OvmfPkg: decompress FVs on S3 resume if SMM_REQUIRE is set

OvmfPkg: decompress FVs on S3 resume if SMM_REQUIRE is set

If OVMF was built with -D SMM_REQUIRE, that implies that the runtime OS is
not trusted and we should defend against it tampering with the firmware's
data.

One such datum is the PEI firmware volume (PEIFV). Normally PEIFV is
decompressed on the first boot by SEC, then the OS preserves it across S3
suspend-resume cycles; at S3 resume SEC just reuses the originally
decompressed PEIFV.

However, if we don't trust the OS, then SEC must decompress PEIFV from the
pristine flash every time, lest we execute OS-injected code or work with
OS-injected data.

Due to how FVMAIN_COMPACT is organized, we can't decompress just PEIFV;
the decompression brings DXEFV with itself, plus it uses a temporary
output buffer and a scratch buffer too, which even reach above the end of
the finally installed DXEFV. For this reason we must keep away a
non-malicious OS from DXEFV too, plus the memory up to
PcdOvmfDecomprScratchEnd.

The delay introduced by the LZMA decompression on S3 resume is negligible.

If -D SMM_REQUIRE is not specified, then PcdSmmSmramRequire remains FALSE
(from the DEC file), and then this patch has no effect (not counting some
changed debug messages).

If QEMU doesn't support S3 (or the user disabled it on the QEMU command
line), then this patch has no effect also.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19037 6f19259b-4bc3-4df7-8a09-765794883524