Re: [PATCH 1/2] x86/random: Retry on RDSEED failure

Kuppuswamy Sathyanarayanan
2024-01-30T15:44:36Z

On 1/30/24 12:30 AM, Kirill A. Shutemov wrote:
> The function rdrand_long() retries 10 times before returning failure to
> the caller. On the other hand, rdseed_long() gives up on the first
> failure.
>
> According to the Intel SDM, both instructions should follow the same
> retry approach. This information can be found in the section titled
> "Random Number Generator Instructions".
>
> To align the behavior of rdseed_long() with rdrand_long(), it should be
> modified to retry 10 times before giving up.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---

Change looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Wondering whether this needs to go to stable trees?

> arch/x86/include/asm/archrandom.h | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
> index 02bae8e0758b..918c5880de9e 100644
> --- a/arch/x86/include/asm/archrandom.h
> +++ b/arch/x86/include/asm/archrandom.h
> @@ -33,11 +33,19 @@ static inline bool __must_check rdrand_long(unsigned long *v)
>
> static inline bool __must_check rdseed_long(unsigned long *v)
> {
> + unsigned int retry = RDRAND_RETRY_LOOPS;
> bool ok;
> - asm volatile("rdseed %[out]"
> - CC_SET(c)
> - : CC_OUT(c) (ok), [out] "=r" (*v));
> - return ok;
> +
> + do {
> + asm volatile("rdseed %[out]"
> + CC_SET(c)
> + : CC_OUT(c) (ok), [out] "=r" (*v));
> +
> + if (ok)
> + return true;
> + } while (--retry);
> +
> + return false;
> }
>
> /*

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer