Re: [edk2-devel] [PATCH v2 2/4] MdeModulePkg/SMM: Disallow unregister SMI handler in other SMI handler

["Laszlo Ersek" <lersek@redhat.com>]

On 2/28/24 03:27, Zhiguang Liu wrote:
> In last patch, we add code support to unregister SMI handler inside
> itself. However, the code doesn't support unregister SMI handler
> insider other SMI handler. While this is not a must-have usage.
> So add check to disallow unregister SMI handler in other SMI handler.
> 
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Jiaxin Wu <jiaxin.wu@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
> ---
>  MdeModulePkg/Core/PiSmmCore/Smi.c | 32 +++++++++++++++++++++++--------
>  1 file changed, 24 insertions(+), 8 deletions(-)
> 
> diff --git a/MdeModulePkg/Core/PiSmmCore/Smi.c b/MdeModulePkg/Core/PiSmmCore/Smi.c
> index 3489c130fd..1bfbc635fc 100644
> --- a/MdeModulePkg/Core/PiSmmCore/Smi.c
> +++ b/MdeModulePkg/Core/PiSmmCore/Smi.c
> @@ -8,7 +8,8 @@
>  
>  #include "PiSmmCore.h"
>  
> -LIST_ENTRY  mSmiEntryList = INITIALIZE_LIST_HEAD_VARIABLE (mSmiEntryList);
> +SMI_HANDLER  *gCurrentSmiHandler = NULL;
> +LIST_ENTRY   mSmiEntryList       = INITIALIZE_LIST_HEAD_VARIABLE (mSmiEntryList);
>  
>  SMI_ENTRY  mRootSmiEntry = {
>    SMI_ENTRY_SIGNATURE,
> @@ -142,13 +143,18 @@ SmiManage (
>      // Link points to may be freed if unregister SMI handler.
>      //
>      Link = Link->ForwardLink;
> -
> -    Status = SmiHandler->Handler (
> -                           (EFI_HANDLE)SmiHandler,
> -                           Context,
> -                           CommBuffer,
> -                           CommBufferSize
> -                           );
> +    //
> +    // Assign gCurrentSmiHandle before calling the SMI handler and
> +    // set to NULL when it returns.
> +    //
> +    gCurrentSmiHandler = SmiHandler;
> +    Status             = SmiHandler->Handler (
> +                                       (EFI_HANDLE)SmiHandler,
> +                                       Context,
> +                                       CommBuffer,
> +                                       CommBufferSize
> +                                       );
> +    gCurrentSmiHandler = NULL;
>  
>      switch (Status) {
>        case EFI_INTERRUPT_PENDING:
> @@ -328,6 +334,16 @@ SmiHandlerUnRegister (
>      return EFI_INVALID_PARAMETER;
>    }
>  
> +  //
> +  // Check if unregister SMI handler inside a SMI Handler
> +  //
> +  if (gCurrentSmiHandler != NULL) {
> +    //
> +    // Only allow to unregister SMI Handler inside itself.
> +    //
> +    ASSERT (gCurrentSmiHandler == SmiHandler);
> +  }
> +
>    SmiEntry = SmiHandler->SmiEntry;
>  
>    RemoveEntryList (&SmiHandler->Link);

(1) Why not:

  if ((gCurrentSmiHandler != NULL) && (gCurrentSmiHandler != SmiHandler)) {
    return EFI_INVALID_PARAMETER;
  }

?

(2) Why do we call the new global variable "gCurrentSmiHandler" rather than "mCurrentSmiHandler"?

Thanks
Laszlo



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