Re: [edk2-devel] [PATCH] OvmfPkg/MemEncryptSevLib: Fix address overflow during PVALIDATE

["Gerd Hoffmann" <kraxel@redhat.com>]

On Fri, Nov 10, 2023 at 08:14:39PM -0600, Michael Roth wrote:
> The struct used for GHCB-based page-state change requests uses a 40-bit
> bit-field for the GFN, which is shifted by PAGE_SHIFT to generate a
> 64-bit address. However, anything beyond 40-bits simply gets shifted off
> when doing this, which will cause issues when dealing with 1TB+
> addresses. Fix this by casting the 40-bit GFN values to 64-bit ones
> prior to shifting it by PAGE_SHIFT.
> 
> Fixes: ade62c18f474 ("OvmfPkg/MemEncryptSevLib: add support to validate system RAM")
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
>  .../BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c    | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
> index 85eb41585b..d52d2940e9 100644
> --- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
> +++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
> @@ -78,13 +78,14 @@ PvalidateRange (
>    IN  BOOLEAN                     Validate
>    )
>  {
> -  UINTN  Address, RmpPageSize, Ret, i;
> +  UINTN                 RmpPageSize, Ret, i;
> +  EFI_PHYSICAL_ADDRESS  Address;
>  
>    for ( ; StartIndex <= EndIndex; StartIndex++) {
>      //
>      // Get the address and the page size from the Info.
>      //
> -    Address     = Info->Entry[StartIndex].GuestFrameNumber << EFI_PAGE_SHIFT;
> +    Address     = ((UINT64)Info->Entry[StartIndex].GuestFrameNumber) << EFI_PAGE_SHIFT;

Minor nit: why cast to UINT64 not EFI_PHYSICAL_ADDRESS?

Otherwise looks good to me.

take care,
  Gerd



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