svn commit: r347239 - head/sys/dev/random

[Michael Tuexen]

> On 8. May 2019, at 02:45, Conrad Meyer <cem at FreeBSD.org> wrote:
> 
> Author: cem
> Date: Wed May  8 00:45:16 2019
> New Revision: 347239
> URL: https://svnweb.freebsd.org/changeset/base/347239
> 
> Log:
>  random: x86 driver: Prefer RDSEED over RDRAND when available
I get a lot of
random_sources_feed: rs_read for hardware device 'Intel Secure Key RNG' returned no entropy.
entries in /var/log/messages now...

Any idea how to turn them off?

Best regards
Michael
> 
>  Per
>  https://software.intel.com/en-us/blogs/2012/11/17/the-difference-between-rdrand-and-rdseed
>  , RDRAND is a PRNG seeded from the same source as RDSEED.  The source is
>  more suitable as PRNG seed material, so prefer it when the RDSEED intrinsic
>  is available (indicated in CPU feature bits).
> 
>  Reviewed by:	delphij, jhb, imp (earlier version)
>  Approved by:	secteam(delphij)
>  Security:	yes
>  Sponsored by:	Dell EMC Isilon
>  Differential Revision:	https://reviews.freebsd.org/D20192
> 
> Modified:
>  head/sys/dev/random/ivy.c
> 
> Modified: head/sys/dev/random/ivy.c
> ==============================================================================
> --- head/sys/dev/random/ivy.c	Wed May  8 00:40:08 2019	(r347238)
> +++ head/sys/dev/random/ivy.c	Wed May  8 00:45:16 2019	(r347239)
> @@ -44,11 +44,13 @@ __FBSDID("$FreeBSD$");
> 
> #include <machine/md_var.h>
> #include <machine/specialreg.h>
> +#include <x86/ifunc.h>
> 
> #include <dev/random/randomdev.h>
> 
> #define	RETRY_COUNT	10
> 
> +static bool has_rdrand, has_rdseed;
> static u_int random_ivy_read(void *, u_int);
> 
> static struct random_source random_ivy = {
> @@ -57,10 +59,9 @@ static struct random_source random_ivy = {
> 	.rs_read = random_ivy_read
> };
> 
> -static inline int
> -ivy_rng_store(u_long *buf)
> +static int
> +x86_rdrand_store(u_long *buf)
> {
> -#ifdef __GNUCLIKE_ASM
> 	u_long rndval;
> 	int retry;
> 
> @@ -75,11 +76,40 @@ ivy_rng_store(u_long *buf)
> 	    : "+r" (retry), "=r" (rndval) : : "cc");
> 	*buf = rndval;
> 	return (retry);
> -#else /* __GNUCLIKE_ASM */
> -	return (0);
> -#endif
> }
> 
> +static int
> +x86_rdseed_store(u_long *buf)
> +{
> +	u_long rndval;
> +	int retry;
> +
> +	retry = RETRY_COUNT;
> +	__asm __volatile(
> +	    "1:\n\t"
> +	    "rdseed	%1\n\t"	/* read randomness into rndval */
> +	    "jc		2f\n\t" /* CF is set on success, exit retry loop */
> +	    "dec	%0\n\t" /* otherwise, retry-- */
> +	    "jne	1b\n\t" /* and loop if retries are not exhausted */
> +	    "2:"
> +	    : "+r" (retry), "=r" (rndval) : : "cc");
> +	*buf = rndval;
> +	return (retry);
> +}
> +
> +DEFINE_IFUNC(static, int, x86_rng_store, (u_long *buf), static)
> +{
> +	has_rdrand = (cpu_feature2 & CPUID2_RDRAND);
> +	has_rdseed = (cpu_stdext_feature & CPUID_STDEXT_RDSEED);
> +
> +	if (has_rdseed)
> +		return (x86_rdseed_store);
> +	else if (has_rdrand)
> +		return (x86_rdrand_store);
> +	else
> +		return (NULL);
> +}
> +
> /* It is required that buf length is a multiple of sizeof(u_long). */
> static u_int
> random_ivy_read(void *buf, u_int c)
> @@ -90,7 +120,7 @@ random_ivy_read(void *buf, u_int c)
> 	KASSERT(c % sizeof(*b) == 0, ("partial read %d", c));
> 	b = buf;
> 	for (count = c; count > 0; count -= sizeof(*b)) {
> -		if (ivy_rng_store(&rndval) == 0)
> +		if (x86_rng_store(&rndval) == 0)
> 			break;
> 		*b++ = rndval;
> 	}
> @@ -104,14 +134,14 @@ rdrand_modevent(module_t mod, int type, void *unused)
> 
> 	switch (type) {
> 	case MOD_LOAD:
> -		if (cpu_feature2 & CPUID2_RDRAND) {
> +		if (has_rdrand || has_rdseed) {
> 			random_source_register(&random_ivy);
> 			printf("random: fast provider: \"%s\"\n", random_ivy.rs_ident);
> 		}
> 		break;
> 
> 	case MOD_UNLOAD:
> -		if (cpu_feature2 & CPUID2_RDRAND)
> +		if (has_rdrand || has_rdseed)
> 			random_source_deregister(&random_ivy);
> 		break;
> 
>