usb: host: xhci: mvebu: Iterate over array indexes instead of using pointer math

Walking the dram->cs array was seen as accesses beyond the first array
item by the compiler. Instead, use the array index directly. This allows
for run-time bounds checking under CONFIG_UBSAN_BOUNDS as well. Seen
with GCC 13 with -fstrict-flex-arrays:

In function 'xhci_mvebu_mbus_config',
    inlined from 'xhci_mvebu_mbus_init_quirk' at ../drivers/usb/host/xhci-mvebu.c:66:2:
../drivers/usb/host/xhci-mvebu.c:37:28: warning: array subscript 0 is outside array bounds of 'const struct mbus_dram_window[0]' [-Warray-bounds=]
   37 |                 writel(((cs->size - 1) & 0xffff0000) | (cs->mbus_attr << 8) |
      |                          ~~^~~~~~

Cc: Mathias Nyman <mathias.nyman@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230204183651.never.663-kees@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/xhci-mvebu.c b/drivers/usb/host/xhci-mvebu.c
index 60651a5..87f1597 100644 (file)
--- a/drivers/usb/host/xhci-mvebu.c
+++ b/drivers/usb/host/xhci-mvebu.c
@@ -32,7 +32,7 @@ static void xhci_mvebu_mbus_config(void __iomem *base,
 
        /* Program each DRAM CS in a seperate window */
        for (win = 0; win < dram->num_cs; win++) {
-               const struct mbus_dram_window *cs = dram->cs + win;
+               const struct mbus_dram_window *cs = &dram->cs[win];
 
                writel(((cs->size - 1) & 0xffff0000) | (cs->mbus_attr << 8) |
                       (dram->mbus_dram_target_id << 4) | 1,