CVE-2025-40222 — tty: serial: sh-sci: fix RSCI FIFO overrun handling

Affected: Linux

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

tty: serial: sh-sci: fix RSCI FIFO overrun handling

The receive error handling code is shared between RSCI and all other SCIF port types, but the RSCI overrun_reg is specified as a memory offset, while for other SCIF types it is an enum value used to index into the sci_port_params->regs array, as mentioned above the sci_serial_in() function.

For RSCI, the overrun_reg is CSR (0x48), causing the sci_getreg() call inside the sci_handle_fifo_overrun() function to index outside the bounds of the regs array, which currently has a size of 20, as specified by SCI_NR_REGS.

Because of this, we end up accessing memory outside of RSCI's rsci_port_params structure, which, when interpreted as a plat_sci_reg, happens to have a non-zero size, causing the following WARN when sci_serial_in() is called, as the accidental size does not match the supported register sizes.

The existence of the overrun_reg needs to be checked because SCIx_SH3_SCIF_REGTYPE has overrun_reg set to SCLSR, but SCLSR is not present in the regs array.

Avoid calling sci_getreg() for port types which don't use standard register handling.

Use the ops->read_reg() and ops->write_reg() functions to properly read and write registers for RSCI, and change the type of the status variable to accommodate the 32-bit CSR register.

sci_getreg() and sci_serial_in() are also called with overrun_reg in the sci_mpxed_interrupt() interrupt handler, but that code pat…

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CVE-2025-40222 — tty: serial: sh-sci: fix RSCI FIFO overrun handling