Proposal: U-Boot memory management

[Ilias Apalodimas]

Hi Simon,

On Fri, 29 Dec 2023 at 07:36, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Ilias,
>
> On Fri, Dec 22, 2023 at 12:02 PM Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
> >
> > Hi Simon
> >
> > I'll respond to the rest more thoroughly but I since I caught this early,
> >
> > [...]
> >
> > >
> > > 5. Avoid calling efi_allocate_pages() and efi_allocate_pool() outside
> > > boot-time services. This solves the problem 6. If memory is needed by
> > > an app, allocate it with malloc() and see 3. There are only two
> > > efi_allocate_pages() (smbios and efi_runtime). There are more calls of
> > > efi_allocate_pool(), but most of these seem easy to fix up. For
> > > example, efi_init_event_log() allocates a buffer, but this can be
> > > allocated in normal malloc() space or in a bloblist.
> >
> > The TCG event log is only valid in the EFI world and is described by
> > the EFI spec extensions [0]. I prefer it to remain as is
>
> How does that relate to [1] ?

We use that today.  The tl;dr is that TF-A measures the early stages,
but doesn't have drivers to extend TPM PCRs. Instead, it creates an
EventLog which hands over to U-Boot. The TPM subsystem searches for
that and if it finds one && PCR0 == 0 replays the EventLog in hardware
and copies it over to EFI memory.

That being said, I'd much prefer using a bloblist for that EventLog
(which also contains information on replaying), over a DT entry that's
only described in TF-A docs. But that's a future improvement.

>
> >
> > >
> > > 6. Don't worry too much about whether EFI will be used for booting.
> > > The cost is likely not that great: use bootstage to measure it as is
> > > done for driver model. Try to minmise the cost of its tables,
> > > particularly for execution time, but otherwise just rely on the
> > > ability to disable EFI_LOADER.
> > >
> > > –
> > >
> > > Regards,
> > > Simon
> >
> > [0] https://trustedcomputinggroup.org/wp-content/uploads/EFI-Protocol-Specification-rev13-160330final.pdf
> > Thanks
> > /Ilias
>
> [1] https://trustedfirmware-a.readthedocs.io/en/latest/components/measured_boot/event_log.html

Cheers
/Ilias