[U-Boot] [RFC] efi_loader: workaround for EDK2's shell.efi

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Thu, Aug 09, 2018 at 07:55:06AM +0100, Alexander Graf wrote:
> 
> 
> On 09.08.18 07:15, AKASHI Takahiro wrote:
> > The commit 21b3edfc964 ("efi_loader: check parameters of CreateEvent")
> > enforces a strict parameter check at CreateEvent().  Unfortunately,
> > however, EDK2's Shell.efi calls this function with notify_tpl == 0.
> > 
> > The patch above does right thing and we'd better fix the issue on EDK2
> > side, and yet we might want a workaround allowing for running un-modified
> > version of EDK2 in short-term solution.
> 
> ... of the EDK2 shell ...
> 
> and it's not just about short term - we always want to be compatible :).

Okay.

> So what's the reason this does not trigger in edk2? Are they considering
> TPL 0 a valid TPL always or did they just forget the check in create
> event? If they always consider TPL 0 valid, we better change
> is_valid_tpl to ensure compatibility with edk2's behavior.

I'm not confident about what Shell's intent is.
Created here is an event to be used to raise a signal for "notification
of Ctrl-C keystrokes," and hence Shell expects such key data to always
be sent to a task whatever its TPL is?

> > The patch provides a minimum mitigation of parameter check.
> > 
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > ---
> >  lib/efi_loader/efi_boottime.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
> > index 2281703f261..e7a19c35415 100644
> > --- a/lib/efi_loader/efi_boottime.c
> > +++ b/lib/efi_loader/efi_boottime.c
> > @@ -627,7 +627,8 @@ efi_status_t efi_create_event(uint32_t type, efi_uintn_t notify_tpl,
> >  		return EFI_INVALID_PARAMETER;
> >  	}
> >  
> > -	if (is_valid_tpl(notify_tpl) != EFI_SUCCESS)
> > +	/* notify_tpl == 0: workaround for EDK2's Shell.efi */
> 
> That comment is too undescriptive. Better write something like "EDK2
> accepts TPL 0 in CreateEvent, so to ensure compatibility we should do
> the same. EDK2 Shell.efi depends on this."

Nice!

Thanks,
-Takahiro AKASHI

> 
> Alex
> 
> > +	if (notify_tpl && (is_valid_tpl(notify_tpl) != EFI_SUCCESS))
> >  		return EFI_INVALID_PARAMETER;
> >  
> >  	evt = calloc(1, sizeof(struct efi_event));
> >