From: Stefano Stabellini stefano.stabellini@xilinx.com
If the xenstore page hasn't been allocated properly, reading the value of the related hvm_param (HVM_PARAM_STORE_PFN) won't actually return error. Instead, it will succeed and return zero.
Instead of attempting to xen_remap a bad guest physical address, detect this condition and return early.
Note that although a guest physical address of zero for HVM_PARAM_STORE_PFN is theoretically possible, it is not a good choice and zero has never been validly used in that capacity.
Cc: stable@vger.kernel.org Signed-off-by: Stefano Stabellini stefano.stabellini@xilinx.com --- drivers/xen/xenbus/xenbus_probe.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c index 94405bb3829e..c89de0062399 100644 --- a/drivers/xen/xenbus/xenbus_probe.c +++ b/drivers/xen/xenbus/xenbus_probe.c @@ -951,6 +951,18 @@ static int __init xenbus_init(void) err = hvm_get_parameter(HVM_PARAM_STORE_PFN, &v); if (err) goto out_error; + /* + * Uninitialized hvm_params are zero and return no error. + * Although it is theoretically possible to have + * HVM_PARAM_STORE_PFN set to zero on purpose, in reality it is + * not zero when valid. If zero, it means that Xenstore hasn't + * been properly initialized. Instead of attempting to map a + * wrong guest physical address return error. + */ + if (v == 0) { + err = -ENOENT; + goto out_error; + } xen_store_gfn = (unsigned long)v; xen_store_interface = xen_remap(xen_store_gfn << XEN_PAGE_SHIFT,