Re: [PATCH v3 6/6] OvmfPkg/QemuVideoDxe: Bypass NULL pointer detection during VBE SHIM installing

[Laszlo Ersek <lersek@redhat.com>]

On 09/28/17 03:03, Jian J Wang wrote:
> QemuVideoDxe driver will link VBE SHIM into page 0. If NULL pointer
> detection is enabled, this driver will fail to load. NULL pointer detection
> bypassing code is added to prevent such problem during boot.
> 
> Please note that Windows 7 will try to access VBE SHIM during boot if it's
> installed, and then cause boot failure. This can be fixed by setting BIT7
> of PcdNullPointerDetectionPropertyMask to disable NULL pointer detection
> after EndOfDxe. As far as we know, there's no other OSs has such issue.
> 
>> According to Laszlo, remove the code disabling/enabling the NULL pointer
>> detection but just ignore the installing if it's enabled
> 
> Cc: Star Zeng <star.zeng@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Michael Kinney <michael.d.kinney@intel.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Ayellet Wolman <ayellet.wolman@intel.com>
> Suggested-by: Ayellet Wolman <ayellet.wolman@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> ---
>  OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf |  1 +
>  OvmfPkg/QemuVideoDxe/VbeShim.c        | 14 ++++++++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf b/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf
> index 577e07b0a8..ff68c99e96 100644
> --- a/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf
> +++ b/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf
> @@ -77,3 +77,4 @@
>  [Pcd]
>    gOptionRomPkgTokenSpaceGuid.PcdDriverSupportedEfiVersion
>    gUefiOvmfPkgTokenSpaceGuid.PcdOvmfHostBridgePciDevId
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdNullPointerDetectionPropertyMask
> diff --git a/OvmfPkg/QemuVideoDxe/VbeShim.c b/OvmfPkg/QemuVideoDxe/VbeShim.c
> index e45a08e887..8ba5522cde 100644
> --- a/OvmfPkg/QemuVideoDxe/VbeShim.c
> +++ b/OvmfPkg/QemuVideoDxe/VbeShim.c
> @@ -75,6 +75,20 @@ InstallVbeShim (
>    UINTN                Printed;
>    VBE_MODE_INFO        *VbeModeInfo;
>  
> +  if ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & (BIT0|BIT7)) == BIT0) {
> +    DEBUG ((
> +      DEBUG_WARN,
> +      "%a: page 0 protected, not installing VBE shim\n",
> +      __FUNCTION__
> +      ));
> +    DEBUG ((
> +      DEBUG_WARN,
> +      "%a: page 0 protection prevents Windows 7 from booting anyway\n",
> +      __FUNCTION__
> +      ));
> +    return;
> +  }
> +
>    Segment0 = 0x00000;
>    SegmentC = 0xC0000;
>    SegmentF = 0xF0000;
> 

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