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From: Kees Cook <keescook@chromium.org>
To: Jason Cooper <jason@lakedaemon.net>
Cc: "Roberts, William C" <william.c.roberts@intel.com>,
	linux-mm@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Russell King - ARM Linux <linux@arm.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Theodore Ts'o" <tytso@mit.edu>, Arnd Bergmann <arnd@arndb.de>,
	Greg KH <gregkh@linuxfoundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	"benh@kernel.crashing.org" <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	"David S. Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"x86@kernel.org" <x86@kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Nick Kralevich <nnk@google.com>,
	Jeffrey Vander Stoep <jeffv@google.com>,
	Mark Salyzyn <salyzyn@android.com>,
	Daniel Cashman <dcashman@android.com>
Subject: Re: [RFC patch 1/6] random: Simplify API for random address requests
Date: Mon, 25 Jul 2016 21:44:27 -0700	[thread overview]
Message-ID: <CAGXu5jKpJwurH5wgsMmaWC4mZLFTRLTT_r4ny3iohSBS2WUDEw@mail.gmail.com> (raw)
In-Reply-To: <20160726030201.6775-1-jason@lakedaemon.net>

On Mon, Jul 25, 2016 at 8:01 PM, Jason Cooper <jason@lakedaemon.net> wrote:
> To date, all callers of randomize_range() have set the length to 0, and
> check for a zero return value.  For the current callers, the only way
> to get zero returned is if end <= start.  Since they are all adding a
> constant to the start address, this is unnecessary.
>
> We can remove a bunch of needless checks by simplifying the API to do
> just what everyone wants, return an address between [start, start +
> range].
>
> While we're here, s/get_random_int/get_random_long/.  No current call
> site is adversely affected by get_random_int(), since all current range
> requests are < MAX_UINT.  However, we should match caller expectations
> to avoid coming up short (ha!) in the future.
>
> Signed-off-by: Jason Cooper <jason@lakedaemon.net>
> ---
>  drivers/char/random.c  | 17 ++++-------------
>  include/linux/random.h |  2 +-
>  2 files changed, 5 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 0158d3bff7e5..1251cb2cbab2 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1822,22 +1822,13 @@ unsigned long get_random_long(void)
>  EXPORT_SYMBOL(get_random_long);
>
>  /*
> - * randomize_range() returns a start address such that
> - *
> - *    [...... <range> .....]
> - *  start                  end
> - *
> - * a <range> with size "len" starting at the return value is inside in the
> - * area defined by [start, end], but is otherwise randomized.
> + * randomize_addr() returns a page aligned address within [start, start +
> + * range]
>   */
>  unsigned long
> -randomize_range(unsigned long start, unsigned long end, unsigned long len)
> +randomize_addr(unsigned long start, unsigned long range)

Also, this series isn't bisectable since randomize_range gets removed
here before the callers are updated. Perhaps add a macro that calls
randomize_addr with a BUG_ON for len != 0? (And then remove it in the
last patch?)

-Kees

>  {
> -       unsigned long range = end - len - start;
> -
> -       if (end <= start + len)
> -               return 0;
> -       return PAGE_ALIGN(get_random_int() % range + start);
> +       return PAGE_ALIGN(get_random_long() % range + start);
>  }
>
>  /* Interface for in-kernel drivers of true hardware RNGs.
> diff --git a/include/linux/random.h b/include/linux/random.h
> index e47e533742b5..1ad877a98186 100644
> --- a/include/linux/random.h
> +++ b/include/linux/random.h
> @@ -34,7 +34,7 @@ extern const struct file_operations random_fops, urandom_fops;
>
>  unsigned int get_random_int(void);
>  unsigned long get_random_long(void);
> -unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);
> +unsigned long randomize_addr(unsigned long start, unsigned long range);
>
>  u32 prandom_u32(void);
>  void prandom_bytes(void *buf, size_t nbytes);
> --
> 2.9.2
>



-- 
Kees Cook
Chrome OS & Brillo Security

  parent reply	other threads:[~2016-07-26  4:44 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-25 18:25 [PATCH] randomize_range: use random long instead of int william.c.roberts
2016-07-25 18:54 ` Kees Cook
2016-07-26  2:18 ` Jason Cooper
2016-07-26  3:01 ` [RFC patch 1/6] random: Simplify API for random address requests Jason Cooper
2016-07-26  3:01   ` [RFC patch 2/6] x86: Use simpler " Jason Cooper
2016-07-26  3:01   ` [RFC patch 3/6] ARM: " Jason Cooper
2016-07-26  3:01   ` [RFC patch 4/6] arm64: " Jason Cooper
2016-07-26  3:01   ` [RFC patch 5/6] tile: " Jason Cooper
2016-07-26  3:02   ` [RFC patch 6/6] unicore32: " Jason Cooper
2016-07-26  3:30   ` [RFC patch 1/6] random: Simplify " Jason Cooper
2016-07-26  4:39     ` Kees Cook
2016-07-26 17:00       ` Jason Cooper
2016-07-26 17:07         ` Kees Cook
2016-07-28 19:02           ` Jason Cooper
2016-07-26 17:33     ` Roberts, William C
2016-07-26  4:44   ` Kees Cook [this message]
2016-07-26 15:55     ` Jason Cooper
2016-07-26 16:40       ` Kees Cook
2016-07-27 13:51   ` [kernel-hardening] " Yann Droneaud

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