Re: [PATCH] coresight: Fix erroneous memset in tmc_read_unprepare_etr

[Suzuki K Poulose]

On 12/06/16 22:06, Mathieu Poirier wrote:
> On 10 June 2016 at 04:31, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> > At the end of a trace collection, we try to clear the entire buffer
> > and enable the ETR back if it was already enabled. But, we would have
> > adjusted the drvdata->buf to point to the beginning of the trace data
> > in the trace buffer @drvdata->vaddr. So, the following code which
> > clears the buffer is dangerous and can cause crashes, like below :
> >
> >          memset(drvdata->buf, 0, drvdata->size);
> >
> >   Unable to handle kernel paging request at virtual address ffffff800a145000
> >   pgd = ffffffc974726000
> >   *pgd=00000009f3e91003, *pud=00000009f3e91003, *pmd=0000000000000000
> >   PREEMPT SMP
> >   Modules linked in:
> >   CPU: 4 PID: 1692 Comm: dd Not tainted 4.7.0-rc2+ #1721
> >   Hardware name: ARM Juno development board (r0) (DT)
> >   task: ffffffc9734a0080 ti: ffffffc974460000 task.ti: ffffffc974460000
> >   PC is at __memset+0x1ac/0x200
> >   LR is at tmc_read_unprepare_etr+0x144/0x1bc
> >   pc : [<ffffff80083a05ac>] lr : [<ffffff800859c984>] pstate: 200001c5
> >   ...
> >   [<ffffff80083a05ac>] __memset+0x1ac/0x200
> >   [<ffffff800859b2e4>] tmc_release+0x90/0x94
> >   [<ffffff8008202f58>] __fput+0xa8/0x1ec
> >   [<ffffff80082030f4>] ____fput+0xc/0x14
> >   [<ffffff80080c3ef8>] task_work_run+0xb0/0xe4
> >   [<ffffff8008088bf4>] do_notify_resume+0x64/0x6c
> >   [<ffffff8008084d5c>] work_pending+0x10/0x14
> >   Code: 91010108 54ffff4a 8b040108 cb050042 (d50b7428)
> >
> > Since we clear the buffer anyway in the following call to
> > tmc_etr_enable_hw(), remove the erroneous memset().
> >
> > Fixes: commit de5461970b3e9e1 ("coresight: tmc: allocating memory when needed")
> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >
> > Mathieu,
> >
> > I think this should go to 4.7. Please push it.
>
> If this [1] didn't make it, this one won't make it either.
> applied it to my tree for merging in the 4.8 cycle.

I think both should go to 4.7, as these fixes real crashes.

Greg,

We have two fixes [1],[2] for coresight driver which fixes Kernel crashes. Could you
please pick them up ?

I could resend them, if you would like.

[1] https://patchwork.kernel.org/patch/9144589/
[2] https://patchwork.kernel.org/patch/9169407/

Thanks
Suzuki


> Thanks,
> Mathieu

> > ---
> >   drivers/hwtracing/coresight/coresight-tmc-etr.c | 9 +++------
> >   1 file changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > index 69e104b..24d99ed 100644
> > --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > @@ -306,13 +306,10 @@ int tmc_read_unprepare_etr(struct tmc_drvdata *drvdata)
> >          if (local_read(&drvdata->mode) == CS_MODE_SYSFS) {
> >                  /*
> >                   * The trace run will continue with the same allocated trace
> > -                * buffer. As such zero-out the buffer so that we don't end
> > -                * up with stale data.
> > -                *
> > -                * Since the tracer is still enabled drvdata::buf
> > -                * can't be NULL.
> > +                * buffer. The trace buffer is cleared in tmc_etr_enable_hw(),
> > +                * so we don't have to explicitly clear it. Also, since the
>
> Yes, very good.
>
> > +                * tracer is still enabled drvdata::buf can't be NULL.
> >                   */
> > -               memset(drvdata->buf, 0, drvdata->size);
> >                  tmc_etr_enable_hw(drvdata);
> >          } else {
> >                  /*
> > --
> > 1.9.1