Re: [PATCH v4 6/6] OvmfPkg/QemuVideoDxe: Bypass NULL pointer detection during VBE SHIM installing

[Laszlo Ersek <lersek@redhat.com>]

On 10/09/17 16:17, 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.
> 
> Cc: Star Zeng <star.zeng@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Michael Kinney <michael.d.kinney@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;
> 

If this patch is entirely identical to the previous version (v3), then
you should have please picked up the review tags from Jordan and myself,
the ones that you got for v3:

http://mid.mail-archive.com/150696711831.2454.16712170525103415248@jljusten-skl

http://mid.mail-archive.com/d1a20be5-8dbf-8ce6-1738-d03b330047cc@redhat.com

This way we can quickly filter out already reviewed patches, and avoid
re-reviewing when there are no changes.


Your cover letter v4 0/6 also does not summarize the changes relative to
v3; in the future please don't forget about that.

Thanks
Laszlo