Re: [Minios-devel] [UNIKRAFT PATCH v2 2/4] lib/ukswrand: Add seed generating function

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

On 18.10.19 14:59, Simon Kuenzer wrote:
> Hey Vlad,
>
> thanks a lot for you work. I have a few comments inline.
>
> Thanks,
>
> Simon
>
> On 16.10.19 17:41, Vlad-Andrei BĂDOIU (78692) wrote:
> > This patch adds a new function, _get_random_seed32 for seed generaton. 
> > If the
> > pre-compiled config option is not selected, then rdrand is used on x86 
> > and
> > ukplat_wall_clock on ARM.
> >
> > Signed-off-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@xxxxxxxxxxxxxxx>
> > ---
> >   lib/ukswrand/Config.uk           |  7 +++++++
> >   lib/ukswrand/include/uk/swrand.h | 20 ++++++++++++++++++++
> >   lib/ukswrand/mwc.c               |  2 +-
> >   3 files changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/ukswrand/Config.uk b/lib/ukswrand/Config.uk
> > index c58371bb..8db3af03 100644
> > --- a/lib/ukswrand/Config.uk
> > +++ b/lib/ukswrand/Config.uk
> > @@ -14,10 +14,17 @@ config LIBUKSWRAND_MWC
> >           Use multiply-with-carry algorithm
> >   endchoice
> > +config LIBUKSWRAND_USE_INITIALSEED
> > +    bool "Use a pre-compiled seed"
> > +    default y
> > +
> > +if LIBUKSWRAND_USE_INITIALSEED
> >   config LIBUKSWRAND_INITIALSEED
> >       int "Initial random seed"
> >       default 23
> Hey, I would rather provide a drop-down menu. This is maybe a little bit 
> more intuitive to use. How about:
> choice
>      prompt "Initial seed"
>      default LIBUKSWRANDR_INITIALSEED_TIME
>
> config LIBUKSWRAND_INITIALSEED_TIME
>      bool "Platform timestamp"
>
> config LIBUKSWRAND_INITIALSEED_RDRAND
>      depends on ARCH_X86_64 && (MARCH_X86_64_COREI7AVXI)
>      bool "`rdrand` instruction"
>
> config LIBUKSWRAND_INITIALSEED_USECONSTANT
>      bool "Compiled-in constant"
> endchoice
>
> config LIBUKSWRAND_INITIALSEED_CONSTANT
>      int "Initial seed constant"
>      depends on LIBUKSWRAND_INITIALSEED_USECONSTANT
>      default 23
>
> Also note that rdrand/rdseed is not available on all x86_64 CPUs. On 
> Intel it got introduced with Ivy-Bridge, afaik.
> > +endif
> > +
> >   config LIBUKSWRAND_DEVFS
> >       bool "Register random and urandom device to devfs"
> >       select LIBDEVFS
> > diff --git a/lib/ukswrand/include/uk/swrand.h 
> > b/lib/ukswrand/include/uk/swrand.h
> > index 77912182..a3a1e227 100644
> > --- a/lib/ukswrand/include/uk/swrand.h
> > +++ b/lib/ukswrand/include/uk/swrand.h
> > @@ -39,6 +39,7 @@
> >   #include <uk/arch/types.h>
> >   #include <uk/plat/lcpu.h>
> >   #include <uk/config.h>
> > +#include <uk/plat/time.h>
> >   #ifdef __cplusplus
> >   extern "C" {
> > @@ -53,6 +54,25 @@ extern struct uk_swrand uk_swrand_def;
> >   void uk_swrand_init_r(struct uk_swrand *r, __u32 seed);
> >   __u32 uk_swrand_randr_r(struct uk_swrand *r);
> > +static inline __u32 _get_random_seed32(void)
> > +{
> > +    __u32 val;
> > +
> > +#ifdef CONFIG_LIBUKSWRAND_USE_INITIALSEED
> > +    return CONFIG_LIBUKSWRAND_INITIALSEED;
> > +#endif
> > +
> > +#ifdef CONFIG_ARCH_X86_64
> > +    asm volatile ("rdrand %%eax;"
> > +        : "=a" (val));
> > +    return val;
> > +#endif
> > +
> > +    /* TODO: Generate the seed randomly on ARM */
> > +    val = (__u32)ukplat_wall_clock();
> With this code, your implementation is now always using the timestamp. I 
> think this was not intended, right? ;-)
> > +    return val;
> > +}
Another thing: maybe move this function (_get_random_seed32()) in the 
generic source file instead (ukswrand/swrand.c). This way you can keep 
it internal to the library. You may also want to put the constructor 
into this file.
> > +
> >   /* Uses the pre-initialized default generator  */
> >   /* TODO: Add assertion when we can test if we are in interrupt 
> > context */
> >   /* TODO: Revisit with multi-CPU support */
> > diff --git a/lib/ukswrand/mwc.c b/lib/ukswrand/mwc.c
> > index 820aa2a2..6d785c07 100644
> > --- a/lib/ukswrand/mwc.c
> > +++ b/lib/ukswrand/mwc.c
> > @@ -99,7 +99,7 @@ __u32 uk_swrand_randr_r(struct uk_swrand *r)
> >   static void _uk_swrand_ctor(void)
> >   {
> >       uk_pr_info("Initialize random number generator...\n");
> > -    uk_swrand_init_r(&uk_swrand_def, CONFIG_LIBUKSWRAND_INITIALSEED);
> > +    uk_swrand_init_r(&uk_swrand_def, _get_random_seed32());
> >   }
> >   UK_CTOR_FUNC(UK_SWRAND_CTOR_PRIO, _uk_swrand_ctor);
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