Re: [edk2-devel] [PATCH v1 1/1] OvmfPkg/QemuVideoDxe: Zero out PixelInformation in QueryMode

["Ard Biesheuvel" <ardb@kernel.org>]

On Tue, 28 Jun 2022 at 11:48, Dimitrije Pavlov <Dimitrije.Pavlov@arm.com> wrote:
>
> Ensure that the PixelInformation field of the
> EFI_GRAPHICS_OUTPUT_MODE_INFORMATION structure is zeroed out in
> EFI_GRAPHICS_OUTPUT_PROTOCOL.QueryMode() and
> EFI_GRAPHICS_OUTPUT_PROTOCOL.SetMode() when PixelFormat is
> PixelBlueGreenRedReserved8BitPerColor.
>
> According to UEFI 2.9 Section 12.9, PixelInformation field of the
> EFI_GRAPHICS_OUTPUT_MODE_INFORMATION structure is valid only if
> PixelFormat is PixelBitMask. This means that firmware is not required
> to fill out the PixelInformation field for other PixelFormat types,
> which implies that the QemuVideoDxe implementation is technically
> correct.
>
> However, not zeroing out those fields will leak the contents of the
> memory returned by the memory allocator, so it is better to explicitly
> set them to zero.
>
> In addition, the SCT test suite relies on PixelInformation always
> having a consistent value, which causes failures.
>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Jeff Booher-Kaeding <Jeff.Booher-Kaeding@arm.com>
> Cc: Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@arm.com>
> Cc: Sunny Wang <Sunny.Wang@arm.com>
> Cc: Jeremy Linton <Jeremy.Linton@arm.com>
>
> Signed-off-by: Dimitrije Pavlov <Dimitrije.Pavlov@arm.com>
> ---
>  OvmfPkg/QemuVideoDxe/Gop.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/OvmfPkg/QemuVideoDxe/Gop.c b/OvmfPkg/QemuVideoDxe/Gop.c
> index 0c4dea7fb6f2..7a9fe208c99c 100644
> --- a/OvmfPkg/QemuVideoDxe/Gop.c
> +++ b/OvmfPkg/QemuVideoDxe/Gop.c
> @@ -31,7 +31,14 @@ QemuVideoCompleteModeInfo (
>      Info->PixelInformation.ReservedMask  0;
>    } else if (ModeData->ColorDepth  32) {
>      DEBUG ((DEBUG_INFO, "PixelBlueGreenRedReserved8BitPerColor\n"));
> -    Info->PixelFormat  PixelBlueGreenRedReserved8BitPerColor;
> +    Info->PixelFormat                    PixelBlueGreenRedReserved8BitPerColor;
> +    Info->PixelInformation.RedMask       0;
> +    Info->PixelInformation.GreenMask     0;
> +    Info->PixelInformation.BlueMask      0;
> +    Info->PixelInformation.ReservedMask  0;

Is this valid C? Or is the patch corrupted by email?


> +  } else {
> +    DEBUG ((DEBUG_ERROR, "%a: Invalid ColorDepth %u", __FUNCTION__, ModeData->ColorDepth));
> +    ASSERT (FALSE);
>    }
>
>    Info->PixelsPerScanLine  Info->HorizontalResolution;
> --
> 2.34.1
>
>
>
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