From nobody Thu Apr 9 18:00:23 2026 Received: from out162-62-58-211.mail.qq.com (out162-62-58-211.mail.qq.com [162.62.58.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 217A433D509; Fri, 6 Mar 2026 09:14:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=162.62.58.211 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772788461; cv=none; b=F3w2Ill8vRZLzzm+5Gr5Zd1XFaEiUmZU46riq3Z65+exOLCbAwS3T0HHXWoy7SpaT03YEPeyZ6+jOTOvMAEmzW4ecDqpIdfsi07WjS/UUWRg5qv3hzsSy8Mb6b+kXGWvdTw50K+6N5GHmIS+TCPiqnhhCe2cNTNI5+r7vm1/slM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772788461; c=relaxed/simple; bh=JKzMlTcipeSWdd4kI5ZolpM+mSx8A4Dj6G+S++QpsY8=; h=Message-ID:From:To:Cc:Subject:Date:In-Reply-To:References: MIME-Version; b=WWoDznP/w2q59PuEYvyQ7ZipCkq1EBZLnWAMxgF4WshYaRdiwZzIEe0VHZ4NnoTHpo8+9chCC5etGKk+Y98bFPIOmMsyJtjHI9mNI5ygEMUeCMDvhboRO1PujST2Y/KgjpKjGHpLPr2F0d0YhFCxrUDWOY7ZFcuqWTVSyPSxkI4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=qq.com; spf=pass smtp.mailfrom=qq.com; dkim=pass (1024-bit key) header.d=qq.com header.i=@qq.com header.b=KMShgcHI; arc=none smtp.client-ip=162.62.58.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=qq.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=qq.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=qq.com header.i=@qq.com header.b="KMShgcHI" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=qq.com; s=s201512; t=1772788448; bh=A5j5LGtzImJEs4JwbuwYYdP2w1Tc4QKsLVwxO5vOn2s=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=KMShgcHIacBIWGvi2iIOSIQGaq3FNgk+sh59Kp40lrk/DezPJpVaBHxZlRGjDxCfR 4GdT0UdakhMz+NtXJlr5MrNdJqlFZEgBBQPRD26SsLxnOETeWk8I283JgkDhGhQIFc 5QvD2y9XBHcy5IKo7VfKp7g7A4zPtA76X/TYNCC8= Received: from localhost.localdomain ([101.6.30.191]) by newxmesmtplogicsvrsza53-0.qq.com (NewEsmtp) with SMTP id 32309E2A; Fri, 06 Mar 2026 17:12:35 +0800 X-QQ-mid: xmsmtpt1772788355t1dzbkko9 Message-ID: X-QQ-XMAILINFO: Od8VqZhFMB3N6T8rBpCruW62bDg84CRETrT5Z1ygtPyhw3g7tTNAG6EFL9/XIy QRZQLURIWVYagYtKVNPOzYvSRsbz6xZmxoEhm1n7Wd5yV7o5g+IRN/6X3WDgFsQe06CTm7Qh0cMY R0Wnazw0hJs8FGX3kGAllTZRi2asrSHs0oxbEpeSm65qjsxw0j0K3v1kZ2r+aLYrt655lZBCMyU/ qn5Bxbw5MECQZDl9GWNqwUKyWM56S/qTvkdGfCkzcovfx1cTl6TGAGeoLU5r8Ey1/U6IhzCU3VXo ndTRdJqldwavaxhN0gPtveNCY8icbUA4YXRirDjOxqzL52nOf/r6YFs9FP6G8Cyqo1SSrGLrSDGo eXApfrhIGoV0pw302ZTm03/0La1XZ8pSBXXNgx+yJKcaYNPKHR8vGeQCgWLEBY5VdcV0l/JcwwQR vUkEtJt9HkKvxSBuKcm6DXgHPZij0I8BFWxTiWpKmrtrTB4J0LvVQxoxmRU7S1HxYTfpWCLTpr2z lRplAgRzpxTZrH/GGNLtM3iYop6DEOmXQiZ8KA1J9F09vKaTh00vvuCGYkNLbQlHybFFrfW/lEnN Xd3KpqnK0HKhH4+jmEioUV/0PSm3Ls5NsvOMfAmJfiKHmhXuUlwOneKXWt5zk4sdBYPRNOO1N6tr rotLaYOyUBsp/N2oADi7RVEu7FoZImjHrA48pGq6vunLpaBLGq5QYJBMea8rhEJIHFvDKQI5HiuS DcZBt9uEeCnw45KpG42o6r334hFTYQXN4+pzrkIIJpUBNwErbjduyFCceZgYUZMbFm5As7apmTQg kr2WKiImQ7lS0gIMpbfa8CFBaddjCwuXWdaWr7l++3eMa6Ys2pk3Oqlv4QXh+th04u2Ycp6mGApA LOtDpspscrj4UmoQSCEuRKd2Cfs1XNgQpzTrjgtSOQhpeRjrGD8CT5KQ9A9lvU5wkcNe50U3p7nN HcYYM55EuVCr0sGJbuLXwaaa5E5C2KpL8kTVRH+LnbGBMsS0EakYvUxSneDyShq47iwb6wmpzCxm Js1IAGiwz/bSSzTKRs X-QQ-XMRINFO: Nq+8W0+stu50tPAe92KXseR0ZZmBTk3gLg== From: xuanqingshi <1356292400@qq.com> To: seanjc@google.com, pbonzini@redhat.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, xuanqingshi <1356292400@qq.com> Subject: [PATCH v2] KVM: x86: Add LAPIC guard in kvm_apic_write_nodecode() Date: Fri, 6 Mar 2026 17:12:32 +0800 X-OQ-MSGID: <20260306091232.2756961-1-1356292400@qq.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" kvm_apic_write_nodecode() dereferences vcpu->arch.apic without first checking whether the in-kernel LAPIC has been initialized. If it has not (e.g. the vCPU was created without an in-kernel LAPIC), the dereference results in a NULL pointer access. While APIC-write VM-Exits are not expected to occur on a vCPU without an in-kernel LAPIC, kvm_apic_write_nodecode() should be robust against such a scenario as a defense-in-depth measure, e.g. to guard against KVM bugs or CPU errata that could generate a spurious APIC-write VM-Exit. Use KVM_BUG_ON() with lapic_in_kernel() instead of a simple WARN_ON_ONCE(), as suggested by Sean Christopherson, so that KVM kills the VM outright rather than letting it continue in a broken state. Found by a VMCS-targeted fuzzer based on syzkaller. Signed-off-by: xuanqingshi <1356292400@qq.com> --- arch/x86/kvm/lapic.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 9381c58d4c85..02f2039d5f99 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -2657,6 +2657,9 @@ void kvm_apic_write_nodecode(struct kvm_vcpu *vcpu, u= 32 offset) { struct kvm_lapic *apic =3D vcpu->arch.apic; =20 + if (KVM_BUG_ON(!lapic_in_kernel(vcpu), vcpu->kvm)) + return; + /* * ICR is a single 64-bit register when x2APIC is enabled, all others * registers hold 32-bit values. For legacy xAPIC, ICR writes need to --=20 2.25.1