Re: [edk2-devel] [PATCH v1 1/1] MdeModulePkg/Variable: TcgMorLockSmm Key Mismatch changes lock state

["Michael Kubacki" <mikuback@linux.microsoft.com>]

Acked-by: Michael Kubacki <michael.kubacki@microsoft.com>

Inline code comment below.

On 4/12/2023 5:25 PM, Abhimanyu Singh wrote:
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4410
> 
> Inside TcgMorLockSmm.c, the SetVariableCheckHandlerMorLock() function
> contains a scenario to prevent a possible dictionary attack on the MorLock
> Key in accordance with the TCG Platform Reset Mitigation Spec v1.10.
> 
> The mechanism to prevent this attack must also change the MorLock Variable
> Value to 0x01 to indicate Locked Without Key.
> 
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Signed-off-by: Abhi Singh <Abhi.Singh@arm.com>
> ---
>   MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c b/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c
> index da1105ff073e..a76db18ef877 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c
> @@ -312,6 +312,10 @@ SetVariableCheckHandlerMorLock (
>         mMorLockState    = MorLockStateLocked;
> 
>         mMorLockKeyEmpty = TRUE;
> 
>         ZeroMem (mMorLockKey, sizeof (mMorLockKey));
> 
> +      //
> 
> +      // Update value to reflect locked without key
> 
> +      //
> 
> +      SetMorLockVariable (MOR_LOCK_DATA_LOCKED_WITHOUT_KEY);

I know the TCG Reset Attack Mitigation Specification requires 
EFI_ACCESS_DENIED to be returned from this function in this case but 
SetMorLockVariable() returns a status code.

I suggest capturing that followed by an ASSERT_EFI_ERROR (Status) to at 
least help raise visibility of unexpected errors in builds with asserts 
enabled.

> 
>         return EFI_ACCESS_DENIED;
> 
>       }
> 
>     }
>