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

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Message-ID: <1515628062.22302.278.camel@infradead.org>
Date:   Wed, 10 Jan 2018 23:47:42 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>,
        "Thomas.Lendacky@....com" <Thomas.Lendacky@....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 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?


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