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