Re: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.

["Yu, Zhang" <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 2/1/2016 11:14 PM, Yu, Zhang wrote:
> On 2/1/2016 9:07 PM, Jan Beulich wrote:
> > > > > On 01.02.16 at 13:49, <wei.liu2@xxxxxxxxxx> wrote:
> > > On Mon, Feb 01, 2016 at 05:15:16AM -0700, Jan Beulich wrote:
> > > > > > > On 01.02.16 at 13:02, <wei.liu2@xxxxxxxxxx> wrote:
> > > > > On Mon, Feb 01, 2016 at 12:52:51AM -0700, Jan Beulich wrote:
> > > > > > > > > On 30.01.16 at 15:38, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > > > > > > On 1/30/2016 12:33 AM, Jan Beulich wrote:
> > > > > > > > > > > On 29.01.16 at 11:45, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > > > > > > > > --- a/xen/arch/x86/hvm/hvm.c
> > > > > > > > > +++ b/xen/arch/x86/hvm/hvm.c
> > > > > > > > > @@ -940,6 +940,8 @@ static int
> > > > > > > > > hvm_ioreq_server_alloc_rangesets(struct
> > > > > hvm_ioreq_server *s,
> > > > > > > > >    {
> > > > > > > > >        unsigned int i;
> > > > > > > > >        int rc;
> > > > > > > > > +    unsigned int max_wp_ram_ranges =
> > > > > > > > > +
> > > > > > > > > s->domain->arch.hvm_domain.params[HVM_PARAM_MAX_WP_RAM_RANGES];
> > > > > > > > You're still losing the upper 32 bits here. Iirc you agreed to
> > > > > > > > range
> > > > > > > > check the value before storing into params[]...
> > > > > > > Thanks, Jan. :)
> > > > > > > In this version, the check is added in routine parse_config_data().
> > > > > > > If option 'max_wp_ram_ranges' is configured with an unreasonable
> > > > > > > value,
> > > > > > > the xl will terminate, before calling xc_hvm_param_set(). Does this
> > > > > > > change meet your requirement? Or maybe did I have some
> > > > > > > misunderstanding
> > > > > > > on this issue?
> > > > > > Checking in the tools is desirable, but the hypervisor shouldn't rely
> > > > > > on any tool side checking.
> > > > > As in hypervisor needs to sanitise all input from toolstack? I don't
> > > > > think Xen does that today.
> > > > If it doesn't, then that's a bug. Note that in many cases (domctl-s
> > > > and alike) such bogus trusting in the tool stack behaving correctly
> > > > is only not a security issue due to XSA-77. Yet with XSA-77 we
> > > > made quite clear that we shouldn't knowingly allow in further such
> > > > issues (it'll be hard enough to find and address all existing ones).
> > > So are you suggesting pulling the check done in toolstack into
> > > hypervisor?
> > I think the check in the tools should stay (allowing for a
> > distinguishable error message to be issued); all I'm saying is
> > that doing the check in the tools is not enough.
> >
> > Jan
> Thank you Jan and Wei. And sorry for the late response.
> But I still do not quite understand. :)
> If tool stack can guarantee the validity of a parameter,
> under which circumstances will hypervisor be threatened?
> I'm not familiar with XSA-77, and I'll read it ASAP.
>
> B.R.
> Yu
Sorry to bother you, Jan.
After a second thought, I guess one of the security concern
is when some APP is trying to trigger the HVMOP_set_param
directly with some illegal values.
So, we need also validate this param in hvm_allow_set_param,
current although hvm_allow_set_param has not performed any
validation other parameters. We need to do this for the new
ones. Is this understanding correct?
Another question is: as to the tool stack side, do you think
an error message would suffice? Shouldn't xl be terminated?

Thanks
Yu

> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel