Subject: Re: [PATCH] x86/retpoline: Fill return stack buffer on vmexit
To: David Woodhouse <dwmw2@infradead.org>,
        Andi Kleen <ak@linux.intel.com>
Cc: Paul Turner <pjt@google.com>, LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>, tglx@linutronix.de,
        Kees Cook <keescook@google.com>,
        Rik van Riel <riel@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Jiri Kosina <jikos@kernel.org>, gnomes@lxorguk.ukuu.org.uk,
        x86@kernel.org, bp@alien8.de, rga@amazon.de
References: <1515624682-3556-1-git-send-email-dwmw@amazon.co.uk>
 <1515628062.22302.278.camel@infradead.org>
From: Tom Lendacky <thomas.lendacky@amd.com>
Message-ID: <15e712cc-3bf3-bc85-7ed4-caeba30a26a4@amd.com>
Date: Wed, 10 Jan 2018 18:14:04 -0600
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On 1/10/2018 5:47 PM, David Woodhouse wrote:
> On Wed, 2018-01-10 at 22:51 +0000, David Woodhouse wrote:
>> In accordance with the Intel and AMD documentation, we need to overwrite
>> all entries in the RSB on exiting a guest, to prevent malicious branch
>> target predictions from affecting the host kernel. This is needed both
>> for retpoline and for IBRS.
>>
>> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
>> ---
>> Untested in this form although it's a variant on what we've had already.
>> I have an army of machines willing to do my bidding but nested virt
>> is non-trivial and I figure I might as well post it as someone else
>> can probably test it in less than the time it takes me to work out how.
> 
> Now smoke tested with Intel VT-x, but not yet on AMD. Tom, would you be
> able to do that?

Yes, I'll try to get to it as soon as I can, but it might be tomorrow
(morning).

Thanks,
Tom

> 
> 
>> This implements the most pressing of the RSB stuffing documented
>> by dhansen (based our discussions) in https://goo.gl/pXbvBE