RE: [EXT] Re: [PATCH v5] i3c: Fix read from unreadable memory at i3c_master_queue_ibi()

[Manjunatha Venkatesh]

> -----Original Message-----
> From: Mukesh Kumar Savaliya <quic_msavaliy@xxxxxxxxxxx>
> Sent: Wednesday, March 26, 2025 12:15 PM
> To: Frank Li <frank.li@xxxxxxx>; Manjunatha Venkatesh
> <manjunatha.venkatesh@xxxxxxx>
> Cc: alexandre.belloni@xxxxxxxxxxx; arnd@xxxxxxxx;
> gregkh@xxxxxxxxxxxxxxxxxxx; bbrezillon@xxxxxxxxxx; linux-
> i3c@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> rvmanjumce@xxxxxxxxx; stable@xxxxxxxxxxxxxxx
> Subject: [EXT] Re: [PATCH v5] i3c: Fix read from unreadable memory at
> i3c_master_queue_ibi()
> 
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> 
> On 3/25/2025 8:13 PM, Frank Li wrote:
> > Subject should be
> >
> > i3c: Add NULL pointer check in i3c_master_queue_ibi()
> >
> yes, Aligned.
> > On Tue, Mar 25, 2025 at 03:53:32PM +0530, Manjunatha Venkatesh wrote:
> >> As part of I3C driver probing sequence for particular device
> >> instance, While adding to queue it is trying to access ibi variable
> >> of dev which is not yet initialized causing "Unable to handle kernel
> >> read from unreadable memory" resulting in kernel panic.
> >>
> >> Below is the sequence where this issue happened.
> >> 1. During boot up sequence IBI is received at host  from the slave device
> >>     before requesting for IBI, Usually will request IBI by calling
> >>     i3c_device_request_ibi() during probe of slave driver.
> >> 2. Since master code trying to access IBI Variable for the particular
> >>     device instance before actually it initialized by slave driver,
> >>     due to this randomly accessing the address and causing kernel panic.
> >> 3. i3c_device_request_ibi() function invoked by the slave driver where
> >>     dev->ibi = ibi; assigned as part of function call
> >>     i3c_dev_request_ibi_locked().
> >> 4. But when IBI request sent by slave device, master code  trying to access
> >>     this variable before its initialized due to this race condition
> >>     situation kernel panic happened.
> >
> > How about commit message as:
> >
> > The I3C master driver may receive an IBI from a target device that has
> > not been probed yet. In such cases, the master calls
> > `i3c_master_queue_ibi()` to queue an IBI work task, leading to "Unable
> > to handle kernel read from unreadable memory" and resulting in a kernel
> panic.
> >
> > Typical IBI handling flow:
> > 1. The I3C master scans target devices and probes their respective drivers.
> > 2. The target device driver calls `i3c_device_request_ibi()` to enable IBI
> >     and assigns `dev->ibi = ibi`.
> > 3. The I3C master receives an IBI from the target device and calls
> >     `i3c_master_queue_ibi()` to queue the target device driver's IBI handler
> >     task.
> >
> > However, since target device events are asynchronous to the I3C probe
> > sequence, step 3 may occur before step 2, causing `dev->ibi` to be
> > `NULL`, leading to a kernel panic.
> >
> > Add a NULL pointer check in `i3c_master_queue_ibi()` to prevent
> > accessing an uninitialized `dev->ibi`, ensuring stability.
> >
> >>
> >> Fixes: 3a379bbcea0af ("i3c: Add core I3C infrastructure")
> >> Cc: stable@xxxxxxxxxxxxxxx
> >> Link:
> >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flor
> >> e.kernel.org%2Flkml%2FZ9gjGYudiYyl3bSe%40lizhi-Precision-Tower-
> 5810%2
> >>
> F&data=05%7C02%7Cmanjunatha.venkatesh%40nxp.com%7Ceda8be8c7abc4
> 3b4ab9
> >>
> 608dd6c31c8e7%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C6387
> 856832
> >>
> 77582903%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYi
> OiIwLjAu
> >>
> MDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%
> 7C%7C
> >>
> &sdata=oyc9Wv%2Fj8HMRFIiIGL9nIw0XvI6FsLK2SvsQJ55H7XI%3D&reserved=
> 0
> >> Signed-off-by: Manjunatha Venkatesh <manjunatha.venkatesh@xxxxxxx>
> >> ---
> >> Changes since v4:
> >>    - Fix added at generic places master.c which is applicable for all
> >> platforms
> >>
> >>   drivers/i3c/master.c | 3 +++
> >>   1 file changed, 3 insertions(+)
> >>
> >> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c index
> >> d5dc4180afbc..c65006aa0684 100644
> >> --- a/drivers/i3c/master.c
> >> +++ b/drivers/i3c/master.c
> >> @@ -2561,6 +2561,9 @@ static void
> i3c_master_unregister_i3c_devs(struct i3c_master_controller *master)
> >>    */
> >>   void i3c_master_queue_ibi(struct i3c_dev_desc *dev, struct i3c_ibi_slot
> *slot)
> >>   {
> >> +    if (!dev->ibi || !slot)
> >> +            return;
> >> +
> 1. Shouldn't this be a Logical AND ? what if slot is non NULL but the IBI is
> NULL ?
> 
[Manjunatha Venkatesh] : I think Logical OR operation is correct,
 Since if any one of the variable is NULL need to return before accessing those variables.
> 2. This being void function, it doesn't say anything to caller if it's successful or
> failed ? Should we make this non void function ?
> if not, i am thinking it may run into multiple attempts, no log too.
[Manjunatha Venkatesh] : If required we can add error print log, Others please confirm your opinion on this.  
> >>      atomic_inc(&dev->ibi->pending_ibis);
> >>      queue_work(dev->ibi->wq, &slot->work);
> >>   }
> >> --
> >> 2.46.1
> >>
> >