From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E62814248D5 for ; Thu, 30 Jul 2026 12:15:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785413756; cv=none; b=YR1iHKPn6yb4kPgyU0tUaEZdHbVtN9a6zJvbV6F8Ov1uUak9fbqzO9oMIUd0ZEgxpoWG5I88FisdZiLUHVFMpwfY7IV5ps41iOZ8u+uYRSLc+mG60sHJJjB/gnfWAA/Bd9P5QStH8hk9QvB5iglh2xS2J+TsIeWPeRtoR+mD54c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785413756; c=relaxed/simple; bh=HkyxaXT1Ods29RklKt9SSTD/7YH7BENaoEiz6AJBwhw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lBXV6+RcL8/best4mSsrzzsfeZCk3Vf0FLfKTWNo+1pdjoBMaQ8ieqG88dCIUATu1jJ8pwy9OX7W8V5XjKUZUQPcYOJLNicKyCgc/f76HcTALeen8eMorv8c96F7hE3dJEi0yRRB14x2QA6omwkt9SRAVDLK9vZoazpab79+IZQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=exPRjSCc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="exPRjSCc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 39C641F00AC4; Thu, 30 Jul 2026 12:15:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785413743; bh=iaD/b/ubu4xLtv/i8Cy8ghOjA3cjehH2I7W62/dAmh8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=exPRjSCcBcpZ0sanso4zH9qnkfO/W7N3IaPDQeMd5mjD2QVuWWCwI0NJIPdaGV3eq 6+T4SaU+Pzsv4/jVCbsjSrfLUZ0LQMjDM+l2LdYFcuAVLc0HgIuWVcgvPV426COCa5 Xh89no1Z8aTY4YBoTWL3W9zOIn23v5zhmhLaoMYOWhlSJjJw9cj0VpH1QE3Z+6V7ZQ +GlKKaKK1fl6WyD514yZ3f1lRTyR+ghigw19WKizBjJV7Zm3G751V2RHZikqeibIXt mKEKl9pGZE/SqQ4K8Pn0aPHVtEZee9QofsyrbC8X97Czcj4bEI7bKhJBsvCn0gPR6C OAZQJrViwDCBQ== From: Sasha Levin To: stable@vger.kernel.org Cc: David Matlack , Sean Christopherson , Sasha Levin Subject: [PATCH 6.6.y 1/2] KVM: Introduce vcpu->wants_to_run Date: Thu, 30 Jul 2026 08:15:40 -0400 Message-ID: <20260730121541.2209429-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026072610-waking-easiest-e330@gregkh> References: <2026072610-waking-easiest-e330@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: David Matlack [ Upstream commit a6816314af5749cd88944bfdceb270c627cdf348 ] Introduce vcpu->wants_to_run to indicate when a vCPU is in its core run loop, i.e. when the vCPU is running the KVM_RUN ioctl and immediate_exit was not set. Replace all references to vcpu->run->immediate_exit with !vcpu->wants_to_run to avoid TOCTOU races with userspace. For example, a malicious userspace could invoked KVM_RUN with immediate_exit=true and then after KVM reads it to set wants_to_run=false, flip it to false. This would result in the vCPU running in KVM_RUN with wants_to_run=false. This wouldn't cause any real bugs today but is a dangerous landmine. Signed-off-by: David Matlack Link: https://lore.kernel.org/r/20240503181734.1467938-2-dmatlack@google.com Signed-off-by: Sean Christopherson Stable-dep-of: e800decd9c0a ("KVM: x86: Only reset TSC Deadline Timer in apic_timer_expired on KVM_RUN") Signed-off-by: Sasha Levin --- arch/arm64/kvm/arm.c | 2 +- arch/mips/kvm/mips.c | 2 +- arch/powerpc/kvm/powerpc.c | 2 +- arch/riscv/kvm/vcpu.c | 2 +- arch/s390/kvm/kvm-s390.c | 2 +- arch/x86/kvm/x86.c | 4 ++-- include/linux/kvm_host.h | 1 + virt/kvm/kvm_main.c | 3 +++ 8 files changed, 11 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index e49ead6d005cc4..d581aedf00190b 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -915,7 +915,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) vcpu_load(vcpu); - if (run->immediate_exit) { + if (!vcpu->wants_to_run) { ret = -EINTR; goto out; } diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c index 231ac052b506b9..f1a99962027a4f 100644 --- a/arch/mips/kvm/mips.c +++ b/arch/mips/kvm/mips.c @@ -436,7 +436,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) vcpu->mmio_needed = 0; } - if (vcpu->run->immediate_exit) + if (!vcpu->wants_to_run) goto out; lose_fpu(1); diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index 6cef200c2404df..0e35668b28302f 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -1858,7 +1858,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) kvm_sigset_activate(vcpu); - if (run->immediate_exit) + if (!vcpu->wants_to_run) r = -EINTR; else r = kvmppc_vcpu_run(vcpu); diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c index 9584d62c96ee74..27f5ffc762dd95 100644 --- a/arch/riscv/kvm/vcpu.c +++ b/arch/riscv/kvm/vcpu.c @@ -676,7 +676,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) return ret; } - if (run->immediate_exit) { + if (!vcpu->wants_to_run) { kvm_vcpu_srcu_read_unlock(vcpu); return -EINTR; } diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 890d850f51f076..bccbb84eb1be65 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -5048,7 +5048,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) if (vcpu->kvm->arch.pv.dumping) return -EINVAL; - if (kvm_run->immediate_exit) + if (!vcpu->wants_to_run) return -EINTR; if (kvm_run->kvm_valid_regs & ~KVM_SYNC_S390_VALID_FIELDS || diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c04277b35e2edf..313fce77e05896 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11224,7 +11224,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) kvm_vcpu_srcu_read_lock(vcpu); if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) { - if (kvm_run->immediate_exit) { + if (!vcpu->wants_to_run) { r = -EINTR; goto out; } @@ -11302,7 +11302,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) WARN_ON_ONCE(vcpu->mmio_needed); } - if (kvm_run->immediate_exit) { + if (!vcpu->wants_to_run) { r = -EINTR; goto out; } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 57c7b4009f5758..17ff73f1b684b5 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -378,6 +378,7 @@ struct kvm_vcpu { bool dy_eligible; } spin_loop; #endif + bool wants_to_run; bool preempted; bool ready; struct kvm_vcpu_arch arch; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index b83f7612f2506c..81024cee82cba3 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -4160,7 +4160,10 @@ static long kvm_vcpu_ioctl(struct file *filp, synchronize_rcu(); put_pid(oldpid); } + vcpu->wants_to_run = !READ_ONCE(vcpu->run->immediate_exit); r = kvm_arch_vcpu_ioctl_run(vcpu); + vcpu->wants_to_run = false; + trace_kvm_userspace_exit(vcpu->run->exit_reason, r); break; } -- 2.53.0