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SubjectRe: [PATCH v4 2/3] random: Return nbytes filled from hw RNG
On Tue, 15 May 2018 13:06:25 +1000
"Tobin C. Harding" <me@tobin.cc> wrote:

> Currently the function get_random_bytes_arch() has return value 'void'.
> If the hw RNG fails we currently fall back to using get_random_bytes().
> This defeats the purpose of requesting random material from the hw RNG
> in the first place.
>
> There are currently no intree users of get_random_bytes_arch().
>
> Only get random bytes from the hw RNG, make function return the number
> of bytes retrieved from the hw RNG.
>
> Signed-off-by: Tobin C. Harding <me@tobin.cc>
> Acked-by: Theodore Ts'o <tytso@mit.edu>
> Signed-off-by: Tobin C. Harding <me@tobin.cc>
> ---
> drivers/char/random.c | 16 +++++++++-------
> include/linux/random.h | 2 +-
> 2 files changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 031d18b31e0f..4b0ec597e783 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1725,26 +1725,28 @@ EXPORT_SYMBOL(del_random_ready_callback);
> * 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.
> + *
> + * Return number of bytes filled in.
> */
> -void get_random_bytes_arch(void *buf, int nbytes)
> +int __must_check get_random_bytes_arch(void *buf, int nbytes)
> {
> char *p = buf;
> + int left = nbytes;

Just a nit, but I know some kernel devs prefer "upside-down-xmas-tree"
style of declarations. Which would make the above:

int left = nbytes;
char *p = buf;

>
> - trace_get_random_bytes_arch(nbytes, _RET_IP_);
> - while (nbytes) {
> + trace_get_random_bytes_arch(left, _RET_IP_);

Nothing to do with this patch series, but I wonder if we should move
the trace event below, and record how much was done.

> + while (left) {
> unsigned long v;
> - int chunk = min(nbytes, (int)sizeof(unsigned long));
> + int chunk = min_t(int, left, (int)sizeof(unsigned long));
>
> if (!arch_get_random_long(&v))
> break;
>
> memcpy(p, &v, chunk);
> p += chunk;
> - nbytes -= chunk;
> + left -= chunk;
> }
>
> - if (nbytes)
> - get_random_bytes(p, nbytes);
> + return nbytes - left;
> }
> EXPORT_SYMBOL(get_random_bytes_arch);
>
> diff --git a/include/linux/random.h b/include/linux/random.h
> index 2ddf13b4281e..f1c9bc5cd231 100644
> --- a/include/linux/random.h
> +++ b/include/linux/random.h
> @@ -38,7 +38,7 @@ extern void get_random_bytes(void *buf, int nbytes);
> extern int wait_for_random_bytes(void);
> extern int add_random_ready_callback(struct random_ready_callback *rdy);
> extern void del_random_ready_callback(struct random_ready_callback *rdy);
> -extern void get_random_bytes_arch(void *buf, int nbytes);
> +extern int __must_check get_random_bytes_arch(void *buf, int nbytes);
>
> #ifndef MODULE
> extern const struct file_operations random_fops, urandom_fops;

Other than that...

Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

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