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From:   "Lendacky, Thomas" <Thomas.Lendacky@amd.com>
To:     Pavel Machek <pavel@ucw.cz>, "tytso@mit.edu" <tytso@mit.edu>,
        "nhorman@tuxdriver.com" <nhorman@tuxdriver.com>
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        "x86@kernel.org" <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Chen Yu <yu.c.chen@intel.com>, Jonathan Corbet <corbet@lwn.net>
Subject: Re: Non-random RDRAND Re: [PATCH] x86/CPU/AMD: Clear RDRAND CPUID bit
 on AMD family 15h/16h
Thread-Topic: Non-random RDRAND Re: [PATCH] x86/CPU/AMD: Clear RDRAND CPUID
 bit on AMD family 15h/16h
Thread-Index: AQHVUuW0/upDXQeDUkyQJLUEYNL76ab7SRKAgADkKwA=
Date:   Thu, 15 Aug 2019 13:01:16 +0000
Message-ID: <0ea34954-10d4-03f9-fce6-d25aa574bb43@amd.com>
References: <776cb5c2d33e7fd0d2893904724c0e52b394f24a.1565817448.git.thomas.lendacky@amd.com>
 <20190814232434.GA31769@amd>
In-Reply-To: <20190814232434.GA31769@amd>
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On 8/14/19 6:24 PM, Pavel Machek wrote:
> On Wed 2019-08-14 21:17:41, Lendacky, Thomas wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> There have been reports of RDRAND issues after resuming from suspend on
>> some AMD family 15h and family 16h systems. This issue stems from BIOS
>> not performing the proper steps during resume to ensure RDRAND continues
>> to function properly.
>=20
> Burn it with fire!
>=20
> I mean... people were afraid RDRAND would be backdoored, and you now
> confirm ... it indeed _is_ backdoored? /., here's news for you!
>=20
> So what is the impact? Does it give random-looking but predictable
> numbers after resume? Does it give all zeros? Something else?

See this article:
https://www.phoronix.com/scan.php?page=3Dnews_item&px=3DAMD-CPUs-RdRand-Sus=
pend

Thanks,
Tom

>=20
>> =20
>> +	rdrand_force	[X86]
>> +			On certain AMD processors, the advertisement of the
>> +			RDRAND instruction has been disabled by the kernel
>> +			because of buggy BIOS support, specifically around the
>> +			suspend/resume path. This option allows for overriding
>> +			that decision if it is known that the BIOS support for
>> +			RDRAND is not buggy on the system.
>=20
> But this is not how we normally deal with buggy BIOSes. We don't want
> user to have to decide this...
>=20
> Should we introduce black-list or white-list of BIOS versions?
>=20
> Hmm. Actually.
>=20
> You are the CPU vendor. Surely you can tell us how to init RDRAND in
> kernel if BIOS failed to do that... can you?
>=20
> 									Pavel
>=20