Re: [edk2-devel] [PATCH v2 2/5] MdePkg/PiFirmwareFile: fix undefined behavior in SECTION_SIZE

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

On 4/18/19 7:47 PM, Laszlo Ersek wrote:
> RH covscan justifiedly reports that accessing
> "EFI_COMMON_SECTION_HEADER.Size", which is of type UINT8[3], through a
> (UINT32*), is undefined behavior:
> 
>> Error: OVERRUN (CWE-119):
>> edk2-89910a39dcfd/OvmfPkg/Sec/SecMain.c:178: overrun-local: Overrunning
>> array of 3 bytes at byte offset 3 by dereferencing pointer
>> "(UINT32 *)((EFI_COMMON_SECTION_HEADER *)(UINTN)Section)->Size".
>> #  176|       Section = (EFI_COMMON_SECTION_HEADER*)(UINTN) CurrentAddress;
>> #  177|
>> #  178|->     Size = SECTION_SIZE (Section);
>> #  179|       if (Size < sizeof (*Section)) {
>> #  180|         return EFI_VOLUME_CORRUPTED;
> 
> Fix this 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
> Issue: scan-1007.txt
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
> 
> Notes:
>     v2:
>     
>     - replace EFI_COMMON_SECTION_HEADER_UNION with individual array element
>       access [Jordan, Phil, 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 a9f3bcc4eb8e..05470538de42 100644
> --- a/MdePkg/Include/Pi/PiFirmwareFile.h
> +++ b/MdePkg/Include/Pi/PiFirmwareFile.h
> @@ -480,8 +480,15 @@ typedef struct {
>    CHAR16                        VersionString[1];
>  } EFI_VERSION_SECTION2;
>  
> -#define SECTION_SIZE(SectionHeaderPtr) \
> -    ((UINT32) (*((UINT32 *) ((EFI_COMMON_SECTION_HEADER *) (UINTN) SectionHeaderPtr)->Size) & 0x00ffffff))
> +///
> +/// The argument passed as the SectionHeaderPtr parameter to the SECTION_SIZE()
> +/// and IS_SECTION2() function-like macros below must not have side effects:
> +/// SectionHeaderPtr is evaluated multiple times.
> +///
> +#define SECTION_SIZE(SectionHeaderPtr) ((UINT32) ( \
> +    (((EFI_COMMON_SECTION_HEADER *) (UINTN) (SectionHeaderPtr))->Size[0]      ) | \
> +    (((EFI_COMMON_SECTION_HEADER *) (UINTN) (SectionHeaderPtr))->Size[1] <<  8) | \
> +    (((EFI_COMMON_SECTION_HEADER *) (UINTN) (SectionHeaderPtr))->Size[2] << 16)))
>  
>  #define IS_SECTION2(SectionHeaderPtr) \
>      (SECTION_SIZE (SectionHeaderPtr) == 0x00ffffff)
> 

Thanks!

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