Re: [edk2-devel] [PATCH v2 11/10] OvmfPkg/Csm/LegacyBiosDxe: Fix Legacy16GetTableAddress call for E820 data

["Laszlo Ersek" <lersek@redhat.com>]

On 06/13/19 10:40, David Woodhouse wrote:
> The DX register is supposed to contain the required alignment for the
> allocation. It was zero, and SeaBIOS doesn't (well, didn't) cope well
> with that. Set it appropriately.
> 
> Also set BX to indicate the regions it's OK to allocate in too. That
> wasn't being initialised and was just using whatever the previous user
> of the structure had left there.
> 
> Finally, actually return an error if the allocation fails. Instead of
> going all the way through into the CSM and just letting it have a bogus
> pointer to the E820 data.
> 
> Signed-off-by: David Woodhouse <dwmw2@infradead.org>
> Reviewed-by: Hao A Wu <hao.a.wu@intel.com>
> ---
>  OvmfPkg/Csm/LegacyBiosDxe/LegacyBootSupport.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/OvmfPkg/Csm/LegacyBiosDxe/LegacyBootSupport.c b/OvmfPkg/Csm/LegacyBiosDxe/LegacyBootSupport.c
> index 211750c012..cd4cd24f42 100644
> --- a/OvmfPkg/Csm/LegacyBiosDxe/LegacyBootSupport.c
> +++ b/OvmfPkg/Csm/LegacyBiosDxe/LegacyBootSupport.c
> @@ -928,7 +928,9 @@ GenericLegacyBoot (
>    if (CopySize > Private->Legacy16Table->E820Length) {
>      ZeroMem (&Regs, sizeof (EFI_IA32_REGISTER_SET));
>      Regs.X.AX = Legacy16GetTableAddress;
> +    Regs.X.BX = (UINT16) 0x0; // Any region
>      Regs.X.CX = (UINT16) CopySize;
> +    Regs.X.DX = (UINT16) 0x4; // Alignment
>      Private->LegacyBios.FarCall86 (
>        &Private->LegacyBios,
>        Private->Legacy16Table->Compatibility16CallSegment,
> @@ -942,6 +944,7 @@ GenericLegacyBoot (
>      Private->Legacy16Table->E820Length  = (UINT32) CopySize;
>      if (Regs.X.AX != 0) {
>        DEBUG ((EFI_D_ERROR, "Legacy16 E820 length insufficient\n"));
> +      return EFI_OUT_OF_RESOURCES;
>      } else {
>        CopyMem (
>          (VOID *)(UINTN) Private->Legacy16Table->E820Pointer,
> 

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