On 04/14/19 09:19, Jordan Justen wrote:
> On 2019-04-12 16:31:20, 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 introducing EFI_COMMON_SECTION_HEADER_UNION, and expressing
>> SECTION_SIZE() in terms of "EFI_COMMON_SECTION_HEADER_UNION.Uint32".
>>
>> Cc: Liming Gao <liming....@intel.com>
>> Cc: Michael D Kinney <michael.d.kin...@intel.com>
>> Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1710
>> Issue: scan-1007.txt
>> Signed-off-by: Laszlo Ersek <ler...@redhat.com>
>> ---
>> MdePkg/Include/Pi/PiFirmwareFile.h | 10 +++++++++-
>> 1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/MdePkg/Include/Pi/PiFirmwareFile.h
>> b/MdePkg/Include/Pi/PiFirmwareFile.h
>> index a9f3bcc4eb8e..4fce8298d1c0 100644
>> --- a/MdePkg/Include/Pi/PiFirmwareFile.h
>> +++ b/MdePkg/Include/Pi/PiFirmwareFile.h
>> @@ -229,16 +229,24 @@ typedef struct {
>> ///
>> UINT8 Size[3];
>> EFI_SECTION_TYPE Type;
>> ///
>> /// Declares the section type.
>> ///
>> } EFI_COMMON_SECTION_HEADER;
>>
>> +///
>> +/// Union that permits accessing EFI_COMMON_SECTION_HEADER as a UINT32
>> object.
>> +///
>> +typedef union {
>> + EFI_COMMON_SECTION_HEADER Hdr;
>> + UINT32 Uint32;
>> +} EFI_COMMON_SECTION_HEADER_UNION;
>> +
>> typedef struct {
>> ///
>> /// A 24-bit unsigned integer that contains the total size of the section
>> in bytes,
>> /// including the EFI_COMMON_SECTION_HEADER.
>> ///
>> UINT8 Size[3];
>>
>> EFI_SECTION_TYPE Type;
>> @@ -476,17 +484,17 @@ typedef struct {
>> /// A UINT16 that represents a particular build. Subsequent builds have
>> monotonically
>> /// increasing build numbers relative to earlier builds.
>> ///
>> UINT16 BuildNumber;
>> CHAR16 VersionString[1];
>> } EFI_VERSION_SECTION2;
>>
>> #define SECTION_SIZE(SectionHeaderPtr) \
>> - ((UINT32) (*((UINT32 *) ((EFI_COMMON_SECTION_HEADER *) (UINTN)
>> SectionHeaderPtr)->Size) & 0x00ffffff))
>> + (((EFI_COMMON_SECTION_HEADER_UNION *) (UINTN)
>> (SectionHeaderPtr))->Uint32 & 0x00ffffff)
>
> Mike, all,
>
> Can we add a typedef for EFI_COMMON_SECTION_HEADER_UNION if it's not
> in the PI spec?
>
> If it's not allowed, I think something like this might work too:
>
> #define SECTION_SIZE(SectionHeaderPtr) \
> (*((UINT32*)(UINTN)(SectionHeaderPtr)) & 0x00ffffff)
(Less importantly:)
It might shut up the static analyzer, but regarding the C standard, it's
equally undefined behavior.
Anyway I don't feel too strongly about this, given that we disable the
strict aliasing / effective type rules in "tools_def.template"
("-fno-strict-aliasing").
> Then again, I see SECTION_SIZE is not in the spec, so maybe it's ok to
> add the typedef.
(More importantly:)
Indeed the doubt you voice about ..._UNION crossed my mind, but then I
too searched the PI spec for SECTION_SIZE, with no hits.
Beyond that, I searched both the PI and UEFI specs, for "_UNION" --
again no hits, despite our definitions of:
- EFI_IMAGE_OPTIONAL_HEADER_UNION
- EFI_GRAPHICS_OUTPUT_BLT_PIXEL_UNION
in
- "MdePkg/Include/IndustryStandard/PeImage.h"
- "MdePkg/Include/Protocol/GraphicsOutput.h"
respectively.
Thanks,
Laszlo
>
> -Jordan
>
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