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Date: Thu, 25 Jan 2018 13:02:25 -0800
From: Andy Lutomirski <>
To: Linus Torvalds <>
Cc: Andy Lutomirski <>, "the arch/x86 maintainers" <>, LKML <>, 
	Greg Kroah-Hartman <>, Alan Cox <>, 
	Jann Horn <>, Samuel Neves <>, 
	Dan Williams <>, 
	Kernel Hardening <>, Borislav Petkov <>
Subject: Re: [PATCH] x86/retpoline/entry: Disable the entire SYSCALL64 fast
 path with retpolines on

On Thu, Jan 25, 2018 at 10:48 AM, Linus Torvalds
<> wrote:
> On Mon, Jan 22, 2018 at 10:55 AM, Linus Torvalds
> <> wrote:
>> Honestly, I'd rather get rid of the fast-path entirely. Compared to
>> all the PTI mess, it's not even noticeable.
> So I looked at how that would be.
> Patch attached. Not really "tested", but I'm running the kernel with
> this patch now, and 'strace' etc works, and honestly, it seems very
> obvious.
> Also, code generation for 'do_syscall_64()' does not look horrible. In
> fact, it doesn't look all that much worse than the fast-path ever did.
> So the biggest impact of this is the extra register saves
> (SAVE_EXTRA_REGS) from setting up the full ptregs. And honestly, I
> hate how that stupid macro still uses "movq reg,off(%rsp)" instead of
> "pushq %reg".
> Considering the diffstat:
>  2 files changed, 2 insertions(+), 121 deletions(-)
> and how those 100+ lines are nasty assembly code, I do think we should
> just do it.

Feel free to Acked-by: Andy Lutomirski <> that patch.

Or I can grab it and send it to -tip.

Re: the trampoline not showing up: if I find some time, I'll try to
wire it up correctly in kallsyms.


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