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From: "Yao, Jiewen" <jiewen.yao@intel.com>
To: "Wang, Jian J" <jian.j.wang@intel.com>, "devel@edk2.groups.io"
	<devel@edk2.groups.io>
CC: "Zhang, Chao B" <chao.b.zhang@intel.com>, Laszlo Ersek <lersek@redhat.com>
Subject: Re: [PATCH 7/9] SecurityPkg/DxeImageVerificationLib: tighten default result of IsForbiddenByDbx()(CVE-2019-14575)
Thread-Topic: [PATCH 7/9] SecurityPkg/DxeImageVerificationLib: tighten
 default result of IsForbiddenByDbx()(CVE-2019-14575)
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Date: Thu, 13 Feb 2020 10:13:21 +0000
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References: <20200206141933.356-1-jian.j.wang@intel.com>
 <20200206141933.356-8-jian.j.wang@intel.com>
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Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

> -----Original Message-----
> From: Wang, Jian J <jian.j.wang@intel.com>
> Sent: Thursday, February 6, 2020 10:20 PM
> To: devel@edk2.groups.io
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Zhang, Chao B
> <chao.b.zhang@intel.com>; Laszlo Ersek <lersek@redhat.com>
> Subject: [PATCH 7/9] SecurityPkg/DxeImageVerificationLib: tighten default
> result of IsForbiddenByDbx()(CVE-2019-14575)
>=20
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3D1608
>=20
> All intermediate results inside this function will be checked and
> returned immediately upon any failure or error, like out-of-resource,
> hash calculation error or certificate retrieval failure.
>=20
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Chao Zhang <chao.b.zhang@intel.com>
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
>  .../DxeImageVerificationLib/DxeImageVerificationLib.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>=20
> diff --git
> a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> index a5dfee0f8e..2236ce98ce 100644
> --- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib=
.c
> +++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib=
.c
> @@ -1240,7 +1240,7 @@ IsForbiddenByDbx (
>    //
>=20
>    // Variable Initialization
>=20
>    //
>=20
> -  IsForbidden       =3D FALSE;
>=20
> +  IsForbidden       =3D TRUE;
>=20
>    Data              =3D NULL;
>=20
>    CertList          =3D NULL;
>=20
>    CertData          =3D NULL;
>=20
> @@ -1257,7 +1257,14 @@ IsForbiddenByDbx (
>    //
>=20
>    DataSize =3D 0;
>=20
>    Status   =3D gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1,
> &gEfiImageSecurityDatabaseGuid, NULL, &DataSize, NULL);
>=20
> +  ASSERT (EFI_ERROR (Status));
>=20
>    if (Status !=3D EFI_BUFFER_TOO_SMALL) {
>=20
> +    if (Status =3D=3D EFI_NOT_FOUND) {
>=20
> +      //
>=20
> +      // Evidently not in dbx if the database doesn't exist.
>=20
> +      //
>=20
> +      IsForbidden =3D FALSE;
>=20
> +    }
>=20
>      return IsForbidden;
>=20
>    }
>=20
>    Data =3D (UINT8 *) AllocateZeroPool (DataSize);
>=20
> @@ -1366,6 +1373,8 @@ IsForbiddenByDbx (
>=20
>=20
>    }
>=20
>=20
>=20
> +  IsForbidden =3D FALSE;
>=20
> +
>=20
>  Done:
>=20
>    if (Data !=3D NULL) {
>=20
>      FreePool (Data);
>=20
> --
> 2.24.0.windows.2