Re: [PATCH] crypto: loongson - Select CRYPTO_RNG

[Eric Biggers]

On Fri, May 22, 2026 at 02:40:38PM +0800, Qunqin Zhao wrote:
> 
> 在 2026/5/22 下午12:03, Eric Biggers 写道:
> > On Fri, May 22, 2026 at 11:41:15AM +0800, Qunqin Zhao wrote:
> > > 在 2026/5/22 上午10:57, Eric Biggers 写道:
> > > > On Fri, May 22, 2026 at 10:52:42AM +0800, Huacai Chen wrote:
> > > > > On Fri, May 22, 2026 at 10:26 AM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> > > > > > This driver registers a rng_alg, so it requires CRYPTO_RNG.
> > > > > > 
> > > > > > Fixes: 766b2d724c8d ("crypto: loongson - add Loongson RNG driver support")
> > > > > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > > > > Closes: https://lore.kernel.org/oe-kbuild-all/202605201622.qWOiiZTV-lkp@xxxxxxxxx/
> > > > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> > > > > Reviewed-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > > > > > ---
> > > > > >    drivers/crypto/loongson/Kconfig | 1 +
> > > > > >    1 file changed, 1 insertion(+)
> > > > > > 
> > > > By the way, do any of the loongson people have any comment on what they
> > > > think the point of this driver is?  It's not registered with the actual
> > > To provide an AF_ALG-based random number generation interface for other
> > > modules and user-space programs.
> > > 
> > > Thanks,
> > > 
> > > Qunqin
> > AF_ALG is a userspace interface; it's not available for in-kernel use.
> > If you mean using crypto_rng directly, note that no kernel code actually
> > uses it other than the tests, the implementation of AF_ALG, and the
> > FIPS-specific code which uses drbg.c specifically.
> > 
> > So, the first half of your justification doesn't make any sense.
> > 
> > As far as the second half: why would a userspace program do that instead
> > of just using the regular Linux RNG (/dev/urandom)?

Could you answer this question?  If there's no answer to this question,
then there's no use case for this driver as-is.

> > AFAIK, the only reason to use a HW RNG directly is for certification
> > reasons.
> > 
> > However, there's also already an interface for that: /dev/hw_random.
> > 
> > So AF_ALG seems completely redundant for this case.
> 
> To be honest, I previously assumed that the `hw_random` was designed
> strictly and exclusively for the TRNG mode.
> 
> Is it architecturally acceptable or common practice for a PRNG mode to
> utilize `hw_random` as well?
> 
> Thanks,

So the Loongson RNG is a PRNG?  Where does it get its entropy from, and
what is its security strength?

- Eric