From: "Tobin C. Harding" <me@tobin.cc>
To: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
"Ted Ts'o" <tytso@mit.edu>, Steven Rostedt <rostedt@goodmis.org>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: Re: Hashed pointer issues
Date: Tue, 1 May 2018 07:23:05 +1000 [thread overview]
Message-ID: <20180430212305.GD22100@eros> (raw)
In-Reply-To: <CAGXu5jKbagUs7cS5y6zRQkgiA0tnD7K0FajwA1Gt+ZCPrc2jfQ@mail.gmail.com>
On Mon, Apr 30, 2018 at 12:16:45PM -0700, Kees Cook wrote:
> On Mon, Apr 30, 2018 at 12:00 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> > On Mon, Apr 30, 2018 at 11:38 AM Kees Cook <keescook@chromium.org> wrote:
> >
> >> Something like this? (Untested.)
> >
> > Looks workable.
> >
> >> + /* If we have hw RNG, start hashing immediately. */
> >> + if (arch_has_random()) {
> >> + get_random_bytes_arch(&ptr_key, sizeof(ptr_key));
> >> + ptr_key_ready();
> >> + return 0;
> >> + }
> >
> > Small tweak: you should check the return value of get_random_bytes_arch(),
> > because in theory it can fail.
> >
> > Sadly, that's not actually how get_random_bytes_arch() really works - it
> > falls back on "get_random_bytes()" on failure instead, which is explicitly
> > against the whole point here.
>
> I just noticed: there are _no_ users of get_random_bytes_arch() ...
> didn't we once use it to feed entropy to the CRNG?
>
> > So I think it would need some tweaking, with a new function entirely
> > (get_random_bytes_arch() with a failure return for "cannot fill buffer").
> >
> > But that would be just a few more lines, because we could make the existing
> > get_random_bytes_arch() just use the failure-case thing.
> >
> > So add a "get_hw_random_bytes()" that does that same loop in
> > get_random_bytes_arch(), but returns the number of bytes it filled in.
> >
> > Then get_random_bytes_arch() turns into
> >
> > got = get_hw_random_bytes(p, nbytes);
> > if (got < nbytes)
> > get_random_bytes(p+got, nbytes-got);
> >
> > and the initialize_ptr_random() use would be something like
> >
> > if (get_hw_random_bytes(&ptr_key, sizeof(ptr_key)) == sizeof(ptr_key)) {
> > ptr_key_ready();
> > return 0;
> > }
> >
> > Hmm?
> >
> > Maybe we could call the "get_hw_random_bytes()" something like
> > "get_early_random_bytes()" and the "use HW for it" is purely an
> > implementation detail?
>
> Yeah, and if we add __must_check, I think this should be fine. Ted,
> any thoughts on this?
>
> Tobin, is this something you've got time to implement and test?
Sure thing, thanks for the opportunity.
Tobin
prev parent reply other threads:[~2018-04-30 21:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-30 15:50 Hashed pointer issues Anna-Maria Gleixner
2018-04-30 16:11 ` Kees Cook
2018-04-30 16:31 ` Linus Torvalds
2018-04-30 16:41 ` Steven Rostedt
2018-04-30 16:57 ` Linus Torvalds
2018-04-30 17:01 ` Linus Torvalds
2018-04-30 17:06 ` Randy Dunlap
2018-04-30 17:12 ` Linus Torvalds
2018-05-01 7:05 ` tcharding
2018-05-03 8:41 ` Geert Uytterhoeven
2018-04-30 18:38 ` Kees Cook
2018-04-30 19:00 ` Linus Torvalds
2018-04-30 19:16 ` Kees Cook
2018-04-30 20:01 ` Linus Torvalds
2018-04-30 20:07 ` Linus Torvalds
2018-04-30 21:23 ` Tobin C. Harding [this message]
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