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xen: detect uninitialized xenbus in xenbus_init 

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@vger.kernel.org
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Link: https://lore.kernel.org/r/20211123210748.1910236-1-sstabellini@kernel.org
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Stefano Stabellini 2021-11-23 13:07:48 -08:00 committed by Greg Kroah-Hartman
parent 173fe1aedf
commit 4f1adc3f57
1 changed files with 23 additions and 0 deletions
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23
drivers/xen/xenbus/xenbus_probe.c
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@ -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,