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

[Leif Lindholm <leif.lindholm@linaro.org>]

On Thu, Aug 09, 2018 at 03:15:38PM +0900, 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.

I find this done in CreatePopulateInstallShellProtocol() in
Application/Shell/ShellProtocol.c, is that the one you see?

> 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.

Where we find non-spec-compliant code in EDK2, we want to fix EDK2.
That doesn't mean that we don't perhaps want to work around it in
U-Boot anyway. But if we do, I would prefer if we could spam the
console a bit as well, to warn people of badly behaving apps.

However...

> 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 */
> +	if (notify_tpl && (is_valid_tpl(notify_tpl) != EFI_SUCCESS))

From the UEFI spec (2.7) description of CreateEvent() boot service:
---
The EVT_NOTIFY_WAIT and EVT_NOTIFY_SIGNAL flags are exclusive. If
neither flag is specified, the caller does not require any
notification concerning the event and the NotifyTpl, NotifyFunction,
and NotifyContext parameters are ignored.
---

So it's not a workaround for Shell specifically.
However, based on that text, something like

    if (type & (EVT_NOTIFY_WAIT | EVT_NOTIFY_SIGNAL))
        if ((is_valid_tpl(notify_tpl) != EFI_SUCCESS))

may resolve this in a more compliant way.

Of course, this may require additional changes to the remainder of the
function.

/
    Leif

>  		return EFI_INVALID_PARAMETER;
>  
>  	evt = calloc(1, sizeof(struct efi_event));
> -- 
> 2.18.0
>