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

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Message-ID: <4aa902e5-24f8-4ae6-bc6b-485b7578fb27@mixaill.net>
Date: Fri, 14 Mar 2025 11:16:41 +0300
From: Mikhail Paulyshka <me@...aill.net>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] x86/rdrand: implement sanity check for RDSEED

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 ]