Messages in this thread | | | Date | Thu, 28 Apr 2022 06:42:30 +0900 | From | Stafford Horne <> | Subject | Re: [PATCH v6 11/17] openrisc: use fallback for random_get_entropy() instead of zero |
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On Sat, Apr 23, 2022 at 11:26:17PM +0200, Jason A. Donenfeld wrote: > In the event that random_get_entropy() can't access a cycle counter or > similar, falling back to returning 0 is really not the best we can do. > Instead, at least calling random_get_entropy_fallback() would be > preferable, because that always needs to return _something_, even > falling back to jiffies eventually. It's not as though > random_get_entropy_fallback() is super high precision or guaranteed to > be entropic, but basically anything that's not zero all the time is > better than returning zero all the time. > > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Jonas Bonn <jonas@southpole.se> > Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> > Cc: Stafford Horne <shorne@gmail.com> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > arch/openrisc/include/asm/timex.h | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/openrisc/include/asm/timex.h b/arch/openrisc/include/asm/timex.h > index d52b4e536e3f..115e89b336cd 100644 > --- a/arch/openrisc/include/asm/timex.h > +++ b/arch/openrisc/include/asm/timex.h > @@ -23,6 +23,9 @@ static inline cycles_t get_cycles(void) > { > return mfspr(SPR_TTCR); > } > +#define get_cycles get_cycles > + > +#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback()) > > /* This isn't really used any more */ > #define CLOCK_TICK_RATE 1000 > -- > 2.35.1
Hi Jason,
This looks OK, but I am wondering why we cannot add this to "include/linux/timex.h" as the default implementation of random_get_entropy if get_cycles is defined. I see there are 2 cases:
1. architectures that define get_cycles, and random_get_entropy is defined in include/linux/timex.h. (openrisc, sparc*, xtensa*, nios2, um*, arm)
2. architectures that define random_get_entropy explicitly (mips, m68k, riscv, x86)
* Those marked with * just define get_cycles as 0.
I would think in "include/linux/timex.h" we could define.
#ifndef random_get_entropy #ifdef get_cycles #define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback()) #else #define random_get_entropy() random_get_entropy_fallback() #endif #endif
For architectures that define get_cycles as 0, they can be cleaned up.
-Stafford
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