Re: [PATCH] efi_64: Fix a missing-check bug in arch/x86/platform/efi/efi_64.c of Linux 5.1

[Gen Zhang]

On Fri, May 17, 2019 at 10:41:28AM +0200, Ard Biesheuvel wrote:
> Returning an error here is not going to make much difference, given
> that the caller of efi_call_phys_prolog() does not bother to check it,
> and passes the result straight into efi_call_phys_epilog(), which
> happily attempts to dereference it.
> 
> So if you want to fix this properly, please fix it at the call site as
> well. I'd prefer to avoid ERR_PTR() and just return NULL for a failed
> allocation though.
Hi Ard,
Thanks for your timely reply!
I think returning NULL in efi_call_phys_prolog() and checking in 
efi_call_phys_epilog() is much better. But I am confused what to return
in efi_call_phys_epilog() if save_pgd is NULL. Definitely not return
-ENOMEM, because efi_call_phys_epilog() returns unsigned long. Could
please light on me to fix this problem?
Thanks
Gen