linux-kernel - Re: [PATCH 4.9 85/96] x86/retpoline: Add initial retpoline support

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Date:   Tue, 16 Jan 2018 11:22:43 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, David Woodhouse <dwmw@...zon.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>, gnomes@...rguk.ukuu.org.uk,
        Rik van Riel <riel@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>, thomas.lendacky@....com,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Paul Turner <pjt@...gle.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>
Subject: Re: [PATCH 4.9 85/96] x86/retpoline: Add initial retpoline support

On 01/15/2018, 01:35 PM, Greg Kroah-Hartman wrote:
> 4.9-stable review patch.  If anyone has any objections, please let me know.

May I ask if somebody has started the 4.4 port yet?

> ------------------
> 
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> commit 76b043848fd22dbf7f8bf3a1452f8c70d557b860 upstream.
> 
> Enable the use of -mindirect-branch=thunk-extern in newer GCC, and provide
> the corresponding thunks. Provide assembler macros for invoking the thunks
> in the same way that GCC does, from native and inline assembler.
> 
> This adds X86_FEATURE_RETPOLINE and sets it by default on all CPUs. In
> some circumstances, IBRS microcode features may be used instead, and the
> retpoline can be disabled.
> 
> On AMD CPUs if lfence is serialising, the retpoline can be dramatically
> simplified to a simple "lfence; jmp *\reg". A future patch, after it has
> been verified that lfence really is serialising in all circumstances, can
> enable this by setting the X86_FEATURE_RETPOLINE_AMD feature bit in addition
> to X86_FEATURE_RETPOLINE.
> 
> Do not align the retpoline in the altinstr section, because there is no
> guarantee that it stays aligned when it's copied over the oldinstr during
> alternative patching.
> 
> [ Andi Kleen: Rename the macros, add CONFIG_RETPOLINE option, export thunks]
> [ tglx: Put actual function CALL/JMP in front of the macros, convert to
>   	symbolic labels ]
> [ dwmw2: Convert back to numeric labels, merge objtool fixes ]
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Acked-by: Arjan van de Ven <arjan@...ux.intel.com>
> Acked-by: Ingo Molnar <mingo@...nel.org>
> Cc: gnomes@...rguk.ukuu.org.uk
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: thomas.lendacky@....com
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Jiri Kosina <jikos@...nel.org>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Kees Cook <keescook@...gle.com>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> Cc: Greg Kroah-Hartman <gregkh@...ux-foundation.org>
> Cc: Paul Turner <pjt@...gle.com>
> Link: https://lkml.kernel.org/r/1515707194-20531-4-git-send-email-dwmw@amazon.co.uk
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
thanks,
-- 
js
suse labs