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Re: [Qemu-devel] [PATCH] nvme: fix oob access issue(CVE-2018-16847)
From: |
Keith Busch |
Subject: |
Re: [Qemu-devel] [PATCH] nvme: fix oob access issue(CVE-2018-16847) |
Date: |
Fri, 2 Nov 2018 09:00:04 -0600 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Fri, Nov 02, 2018 at 11:54:21AM +0100, Kevin Wolf wrote:
> Am 02.11.2018 um 02:22 hat Li Qiang geschrieben:
> > Currently, the nvme_cmb_ops mr doesn't check the addr and size.
> > This can lead an oob access issue. This is triggerable in the guest.
> > Add check to avoid this issue.
> >
> > Fixes CVE-2018-16847.
> >
> > Reported-by: Li Qiang <address@hidden>
> > Reviewed-by: Paolo Bonzini <address@hidden>
> > Signed-off-by: Li Qiang <address@hidden>
> > ---
> > hw/block/nvme.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > index fc7dacb..d097add 100644
> > --- a/hw/block/nvme.c
> > +++ b/hw/block/nvme.c
> > @@ -1175,6 +1175,10 @@ static void nvme_cmb_write(void *opaque, hwaddr
> > addr, uint64_t data,
> > unsigned size)
> > {
> > NvmeCtrl *n = (NvmeCtrl *)opaque;
> > +
> > + if (addr + size > NVME_CMBSZ_GETSIZE(n->bar.cmbsz)) {
>
> What prevents a guest from moving the device to the end of the address
> space and causing an integer overflow in addr + size?
>
> If this happens, we still have .max_access_size = 8. The next question is
> then, is NVME_CMBSZ_GETSIZE guaranteed to be at least 8? I suppose yes,
> but do we want to rely on this for security?
>
> Kevin
The nvme spec at least doesn't allow a way to express a CMB that isn't
at a minimum 4k aligned and sized, so 8 byte access should always be
within the boundary.