[PATCH v2] efi_loader: Don't limit the StMM buffer size explicitly

[Jens Wiklander]

Hi Ilias,

On Sat, Dec 25, 2021 at 8:39 PM Ilias Apalodimas
<ilias.apalodimas at linaro.org> wrote:
>
> On Sat, Dec 25, 2021 at 05:13:23PM +0100, Heinrich Schuchardt wrote:
> > On 12/25/21 16:04, Ilias Apalodimas wrote:
> > >
> > >
> > > On Sat, 25 Dec 2021, 16:28 Heinrich Schuchardt, <xypron.glpk at gmx.de
> > > <mailto:xypron.glpk at gmx.de>> wrote:
> > >
> > >
> > >
> > >     Am 25. Dezember 2021 12:16:29 MEZ schrieb Ilias Apalodimas
> > >     <ilias.apalodimas at linaro.org <mailto:ilias.apalodimas at linaro.org>>:
> > >      >> >
> > >      >[...]
> > >      >> >    rc = tee_invoke_func(conn.tee, &arg, 2, param);
> > >      >> >    tee_shm_free(shm);
> > >      >> > +  /*
> > >      >> > +   * Although the max payload is configurable on StMM, we
> > >     only share
> > >      >> > +   * four pages from OP-TEE for the non-secure buffer used to
> > >     communicate
> > >      >> > +   * with StMM. OP-TEE will reject anything bigger than that
> > >     and will
> > >      >> > +   * return.  So le'ts at least warn users
> > >      >> > +   */
> >
> > The comment mentioning four pages does not make too much sense to me as
> > both OP-TEE as well as U-Boot can be configured to other sizes.
> >
>
> The pages that op-tee uses are not configurable.  What is configurable is
> the number of pages you can request op-tee to map from the non-secure
> world for u-boot sharing.  However the four page restriction I refer to
> is an internal op-tee one and refers to the non-secure world buffer it
> shares with StandAloneMM, not u-boot [1]

The commit message suggests that we may try to use an even larger
buffer if needed. A comment here in the code mentioning how this works
should be useful.

Cheers,
Jens

>
> [...]
>
> [1] https://github.com/OP-TEE/optee_os/blob/master/core/arch/arm/kernel/stmm_sp.c#L73
> Cheers
> /Ilias