBf/JWH+QFkCS5/3YXU nIePRhF90p6j1XJW3rMk6fVn6XQJ8uXOl0/iztNujPDtw+Ll+z7rf7BCHqXtPd4OAAJiW1HuXKy Xn4bybg== X-Google-Smtp-Source: AGHT+IEKgvy0wUgCv5T8CNLcmWcQSEO5ENvBe1HV5y63XOGG6rep4wBvG0goTUcSpE7EICJuck+LW8gP5+Y= X-Received: from pjbqd11.prod.google.com ([2002:a17:90b:3ccb:b0:339:ae3b:2bc7]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:134e:b0:33b:dec9:d9aa with SMTP id 98e67ed59e1d1-3408308c667mr906032a91.25.1761850688619; Thu, 30 Oct 2025 11:58:08 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 30 Oct 2025 11:58:02 -0700 In-Reply-To: <20251030185802.3375059-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251030185802.3375059-1-seanjc@google.com> X-Mailer: git-send-email 2.51.1.930.gacf6e81ea2-goog Message-ID: <20251030185802.3375059-3-seanjc@google.com> Subject: [PATCH 2/2] KVM: x86: Harden KVM against imbalanced load/put of guest FPU state From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Potapenko Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Assert, via KVM_BUG_ON(), that guest FPU state isn't/is in use when loading/putting the FPU to help detect KVM bugs without needing an assist from KASAN. If an imbalanced load/put is detected, skip the redundant load/put to avoid clobbering guest state and/or crashing the host. Note, kvm_access_xstate_msr() already provides a similar assertion. Signed-off-by: Sean Christopherson Reviewed-by: Chao Gao --- arch/x86/kvm/x86.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index d1e048d14e88..67e5f735adf2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11807,6 +11807,9 @@ static int complete_emulated_mmio(struct kvm_vcpu *= vcpu) /* Swap (qemu) user FPU context for the guest FPU context. */ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu) { + if (KVM_BUG_ON(vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm)) + return; + /* Exclude PKRU, it's restored separately immediately after VM-Exit. */ fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, true); trace_kvm_fpu(1); @@ -11815,6 +11818,9 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcp= u) /* When vcpu_run ends, restore user space FPU context. */ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu) { + if (KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm)) + return; + fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, false); ++vcpu->stat.fpu_reload; trace_kvm_fpu(0); --=20 2.51.1.930.gacf6e81ea2-goog