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Subject: Re: [tip: x86/urgent] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD
 family 15h/16h
To:     Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org
Cc:     linux-tip-commits@vger.kernel.org,
        "x86@kernel.org" <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, stable@vger.kernel.org,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Nathan Chancellor <natechancellor@gmail.com>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Juergen Gross <jgross@suse.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Ingo Molnar <mingo@redhat.com>, Chen Yu <yu.c.chen@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Borislav Petkov <bp@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>
References: <7543af91666f491547bd86cebb1e17c66824ab9f.1566229943.git.thomas.lendacky@amd.com>
 <156652264945.9541.4969272027980914591.tip-bot2@tip-bot2>
 <20190824181929.GA18551@amd>
From:   "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <409703ae-6d70-3f6a-d6fc-b7dada3c2797@zytor.com>
Date:   Sat, 24 Aug 2019 14:35:40 -0700
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On 8/24/19 11:19 AM, Pavel Machek wrote:
> On Fri 2019-08-23 01:10:49, tip-bot2 for Tom Lendacky wrote:
>> The following commit has been merged into the x86/urgent branch of tip:
>>
>> Commit-ID:     c49a0a80137c7ca7d6ced4c812c9e07a949f6f24
>> Gitweb:        https://git.kernel.org/tip/c49a0a80137c7ca7d6ced4c812c9e07a949f6f24
>> Author:        Tom Lendacky <thomas.lendacky@amd.com>
>> AuthorDate:    Mon, 19 Aug 2019 15:52:35 
>> Committer:     Borislav Petkov <bp@suse.de>
>> CommitterDate: Mon, 19 Aug 2019 19:42:52 +02:00
>>
>> x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h
>>
>> There have been reports of RDRAND issues after resuming from suspend on
>> some AMD family 15h and family 16h systems. This issue stems from a BIOS
>> not performing the proper steps during resume to ensure RDRAND continues
>> to function properly.
> 
> There are quite a few unanswered questions here.
> 
> a) Is there/should there be CVE for this?
> 
> b) Can we perform proper steps in kernel, thus making RDRAND usable
> even when BIOS is buggy?
> 

The kernel should at least be able to set its internal "CPUID" bit, visible
through /proc/cpuinfo.

	-hpa