From nobody Thu Apr 10 19:01:23 2025 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 28213205E31 for ; Tue, 1 Apr 2025 15:05:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743519908; cv=none; b=koLjUxvVp/VxSoK0bpEXnYJkkrpRjqNoFI1S2u40qHgpjpZ47o1gBRjMBVww/hVkcSsVpY3wNPU5qJNCPXc6gBkl5IpfApQ21elm50O30l0oKki/J/4kqWEH2wwei50SYSOK66qqVGkYHKfrKb+OZZQbew7IjlLyoLeQ/TduSvE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743519908; c=relaxed/simple; bh=F/RiXgmrpmTiv2QvtvjdUGI+ud9Yccr9L3aXP3dOP60=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=LUNiuXFqjmqzALOWwRVW4ClHobZQujLodztaoyjsIlEiHgQP/nEwBN88U/gU3hrBzucclBySkfIgfiz7IiHdI4p0ErppAY9tRhFh5JSdnY8SeCxWdYByk1xUA7+o0emyhQxKjsVSwNehQqPKz8x0VAmGZyrMNVeVjoQZSJ6vCr0= 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=HFDrBqtl; arc=none smtp.client-ip=209.85.214.201 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="HFDrBqtl" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-22647ff3cf5so92204365ad.0 for ; Tue, 01 Apr 2025 08:05:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1743519906; x=1744124706; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:reply-to:from:to:cc :subject:date:message-id:reply-to; bh=+IgyuGHrG6KOz4ioK+lLzhnnHjxowzYSohAuohKgopQ=; b=HFDrBqtlYe/Hd++C1UvM94aVgbuvTyO3XhAOHdRkE71dQIKBO4q41rI7ui0PlON+Jd orEFlOegFTbkr3ndZT5PyDreBR91eIQxfaMJa1F31cE86lSwn5KX+gUIjth9zHMmbG1A 7iUg+crEl5xPK81dln8ZWO7RtnMUppbzdZlaJsMzYms8FcPIF+aS8/QouJHTP/N4Lf9j nlEvNHBpvIftGaWwKaiVsoZ2VIorv5tiIKtlcVumxacT31zdyRfyZ5l/3N8VDs8YjNnH 5HXLgzjcEWwdsYhMvY3jbiAj3sC5aO42HhEMRkzpjDvYawb7yq5wKeamjw5+8Np4vCK2 UPmg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1743519906; x=1744124706; h=cc:to:from:subject:message-id:mime-version:date:reply-to :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=+IgyuGHrG6KOz4ioK+lLzhnnHjxowzYSohAuohKgopQ=; b=v9hIZnaZa+Epc8r9hdlwHqR2ZVoDSjI8OV3aksTIepvGRJYMWxR+Njaidz8zRC19LP f+00wS7AehRmUNM1N5vUyEs2br8km7O5kR3td3jTfekOUa6CjU2dtAiDy6PDrEpPFJ30 vy2SgE15tJbUU15mo3D+/5X9f+2CtuRVvaI2VrTGDsFIcuSudvpi9gHXvc/HVnkl/4Mj jyfMM6HOSeppLC7M07eEN8pdMenLNOH3yMRsPCx4jS582iug4ktMHU7VMB+rhL5d6xlo KwlvP/PRUGQ9Gx9NiBoKxkpN6mqS9V/YMDO7n/q/F1SRQoMm9OVIM7okYvgIOmMmUirL ELxg== X-Forwarded-Encrypted: i=1; AJvYcCXbUo7Q4aFIH/mNeMlPk+PtPeur95S9azcTOqDzfCguPDa2g2i74Ceh8QRTOzfy5mniBNc4p9W3QuzEsKg=@vger.kernel.org X-Gm-Message-State: AOJu0Yyo7Od4vf1FGBgm/tC2T2p9vAfcBJx16p2jq585YTuYJTB38Jny tHJFOKMqxSCVJ/KIvAI8iyil23CmHqbaImUQKcLrf1x3qWsMnqLoF3oZsggL95/DoQtDmkkzZ8Y Iwg== X-Google-Smtp-Source: AGHT+IG7JAm6yR31fSBvMf2GU4Ds1vfmbHR0/eLzAEDvkzcrRzepC4l8s3OVsGvLjol1VPLnWhQsYXPcmd8= X-Received: from pfbgu25.prod.google.com ([2002:a05:6a00:4e59:b0:736:a320:25bd]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:1493:b0:739:4a30:b900 with SMTP id d2e1a72fcca58-7398037e24amr18537552b3a.7.1743519906429; Tue, 01 Apr 2025 08:05:06 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 1 Apr 2025 08:05:04 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.49.0.472.ge94155a9ec-goog Message-ID: <20250401150504.829812-1-seanjc@google.com> Subject: [PATCH] KVM: x86: Acquire SRCU in KVM_GET_MP_STATE to protect guest memory accesses From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Acquire a lock on kvm->srcu when userspace is getting MP state to handle a rather extreme edge case where "accepting" APIC events, i.e. processing pending INIT or SIPI, can trigger accesses to guest memory. If the vCPU is in L2 with INIT *and* a TRIPLE_FAULT request pending, then getting MP state will trigger a nested VM-Exit by way of ->check_nested_events(), and emuating the nested VM-Exit can access guest memory. The splat was originally hit by syzkaller on a Google-internal kernel, and reproduced on an upstream kernel by hacking the triple_fault_event_test selftest to stuff a pending INIT, store an MSR on VM-Exit (to generate a memory access on VMX), and do vcpu_mp_state_get() to trigger the scenario. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D WARNING: suspicious RCU usage 6.14.0-rc3-b112d356288b-vmx/pi_lockdep_false_pos-lock #3 Not tainted ----------------------------- include/linux/kvm_host.h:1058 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active =3D 2, debug_locks =3D 1 1 lock held by triple_fault_ev/1256: #0: ffff88810df5a330 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0x8b= /0x9a0 [kvm] stack backtrace: CPU: 11 UID: 1000 PID: 1256 Comm: triple_fault_ev Not tainted 6.14.0-rc3-= b112d356288b-vmx #3 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack_lvl+0x7f/0x90 lockdep_rcu_suspicious+0x144/0x190 kvm_vcpu_gfn_to_memslot+0x156/0x180 [kvm] kvm_vcpu_read_guest+0x3e/0x90 [kvm] read_and_check_msr_entry+0x2e/0x180 [kvm_intel] __nested_vmx_vmexit+0x550/0xde0 [kvm_intel] kvm_check_nested_events+0x1b/0x30 [kvm] kvm_apic_accept_events+0x33/0x100 [kvm] kvm_arch_vcpu_ioctl_get_mpstate+0x30/0x1d0 [kvm] kvm_vcpu_ioctl+0x33e/0x9a0 [kvm] __x64_sys_ioctl+0x8b/0xb0 do_syscall_64+0x6c/0x170 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c841817a914a..3712dde0bf9d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11786,6 +11786,8 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu= *vcpu, if (kvm_mpx_supported()) kvm_load_guest_fpu(vcpu); =20 + kvm_vcpu_srcu_read_lock(vcpu); + r =3D kvm_apic_accept_events(vcpu); if (r < 0) goto out; @@ -11799,6 +11801,8 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu= *vcpu, mp_state->mp_state =3D vcpu->arch.mp_state; =20 out: + kvm_vcpu_srcu_read_unlock(vcpu); + if (kvm_mpx_supported()) kvm_put_guest_fpu(vcpu); vcpu_put(vcpu); base-commit: 782f9feaa9517caf33186dcdd6b50a8f770ed29b --=20 2.49.0.472.ge94155a9ec-goog