netdev - Re: [PATCH v2 0/2] vhost: Skip access checks on GIOVAs

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Date:   Thu, 1 Oct 2020 08:46:29 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Greg Kurz <groug@...d.org>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        qemu-devel@...gnu.org, Laurent Vivier <laurent@...ier.eu>,
        David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH v2 0/2] vhost: Skip access checks on GIOVAs

On Tue, Sep 29, 2020 at 06:30:20PM +0200, Greg Kurz wrote:
> This series addresses some misuse around vring addresses provided by
> userspace when using an IOTLB device. The misuse cause failures of
> the VHOST_SET_VRING_ADDR ioctl on POWER, which in turn causes QEMU
> to crash at migration time.
> 
> While digging some more I realized that log_access_ok() can also be 
> passed a GIOVA (vq->log_addr) even though log_used() will never log
> anything at that address. I could observe addresses beyond the end
> of the log bitmap being passed to access_ok(), but it didn't have any
> impact because the addresses were still acceptable from an access_ok()
> standpoint. Adding a second patch to fix that anyway.
> 
> Note that I've also posted a patch for QEMU so that it skips the used
> structure GIOVA when allocating the log bitmap. Otherwise QEMU fails to
> allocate it because POWER puts GIOVAs very high in the address space (ie.
> over 0x800000000000000ULL).
> 
> https://patchwork.ozlabs.org/project/qemu-devel/patch/160105498386.68108.2145229309875282336.stgit@bahia.lan/

I queued this. Jason, can you ack please?

> v2:
>  - patch 1: move the (vq->ioltb) check from vhost_vq_access_ok() to
>             vq_access_ok() as suggested by MST
>  - patch 2: new patch
> 
> ---
> 
> Greg Kurz (2):
>       vhost: Don't call access_ok() when using IOTLB
>       vhost: Don't call log_access_ok() when using IOTLB
> 
> 
>  drivers/vhost/vhost.c |   32 ++++++++++++++++++++++++--------
>  1 file changed, 24 insertions(+), 8 deletions(-)
> 
> --
> Greg