[PATCH v2] MdeModulePkg/Variable: TcgMorLockSmm Key Mismatch changes lock state

[PATCH v2] MdeModulePkg/Variable: TcgMorLockSmm Key Mismatch changes lock state

[Abhimanyu Singh]

From: Abhi Singh <Abhi.Singh@arm.com>

REF:  https://bugzilla.tianocore.org/show_bug.cgi?id=4410
REPO: https://github.com/tianocore/edk2/commit/7c9e1303fce5d49f8b597b4afd99ed855faaffaa 

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.

ASSERT_EFI_ERROR is added for error visibility since SetMorLockVariable
returns a status code

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>

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

Notes:
    v2:
    - capturing return status of SetMorLockVariable
      with ASSERT_EFI_ERROR for visibility [Michael]

 MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c b/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c
index da1105ff07..28e8cc55d9 100644
--- a/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c
+++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c
@@ -312,6 +312,11 @@ SetVariableCheckHandlerMorLock (
       mMorLockState    = MorLockStateLocked;
       mMorLockKeyEmpty = TRUE;
       ZeroMem (mMorLockKey, sizeof (mMorLockKey));
+      //
+      // Update value to reflect locked without key
+      //
+      Status = SetMorLockVariable (MOR_LOCK_DATA_LOCKED_WITHOUT_KEY);
+      ASSERT_EFI_ERROR (Status);
       return EFI_ACCESS_DENIED;
     }
   }
-- 
2.34.1

Re: [edk2-devel] [PATCH v2] MdeModulePkg/Variable: TcgMorLockSmm Key Mismatch changes lock state

[Abhimanyu Singh]

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Hi Liming and Jian,

Could you please review this patch? Michael has taken a look over and given Acked-by.

Thanks,
Abhi

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