From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (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 3FEE3B67E for ; Wed, 8 Apr 2026 00:14:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775607286; cv=none; b=OeD82Az1GFN6XKztJXR+KKEvW8Iy7pEK5bonpVcQw0axllvoJ8qjFIggPL5KYqZ8GDe3SSSXvBJQ/ARD0VqZUg+a4Skwsf9XgDFNXbHT0RKf6RnQQBeITf7OJ5PoGxsQ4h/tvFGWIBnkzHm2rKE1FAeltXIlsSK8KP9BZXMbiX4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775607286; c=relaxed/simple; bh=myshdu0wUsQa43X+Mru0as+d76NbzjD6qLvfjjN9vz4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=jLB9pHFL+v7rY4IW3tO1J07p7gpgiNV/wpvmFtQ9BZHkIHLC0Mc/IHjUQ0SISsJvad2vugsgcMDPKhUwKtfZixrpB+xU6UMoxxW4KMryc3Vf485bfB2Q+gJfFUK+9l5zSMrE1T9mD99+p6avzAXMUYzjlFEqZarU6520xa0gwvA= 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=K9C73GAa; arc=none smtp.client-ip=209.85.215.202 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="K9C73GAa" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-c76c62eb15bso2276148a12.0 for ; Tue, 07 Apr 2026 17:14:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1775607283; x=1776212083; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=tgTCX/ofbDOTHq/UdV0rpq2HLJ8Mx4LSdkKD0Ovj9BY=; b=K9C73GAaqJIbqJg+FgDyESOby6IA0WzKVZg9UruFfcjdTgteVCJY8Il2gJFbLKz0S2 Gm5EOmh/bewVpsqVSAW88gFO6VgRkwgv1t2fZgqpEDh+8VCyguNQuPV9961DkYWZtpsm JyMC7ouH9+gKM4Mhto2s/q9q6PcKe5d2xjMTbYT22SJGQTf26nGG4VtXDOFvlNo6AD9C ooSSTPzVwNDFDosox6dEQdCoZTS50lcZiRiWtll9+li260sV2UFUGfA9SLOwWCOXFm6s KnwcrlF8pqshebYRc1jIulg3ErX4lRPZdQb8+7BSQS2XslWNeSwxGgc4sqayBI1lUBBv qqug== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775607283; x=1776212083; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=tgTCX/ofbDOTHq/UdV0rpq2HLJ8Mx4LSdkKD0Ovj9BY=; b=mZJIXWE7LpMgc6mYSbcm0NfdvEory+ZDZ1daejQxYa0tXqu1KnK7ncXY6hwTfNL//x xHC0X9sIT+4o7dQsVEXg3Qo4IHiQS8xhHAbU4Dh54YSi+9GyiacuzSRbFbUMRNMX4ZPR TnY2QgKVl4ZqZvVnGt1F0PUNjf2vLIVUIKD/dkB/r4uKAE2DYwBtI3Nx5hvkUIUPkfPR YUorhQkbfKSuq3SXsAKLU6gd1zVqHWjfQjaARL65qp9rdvbD0nq78fiHn8sxQQ7h4TQK 83dmRWSjN4UFs4ueu3dvAFHyuy1N7oEwje6j0ugKwaOoG8jfZ0GbuEPixMTwD7/reTst WPeQ== X-Forwarded-Encrypted: i=1; AJvYcCVO7CZ2UuuogEg49FdNPwA6AZrPbZ7fn+xUCecyPHJLXZaFnnaY8gsNb4dCbPUDErlrohTXDCPGyP5m+MI=@vger.kernel.org X-Gm-Message-State: AOJu0Yx0gdVKKrMebdTHO5fdP0klPgOHAG5ukddddaL9sr147AoNs5te k6AoQkunVVuYqznnq0S5CcKxksSuBU7EajBJWfv+MZhZxxRPji+yx8WtGf+kpvDVSEffRBYheo9 K8Pcg2w== X-Received: from pfbic2.prod.google.com ([2002:a05:6a00:8a02:b0:82c:efb6:4087]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:2393:b0:82c:dd31:b83d with SMTP id d2e1a72fcca58-82d0dba0775mr18933513b3a.38.1775607283332; Tue, 07 Apr 2026 17:14:43 -0700 (PDT) Date: Tue, 7 Apr 2026 17:14:36 -0700 In-Reply-To: <20260312234823.3120658-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260312234823.3120658-1-seanjc@google.com> X-Mailer: git-send-email 2.53.0.1213.gd9a14994de-goog Message-ID: <177560706203.1572452.5325835766446538096.b4-ty@google.com> Subject: Re: [PATCH v2 0/2] KVM: x86: Syzkaller nested_run_pending defense From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Yosry Ahmed Content-Type: text/plain; charset="utf-8" On Thu, 12 Mar 2026 16:48:21 -0700, Sean Christopherson wrote: > Stop playing a losing game of whack-a-mole with syzkaller over > nested_run_pending, and simply treat the flag as "untrusted" if userspace gains > control of the vCPU. I.e. don't WARN if userspace _may_ have stuffed vCPU > state to force an impossible VM-Exit. > > The signal:noise ratio for nested_run_pending WARNs when syzkaller is fuzzing > nVMX/nSVM is awful, and playing whack-a-mole with syzkaller is doing more harm > that good at this point. While it's possible syzkaller could find an actual > KVM bug by stuffing vCPU state, if the _only_ symptom is the nested_run_pending > WARN, then in theory the bug should also be hittable by stuffing L2 state prior > to nested VM-Enter. > > [...] Applied to kvm-x86 nested. [1/2] KVM: x86: Move nested_run_pending to kvm_vcpu_arch https://github.com/kvm-x86/linux/commit/3d4470d71fbf [2/2] KVM: x86: Suppress WARNs on nested_run_pending after userspace exit https://github.com/kvm-x86/linux/commit/7212094baef5 -- https://github.com/kvm-x86/linux/tree/next