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SubjectRe: [PATCH 4.9 85/96] x86/retpoline: Add initial retpoline support
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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@amazon.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@amazon.co.uk>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Acked-by: Arjan van de Ven <arjan@linux.intel.com>
> Acked-by: Ingo Molnar <mingo@kernel.org>
> Cc: gnomes@lxorguk.ukuu.org.uk
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: thomas.lendacky@amd.com
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Jiri Kosina <jikos@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Kees Cook <keescook@google.com>
> Cc: Tim Chen <tim.c.chen@linux.intel.com>
> Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
> Cc: Paul Turner <pjt@google.com>
> Link: https://lkml.kernel.org/r/1515707194-20531-4-git-send-email-dwmw@amazon.co.uk
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
thanks,
--
js
suse labs

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