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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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


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