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

[Jiri Slaby]

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@xxxxxxxxxxxx>
> 
> 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@xxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Acked-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: gnomes@xxxxxxxxxxxxxxxxxxx
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Cc: thomas.lendacky@xxxxxxx
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Jiri Kosina <jikos@xxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxx>
> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxxx>
> Cc: Paul Turner <pjt@xxxxxxxxxx>
> Link: https://lkml.kernel.org/r/1515707194-20531-4-git-send-email-dwmw@xxxxxxxxxxxx
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
thanks,
-- 
js
suse labs