[edk2-devel] [PATCH 1/4] OvmfPkg/PlatformPei: don't track BS Code/Data in default MemTypeInfo HOB

[Laszlo Ersek]

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 at arm.com>
Cc: Jiewen Yao <jiewen.yao at intel.com>
Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Philippe Mathieu-Daudé <philmd at redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2706
Signed-off-by: Laszlo Ersek <lersek at 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 }
 };
 
-- 
2.19.1.3.g30247aa5d201



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