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Message-ID: <CAMuHMdUn5cd++TeWQvwLhFYQ7_iwwrRT0pdiENVRvOTGbDmGOw@mail.gmail.com>
Date: Thu, 6 Nov 2025 17:55:54 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@...esas.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>,
Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
Thierry Bultel <thierry.bultel.yh@...renesas.com>,
Wolfram Sang <wsa+renesas@...g-engineering.com>, Nam Cao <namcao@...utronix.de>,
Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>, linux-kernel@...r.kernel.org,
linux-serial@...r.kernel.org, stable@...r.kernel.org,
Biju Das <biju.das.jz@...renesas.com>, linux-reneas-soc@...r.kernel.org
Subject: Re: [PATCH] tty: serial: sh-sci: fix RSCI FIFO overrun handling
CC Biju, linux-renesas-soc
On Thu, 6 Nov 2025 at 17:54, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Cosmin,
>
> On Tue, 23 Sept 2025 at 17:47, Cosmin Tanislav
> <cosmin-gabriel.tanislav.xa@...esas.com> wrote:
> > 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 ]---
> >
> > Cc: stable@...r.kernel.org
> > Fixes: 0666e3fe95ab ("serial: sh-sci: Add support for RZ/T2H SCI")
> > Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@...esas.com>
>
> Thanks for your patch, which is now commit ef8fef45c74b5a00 ("tty:
> serial: sh-sci: fix RSCI FIFO overrun handling") in v6.18-rc3.
>
> > --- a/drivers/tty/serial/sh-sci.c
> > +++ b/drivers/tty/serial/sh-sci.c
> > @@ -1014,16 +1014,18 @@ static int sci_handle_fifo_overrun(struct uart_port *port)
> > struct sci_port *s = to_sci_port(port);
> > const struct plat_sci_reg *reg;
> > int copied = 0;
> > - u16 status;
> > + u32 status;
> >
> > - reg = sci_getreg(port, s->params->overrun_reg);
> > - if (!reg->size)
> > - return 0;
> > + if (s->type != SCI_PORT_RSCI) {
> > + reg = sci_getreg(port, s->params->overrun_reg);
> > + if (!reg->size)
> > + return 0;
> > + }
> >
> > - status = sci_serial_in(port, s->params->overrun_reg);
> > + status = s->ops->read_reg(port, s->params->overrun_reg);
> > if (status & s->params->overrun_mask) {
> > status &= ~s->params->overrun_mask;
> > - sci_serial_out(port, s->params->overrun_reg, status);
> > + s->ops->write_reg(port, s->params->overrun_reg, status);
> >
> > port->icount.overrun++;
> >
>
> Ouch, this is really becoming fragile, and thus hard to maintain.
> See also "[PATCH v2 2/2] serial: sh-sci: Fix deadlock during RSCI FIFO
> overrun error".
> Are you sure this is the only place where that can happen?
> sci_getreg() and sci_serial_{in,out}() are used all over the place.
>
> [1] https://lore.kernel.org/20251029082101.92156-3-biju.das.jz@bp.renesas.com/
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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