Re: [edk2-devel] [PATCH 1/1] SecurityPkg: Fix incorrect return value in documentation

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

Hi Phil,

On 02/04/20 23:26, Philippe Mathieu-Daudé wrote:
> The DxeTpmMeasureBootHandler and DxeTpm2MeasureBootHandler handlers
> are SECURITY2_FILE_AUTHENTICATION_HANDLER prototype. This prototype
> can not return EFI_INVALID_PARAMETER.
> 
> The prototype documentation states it returns EFI_ACCESS_DENIED if:
> 
>   "The file specified by File and FileBuffer did not authenticate,
>    and the platform policy dictates that the DXE Foundation may not
>    use File."
> 
> Note in practice both functions return EFI_SECURITY_VIOLATION:
> 
>   "The file specified by DevicePath and FileBuffer did not
>    authenticate, and the platform policy dictates that the file
>    should be placed in the untrusted state. The image has been
>    added to the file execution table."
> 
> Noticed while reviewing commit 6d57592740cdd0b6868baeef7929d6e6fef.
> 
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Chao Zhang <chao.b.zhang@intel.com>
> Signed-off-by: Philippe Mathieu-Daude <philmd@redhat.com>
> ---
>  .../Library/DxeTpm2MeasureBootLib/DxeTpm2MeasureBootLib.c       | 2 +-
>  SecurityPkg/Library/DxeTpmMeasureBootLib/DxeTpmMeasureBootLib.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/SecurityPkg/Library/DxeTpm2MeasureBootLib/DxeTpm2MeasureBootLib.c b/SecurityPkg/Library/DxeTpm2MeasureBootLib/DxeTpm2MeasureBootLib.c
> index 04b9b0d7fbf3..0c07f65c6835 100644
> --- a/SecurityPkg/Library/DxeTpm2MeasureBootLib/DxeTpm2MeasureBootLib.c
> +++ b/SecurityPkg/Library/DxeTpm2MeasureBootLib/DxeTpm2MeasureBootLib.c
> @@ -384,7 +384,7 @@ Finish:
>    and other exception operations.  The File parameter allows for possible logging
>    within the SAP of the driver.
>  
> -  If File is NULL, then EFI_INVALID_PARAMETER is returned.
> +  If File is NULL, then EFI_ACCESS_DENIED is returned.
>  
>    If the file specified by File with an authentication status specified by
>    AuthenticationStatus is safe for the DXE Core to use, then EFI_SUCCESS is returned.

I've tried seeing where this code actually returns
EFI_INVALID_PARAMETER, but I can't find it. If File is NULL in
DxeTpm2MeasureBootHandler(), then first we seem to do:

  OrigDevicePathNode = DuplicateDevicePath (File);

which I believe will produce a NULL. Then we seem to pass this NULL
around a little bit, so I think there's a fair chance of crashing there.

I wonder if this code should be fixed, to check "File" in the first
place, and then return EFI_ACCESS_DENIED.

There are also some other places in the function that could apparently
return a wide array of error codes -- FvbProtocol->GetPhysicalAddress()
(EFI_UNSUPPORTED?), PeCoffLoaderGetImageInfo(), etc.

I do agree this patch is an improvement, however; at least it says what
*should* be returned. So with that in mind:

Acked-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo

> diff --git a/SecurityPkg/Library/DxeTpmMeasureBootLib/DxeTpmMeasureBootLib.c b/SecurityPkg/Library/DxeTpmMeasureBootLib/DxeTpmMeasureBootLib.c
> index 1f2eed29a1df..0dccbb66eb26 100644
> --- a/SecurityPkg/Library/DxeTpmMeasureBootLib/DxeTpmMeasureBootLib.c
> +++ b/SecurityPkg/Library/DxeTpmMeasureBootLib/DxeTpmMeasureBootLib.c
> @@ -678,7 +678,7 @@ Finish:
>    and other exception operations.  The File parameter allows for possible logging
>    within the SAP of the driver.
>  
> -  If File is NULL, then EFI_INVALID_PARAMETER is returned.
> +  If File is NULL, then EFI_ACCESS_DENIED is returned.
>  
>    If the file specified by File with an authentication status specified by
>    AuthenticationStatus is safe for the DXE Core to use, then EFI_SUCCESS is returned.
>