linux-kernel - Re: [PATCH] x86/retpoline: Fill return stack buffer on vmexit

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Message-ID: <15e712cc-3bf3-bc85-7ed4-caeba30a26a4@amd.com>
Date:   Wed, 10 Jan 2018 18:14:04 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>
Cc:     Paul Turner <pjt@...gle.com>, LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk,
        x86@...nel.org, bp@...en8.de, rga@...zon.de
Subject: Re: [PATCH] x86/retpoline: Fill return stack buffer on vmexit

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@...zon.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