Re: [PATCH 0/2] x86/rdrand: implement sanity check for RDSEED

[Mikhail Paulyshka]

On 3/13/25 8:32 PM, Borislav Petkov wrote:
> On Wed, Mar 12, 2025 at 03:31:28PM +0300, Mikhail Paulyshka wrote:
> > On the AMD Cyan Skillfish (Family 0x17 Model 0x47 Stepping 0x0), which
> > is a Zen2-based APU found on the AMD BC-250 board, there is a situation
> > where RDRAND works fine, but RDSEED generates FF.
> On every read? Or only sometimes?

I didn't find a situation where it returns something different, so yes, 
I believe it happens on every read and tested on 3+ hardware samples.

> Is CF clear when it returns FF?


Just right after rdseed %edx


# info registers edx

edx 0xffffffff -1


# info registers eflags

eflags 0x203 [ CF IF ]