linux-kernel - Re: [PATCH 7/7] vfio/pci: Remove map-on-fault behavior

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YRJC1buKp67kGemh@infradead.org>
Date:   Tue, 10 Aug 2021 11:11:49 +0200
From:   Christoph Hellwig <hch@...radead.org>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, peterx@...hat.com
Subject: Re: [PATCH 7/7] vfio/pci: Remove map-on-fault behavior

On Thu, Aug 05, 2021 at 11:08:21AM -0600, Alex Williamson wrote:
> +void vfio_pci_test_and_up_write_memory_lock(struct vfio_pci_device *vdev)
> +{
> +	if (vdev->zapped_bars && __vfio_pci_memory_enabled(vdev)) {
> +		WARN_ON(vfio_device_io_remap_mapping_range(&vdev->vdev,
> +			VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX),
> +			VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX) -
> +			VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX)));
> +		vdev->zapped_bars = false;

Doing actual work inside a WARN_ON is pretty nasty.  Also the non-ONCE
version here will lead to massive log splatter if it actually hits.

I'd prefer something like:

	loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
	loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);

	if (vdev->zapped_bars && __vfio_pci_memory_enabled(vdev)) {
		if (!vfio_device_io_remap_mapping_range(&vdev->vdev, start,
				end - start))
			vdev->zapped_bars = false;
		WARN_ON_ONCE(vdev->zapped_bars);

>  	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> -	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);

What is the story with this appearing earlier and disappearing here
again?

> +extern void vfio_pci_test_and_up_write_memory_lock(struct vfio_pci_device
> +						   *vdev);

No need for the extern.