Re: [PATCH 1/4] OvmfPkg/PlatformPei: don't track BS Code/Data in default MemTypeInfo HOB

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 5/8/20 2:16 PM, Laszlo Ersek wrote:
> In commit d42fdd6f8384 ("OvmfPkg: improve SMM comms security with adaptive
> MemoryTypeInformation", 2020-03-12), we enabled the boot-to-boot tracking
> of the usages of various UEFI memory types.
> 
> Both whitepapers listed in that commit recommend that BS Code/Data type
> memory *not* be tracked. This recommendation was confirmed by Jiewen in
> the following two messages as well:
> 
> [1] https://edk2.groups.io/g/devel/message/55741
>      http://mid.mail-archive.com/74D8A39837DF1E4DA445A8C0B3885C503F97B579@shsmsx102.ccr.corp.intel.com
> 
> [2] https://edk2.groups.io/g/devel/message/55749
>      http://mid.mail-archive.com/74D8A39837DF1E4DA445A8C0B3885C503F97BDC5@shsmsx102.ccr.corp.intel.com
> 
> While tracking BS Code/Data type memory has one benefit (it de-fragments
> the UEFI memory map), the downsides outweigh it. Spikes in BS Data type
> memory usage are not uncommon in particular, and they may have the
> following consequences:
> 
> - such reboots during normal boot that look "spurious" to the end user,
>    and have no SMM security benefit,
> 
> - a large BS Data record in MemoryTypeInformation may cause issues when
>    the DXE Core tries to prime the according bin(s), but the system's RAM
>    size has been reduced meanwhile.
> 
> Removing the BS Code/Data entries from MemoryTypeInformation leads to a
> bit more fragmentation in the UEFI memory map, but that should be
> harmless.
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2706
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
>   OvmfPkg/PlatformPei/MemTypeInfo.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/OvmfPkg/PlatformPei/MemTypeInfo.c b/OvmfPkg/PlatformPei/MemTypeInfo.c
> index 863c6f382680..8100a2db7d44 100644
> --- a/OvmfPkg/PlatformPei/MemTypeInfo.c
> +++ b/OvmfPkg/PlatformPei/MemTypeInfo.c
> @@ -31,8 +31,6 @@ STATIC EFI_MEMORY_TYPE_INFORMATION mDefaultMemoryTypeInformation[] = {
>     { EfiReservedMemoryType,  0x004 },
>     { EfiRuntimeServicesData, 0x024 },
>     { EfiRuntimeServicesCode, 0x030 },
> -  { EfiBootServicesCode,    0x180 },
> -  { EfiBootServicesData,    0xF00 },
>     { EfiMaxMemoryType,       0x000 }
>   };
>   
> 

Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>