From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx> commit 36e8f60f0867d3b70d398d653c17108459a04efe upstream. 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. Also recognize all bits set as an invalid value. For 32-bit Linux, any pfn above ULONG_MAX would get truncated. Pfns above ULONG_MAX should never be passed by the Xen tools to HVM guests anyway, so check for this condition and return early. Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx> Reviewed-by: Juergen Gross <jgross@xxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> Link: https://lore.kernel.org/r/20211123210748.1910236-1-sstabellini@xxxxxxxxxx Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/xen/xenbus/xenbus_probe.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) --- a/drivers/xen/xenbus/xenbus_probe.c +++ b/drivers/xen/xenbus/xenbus_probe.c @@ -886,6 +886,29 @@ 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. + * + * Also recognize all bits set as an invalid value. + */ + if (!v || !~v) { + err = -ENOENT; + goto out_error; + } + /* Avoid truncation on 32-bit. */ +#if BITS_PER_LONG == 32 + if (v > ULONG_MAX) { + pr_err("%s: cannot handle HVM_PARAM_STORE_PFN=%llx > ULONG_MAX\n", + __func__, v); + err = -EINVAL; + goto out_error; + } +#endif xen_store_gfn = (unsigned long)v; xen_store_interface = xen_remap(xen_store_gfn << XEN_PAGE_SHIFT,
