Re: [PATCH] i2c: i801: Don't generate an interrupt on bus reset

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

Hi

On 5/25/21 6:03 PM, Jean Delvare wrote:
> Now that the i2c-i801 driver supports interrupts, setting the KILL bit
> in a attempt to recover from a timed out transaction triggers an
> interrupt. Unfortunately, the interrupt handler (i801_isr) is not
> prepared for this situation and will try to process the interrupt as
> if it was signaling the end of a successful transaction. In the case
> of a block transaction, this can result in an out-of-range memory
> access.
> 
> This condition was reproduced several times by syzbot:
> https://syzkaller.appspot.com/bug?extid=ed71512d469895b5b34e
> https://syzkaller.appspot.com/bug?extid=8c8dedc0ba9e03f6c79e
> https://syzkaller.appspot.com/bug?extid=c8ff0b6d6c73d81b610e
> https://syzkaller.appspot.com/bug?extid=33f6c360821c399d69eb
> https://syzkaller.appspot.com/bug?extid=be15dc0b1933f04b043a
> https://syzkaller.appspot.com/bug?extid=b4d3fd1dfd53e90afd79
> 
> So disable interrupts while trying to reset the bus. Interrupts will
> be enabled again for the following transaction.
> 
> Fixes: 636752bcb517 ("i2c-i801: Enable IRQ for SMBus transactions")
> Reported-by: syzbot+b4d3fd1dfd53e90afd79@syzkaller.appspotmail.com
> Signed-off-by: Jean Delvare <jdelvare@suse.de>
> Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> ---
>   drivers/i2c/busses/i2c-i801.c |    6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
> 
I hope I managed to test this properly. At least I was able to trigger 
KASAN quite easily and after your patch not anymore.

My test was to run "i2cdump -y 0 0x50 i" a few times with this hack:

--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -653,6 +653,7 @@ static irqreturn_t i801_isr(int irq, void *dev_id)
  	struct i801_priv *priv = dev_id;
  	u16 pcists;
  	u8 status;
+	static int count = 0;

  	/* Confirm this is our interrupt */
  	pci_read_config_word(priv->pci_dev, SMBPCISTS, &pcists);
@@ -676,8 +677,10 @@ static irqreturn_t i801_isr(int irq, void *dev_id)
  	status &= SMBHSTSTS_INTR | STATUS_ERROR_FLAGS;
  	if (status) {
  		outb_p(status, SMBHSTSTS(priv));
-		priv->status = status;
-		wake_up(&priv->waitq);
+		if ((count++ % 10)) {
+				priv->status = status;
+				wake_up(&priv->waitq);
+		}
  	}

  	return IRQ_HANDLED;

Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>