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Subject: Re: [PATCH] OvmfPkg/X86QemuLoadImageLib: handle EFI_ACCESS_DENIED from LoadImage()
To: Laszlo Ersek <lersek@redhat.com>,
 edk2-devel-groups-io <devel@edk2.groups.io>
Cc: Jordan Justen <jordan.l.justen@intel.com>,
 =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <philmd@redhat.com>
References: <20200605235242.32442-1-lersek@redhat.com>
From: "Ard Biesheuvel" <ard.biesheuvel@arm.com>
Message-ID: <3a51e349-44f8-617c-6782-9a56413f2c6e@arm.com>
Date: Mon, 8 Jun 2020 10:15:00 +0200
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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.
>=20
> If the platform policy is DENY_EXECUTE_ON_SECURITY_VIOLATION, then
> LoadImage() returns EFI_ACCESS_DENIED (and the image does not remain
> loaded).
>=20
> (Before <https://bugzilla.tianocore.org/show_bug.cgi?id=3D2129>, this
> difference would be masked, as DxeImageVerificationLib would incorrectl=
y
> return EFI_SECURITY_VIOLATION for DENY_EXECUTE_ON_SECURITY_VIOLATION as
> well.)
>=20
> In X86QemuLoadImageLib, proceed to the legacy Linux/x86 Boot Protocol u=
pon
> seeing EFI_ACCESS_DENIED too.
>=20
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Philippe Mathieu-Daud=C3=A9 <philmd@redhat.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3D2785
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

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

> ---
>=20
> Notes:
>      Repo:   https://pagure.io/lersek/edk2.git
>      Branch: x86_qlil_access_denied
>=20
>   OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c | 14 ++++++=
++++----
>   1 file changed, 10 insertions(+), 4 deletions(-)
>=20
> 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;
>  =20
>     case EFI_SECURITY_VIOLATION:
> +    //
> +    // Since the image has been loaded, we need to unload it before pr=
oceeding
> +    // 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 fa=
iled to
>       // authenticate. For compatibility reasons, we fall back to the l=
egacy
> -    // loader in this case. Since the image has been loaded, we need t=
o unload
> -    // it before proceeding
> -    //
> -    gBS->UnloadImage (KernelImageHandle);
> +    // loader in this case.
>       //
>       // Fall through
>       //
>=20