> Eric Anholt <eric@xxxxxxxxxx> hat am 27. Dezember 2018 um 19:15 geschrieben: > > > Stefan Wahren <stefan.wahren@xxxxxxxx> writes: > > > Hi Paul, > > > >> Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> hat am 24. Dezember 2018 um 10:10 geschrieben: > >> > >> > >> Hi, > >> > >> On Sat, 2018-12-22 at 13:19 +0100, Stefan Wahren wrote: > >> > Hi Paul, > >> > > >> > > Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> hat am 21. Dezember 2018 um 13:11 geschrieben: > >> > > > >> > > > >> > > The driver's interrupt handler checks whether a message is currently > >> > > being handled with the curr_msg pointer. When it is NULL, the interrupt > >> > > is considered to be unexpected. Similarly, the i2c_start_transfer > >> > > routine checks for the remaining number of messages to handle in > >> > > num_msgs. > >> > > > >> > > However, these values are never cleared and always keep the message and > >> > > number relevant to the latest transfer (which might be done already and > >> > > the underlying message memory might have been freed). > >> > > > >> > > When an unexpected interrupt hits with the DONE bit set, the isr will > >> > > then try to access the flags field of the curr_msg structure, leading > >> > > to a fatal page fault. > >> > > > >> > > Fix the issue by systematically clearing curr_msg and num_msgs in the > >> > > driver-wide device structure when a transfer is considered complete. > >> > > > >> > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> > >> > > --- > >> > > drivers/i2c/busses/i2c-bcm2835.c | 3 +++ > >> > > 1 file changed, 3 insertions(+) > >> > > > >> > > diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c > >> > > index 44deae78913e..5486252f5f2f 100644 > >> > > --- a/drivers/i2c/busses/i2c-bcm2835.c > >> > > +++ b/drivers/i2c/busses/i2c-bcm2835.c > >> > > @@ -298,6 +298,9 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], > >> > > return -ETIMEDOUT; > >> > > } > >> > > > >> > > + i2c_dev->curr_msg = NULL; > >> > > + i2c_dev->num_msgs = 0; > >> > > >> > AFAIU this would reduce the chance of a use-after-free dramatically but not completely. > >> > >> Do you have a specific case of use-after-free related to these > >> variables in mind that this cleanup would not fix (except for the > >> timeout case)? > > > > okay i was wrong about the use-after-free. But i'm not sure about this scenario on the I2C bus shared with the VC4: > > > > 1. ARM core starts I2C transfer (bcm2835_i2c_start_transfer) > > 2. VC4 triggers a BCM2835_I2C_S_DONE interrupt > > 3. ARM core catches this interrupt before the VC4 > > We don't share I2C buses with VC4, though, right? That would just be > totally broken. All i remember is this comment on Github: https://github.com/anholt/linux/issues/89#issuecomment-280111496 and currently all 3 I2C busses are enabled for the ARM core in bcm2835-rpi.dtsi. Stefan
