linux-kernel - Re: [PATCH] efi_64: Fix a missing-check bug in arch/x86/platform/efi/efi

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Date:   Fri, 17 May 2019 11:24:27 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Gen Zhang <blackgod016574@...il.com>,
        linux-efi <linux-efi@...r.kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] efi_64: Fix a missing-check bug in arch/x86/platform/efi/efi_64.c
 of Linux 5.1

On Fri, 17 May 2019 at 11:06, Gen Zhang <blackgod016574@...il.com> wrote:
>
> 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?


If efi_call_phys_prolog() returns NULL, the calling function should
abort and never call efi_call_phys_epilog().