CVE-2026-46022: misc: ibmasm: fix OOB MMIO read in ibmasm_handle_mouse_interrupt()

In the Linux kernel, the following vulnerability has been resolved:

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

ibmasmhandlemouseinterrupt() performs an out-of-bounds MMIO read when the queue reader or writer index from hardware exceeds REMOTEQUEUESIZE (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 getqueuereader() and getqueuewriter() return raw readl() values that are passed directly into getqueueentry(), which computes:

queuebegin + reader sizeof(struct remoteinput)

with no bounds check. This unchecked MMIO address is then passed to memcpyfromio(), 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 REMOTEQUEUESIZE at the top of the loop body, before any call to getqueueentry(). On an out-of-range value, reset the reader register to 0 via setqueuereader() before breaking, so that normal queue operation can resume if the corrupted hardware state is transient.