CVE-2025-40222
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-12-04

Last updated on: 2025-12-04

Assigner: kernel.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 ]---
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Meta Information
Published
2025-12-04
Last Modified
2025-12-04
Generated
2026-05-07
AI Q&A
2025-12-04
EPSS Evaluated
2026-05-05
NVD
CVE-2025-40222
EUVD
EUVD-2025-201237
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
renesas rz_t2h *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability is in the Linux kernel's serial driver for Renesas RZ/T2H hardware. It involves incorrect handling of a register called overrun_reg for the RSCI port type. The code mistakenly treats overrun_reg as an index into an array when it is actually a memory offset, causing out-of-bounds memory access. This leads to invalid register access warnings and potential instability or crashes in the kernel when handling serial port receive errors.


How can this vulnerability impact me? :

The vulnerability can cause the Linux kernel to access memory outside of intended bounds, which may lead to kernel warnings, instability, or crashes. This can affect system reliability and potentially cause denial of service on affected devices using the RZ/T2H serial driver.


How can this vulnerability be detected on my network or system? Can you suggest some commands?

This vulnerability can be detected by monitoring system logs for warnings related to invalid register access in the sh-sci serial driver, specifically messages like 'WARNING: CPU: 0 PID: 0 at drivers/tty/serial/sh-sci.c:522 sci_serial_in'. You can check the kernel log using the command: dmesg | grep -i 'sci_serial_in' or dmesg | grep -i 'sh-sci'. Additionally, monitoring for WARN messages related to FIFO overrun handling in the serial driver may help detect the issue.


What immediate steps should I take to mitigate this vulnerability?

Immediate mitigation involves updating the Linux kernel to a version where the vulnerability is fixed, as the issue is resolved by correcting the RSCI FIFO overrun handling in the sh-sci serial driver. Avoid using affected serial port types or disable the affected serial driver if possible until a patched kernel is applied. There are no configuration workarounds mentioned, so applying the official fix is the recommended step.


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