[PATCH] efi_loader: optional persistence of variables

[Tom Saeger]

On Tue, Mar 22, 2022 at 11:33:20PM +0100, Heinrich Schuchardt wrote:
> On 3/22/22 23:16, Tom Saeger wrote:
> > On Tue, Mar 22, 2022 at 10:41:40PM +0100, Heinrich Schuchardt wrote:
> > > On 3/22/22 22:21, Tom Saeger wrote:
> > > > Since be66b89da306 ("efi_loader: configuration of variables store")
> > > > the choice of EFI_VARIABLE_FILE_STORE or EFI_MM_COMM_TEE
> > > > is mutually-exclusive, however efi_var_to_file also allows
> > > > for "neither".  Set Kconfig choice optional.
> > > > 
> > > > Signed-off-by: Tom Saeger <tom.saeger at oracle.com>
> > > > ---
> > > >    lib/efi_loader/Kconfig | 1 +
> > > >    1 file changed, 1 insertion(+)
> > > > 
> > > > diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
> > > > index e5e35fe51f65..9add2a286ff4 100644
> > > > --- a/lib/efi_loader/Kconfig
> > > > +++ b/lib/efi_loader/Kconfig
> > > > @@ -44,6 +44,7 @@ config EFI_SETUP_EARLY
> > > > 
> > > >    choice
> > > >    	prompt "Store for non-volatile UEFI variables"
> > > > +	optional
> > > 
> > > Storing non-volatile variables is required by the UEFI specification.
> > > 
> > > How should a user understand that a boot option he just created vanishes
> > > upon reboot?
> > > 
> > > Please, explain your use case.
> > 
> > bootefi ${kernel_addr}
> > 
> > in this case linux kernel for an Armv8 platform.
> > This platform does not want or need any variables to persist.
> > 
> > bootefi eventually calls efi_var_from_file(), where *NOT* defining
> > CONFIG_EFI_VARIABLE_FILE_STORE would allow this use case to work,
> > otherwise it fails.  This was possible before
> > be66b89da306 ("efi_loader: configuration of variables store").
> 
> Please, describe exactly what does not work. Is it building or is it
> running the bootefi command?

after be66b89da306 CONFIG_EFI_VARIABLE_FILE_STORE is now selected due to
Kconfig choice.  This is the difference.

It fails while running, but the difference is the build.
I'd rather configure for the old behavior - that being return
EFI_SUCCESS from efi_var_from_file() when CONFIG_EFI_VARIABLE_FILE_STORE
isn't defined.

The call-stack is something like:

do_bootefi->efi_init_obj_list->efi_init_variables->efi_var_from_file

> 
> Does your system have an ESP?
> 
> Where does bootefi fail?
> 
> Best regards
> 
> Heinrich
> 
> > 
> > Thoughts?
> > 
> > --Tom
> > 
> > > 
> > > Best regards
> > > 
> > > Heinrich
> > > 
> > > >    	default EFI_VARIABLE_FILE_STORE
> > > >    	help
> > > >    	  Select where non-volatile UEFI variables shall be stored.
> > > > 
> > > > base-commit: 5f68470d69f853b1652ebe93525b60064717fe2e
> > > 
>