Re: [4.19.y PATCH 1/3] efi/x86/Add missing error handling to old_memmap 1:1 mapping code

Greg KH
2019-06-29T09:11:05Z

On Sat, Jun 29, 2019 at 10:47:00AM +0200, Ard Biesheuvel wrote:
> On Sat, 29 Jun 2019 at 08:57, Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Fri, Jun 28, 2019 at 11:42:13AM -0700, Srivatsa S. Bhat wrote:
> > > From: Gen Zhang <blackgod016574@gmail.com>
> > >
> > > commit 4e78921ba4dd0aca1cc89168f45039add4183f8e upstream.
> > >
> > > The old_memmap flow in efi_call_phys_prolog() performs numerous memory
> > > allocations, and either does not check for failure at all, or it does
> > > but fails to propagate it back to the caller, which may end up calling
> > > into the firmware with an incomplete 1:1 mapping.
> > >
> > > So let's fix this by returning NULL from efi_call_phys_prolog() on
> > > memory allocation failures only, and by handling this condition in the
> > > caller. Also, clean up any half baked sets of page tables that we may
> > > have created before returning with a NULL return value.
> > >
> > > Note that any failure at this level will trigger a panic() two levels
> > > up, so none of this makes a huge difference, but it is a nice cleanup
> > > nonetheless.
> >
> > With a description like this, why is this needed in a stable kernel if
> > it does not really fix anything useful?
> >
>
> Because it fixes a 'CVE', remember? :-)

No, I don't remember that at all.

Remember, I get 1000+ emails a day to do something with, and hence, have
the short-term memory of prior emails of a squirrel.

Also, CVEs mean nothing, anyone can get one and they are impossible to
revoke, so don't treat them like they are "authoritative" at all.

greg k-h