drivers/xen/xenbus/xenbus_probe.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
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.
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>
---
Changes in v4:
- say "all bits set" instead of INVALID_PFN
- improve check
Changes in v3:
- improve in-code comment
- improve check
Changes in v2:
- add check for ULLONG_MAX (unitialized)
- add check for ULONG_MAX #if BITS_PER_LONG == 32 (actual error)
- add pr_err error message
drivers/xen/xenbus/xenbus_probe.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 94405bb3829e..251b26439733 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -951,6 +951,29 @@ 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,
--
2.25.1
On 11/23/21 4:07 PM, Stefano Stabellini wrote: > 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. > > 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> Applied to for-linus-5.16c -boris
On 23.11.2021 22:07, Stefano Stabellini wrote: > 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. > > 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: Jan Beulich <jbeulich@suse.com>
On 23.11.21 22:07, Stefano Stabellini wrote: > 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. > > 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> Juergen
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