Re: [PATCH 3/7] mtd: spi-nor: add restriction for nmaps in smpt parser

[<Tudor.Ambarus@microchip.com>]

On 11/08/2018 04:15 PM, Boris Brezillon wrote:
> On Thu, 8 Nov 2018 13:58:45 +0000
> <Tudor.Ambarus@microchip.com> wrote:
> 
>> On 11/08/2018 02:54 PM, Boris Brezillon wrote:
>>> On Thu, 8 Nov 2018 11:07:11 +0000
>>> <Tudor.Ambarus@microchip.com> wrote:
>>>   
>>>> The map selector is limited to a maximum of 8 bits, allowing
>>>> for a maximum of 256 possible map configurations. The total
>>>> number of map configurations should be addressable by the
>>>> total number of bits described by the detection commands.
>>>>
>>>> For example: if there are five to eight possible sector map
>>>> configurations, at least three configuration detection commands
>>>> will be needed to extract three bits of configuration selection
>>>> information from the device in order to identify which configuration
>>>> is currently in use.
>>>>
>>>> Suggested-by: Boris Brezillon <boris.brezillon@bootlin.com>  
>>>
>>> I don't remember suggesting this :-).  
>>
>> I see this when you discussed with Yogesh:
>>
>> +       for (nmaps = 0; i< smpt_len; nmaps++) {
>> +               if(!(smpt[i] & SMPT_DESC_TYPE_MAP)) {
>> +                       i += 2;
>> +                       continue;
>> +               }
>> +
>> +               if(!map_id_is_valid) {
>> +                       if (nmaps) {
>> +                               ret = NULL;
>> +                               break;
>> +                       }
>>
>> If I understand correctly, you meant that if there are no detection commands,
>> and more than a configuration map, then return an error.
> 
> Yes, because in this case we have no way to know what config is
> currently selected.
> 
>>
>> This is correct in my opinion. What I did was to generalize this idea. If smtp
>> defines more maps than you can select using detection commands, return error.
> 
> AFAICT you're no longer checking that map_id is valid (see below).
> 
>>
>> +
>> +                       ret = smpt+i;
>> +               } else if (map_id == SMPT_MAP_ID(smpt[i])) {
>> +                       ret = smpt+i;
>> +                       break;
>> +               }
>> +
>>                 /* increment the table index to the next map */
>>                 i += SMPT_MAP_REGION_COUNT(smpt[i]) + 1;
>>         }
>>
>>>   
>>>> Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
>>>> ---
>>>>  drivers/mtd/spi-nor/spi-nor.c | 15 +++++++++++++--
>>>>  1 file changed, 13 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>>>> index 59dcedb08691..bd1866d714f2 100644
>>>> --- a/drivers/mtd/spi-nor/spi-nor.c
>>>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>>>> @@ -2868,7 +2868,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
>>>>  	const u32 *ret = NULL;
>>>>  	u32 addr;
>>>>  	int err;
>>>> -	u8 i;
>>>> +	u8 i, ncmds, nmaps;
>>>>  	u8 addr_width, read_opcode, read_dummy;
>>>>  	u8 read_data_mask, data_byte, map_id;
>>>>  
>>>> @@ -2877,6 +2877,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
>>>>  	read_opcode = nor->read_opcode;
>>>>  
>>>>  	map_id = 0;
>>>> +	ncmds = 0;
>>>>  	/* Determine if there are any optional Detection Command Descriptors */
>>>>  	for (i = 0; i < smpt_len; i += 2) {
>>>>  		if (smpt[i] & SMPT_DESC_TYPE_MAP)
>>>> @@ -2896,6 +2897,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
>>>>  		 * Configuration that is currently in use.
>>>>  		 */
>>>>  		map_id = map_id << 1 | !!(data_byte & read_data_mask);
>>>> +		ncmds++;
>>>>  	}
>>>>  
>>>>  	/*
>>>> @@ -2905,7 +2907,16 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
>>>>  	 *
>>>>  	 * Find the matching configuration map.
>>>>  	 */
>>>> -	while (i < smpt_len) {
>>>> +	for (nmaps = 0; i < smpt_len; nmaps++) {
>>>> +		/*
>>>> +		 * The map selector is limited to a maximum of 8 bits, allowing
>>>> +		 * for a maximum of 256 possible map configurations. The total
>>>> +		 * number of map configurations should be addressable by the
>>>> +		 * total number of bits described by the detection commands.
>>>> +		 */
>>>> +		if (ncmds && nmaps >= (1 << (ncmds + 1)))
>>>> +			break;
> 
> You're no longer checking that when ncmds == 0 nmaps has to be 1. So,
> say the chip exposed no smpt commands and has several maps defined,
> map_id will be 0 while it should have be "undefined". My version
> would return an error, but yours tries to find map_id 0.

yep, I missed the ncmds == 0 case.

> 
>>>> +  
>>>
>>> Maybe I missed something but it sounds like this change is just
>>> optimizing the SPMT parsing a bit, and to be honest, I'm not sure this
>>> is really needed. Most of the time, smpt_len will be rather small, so
>>> trying to bail out earlier is not bringing much perf improvements.  
>>
>> It's rather a smtp validity check. I want to return an error if there are not
>> enough detection commands to identify the map id.
> 
> You would have failed the same way without this validity check after a
> maximum of smpt_len iterations, right?
> 

Right. The correct fix would be to count nmaps in a loop, then do these checks,
and if all ok, search for the map_id in another loop :).