[Intel-wired-lan] [PATCH v2 1/1] e1000e: Fix possible overflow in LTR decoding

[Neftin, Sasha]

On 4/6/2022 08:34, Paul Menzel wrote:
> Dear Sasha,
> 
> 
> Thank you for your patch.
> 
> Am 05.04.22 um 17:56 schrieb Sasha Neftin:
>> When we decode the latency and the max_latency u16 value does not fill
>> the required size
> 
> Do you mean “fit into” or “is too small for the required size”?
> 
>> and could lead to the wrong LTR representation.
> 
> Maybe give an example of values leading to incorrect behavior?
> 
>> Replace the u16 type with the u32 type and allow corrected LTR
>> representation.
> 
> Maybe: Increase the variable size from u16 to u32, so the decoded 
> latency can be represented. Why are 32 bit enough? Why not 64 bit?
Hello Paul,
Scaling represented as:
scale 0 - 1         (2^(5*0)) = 2^0
scale 1 - 32        (2^(5 *1))= 2^5
scale 2 - 1024      (2^(5 *2)) =2^10
scale 3 - 32768     (2^(5 *3)) =2^15
scale 4 – 1048576   (2^(5 *4)) = 2^20
scale 5 – 33554432  (2^(5 *4)) = 2^25
scale 4 and scale 5 required 20 and 25 bits respectively.
scale 6 reserved.
> 
> Please use 75 characters per line.
> 
>> Fixes: 44a13a5d99c7 ("e1000e: Fix the max snoop/no-snoop latency for 
>> 10M")
>> Reported-by: James Hutchinson <jahutchinson99 at googlemail.com>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215689
>> Suggested-by: Dima Ruinskiy <dima.ruinskiy at intel.com>
>> Signed-off-by: Sasha Neftin <sasha.neftin at intel.com>
> 
> Add
> 
> Tested-by: James Hutchinson <jahutchinson99 at googlemail.com> (I219-V (rev 
> 30))
I will let James add this tag.
> 
>> ---
>> v2: added link tag
>>
>>   drivers/net/ethernet/intel/e1000e/ich8lan.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/intel/e1000e/ich8lan.c 
>> b/drivers/net/ethernet/intel/e1000e/ich8lan.c
>> index d60e2016d03c..e6c8e6d5234f 100644
>> --- a/drivers/net/ethernet/intel/e1000e/ich8lan.c
>> +++ b/drivers/net/ethernet/intel/e1000e/ich8lan.c
>> @@ -1009,8 +1009,8 @@ static s32 e1000_platform_pm_pch_lpt(struct 
>> e1000_hw *hw, bool link)
>>   {
>>       u32 reg = link << (E1000_LTRV_REQ_SHIFT + 
>> E1000_LTRV_NOSNOOP_SHIFT) |
>>           link << E1000_LTRV_REQ_SHIFT | E1000_LTRV_SEND;
>> -    u16 max_ltr_enc_d = 0;    /* maximum LTR decoded by platform */
>> -    u16 lat_enc_d = 0;    /* latency decoded */
>> +    u32 max_ltr_enc_d = 0;    /* maximum LTR decoded by platform */
>> +    u32 lat_enc_d = 0;    /* latency decoded */
>>       u16 lat_enc = 0;    /* latency encoded */
>>       if (link) {
> 
> The diff looks good.
Thanks
> 
> 
> Kind regards,
> 
> Paul
Sasha