Re: [PATCH v6 0/4] enable early printing of hashed pointers

Tobin C. Harding
2018-06-06T23:30:29Z

On Wed, Jun 06, 2018 at 03:02:20PM +0200, Thomas Gleixner wrote:
> On Mon, 28 May 2018, Tobin C. Harding wrote:
>
> > Currently printing pointers early in the boot sequence can result in a
> > dummy string '(____ptrval____)' being printed. While resolving this
> > issue it was noticed that we can use the hw RNG if available for hashing
> > pointers.
> >
> > Patch one and two do the ground work to be able to use hw RNG removing
> > from get_random_bytes_arch() the call to get_random_bytes() and
> > returning the number of bytes of random material successfully returned.
> >
> > Patch three uses the hw RNG to get keying material if it is available.
> >
> > Patch four further assists debugging early in the boot sequence for
> > machines that do not have a hw RNG by adding a command line option
> > 'debug_boot_weak_hash'. If enabled, non-cryptographically secure hashing
> > is used instead of siphash so we can hash at any time.
> >
> > During the versions of this set I have been totally confused about which
> > patches go through which tree. This version again puts all 4 patches
> > together in the hope they will go through Andrew's tree.
> >
> >
> > Steve,
> >
> > Could you please take a quick squiz at the final 2 patches if you get a
> > chance. I assumed we are in preemptible context during early_init based
> > on your code (and code comment) and called static_branch_disable()
> > directly if hw RNG returned keying material. It's a pretty simple
> > change but I'd love to get someone else to check I've not noob'ed it.
>
> early_initcalls() are not that early :) They run in thread context fully
> preemtible so calling static_branch_disable() is perfectly fine.

Thanks for the explanation.

Tobin.