On Thu, 7 Mar 2024 at 12:13, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Thu, 7 Mar 2024 at 12:08, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> >
> > Hi Muhammad,
> >
> > Thanks for the report.
> >
> > On Thu, 7 Mar 2024 at 12:02, Muhammad Usama Anjum
> > <usama.anjum@xxxxxxxxxxxxx> wrote:
> > >
> > > Hi,
> > >
> > > The recent patch:
> > > 276805fb9c305: efi/libstub: Add get_event_log() support for CC platforms
> > > has introduced
> > > #define EFI_CC_EVENT_LOG_FORMAT_TCG_2 0x00000002
> > >
> > > But EFI_TCG2_EVENT_LOG_FORMAT_TCG_2 has the same numerical value:
> > > #define EFI_TCG2_EVENT_LOG_FORMAT_TCG_2 0x2
> > >
> > > Thus there is dead code in efi_retrieve_tcg2_eventlog() i.e, multiple if
> > > conditions with (version == 2) I'm unable to decide on what is wrong and
> > > what is right here. Please have a look.
> > >
> >
> > Why is this a problem? The compiler will recognize this and simplify
> > the conditional. The code as written is semantically correct, the fact
> > that the symbolic constants resolve to the same numerical value is
> > just an implementation detail.
>
> Ah hold on. I see what you mean now:
>
> if (version == EFI_TCG2_EVENT_LOG_FORMAT_TCG_2)
> final_events_table = get_efi_config_table(LINUX_EFI_TPM_FINAL_LOG_GUID);
> + else if (version == EFI_CC_EVENT_LOG_FORMAT_TCG_2)
> + final_events_table = get_efi_config_table(LINUX_EFI_CC_FINAL_LOG_GUID);
>
> Yes, that is broken.
Could we fix it like this perhaps?
--- a/drivers/firmware/efi/libstub/tpm.c
+++ b/drivers/firmware/efi/libstub/tpm.c
@@ -75,8 +75,7 @@
*
* CC Event log also uses TCG2 format, handle it same as TPM2.
*/
if (version > EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2) {
/*
* The TCG2 log format has variable length entries,
* and the information to decode the hash algorithms
@@ -109,10 +108,11 @@
* Figure out whether any events have already been logged to the
* final events structure, and if so how much space they take up
*/
if (version > EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2)
final_events_table =
get_efi_config_table(LINUX_EFI_TPM_FINAL_LOG_GUID) ?:
get_efi_config_table(LINUX_EFI_CC_FINAL_LOG_GUID);
