From: Linus Torvalds <torvalds@linux-foundation.org>
To: Kees Cook <keescook@chromium.org>
Cc: tcharding <me@tobin.cc>, Steven Rostedt <rostedt@goodmis.org>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Hashed pointer issues
Date: Mon, 30 Apr 2018 19:00:49 +0000 [thread overview]
Message-ID: <CA+55aFyreOY8uzOkkDkU=WttNfbH2_6nStfsm9j2T6F5ZyntHg@mail.gmail.com> (raw)
In-Reply-To: <CAGXu5jLVJxDJcbhrQU5-wduaP+OvePXP8VvCFMrJ47pYD-zaXg@mail.gmail.com>
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.
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?
Linus
next prev parent reply other threads:[~2018-04-30 19:01 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 [this message]
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
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