Re: [PATCH] efi: Work around bogus pointers in BGRT

[Josh Triplett <josh@joshtriplett.org>]

On Fri, May 24, 2013 at 06:15:16PM -0700, Andy Lutomirski wrote:
> On Thu, May 23, 2013 at 10:37 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> > On Fri, May 17, 2013 at 02:05:33PM -0700, Andy Lutomirski wrote:
> >> The MSI MS-7760 supplies a BGRT marked "invalid" that contains a
> >> pointer to nowhere.  Since an "invalid" BGRT isn't particularly
> >> useful (userspace isn't supposed to use it anyway), ignore the BGRT
> >> if it's marked "invalid" and the pointer points outside of EFI boot
> >> services space.
> >>
> >> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> >
> > I'd suggest generalizing the comment to not just mention the one system
> > you observed it on.  In any case, I'm fine with this patch, but I seem
> > to recall Matthew Garrett having some objections to ignoring the BGRT
> > when the valid bit is not set.  Also, if you're going to do so, you
> > might as well not expose the valid bit to userspace.
> 
> Hmm.
> 
> Not exposing the valid bit to userspace would be a bit odd -- it's
> part of a bitfield which (in principle, I think) could have other bits
> defined.
> 
> One option would be to still load the bgrt table if invalid but to not
> try to load the image and to therefore not show that sysfs attribute.
> I don't know what this would break because I don't know what userspace
> programs actually use bgrt.

That sounds sensible to me: there's a BGRT, so load it and expose it,
but with "valid" not set, don't attempt to look at the image.

- Josh Triplett