misc: ibmasm: fix OOB MMIO read in ibmasm_handle_mouse_interrupt()

ibmasm_handle_mouse_interrupt() performs an out-of-bounds MMIO read
when the queue reader or writer index from hardware exceeds
REMOTE_QUEUE_SIZE (60).

A compromised service processor can trigger this by writing an
out-of-range value to the reader or writer MMIO register before
asserting an interrupt. Since writer is re-read from hardware on
every loop iteration, it can also be set to an out-of-range value
after the loop has already started.

The root cause is that get_queue_reader() and get_queue_writer() return
raw readl() values that are passed directly into get_queue_entry(),
which computes:

queue_begin + reader * sizeof(struct remote_input)

with no bounds check. This unchecked MMIO address is then passed to
memcpy_fromio(), reading 8 bytes from unintended device registers.
For sufficiently large values the address falls outside the PCI BAR
mapping entirely, triggering a machine check exception.

Fix by checking both indices against REMOTE_QUEUE_SIZE at the top of
the loop body, before any call to get_queue_entry(). On an out-of-range
value, reset the reader register to 0 via set_queue_reader() before
breaking, so that normal queue operation can resume if the corrupted
hardware state is transient.

Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Fixes: 278d72ae8803 ("[PATCH] ibmasm driver: redesign handling of remote control events")
Cc: stable@vger.kernel.org
Cc: ychen@northwestern.edu
Signed-off-by: Tyllis Xu <LivelyCarpet87@gmail.com>
Link: https://patch.msgid.link/20260308062108.258940-1-LivelyCarpet87@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>