On Thu, Feb 10, 2022 at 10:41:53PM +0800, Sandy Harris wrote:
> This function gets random data from the best available source
>
> The current code has a sequence in several places that calls one or
> more of arch_get_random_long() or related functions, checks the
> return value(s) and on failure falls back to random_get_entropy().
> get_source long() is intended to replace all such sequences.
>
> This is better in several ways. In the fallback case it gives
> much more random output than random_get_entropy(). It never
> wastes effort by calling arch_get_random_long() et al. when
> the relevant config variables are not set. When it does use
> arch_get_random_long(), it does not deliver raw output from
> that function but masks it by mixing with stored random data.
>
> Signed-off-by: Sandy Harris <sandyinchina@xxxxxxxxx>
> ---
> drivers/char/random.c | 74 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 74 insertions(+)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 9edf65ad4259..6c77fd056f66 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1031,6 +1031,80 @@ static void xtea_rekey(void)
> xtea_iterations = 0 ;
> }
>
> +/**************************************************************************
> + * Load a 64-bit word with data from whatever source we have
> + *
> + * arch_get_random_long()
> + * hardware RNG
> + * emulated HWRNG in a VM
> + *
> + * When there are two sources, alternate.
> + * If you have no better source, or if one fails,
> + * fall back to get_xtea_long()
> + *
> + * This function always succeeds, which allows some
> + * simplifications elsewhere in the code.
> + *
> + * This is intended only for use inside the kernel.
> + * Any data sent to user space should come from the
> + * chacha-based crng construction.
> + ***************************************************************************/
> +
> +static int load_count = 0;
> +#define COUNT_RESTART 128
> +
> +/*
> + * Add a mask variable so we can avoid using data
> + * from any source directly as output.
> + */
> +static unsigned long source_mask ;
> +
> +/*
> + * Use xtea sometimes even if we have a good source
> + * Avoids trusting the source completely
> + */
> +#define MIX_MASK 15
> +
> +static void get_source_long(unsigned long *x)
> +{
> + int a, b ;
> + int ret = 0 ;
> +
Hi,
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