lkml.org 
[lkml]   [2012]   [Aug]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[ 52/82] random: add new get_random_bytes_arch() function
    Date
    From: Greg KH <gregkh@linuxfoundation.org>

    3.5-stable review patch. If anyone has any objections, please let me know.

    ------------------

    From: Theodore Ts'o <tytso@mit.edu>

    commit c2557a303ab6712bb6e09447df828c557c710ac9 upstream.

    Create a new function, get_random_bytes_arch() which will use the
    architecture-specific hardware random number generator if it is
    present. Change get_random_bytes() to not use the HW RNG, even if it
    is avaiable.

    The reason for this is that the hw random number generator is fast (if
    it is present), but it requires that we trust the hardware
    manufacturer to have not put in a back door. (For example, an
    increasing counter encrypted by an AES key known to the NSA.)

    It's unlikely that Intel (for example) was paid off by the US
    Government to do this, but it's impossible for them to prove otherwise
    --- especially since Bull Mountain is documented to use AES as a
    whitener. Hence, the output of an evil, trojan-horse version of
    RDRAND is statistically indistinguishable from an RDRAND implemented
    to the specifications claimed by Intel. Short of using a tunnelling
    electronic microscope to reverse engineer an Ivy Bridge chip and
    disassembling and analyzing the CPU microcode, there's no way for us
    to tell for sure.

    Since users of get_random_bytes() in the Linux kernel need to be able
    to support hardware systems where the HW RNG is not present, most
    time-sensitive users of this interface have already created their own
    cryptographic RNG interface which uses get_random_bytes() as a seed.
    So it's much better to use the HW RNG to improve the existing random
    number generator, by mixing in any entropy returned by the HW RNG into
    /dev/random's entropy pool, but to always _use_ /dev/random's entropy
    pool.

    This way we get almost of the benefits of the HW RNG without any
    potential liabilities. The only benefits we forgo is the
    speed/performance enhancements --- and generic kernel code can't
    depend on depend on get_random_bytes() having the speed of a HW RNG
    anyway.

    For those places that really want access to the arch-specific HW RNG,
    if it is available, we provide get_random_bytes_arch().

    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 29 ++++++++++++++++++++++++-----
    include/linux/random.h | 1 +
    2 files changed, 25 insertions(+), 5 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -1038,17 +1038,34 @@ static ssize_t extract_entropy_user(stru

    /*
    * This function is the exported kernel interface. It returns some
    - * number of good random numbers, suitable for seeding TCP sequence
    - * numbers, etc.
    + * number of good random numbers, suitable for key generation, seeding
    + * TCP sequence numbers, etc. It does not use the hw random number
    + * generator, if available; use get_random_bytes_arch() for that.
    */
    void get_random_bytes(void *buf, int nbytes)
    {
    + extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
    +}
    +EXPORT_SYMBOL(get_random_bytes);
    +
    +/*
    + * This function will use the architecture-specific hardware random
    + * number generator if it is available. The arch-specific hw RNG will
    + * almost certainly be faster than what we can do in software, but it
    + * is impossible to verify that it is implemented securely (as
    + * opposed, to, say, the AES encryption of a sequence number using a
    + * key known by the NSA). So it's useful if we need the speed, but
    + * only if we're willing to trust the hardware manufacturer not to
    + * have put in a back door.
    + */
    +void get_random_bytes_arch(void *buf, int nbytes)
    +{
    char *p = buf;

    while (nbytes) {
    unsigned long v;
    int chunk = min(nbytes, (int)sizeof(unsigned long));
    -
    +
    if (!arch_get_random_long(&v))
    break;

    @@ -1057,9 +1074,11 @@ void get_random_bytes(void *buf, int nby
    nbytes -= chunk;
    }

    - extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
    + if (nbytes)
    + extract_entropy(&nonblocking_pool, p, nbytes, 0, 0);
    }
    -EXPORT_SYMBOL(get_random_bytes);
    +EXPORT_SYMBOL(get_random_bytes_arch);
    +

    /*
    * init_std_data - initialize pool with system data
    --- a/include/linux/random.h
    +++ b/include/linux/random.h
    @@ -56,6 +56,7 @@ extern void add_input_randomness(unsigne
    extern void add_interrupt_randomness(int irq, int irq_flags);

    extern void get_random_bytes(void *buf, int nbytes);
    +extern void get_random_bytes_arch(void *buf, int nbytes);
    void generate_random_uuid(unsigned char uuid_out[16]);

    #ifndef MODULE



    \
     
     \ /
      Last update: 2012-08-13 23:03    [W:3.029 / U:1.232 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site