PCI: hv: Annotate struct hv_dr_state with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct hv_dr_state.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Link: https://lore.kernel.org/linux-pci/20230922175257.work.900-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Acked-by: Wei Liu <wei.liu@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Krzysztof Wilczyński <kw@linux.com>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: linux-hyperv@vger.kernel.org
Cc: linux-pci@vger.kernel.org

drivers/pci/controller/pci-hyperv.c

@@ -545,7 +545,7 @@ struct hv_pcidev_description {
 struct hv_dr_state {
 	struct list_head list_entry;
 	u32 device_count;
-	struct hv_pcidev_description func[];
+	struct hv_pcidev_description func[] __counted_by(device_count);
 };
 
 struct hv_pci_dev {