Re: [edk2-devel] [PATCH v2 4/5] MdePkg/PiFirmwareFile: fix undefined behavior in FFS_FILE_SIZE

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 4/18/19 7:47 PM, Laszlo Ersek wrote:
> Accessing "EFI_FFS_FILE_HEADER.Size", which is of type UINT8[3], through a
> (UINT32*), is undefined behavior. Fix it by accessing the array elements
> individually.
> 
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1710
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
> 
> Notes:
>     v2:
>     
>     - eliminate intermediate macros [Mike]
> 
>  MdePkg/Include/Pi/PiFirmwareFile.h | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/MdePkg/Include/Pi/PiFirmwareFile.h b/MdePkg/Include/Pi/PiFirmwareFile.h
> index 05470538de42..ec7729e9c36e 100644
> --- a/MdePkg/Include/Pi/PiFirmwareFile.h
> +++ b/MdePkg/Include/Pi/PiFirmwareFile.h
> @@ -179,8 +179,15 @@ typedef struct {
>  #define IS_FFS_FILE2(FfsFileHeaderPtr) \
>      (((((EFI_FFS_FILE_HEADER *) (UINTN) FfsFileHeaderPtr)->Attributes) & FFS_ATTRIB_LARGE_FILE) == FFS_ATTRIB_LARGE_FILE)
>  
> -#define FFS_FILE_SIZE(FfsFileHeaderPtr) \
> -    ((UINT32) (*((UINT32 *) ((EFI_FFS_FILE_HEADER *) (UINTN) FfsFileHeaderPtr)->Size) & 0x00ffffff))
> +///
> +/// The argument passed as the FfsFileHeaderPtr parameter to the
> +/// FFS_FILE_SIZE() function-like macro below must not have side effects:
> +/// FfsFileHeaderPtr is evaluated multiple times.
> +///
> +#define FFS_FILE_SIZE(FfsFileHeaderPtr) ((UINT32) ( \
> +    (((EFI_FFS_FILE_HEADER *) (UINTN) (FfsFileHeaderPtr))->Size[0]      ) | \
> +    (((EFI_FFS_FILE_HEADER *) (UINTN) (FfsFileHeaderPtr))->Size[1] <<  8) | \
> +    (((EFI_FFS_FILE_HEADER *) (UINTN) (FfsFileHeaderPtr))->Size[2] << 16)))
>  
>  #define FFS_FILE2_SIZE(FfsFileHeaderPtr) \
>      ((UINT32) (((EFI_FFS_FILE_HEADER2 *) (UINTN) FfsFileHeaderPtr)->ExtendedSize))
> 

Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>