[U-Boot] [PATCH] RFC: dm: Add pointer checking for allocated data

[Simon Glass]

Hi Masahiro,

On 13 July 2015 at 22:36, Masahiro Yamada <yamada.masahiro at socionext.com> wrote:
> Hi Simon,
>
>
>
>
> 2015-07-09 23:15 GMT+09:00 Simon Glass <sjg at chromium.org>:
>> With driver model drivers can have things stored in several places. There is
>> driver-private data, then the uclass can attach things to a device. If the
>> device is on a bus then its bus may attach parent data to the device too.
>>
>> At present everything is done through void pointers.
>
> This is also true for driver private data in Linux.
>

Yes.

>
>
>> It would be nice to
>> have a way to check that the correct C struct is used in each case.
>>
>> Here is a proposed implementation of a way of checking structures in driver
>> model. It relies on turning the existing dev_get_priv() function into a
>> macro which (if checking is enabled) checks that the structure names match.
>> Each xxx_auto_alloc_size turns into a structure containing a string (the
>> structure name) and the size.
>>
>> The dev_get_priv() macro has an extra parameter which is the structure being
>> accessed:
>>
>>         struct eth_pdata *priv = dev_get_priv(dev, struct eth_pdata);
>>
>> and you get an error like this when things are wrong:
>
> In which scenario do things go wrong?
> It is still unclear to me why we need this sanity check.

Here struct eth_pdata is the structure for the platform data. So you should use:

       struct eth_pdata *plat = dev_get_platdata(dev, struct eth_pdata);

That is the error - we are using the platdata structure to access
priv. At present there is no way to detect these errors except by
inspection (or perhaps crash / strange behaviour).

>
>
>
>> Invalid access to device priv: dev=eth at 10002000, expecting
>>    'struct eth_sandbox_priv', requested 'struct eth_pdata'
>>
>> A new Kconfg option is added to turn this on, since it bloats the code a
>> little.
>>
>> The next step would be to extend it to all pointers in the device and
>> uclass. This is mostly a mechanical code change.
>>
>> Finally we should have a way of checking that the device pointer itself is
>> valid. For example if someone passes an invalid address like 0x12345 as the
>> 'struct udevice' then at present we will dutifully look for the devices'
>> driver and perform an invalid memory access.
>>
>> If we want to check for memory corruption one way would be to add a magic
>> numnber before each allocated memory area. Perhaps this is more the role
>> of dlmalloc(), but if required it could be attached to Masahiro's devres
>> feature, which already prepends some data to every allocated area.
>>
>> Comments welcome. I'd like to figure this out soon as it involves trivial
>> but invasive patches to change each driver.
>>
>> Signed-off-by: Simon Glass <sjg at chromium.org>
>> ---
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>> diff --git a/arch/x86/cpu/mp_init.c b/arch/x86/cpu/mp_init.c
>> index e686b28..e835b43 100644
>> --- a/arch/x86/cpu/mp_init.c
>> +++ b/arch/x86/cpu/mp_init.c
>> @@ -238,7 +238,7 @@ static int load_sipi_vector(atomic_t **ap_countp)
>>
>>         params->stack_size = CONFIG_AP_STACK_SIZE;
>>         size = params->stack_size * CONFIG_MAX_CPUS;
>> -       stack = memalign(size, 4096);
>> +       stack = memalign(4096, size);
>>         if (!stack)
>>                 return -ENOMEM;
>>         params->stack_top = (u32)(stack + size);
>
>
> This change seems unrelated to the subject of this patch.
>

Yes, I'll respin it properly when we work out what to do.

Regards,
Simon