Re: [PATCH] OvmfPkg/X86QemuLoadImageLib: handle EFI_ACCESS_DENIED from LoadImage()

["Ard Biesheuvel" <ard.biesheuvel@arm.com>]

On 6/6/20 1:52 AM, Laszlo Ersek wrote:
> When an image fails Secure Boot validation, LoadImage() returns
> EFI_SECURITY_VIOLATION if the platform policy is
> DEFER_EXECUTE_ON_SECURITY_VIOLATION.
> 
> If the platform policy is DENY_EXECUTE_ON_SECURITY_VIOLATION, then
> LoadImage() returns EFI_ACCESS_DENIED (and the image does not remain
> loaded).
> 
> (Before <https://bugzilla.tianocore.org/show_bug.cgi?id=2129>, this
> difference would be masked, as DxeImageVerificationLib would incorrectly
> return EFI_SECURITY_VIOLATION for DENY_EXECUTE_ON_SECURITY_VIOLATION as
> well.)
> 
> In X86QemuLoadImageLib, proceed to the legacy Linux/x86 Boot Protocol upon
> seeing EFI_ACCESS_DENIED too.
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2785
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

> ---
> 
> Notes:
>      Repo:   https://pagure.io/lersek/edk2.git
>      Branch: x86_qlil_access_denied
> 
>   OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c | 14 ++++++++++----
>   1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c b/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c
> index ef753be7ea90..931553c0c1fb 100644
> --- a/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c
> +++ b/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c
> @@ -319,13 +319,19 @@ QemuLoadKernelImage (
>       return EFI_NOT_FOUND;
>   
>     case EFI_SECURITY_VIOLATION:
> +    //
> +    // Since the image has been loaded, we need to unload it before proceeding
> +    // to the EFI_ACCESS_DENIED case below.
> +    //
> +    gBS->UnloadImage (KernelImageHandle);
> +    //
> +    // Fall through
> +    //
> +  case EFI_ACCESS_DENIED:
>       //
>       // We are running with UEFI secure boot enabled, and the image failed to
>       // authenticate. For compatibility reasons, we fall back to the legacy
> -    // loader in this case. Since the image has been loaded, we need to unload
> -    // it before proceeding
> -    //
> -    gBS->UnloadImage (KernelImageHandle);
> +    // loader in this case.
>       //
>       // Fall through
>       //
>