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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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?

Wei.

> Jan
> 

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