From: Kees Cook <keescook@chromium.org>
To: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
"Theodore Ts'o" <tytso@mit.edu>,
Eric Biggers <ebiggers3@gmail.com>,
"ebiggers@google.com" <ebiggers@google.com>,
"herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
David Laight <David.Laight@aculab.com>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"luto@kernel.org" <luto@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jpoimboe@redhat.com" <jpoimboe@redhat.com>,
"jannh@google.com" <jannh@google.com>,
"Perla, Enrico" <enrico.perla@intel.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall
Date: Tue, 30 Apr 2019 11:01:02 -0700 [thread overview]
Message-ID: <CAGXu5jK108afSxMp6qtcdEr-D-ONz80L0C_4p2oLsMsDWvK=zw@mail.gmail.com> (raw)
In-Reply-To: <2236FBA76BA1254E88B949DDB74E612BA4C6A4D7@IRSMSX102.ger.corp.intel.com>
On Tue, Apr 30, 2019 at 10:51 AM Reshetova, Elena
<elena.reshetova@intel.com> wrote:
> base: Simple syscall: 0.1761 microseconds
> get_random_bytes (4096 bytes per-cpu buffer): 0.1793 microsecons
> get_random_bytes (64 bytes per-cpu buffer): 0.1866 microsecons
The 4096 size seems pretty good.
> Below is a snip of what I quickly did (relevant parts) to get these numbers.
> I do initial population of per-cpu buffers in late_initcall, but
> practice shows that rng might not always be in good state by then.
> So, we might not have really good randomness then, but I am not sure
> if this is a practical problem since it only applies to system boot and by
> the time it booted, it already issued enough syscalls that buffer gets refilled
> with really good numbers.
> Alternatively we can also do it on the first syscall that each cpu gets, but I
> am not sure if that is always guaranteed to have a good randomness.
Populating at first syscall seems like a reasonable way to delay. And
I agree: I think we should not be too concerned about early RNG state:
we should design for the "after boot" behaviors.
> diff --git a/lib/percpu-random.c b/lib/percpu-random.c
> new file mode 100644
> index 000000000000..3f92c44fbc1a
> --- /dev/null
> +++ b/lib/percpu-random.c
> @@ -0,0 +1,49 @@
> +#include <linux/types.h>
> +#include <linux/percpu.h>
> +#include <linux/random.h>
> +
> +static DEFINE_PER_CPU(struct rnd_buffer, stack_rand_offset) __latent_entropy;
> +
> +
> +/*
> + * Generate some initially weak seeding values to allow
> + * to start the prandom_u32() engine.
> + */
> +static int __init stack_rand_offset_init(void)
> +{
> + int i;
> +
> + /* exctract bits to out per-cpu rand buffers */
> + for_each_possible_cpu(i) {
> + struct rnd_buffer *buffer = &per_cpu(stack_rand_offset, i);
> + buffer->byte_counter = 0;
> + /* if rng is not initialized, this won't extract us good stuff
> + * but we cannot wait for rng to initialize either */
> + get_random_bytes(&(buffer->buffer), sizeof(buffer->buffer));
Instead of doing get_random_bytes() here, just set byte_counter =
RANDOM_BUFFER_SIZE and let random_get_byte() do the work on a per-cpu
basis?
> +
> + }
> +
> + return 0;
> +}
> +late_initcall(stack_rand_offset_init);
> +
> +unsigned char random_get_byte(void)
> +{
> + struct rnd_buffer *buffer = &get_cpu_var(stack_rand_offset);
> + unsigned char res;
> +
> + if (buffer->byte_counter >= RANDOM_BUFFER_SIZE) {
> + get_random_bytes(&(buffer->buffer), sizeof(buffer->buffer));
> + buffer->byte_counter = 0;
> + }
> +
> + res = buffer->buffer[buffer->byte_counter];
> + buffer->buffer[buffer->byte_counter] = 0;
> + buffer->byte_counter ++;
> + put_cpu_var(stack_rand_offset);
> + return res;
> +}
> +EXPORT_SYMBOL(random_get_byte);
Otherwise, sure, looks good. I remain worried about info leaks of the
percpu area causing pain down the road, but we find a safer way to do
this, we can do it later.
--
Kees Cook
next prev parent reply other threads:[~2019-04-30 18:01 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-15 6:09 [PATCH] x86/entry/64: randomize kernel stack offset upon syscall Elena Reshetova
2019-04-15 7:25 ` Ingo Molnar
2019-04-15 8:44 ` Reshetova, Elena
2019-04-16 7:34 ` Ingo Molnar
2019-04-16 11:10 ` Reshetova, Elena
2019-04-16 12:08 ` Peter Zijlstra
2019-04-16 12:45 ` David Laight
2019-04-16 15:43 ` Theodore Ts'o
2019-04-16 16:07 ` Peter Zijlstra
2019-04-16 16:47 ` Reshetova, Elena
2019-04-17 9:28 ` David Laight
2019-04-17 15:15 ` Theodore Ts'o
2019-04-17 15:40 ` Kees Cook
2019-04-17 15:53 ` David Laight
2019-04-24 11:42 ` Reshetova, Elena
2019-04-24 13:33 ` David Laight
2019-04-25 11:23 ` Reshetova, Elena
2019-04-26 11:33 ` Reshetova, Elena
2019-04-26 14:01 ` Theodore Ts'o
2019-04-26 17:44 ` Eric Biggers
2019-04-26 18:02 ` Theodore Ts'o
2019-04-27 13:59 ` Andy Lutomirski
2019-04-29 8:04 ` Reshetova, Elena
2019-04-26 18:34 ` Andy Lutomirski
2019-04-29 7:46 ` Reshetova, Elena
2019-04-29 16:08 ` Andy Lutomirski
2019-04-30 17:51 ` Reshetova, Elena
2019-04-30 18:01 ` Kees Cook [this message]
2019-05-01 8:23 ` David Laight
2019-05-02 8:07 ` Reshetova, Elena
2019-05-01 8:41 ` David Laight
2019-05-01 23:33 ` Andy Lutomirski
2019-05-02 8:15 ` Reshetova, Elena
2019-05-02 9:23 ` David Laight
2019-05-02 14:47 ` Andy Lutomirski
2019-05-02 15:08 ` Ingo Molnar
2019-05-02 16:32 ` Andy Lutomirski
2019-05-02 16:43 ` Ingo Molnar
2019-05-03 16:40 ` Andy Lutomirski
2019-05-02 16:34 ` David Laight
2019-05-02 16:45 ` Ingo Molnar
2019-05-03 16:17 ` Reshetova, Elena
2019-05-03 16:40 ` David Laight
2019-05-03 19:10 ` Linus Torvalds
2019-05-06 6:47 ` Reshetova, Elena
2019-05-06 7:01 ` Reshetova, Elena
2019-05-08 11:18 ` Reshetova, Elena
2019-05-08 11:32 ` Ingo Molnar
2019-05-08 13:22 ` Reshetova, Elena
2019-05-09 5:59 ` Ingo Molnar
2019-05-09 7:01 ` Reshetova, Elena
2019-05-09 8:43 ` Ingo Molnar
2019-05-11 22:45 ` Andy Lutomirski
2019-05-12 0:12 ` Kees Cook
2019-05-12 8:02 ` Ingo Molnar
2019-05-12 14:33 ` Kees Cook
2019-05-28 12:28 ` Reshetova, Elena
2019-05-28 13:33 ` Theodore Ts'o
2019-05-29 10:13 ` Reshetova, Elena
2019-05-29 10:51 ` David Laight
2019-05-29 18:35 ` Kees Cook
2019-05-29 18:37 ` Kees Cook
2019-07-29 11:41 ` Reshetova, Elena
2019-07-30 18:07 ` Kees Cook
2019-08-01 6:35 ` Reshetova, Elena
2019-05-09 7:03 ` Reshetova, Elena
2019-05-06 7:32 ` Reshetova, Elena
2019-04-29 7:49 ` Reshetova, Elena
2019-04-26 17:37 ` Edgecombe, Rick P
2019-04-17 6:24 ` Ingo Molnar
2019-04-16 18:19 ` Reshetova, Elena
[not found] <20190408061358.21288-1-elena.reshetova@intel.com>
2019-04-08 12:49 ` Josh Poimboeuf
2019-04-08 13:30 ` Reshetova, Elena
2019-04-08 16:21 ` Kees Cook
2019-04-10 8:26 ` Ingo Molnar
2019-04-10 9:00 ` Reshetova, Elena
2019-04-10 10:17 ` Ingo Molnar
2019-04-10 10:24 ` Reshetova, Elena
2019-04-10 14:52 ` Andy Lutomirski
2019-04-12 5:36 ` Reshetova, Elena
2019-04-12 21:16 ` Andy Lutomirski
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