[PATCH 15/32] efi: lmb: Avoid access to _start

[Simon Glass]

Hi Tom,

On Mon, 3 Feb 2025 at 13:09, Tom Rini <trini at konsulko.com> wrote:
>
> On Mon, Feb 03, 2025 at 10:42:08AM -0700, Simon Glass wrote:
>
> > The app does not have this symbol. Also the memory where the app is
> > loaded is not under U-Boot's control. Disable this reservation for
> > the EFI app.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > ---
> >
> >  lib/lmb.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/lmb.c b/lib/lmb.c
> > index 588787d2a90..420eae4d0b8 100644
> > --- a/lib/lmb.c
> > +++ b/lib/lmb.c
> > @@ -560,7 +560,8 @@ static void lmb_reserve_uboot_region(void)
> >               lmb_reserve_flags(rsv_start, bank_end - rsv_start + 1,
> >                                 LMB_NOOVERWRITE);
> >
> > -             if (gd->flags & GD_FLG_SKIP_RELOC)
> > +             if (!IS_ENABLED(CONFIG_EFI_APP) &&
> > +                 (gd->flags & GD_FLG_SKIP_RELOC))
> >                       lmb_reserve_flags((phys_addr_t)(uintptr_t)_start,
> >                                         gd->mon_len, LMB_NOOVERWRITE);
>
> What prevents U-Boot from overwriting itself, with U-Boot commands? Also
> how is this linking today? I see lmb_reserve_uboot_region in
> efi-x86_app64 for example.

The only memory U-Boot can use when running as an EFI app is that
which it has allocated using EFI calls. The actual U-Boot code is
certainly in memory somewhere, but does not lie between gd->ram_start
and (gd->ram_start + gd->ram_size)

Regards,
Simon