From mboxrd@z Thu Jan 1 00:00:00 1970 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 E9D4A28B7CC for ; Mon, 25 Aug 2025 20:42:45 +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=1756154567; cv=none; b=eex5M9g+lGsalqMmO68f2ekPQ+luKY9QmYKfpAHX6XCVDoO/JY5xR9oxfsN5+2lOj6T6uzeSJLOOSo0ZbveFzLYmhOjKvv9DngBYOVx6d7lw3B9FsuXYEOAIBRwOCeBonht7RazG8muSkwj2rnpJsnaKEe76VQmacaMXEwVifzw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756154567; c=relaxed/simple; bh=XMa1j4FdMALHD0hf0wfEKQnDwESr8sg2LTJHccbCsmI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=cOklxGr+1JCAQYj4o0yOeptOW9HzOV1dpIHuY3snH076GehbrQZ0wbP95xzlEDDoEK73Y+QpOSy8SO/Mu8ytOdtsTMce3nn/X3nPjwhWyq4QOzJKYiCkt0KAamRXhwKtjFEoO8TF3s7JvOPysi+Y7kdY587oDVU5WwTn4S1GoFQ= 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=R0zPakmW; 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="R0zPakmW" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-32515ec1faeso3408077a91.1 for ; Mon, 25 Aug 2025 13:42:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1756154565; x=1756759365; 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=56UPUwX1rhvBWEK2XIxfwcL0cy2jj3AnLwxGUdvXCzY=; b=R0zPakmWyBB+pHPf/KWhseKXp+1fF9DZS/YD1Di2Xm14W22H1mm09zJntznciYLJLm nvW4Dhf6E4B/LGtQy9JT0cy4vcvN0PIsYUg1KndD3Mni32wa9EYThZ4A7NlBJQ8lRzIU AwQz4Jr95/dTn0+q+j32GP1qXExORRKfOBKBLYjuFlZXaITa2iTGxGDFFo07iIauUi9f DSQGSACMOChm6a8PUgYAx75TnjiyDBa7ZDUsGkWG628kwA/1YLOGBW8HlBsTuC5iz+9e I3y1uTwXLRoUcmGrdwedX3EdkIQjWVrovctN5Ka/ZdP9kFwVgh2mxuo5yGtAZEzxCcpg LreA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1756154565; x=1756759365; 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=56UPUwX1rhvBWEK2XIxfwcL0cy2jj3AnLwxGUdvXCzY=; b=jL7KE8KzwXbuyKChGFbvFWgVaEu1ZLfaupivNmSp1h/4ERJ8VnwVq6Q2twT50mGrjY chUXSHCRl686+LO7lRXJrVRp5rrJ2811Ge3khAAqGxubNWWjzh29uyv6wekKDSR/lUtu G56iRt2NjYR4HMFuIMS0FcjczmPyFWv72WIwKU+rKXtGRNG808jv+6yRPFOMqJjCtccB ycBPz2IMgaZK6MvzPDngcCZO5NVuAQjTP5Tr1OKTs52wPWwVgD6YdP/BjpMHQAIdgGFz dDnTfxCj209Qeepqh35BFq7WTk13ZV7Fnn6Yu18maLCY3SRtvMxK6IeDKXKnAvDngCoP FnpQ== X-Forwarded-Encrypted: i=1; AJvYcCUUExfhiBGiq8Yfw4PgurVOxi7DOxO4LqGuFhxTytWud/EXnDpO5LJtCCr2GeAV6AMJk2M=@vger.kernel.org X-Gm-Message-State: AOJu0Yz7YlAdWhu54BAXUF2CAhKrkyFrSxCJeNqAbCEWm4E0V765ktbx x5/a769H5CpA3SSk4muhZFgDUcz5QF59qzXyhZGgBO8Po/c44wsRGbbPVtqDJIe7QWYis8j+lIc KY1P8ww== X-Google-Smtp-Source: AGHT+IFE68eL9cCsnSsmh+IHzY3LK4YmEJGjRX2EKzAva69U2rx47Leg3XgcP7SQvqX0sM+qrYaZI/PA1lQ= X-Received: from pjf15.prod.google.com ([2002:a17:90b:3f0f:b0:31e:fac4:4723]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4b4b:b0:325:6598:30fb with SMTP id 98e67ed59e1d1-32565983489mr10055495a91.29.1756154565125; Mon, 25 Aug 2025 13:42:45 -0700 (PDT) Date: Mon, 25 Aug 2025 13:42:43 -0700 In-Reply-To: <20250822080203.27247-1-yan.y.zhao@intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250822080100.27218-1-yan.y.zhao@intel.com> <20250822080203.27247-1-yan.y.zhao@intel.com> Message-ID: Subject: Re: [PATCH v3 1/3] KVM: Do not reset dirty GFNs in a memslot not enabling dirty tracking From: Sean Christopherson To: Yan Zhao Cc: pbonzini@redhat.com, peterx@redhat.com, rick.p.edgecombe@intel.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Fri, Aug 22, 2025, Yan Zhao wrote: > Do not allow resetting dirty GFNs in memslots that do not enable dirty > tracking. > > vCPUs' dirty rings are shared between userspace and KVM. After KVM sets > dirtied entries in the dirty rings, userspace is responsible for > harvesting/resetting these entries and calling the ioctl > KVM_RESET_DIRTY_RINGS to inform KVM to advance the reset_index in the dirty > rings and invoke kvm_arch_mmu_enable_log_dirty_pt_masked() to clear the > SPTEs' dirty bits or perform write protection of the GFNs. > > Although KVM does not set dirty entries for GFNs in a memslot that does not > enable dirty tracking, userspace can write arbitrary data into the dirty > ring. This makes it possible for misbehaving userspace to specify that it > has harvested a GFN from such a memslot. When this happens, KVM will be > asked to clear dirty bits or perform write protection for GFNs in a memslot > that does not enable dirty tracking, which is undesirable. > > For TDX, this unexpected resetting of dirty GFNs could cause inconsistency > between the mirror SPTE and the external SPTE in hardware (e.g., the mirror > SPTE has no write bit while the external SPTE is writable). When > kvm_dirty_log_manual_protect_and_init_set() is true and huge pages are > enabled in TDX, this could even lead to kvm_mmu_slot_gfn_write_protect() > being called and trigger KVM_BUG_ON() due to permission reduction changes > in the huge mirror SPTEs. > Sounds like this needs a Fixes and Cc: stable? > Signed-off-by: Yan Zhao > --- > virt/kvm/dirty_ring.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c > index 02bc6b00d76c..b38b4b7d7667 100644 > --- a/virt/kvm/dirty_ring.c > +++ b/virt/kvm/dirty_ring.c > @@ -63,7 +63,13 @@ static void kvm_reset_dirty_gfn(struct kvm *kvm, u32 slot, u64 offset, u64 mask) > > memslot = id_to_memslot(__kvm_memslots(kvm, as_id), id); > > - if (!memslot || (offset + __fls(mask)) >= memslot->npages) > + /* > + * Userspace can write arbitrary data into the dirty ring, making it > + * possible for misbehaving userspace to try to reset an out-of-memslot > + * GFN or a GFN in a memslot that isn't being dirty-logged. > + */ > + if (!memslot || (offset + __fls(mask)) >= memslot->npages || > + !kvm_slot_dirty_track_enabled(memslot)) Maybe check for dirty tracking being enabled before checking the range? Purely because checking if _any_ gfn can be recorded seems like something that should be checked before a specific gfn can be recorded. I.e. if (!memslot || !kvm_slot_dirty_track_enabled(memslot) || (offset + __fls(mask)) >= memslot->npages) > return; > > KVM_MMU_LOCK(kvm); > -- > 2.43.2 >