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MdeModulePkg/Variable/RuntimeDxe: delete & lock MOR in the absence of SMM

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VariableRuntimeDxe deletes and locks the MorLock variable in
MorLockInit(), with the argument that any protection provided by MorLock
can be circumvented if MorLock can be overwritten by unprivileged code
(i.e., outside of SMM).

Extend the argument and the logic to the MOR variable, which is supposed
to be protected by MorLock. Pass Attributes=0 when deleting MorLock and
MOR both.

This change was suggested by Star; it is inspired by earlier VariableSmm
commit fda8f631edbb ("MdeModulePkg/Variable/RuntimeDxe: delete and lock
OS-created MOR variable", 2017-10-03).

Cc: Eric Dong <eric.dong@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Suggested-by: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
This commit is contained in:
Laszlo Ersek 2017-10-10 13:44:16 +02:00
parent 6161123be2
commit 704b71d7e1
1 changed files with 27 additions and 3 deletions
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30
MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockDxe.c
View File

@ -78,15 +78,39 @@ MorLockInit (
VariableServiceSetVariable (
MEMORY_OVERWRITE_REQUEST_CONTROL_LOCK_NAME,
&gEfiMemoryOverwriteRequestControlLockGuid,
EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
0,
NULL
0, // Attributes
0, // DataSize
NULL // Data
);
//
// Need set this variable to be read-only to prevent other module set it.
//
VariableLockRequestToLock (&mVariableLock, MEMORY_OVERWRITE_REQUEST_CONTROL_LOCK_NAME, &gEfiMemoryOverwriteRequestControlLockGuid);
//
// The MOR variable can effectively improve platform security only when the
// MorLock variable protects the MOR variable. In turn MorLock cannot be made
// secure without SMM support in the platform firmware (see above).
//
// Thus, delete the MOR variable, should it exist for any reason (some OSes
// are known to create MOR unintentionally, in an attempt to set it), then
// also lock the MOR variable, in order to prevent other modules from
// creating it.
//
VariableServiceSetVariable (
MEMORY_OVERWRITE_REQUEST_VARIABLE_NAME,
&gEfiMemoryOverwriteControlDataGuid,
0, // Attributes
0, // DataSize
NULL // Data
);
VariableLockRequestToLock (
&mVariableLock,
MEMORY_OVERWRITE_REQUEST_VARIABLE_NAME,
&gEfiMemoryOverwriteControlDataGuid
);
return EFI_SUCCESS;
}