Re: [PATCH] MdePkg/BasePeCoffLib: skip runtime relocation if relocation info is invalid.

[Laszlo Ersek <lersek@redhat.com>]

On 01/25/19 00:18, Neo Hsueh wrote:
> 1.Skip runtime relocation for PE images that provide invalid relocation
>   infomation (ex: RelocDir->Size = 0) to fix a hang observed while booting
>   Windows.
> 2.Add a magic number check for PE32+ image.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Neo Hsueh <hong-chihx.hsueh@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Dandan Bi <dandan.bi@intel.com>
> ---
>  MdePkg/Library/BasePeCoffLib/BasePeCoff.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)

I can't comment on the technical details of the patch, but I have some
comments on the organization of the patch.

First, the two changes that it implements should be separate patches.

> diff --git a/MdePkg/Library/BasePeCoffLib/BasePeCoff.c b/MdePkg/Library/BasePeCoffLib/BasePeCoff.c
> index 1bd079ad6a..6477ef0759 100644
> --- a/MdePkg/Library/BasePeCoffLib/BasePeCoff.c
> +++ b/MdePkg/Library/BasePeCoffLib/BasePeCoff.c
> @@ -1725,11 +1725,18 @@ PeCoffLoaderRelocateImageForRuntime (
>      NumberOfRvaAndSizes = Hdr.Pe32->OptionalHeader.NumberOfRvaAndSizes;
>      DataDirectory = (EFI_IMAGE_DATA_DIRECTORY *)&(Hdr.Pe32->OptionalHeader.DataDirectory[0]);
>    } else {
> +    if (Hdr.Pe32Plus->OptionalHeader.Magic == EFI_IMAGE_NT_OPTIONAL_HDR64_MAGIC) {
> +      //
> +      // Use PE32+ offset
> +      //
> +      NumberOfRvaAndSizes = Hdr.Pe32Plus->OptionalHeader.NumberOfRvaAndSizes;
> +      DataDirectory = (EFI_IMAGE_DATA_DIRECTORY *)&(Hdr.Pe32Plus->OptionalHeader.DataDirectory[0]);
> +    } else {
>      //
> -    // Use PE32+ offset
> +    // Not a valid PE image so Exit
>      //
> -    NumberOfRvaAndSizes = Hdr.Pe32Plus->OptionalHeader.NumberOfRvaAndSizes;
> -    DataDirectory = (EFI_IMAGE_DATA_DIRECTORY *)&(Hdr.Pe32Plus->OptionalHeader.DataDirectory[0]);
> +    return;
> +    }
>    }
>  
>    //

Second, my understanding is that in edk2, we don't do

  if (Condition1) {
  } else {
    if (Condition2) {
    } else {
    }
  }

Instead, we prefer

  if (Condition1) {
  } else if (Condition2) {
  } else {
  }

As far as I know, this is the only construct where we don't require
braces after an "else". See:

https://edk2-docs.gitbooks.io/edk-ii-c-coding-standards-specification/content/5_source_files/57_c_programming.html#57342-when-an-else-is-used-it-may-start-on-the-same-line-as-the-close-brace-of-the-if-or-be-on-the-following-line-and-aligned-with-the-closing-brace


Third, the return statement and the comment are not properly indented in
the last branch.

Thanks
Laszlo

> @@ -1746,6 +1753,12 @@ PeCoffLoaderRelocateImageForRuntime (
>                                                                              RelocDir->VirtualAddress + RelocDir->Size - 1,
>                                                                              0
>                                                                              );
> +    if (RelocBase == NULL || RelocBaseEnd == NULL || RelocBaseEnd < RelocBase) {
> +      //
> +      // relocation block is not valid, just return
> +      //
> +      return;
> +    }
>    } else {
>      //
>      // Cannot find relocations, cannot continue to relocate the image, ASSERT for this invalid image.
>