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





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

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