[PATCH 1/2] i2c: imx-lpi2c: clean rx/tx buffers upon new message

[Emanuele Ghidoli]

On 30/01/2023 16:32, Alexander Stein wrote:
> When start sending a new message clear the Rx & Tx buffer pointers in
> order to avoid using stale pointers.
> 
> Signed-off-by: Alexander Stein <alexander.stein at ew.tq-group.com>
> ---
> I noticed an ambigous stack corruption once my rtc-pcf85063 driver probes.
> 
> [    2.695684] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: pcf85063_rtc_read_time+0x10/0x100
> [    2.706669] CPU: 1 PID: 63 Comm: kworker/u8:2 Not tainted 6.2.0-rc6-next-20230130+ #1185 ca067559321ae817c063baccdba80d328f10f73
> [    2.718331] Hardware name: TQ-Systems i.MX8QXP TQMa8XQP on MBa8Xx (DT)
> [    2.724866] Workqueue: events_unbound deferred_probe_work_func
> [    2.730712] Call trace:
> [    2.733161]  dump_backtrace+0x9c/0x11c
> [    2.736914]  show_stack+0x14/0x1c
> [    2.740232]  dump_stack_lvl+0x5c/0x78
> [    2.743907]  dump_stack+0x14/0x1c
> [    2.747225]  panic+0x34c/0x39c
> [    2.750283]  __ktime_get_real_seconds+0x0/0xc
> [    2.754653]  pcf85063_ioctl+0x0/0xf0
> [    2.758232]  __rtc_read_time+0x44/0x114
> [    2.762081]  __rtc_read_alarm+0x258/0x460
> [    2.766095]  __devm_rtc_register_device+0x174/0x2b4
> [    2.770986]  pcf85063_probe+0x258/0x4d4
> [    2.774825]  i2c_device_probe+0x100/0x33c
> 
> The backtrace did not indicate the actual cause of it. Checking the code the
> RTC driver seemed to be ok, so it has to be in the i2c bus driver.
> At some point I noticed that I see both Rx and Tx interrupts at the same time,
> which is odd. Also both rx_buf and tx_buf was set simultaneously. Clearly
> a bug to me.
> Clearing the buffer pointers upon each new i2c message triggered a NULL
> pointer dereference:
> 
> [    2.694923] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000001
> [    2.703730] Mem abort info:
> [    2.706525]   ESR = 0x0000000096000004
> [    2.710278]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    2.715595]   SET = 0, FnV = 0
> [    2.718653]   EA = 0, S1PTW = 0
> [    2.721798]   FSC = 0x04: level 0 translation fault
> [    2.726680] Data abort info:
> [    2.729556]   ISV = 0, ISS = 0x00000004
> [    2.733387]   CM = 0, WnR = 0
> [    2.736358] [0000000000000001] user address but active_mm is swapper
> [    2.742719] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
> [    2.748990] Modules linked in:
> [    2.752051] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.2.0-rc6-next-20230130+ #1184 44a8abebca6bfabc93e20ac52bce
> 47da7f92cec1
> [    2.763368] Hardware name: TQ-Systems i.MX8QXP TQMa8XQP on MBa8Xx (DT)
> [    2.769902] pstate: 800000c5 (Nzcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [    2.776868] pc : lpi2c_imx_write_txfifo+0x44/0xb0
> [    2.781585] lr : lpi2c_imx_isr+0x60/0x8c
> [    2.785512] sp : ffff800008003ef0
> [    2.788831] x29: ffff800008003ef0 x28: ffff8000099c1ec0 x27: 00000000bfe632c8
> [    2.795980] x26: 0000000000000000 x25: ffff800009b935ed x24: ffff800009a4d4c0
> [    2.803130] x23: ffff00000365e800 x22: 0000000000000128 x21: 0000000000000000
> [    2.810280] x20: ffff0000033f4080 x19: 0000000003000103 x18: 0000000000000000
> [    2.817430] x17: ffff80003688a000 x16: ffff800008000000 x15: 0000000000000000
> [    2.824579] x14: 0000000000000000 x13: ffff8000099d1db8 x12: 0000000000000000
> [    2.831729] x11: ffff800009503180 x10: 0000000000000a80 x9 : ffff8000099b3d20
> [    2.838879] x8 : ffff8000099c29a0 x7 : 00000000000000c0 x6 : ffff000002838028
> [    2.846029] x5 : 0000000000000002 x4 : 0000000000000000 x3 : 0000000000000000
> [    2.849626] imx-scu system-controller: RPC send msg timeout
> [    2.853178] x2 : ffff800009c88060 x1 : 0000000000000001 x0 : ffff0000033f4080
> [    2.858764]  enet1: failed to power off resource 252 ret -110
> [    2.865897] Call trace:
> [    2.865901]  lpi2c_imx_write_txfifo+0x44/0xb0
> [    2.878443]  __handle_irq_event_percpu+0x5c/0x188
> [    2.883151]  handle_irq_event+0x48/0xb0
> 
> $ ./scripts/faddr2line build_arm64/vmlinux lpi2c_imx_write_txfifo+0x44/0xb0
> lpi2c_imx_write_txfifo+0x44/0xb0:
> lpi2c_imx_write_txfifo at drivers/i2c/busses/i2c-imx-lpi2c.c:364
> 
> This now clearly pinpoints the wrong access which previously corrupted the
> stack. The error leading to this wrong access is addressed in the
> following patch.
> 
>   drivers/i2c/busses/i2c-imx-lpi2c.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
> index 188f2a36d2fd..c6d0225246e6 100644
> --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> @@ -463,6 +463,8 @@ static int lpi2c_imx_xfer(struct i2c_adapter *adapter,
>   		if (num == 1 && msgs[0].len == 0)
>   			goto stop;
>   
> +		lpi2c_imx->rx_buf = NULL;
> +		lpi2c_imx->tx_buf = NULL;
>   		lpi2c_imx->delivered = 0;
>   		lpi2c_imx->msglen = msgs[i].len;
>   		init_completion(&lpi2c_imx->complete);

Hello,
I have same problem with rtc-ds1307 driver and NXP imx8x (using ic2-imx-lpi2c.c bus driver).
I do not have the full stack trace but I'm sure is very similar:
[   10.750015] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: ds1307_get_time+0x2a4/0x2c4 [rtc_ds1307]

Your patches are fixing this too and they seem good to me.
About the [2/2] patch your approach sound better to me than the downstream approach.

Emanuele Ghidoli