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SubjectRe: [PATCH] acpi: cppc: Prevent cpc_desc_ptr points to the invalid data
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Hi Ashwin,

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

On Fri, May 27, 2016 at 9:10 AM, Ashwin Chaugule
<ashwin.chaugule@linaro.org> wrote:
> On 25 May 2016 at 15:09, Hoan Tran <hotran@apm.com> 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@apm.com>
>> ---
>> 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.
>
> Thanks,
> Ashwin.

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