linux-kernel - Re: [PATCH v2.1] x86/retpoline: Fill return stack buffer on vmexit

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Message-ID: <20180111122607.GZ6176@hirez.programming.kicks-ass.net>
Date:   Thu, 11 Jan 2018 13:26:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Woodhouse <dwmw@...zon.co.uk>
Cc:     Andi Kleen <ak@...ux.intel.com>, 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>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk,
        x86@...nel.org, bp@...en8.de, rga@...zon.de,
        thomas.lendacky@....com, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v2.1] x86/retpoline: Fill return stack buffer on vmexit

On Thu, Jan 11, 2018 at 11:37:18AM +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>

Tested this on my AMD Interlagos, seems to work.

Tested-by: Peter Zijlstra (Intel) <peterz@...radead.org>