On 17.11.2021 03:11, Stefano Stabellini wrote:
--- 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;}
If such a check gets added, then I think known-invalid frame numbers should be covered at even higher a priority than zero. This would, for example, also mean to ...
xen_store_gfn = (unsigned long)v;
... stop silently truncating a value here.
By covering them we would then have the option to pre-fill PFN params with, say, ~0 in the hypervisor (to clearly identify them as invalid, rather than having to guess at the validity of 0). I haven't really checked yet whether such a change would be compatible with existing software ...
Jan