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From: Kees Cook <keescook@chromium.org>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	"Tobin C. Harding" <me@tobin.cc>
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 11:38:42 -0700	[thread overview]
Message-ID: <CAGXu5jLVJxDJcbhrQU5-wduaP+OvePXP8VvCFMrJ47pYD-zaXg@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFyNqnrM=_5pMgEeL20jVKN7MgWKG52pbaR0FayO=5VuXw@mail.gmail.com>

On Mon, Apr 30, 2018 at 10:01 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Apr 30, 2018 at 9:57 AM Linus Torvalds <
> torvalds@linux-foundation.org> wrote:
>
>> Although in *practice* we'd have tons of entropy on any modern development
>> CPU too, since any new hardware will have the hardware random number
>> generation. Some overly cautious person might not trust it, of course.
>
> In fact, maybe that's the right policy. Avoid a boot-time parameter by just
> saying
>
>   "if you have hardware random number generation, we can fill entropy
> immediately"

Something like this? (Untested.)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 30c0cb8cc9bc..2d8615f14dc9 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1672,9 +1672,8 @@ char *pointer_string(char *buf, char *end, const
void *ptr,
 static bool have_filled_random_ptr_key __read_mostly;
 static siphash_key_t ptr_key __read_mostly;

-static void fill_random_ptr_key(struct random_ready_callback *unused)
+static void ptr_key_ready(void)
 {
-       get_random_bytes(&ptr_key, sizeof(ptr_key));
        /*
         * have_filled_random_ptr_key==true is dependent on get_random_bytes().
         * ptr_to_id() needs to see have_filled_random_ptr_key==true
@@ -1684,14 +1683,28 @@ static void fill_random_ptr_key(struct
random_ready_callback *unused)
        WRITE_ONCE(have_filled_random_ptr_key, true);
 }

+static void fill_random_ptr_key(struct random_ready_callback *unused)
+{
+       get_random_bytes(&ptr_key, sizeof(ptr_key));
+       ptr_key_ready();
+}
+
 static struct random_ready_callback random_ready = {
        .func = fill_random_ptr_key
 };

 static int __init initialize_ptr_random(void)
 {
-       int ret = add_random_ready_callback(&random_ready);
+       int ret;
+
+       /* 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;
+       }

+       ret = add_random_ready_callback(&random_ready);
        if (!ret) {
                return 0;
        } else if (ret == -EALREADY) {


>
> No kernel command line needed in practice any more. That's assuming any
> kernel developer will have an IvyBridge or newer.
>
> The "I don't trust my hardware" people can still disable that with
> "nordrand".
>
> Hmm?
>
>                     Linus



-- 
Kees Cook
Pixel Security

  parent reply	other threads:[~2018-04-30 18:38 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-30 15:50 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 [this message]
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

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