Re: [edk2-devel] [PATCH] SecurityPkg/Tcg2PhysicalPresenceLib: Fix incorrect TCG VER comparision

["Stefan Berger" <stefanb@linux.ibm.com>]

On 7/10/20 9:53 AM, Stefan Berger wrote:
> On 7/10/20 1:43 AM, Laszlo Ersek wrote:
>> (+Marc-André, Stefan)
>>
>> On 07/10/20 02:44, Gao, Zhichao wrote:
>>> This bug is not obeserved by me. But I view the code. The condition 
>>> is incorrect and it would affect the TCG operation:
>>>      if (!mIsTcg2PPVerLowerThan_1_3) {
>>>          if (OperationRequest < 
>>> TCG2_PHYSICAL_PRESENCE_VENDOR_SPECIFIC_OPERATION) {
>>>            //
>>>            // TCG2 PP1.3 spec defined operations that are reserved 
>>> or un-implemented
>>>            //
>>>            return TCG_PP_GET_USER_CONFIRMATION_NOT_IMPLEMENTED;
>>>          }
>>>        } else {
>>>         //
>>>         // TCG PP lower than 1.3. (1.0, 1.1, 1.2)
>>>         //
>>>         if (OperationRequest <= TCG2_PHYSICAL_PRESENCE_NO_ACTION_MAX) {
>>>           RequestConfirmed = TRUE;
>>>         } else if (OperationRequest < 
>>> TCG2_PHYSICAL_PRESENCE_VENDOR_SPECIFIC_OPERATION) {
>>>           return TCG_PP_GET_USER_CONFIRMATION_NOT_IMPLEMENTED;
>>>         }
>>>        }
>>>
>> I've found that code myself, but I'm not familiar enough with TPM PPI
>> stuff to understand immediately the effects of this change. I can see
>> that where we used to return
>> TCG_PP_GET_USER_CONFIRMATION_NOT_IMPLEMENTED before, we could now assign
>> "RequestConfirmed = TRUE", and vice versa, due to
>> "mIsTcg2PPVerLowerThan_1_3" being potentially inverted.
>>
>> But what does that *mean*? What is the behavioral change that human
>> end-users, or software components, will experience?
>
>
> The above code snipped is located in a default branch of a large 
> switch statement that handles most of the common PPI operations 
> independent of this change, so that at least is good.
>
> I would say that in the worst case some of the operations not 
> otherwise handled may have mistakenly failed or could have been 
> executed without user confirmation/interaction. On Linux at least PPI 
> requests can only be sent by root.


I am running a somewhat dated version of edk2 (Fedora 31). The 
operations advertised are: 0,5,14,21,22,23,24,33,96,97. All of these are 
individually handled in the switch statement, so there should no be any 
impact. I am currently not aware of whether this list can be extended 
with some sort of module.


>
>
>>
>> Thanks
>> Laszlo
>>
>>> So I think it should be fixed.
>>>
>>> Thanks,
>>> Zhichao
>>>
>>>> -----Original Message-----
>>>> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of 
>>>> Laszlo Ersek
>>>> Sent: Thursday, July 9, 2020 6:02 PM
>>>> To: devel@edk2.groups.io; Gao, Zhichao <zhichao.gao@intel.com>
>>>> Cc: Terry Lee <terry.lee@hpe.com>; Yao, Jiewen 
>>>> <jiewen.yao@intel.com>; Wang,
>>>> Jian J <jian.j.wang@intel.com>; Zhang, Chao B <chao.b.zhang@intel.com>
>>>> Subject: Re: [edk2-devel] [PATCH] 
>>>> SecurityPkg/Tcg2PhysicalPresenceLib: Fix
>>>> incorrect TCG VER comparision
>>>>
>>>> On 07/09/20 04:46, Gao, Zhichao wrote:
>>>>> From: Terry Lee <terry.lee@hpe.com>
>>>>>
>>>>> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2697
>>>>>
>>>>> Tcg2PhysicalPresenceLibConstructor set the module variable
>>>>> mIsTcg2PPVerLowerThan_1_3 with incorrect TCG version comparision.
>>>>>
>>>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>>>> Cc: Jian J Wang <jian.j.wang@intel.com>
>>>>> Cc: Chao Zhang <chao.b.zhang@intel.com>
>>>>> Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
>>>>> ---
>>>>> .../SmmTcg2PhysicalPresenceLib/SmmTcg2PhysicalPresenceLib.c | 2 +-
>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git
>>>>> a/SecurityPkg/Library/SmmTcg2PhysicalPresenceLib/SmmTcg2PhysicalPresen 
>>>>>
>>>>> ceLib.c
>>>>> b/SecurityPkg/Library/SmmTcg2PhysicalPresenceLib/SmmTcg2PhysicalPresen 
>>>>>
>>>>> ceLib.c
>>>>> index 1c46d5e69d..8afaa0a785 100644
>>>>> ---
>>>>> a/SecurityPkg/Library/SmmTcg2PhysicalPresenceLib/SmmTcg2PhysicalPresen 
>>>>>
>>>>> ceLib.c
>>>>> +++ 
>>>>> b/SecurityPkg/Library/SmmTcg2PhysicalPresenceLib/SmmTcg2PhysicalPr
>>>>> +++ esenceLib.c
>>>>> @@ -387,7 +387,7 @@ Tcg2PhysicalPresenceLibConstructor ( {
>>>>>     EFI_STATUS  Status;
>>>>>
>>>>> -  if (AsciiStrnCmp(PP_INF_VERSION_1_2, (CHAR8
>>>>> *)PcdGetPtr(PcdTcgPhysicalPresenceInterfaceVer),
>>>>> sizeof(PP_INF_VERSION_1_2) - 1) <= 0) {
>>>>> +  if (AsciiStrnCmp(PP_INF_VERSION_1_2, (CHAR8
>>>>> + *)PcdGetPtr(PcdTcgPhysicalPresenceInterfaceVer),
>>>>> + sizeof(PP_INF_VERSION_1_2) - 1) >= 0) {
>>>>>       mIsTcg2PPVerLowerThan_1_3 = TRUE;
>>>>>     }
>>>>>
>>>>>
>>>> What is the practical impact of this bug / fix?
>>>>
>>>> Thanks
>>>> Laszlo
>>>>
>>>>
>>>>
>>
>>
>>
>
>
> 
>