linux-cve-announce - CVE-2025-40222: tty: serial: sh-sci: fix RSCI FIFO overrun handling

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Message-ID: <2025120456-CVE-2025-40222-1901@gregkh>
Date: Thu,  4 Dec 2025 16:31:57 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40222: tty: serial: sh-sci: fix RSCI FIFO overrun handling

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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 path is not used
for RSCI, as it does not have a muxed interrupt.

------------[ cut here ]------------
Invalid register access
WARNING: CPU: 0 PID: 0 at drivers/tty/serial/sh-sci.c:522 sci_serial_in+0x38/0xac
Modules linked in: renesas_usbhs at24 rzt2h_adc industrialio_adc sha256 cfg80211 bluetooth ecdh_generic ecc rfkill fuse drm backlight ipv6
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.17.0-rc1+ #30 PREEMPT
Hardware name: Renesas RZ/T2H EVK Board based on r9a09g077m44 (DT)
pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : sci_serial_in+0x38/0xac
lr : sci_serial_in+0x38/0xac
sp : ffff800080003e80
x29: ffff800080003e80 x28: ffff800082195b80 x27: 000000000000000d
x26: ffff8000821956d0 x25: 0000000000000000 x24: ffff800082195b80
x23: ffff000180e0d800 x22: 0000000000000010 x21: 0000000000000000
x20: 0000000000000010 x19: ffff000180e72000 x18: 000000000000000a
x17: ffff8002bcee7000 x16: ffff800080000000 x15: 0720072007200720
x14: 0720072007200720 x13: 0720072007200720 x12: 0720072007200720
x11: 0000000000000058 x10: 0000000000000018 x9 : ffff8000821a6a48
x8 : 0000000000057fa8 x7 : 0000000000000406 x6 : ffff8000821fea48
x5 : ffff00033ef88408 x4 : ffff8002bcee7000 x3 : ffff800082195b80
x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff800082195b80
Call trace:
 sci_serial_in+0x38/0xac (P)
 sci_handle_fifo_overrun.isra.0+0x70/0x134
 sci_er_interrupt+0x50/0x39c
 __handle_irq_event_percpu+0x48/0x140
 handle_irq_event+0x44/0xb0
 handle_fasteoi_irq+0xf4/0x1a0
 handle_irq_desc+0x34/0x58
 generic_handle_domain_irq+0x1c/0x28
 gic_handle_irq+0x4c/0x140
 call_on_irq_stack+0x30/0x48
 do_interrupt_handler+0x80/0x84
 el1_interrupt+0x34/0x68
 el1h_64_irq_handler+0x18/0x24
 el1h_64_irq+0x6c/0x70
 default_idle_call+0x28/0x58 (P)
 do_idle+0x1f8/0x250
 cpu_startup_entry+0x34/0x3c
 rest_init+0xd8/0xe0
 console_on_rootfs+0x0/0x6c
 __primary_switched+0x88/0x90
---[ end trace 0000000000000000 ]---

The Linux kernel CVE team has assigned CVE-2025-40222 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.17 with commit 0666e3fe95ab55c295984f2f51277ec27d3f190c and fixed in 6.17.6 with commit 2ec9bbd09a6cdf5b8c726be34f29630faf585d07
	Issue introduced in 6.17 with commit 0666e3fe95ab55c295984f2f51277ec27d3f190c and fixed in 6.18 with commit ef8fef45c74b5a0059488fda2df65fa133f7d7d0

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-40222
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/tty/serial/sh-sci.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/2ec9bbd09a6cdf5b8c726be34f29630faf585d07
	https://git.kernel.org/stable/c/ef8fef45c74b5a0059488fda2df65fa133f7d7d0