Re: [PATCH] acpi: cppc: Prevent cpc_desc_ptr points to the invalid data

[Hoan Tran]

On Tue, May 31, 2016 at 12:29 PM, Ashwin Chaugule
<ashwin.chaugule@xxxxxxxxxx> wrote:
>
> On 27 May 2016 at 12:41, Hoan Tran <hotran@xxxxxxx> wrote:
> > Hi Ashwin,
>
> Hi,
>
> >
> > Yes, I saw kernel crash.
> > As cpc_desc_ptr is not NULL, cppc_cpufreq_init() still can pass then
> > crash during cppc_get_perf_caps() access CPPC shared memory.
> >
> > It's not only "PCC channel request fail" can create this issue but
> > "acpi_get_psd() fail" also creates it
> >
> > Thanks
> > Hoan
>
>
> Just for future reference. :)
>
> https://web.archive.org/web/20080722025748/http://www.zip.com.au/~akpm/linux/patches/stuff/top-posting.txt
>
>
> >
> > On Fri, May 27, 2016 at 9:10 AM, Ashwin Chaugule
> > <ashwin.chaugule@xxxxxxxxxx> wrote:
> >> On 25 May 2016 at 15:09, Hoan Tran <hotran@xxxxxxx> wrote:
> >>> When CPPC fails to request PCC channel, the CPC data is freed
> >>> and cpc_desc_ptr points to the invalid data. This change prevents
> >>> this issue by moving cpc_desc_ptr assignment after PCC channel
> >>> request.
> >>>
> >>> Signed-off-by: Hoan Tran <hotran@xxxxxxx>
> >>> ---
> >>>  drivers/acpi/cppc_acpi.c | 6 +++---
> >>>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> >>> index 8adac69..85fd8f7 100644
> >>> --- a/drivers/acpi/cppc_acpi.c
> >>> +++ b/drivers/acpi/cppc_acpi.c
> >>> @@ -595,9 +595,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
> >>>         /* Store CPU Logical ID */
> >>>         cpc_ptr->cpu_id = pr->id;
> >>>
> >>> -       /* Plug it into this CPUs CPC descriptor. */
> >>> -       per_cpu(cpc_desc_ptr, pr->id) = cpc_ptr;
> >>> -
> >>>         /* Parse PSD data for this CPU */
> >>>         ret = acpi_get_psd(cpc_ptr, handle);
> >>>         if (ret)
> >>> @@ -610,6 +607,9 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
> >>>                         goto out_free;
> >>>         }
> >>>
> >>> +       /* Plug PSD data into this CPUs CPC descriptor. */
> >>> +       per_cpu(cpc_desc_ptr, pr->id) = cpc_ptr;
> >>> +
> >>
> >> Are you seeing a real problem without this change? I'm missing where
> >> this pointer is dereferenced if the PCC channel request fails.
> >>
>
> So, after freeing the cpc_ptr, we need to NULL the per-cpu pointer as
> well. Alternately, not assign it until everything passes and rely on
> the static declaration, which is the path you've taken here.
>
> Acked-by: Ashwin Chaugule <ashwin.chaugule@xxxxxxxxxx>

Hi Rafael,

Do you have plan to apply this patch ?

Thanks
Hoan