[edk2-devel] [PATCH 1/1] OvmfPkg: Only import DxeTpmMeasurementLib when TPM is enabled
Laszlo Ersek
lersek at redhat.com
Wed Jul 3 19:49:26 UTC 2019
Hi Gary,
On 07/03/19 12:22, Gary Lin wrote:
> DxeTpmMeasurementLib is only useful when TPM is enabled.
>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Marc-André Lureau <marcandre.lureau at redhat.com>
> Cc: Stefan Berger <stefanb at linux.ibm.com>
> Signed-off-by: Gary Lin <glin at suse.com>
> ---
> OvmfPkg/OvmfPkgIa32.dsc | 10 +++++++---
> OvmfPkg/OvmfPkgIa32X64.dsc | 10 +++++++---
> OvmfPkg/OvmfPkgX64.dsc | 10 +++++++---
> 3 files changed, 21 insertions(+), 9 deletions(-)
This is a good patch, thank you for it. I see two opportunities for
improvement.
(1) There's something weird going on with your newline characters. The
view I get (in both my INBOX and in my list folder) is identical to
mail-archive.com's view:
http://mid.mail-archive.com/20190703102228.25441-1-glin@suse.com
Can you double check your settings, please?
(2) The commit message should be more convincing. How about this:
-----------
(a) OvmfPkg first had to resolve the TpmMeasurementLib class -- for
SECURE_BOOT_ENABLE only -- when the DxeImageVerificationLib instance
became dependent on TpmMeasurementLib. For details, refer to commit
0d28d286bf4d ("OvmfPkg: resolve TpmMeasurementLib dependency
introduced in r14687", 2013-09-21).
(b) At the time, only one instance of TpmMeasurementLib existed, namely
DxeTpmMeasurementLib. This lib instance didn't do anything -- like it
was desirable for OVMF --, because OVMF didn't include any Tcg / TrEE
protocol implementations.
(c) In commit 308521b13354 ("MdeModulePkg: Move TpmMeasurementLib
LibraryClass from SecurityPkg", 2015-07-01), TpmMeasurementLibNull was
introduced.
(d) In commit 285542ebbb03 ("OvmfPkg: Link AuthVariableLib for following
merged variable driver deploy", 2015-07-01), a TpmMeasurementLib
resolution became necessary regardless of SECURE_BOOT_ENABLE. And so
TpmMeasurementLib was resolved to TpmMeasurementLibNull in OVMF, but
only in the non-SECURE_BOOT_ENABLE case. This step -- possibly, the
larger series containing commit 285542ebbb03 -- missed an opportunity
for simplification: given (b), the DxeTpmMeasurementLib instance
should have been simply replaced with the TpmMeasurementLibNull
instance, regardless of SECURE_BOOT_ENABLE.
(e) In commit 1abfa4ce4835 ("Add TPM2 support defined in trusted computing
group.", 2015-08-13), the TrEE dependency was replaced with a Tcg2
dependency in DxeTpmMeasurementLib.
(f) Starting with commit 0c0a50d6b3ff ("OvmfPkg: include Tcg2Dxe module",
2018-03-09), OVMF would include a Tcg2 protocol implementation,
thereby satisfying DxeTpmMeasurementLib's dependency. With
TPM2_ENABLE, it would actually make sense to consume
DxeTpmMeasurementLib -- however, DxeTpmMeasurementLib would never be
used without SECURE_BOOT_ENABLE.
Therefore, we have the following four scenarios:
- TPM2_ENABLE + SECURE_BOOT_ENABLE: works as expected.
- Neither enabled: works as expected.
- Only TPM2_ENABLE: this build is currently incorrect, because
Variable/RuntimeDxe consumes TpmMeasurementLib directly, but
TpmMeasureAndLogData() will never reach the TPM because we link
TpmMeasurementLibNull into the variable driver. This is a problem from
the larger series containing (f).
- Only SECURE_BOOT_ENABLE: this build works as expected, but it is
wasteful -- given that the protocol database will never contain Tcg2
without TPM2_ENABLE, we should simply use TpmMeasurementLibNull. This is
a problem from (d).
Resolving TpmMeasurementLib to DxeTpmMeasurementLib as a function of
*only* TPM2_ENABLE, we can fix / optimize the last two cases.
-----------
To reflect the reasoning in the subject line, I suggest:
OvmfPkg: use DxeTpmMeasurementLib if and only if TPM2_ENABLE
If you agree, please submit a v2 like this.
Thanks!
Laszlo
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