linux-kernel - Re: [PATCH v3 03/13] x86/retpoline/entry: Convert entry assembler indirect jumps

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Date:   Thu, 4 Jan 2018 06:46:33 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     David Woodhouse <dwmw@...zon.co.uk>, ak@...ux.intel.com
Cc:     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>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v3 03/13] x86/retpoline/entry: Convert entry assembler
 indirect jumps

On 01/04/2018 06:37 AM, David Woodhouse wrote:
> KPTI complicates this a little; the one in entry_SYSCALL_64_trampoline
> can't just jump to the thunk because the thunk isn't mapped. So it gets
> its own copy of the thunk, inline.

This one call site isn't too painful, of course.

But, is there anything keeping us from just sticking the thunk in the
entry text section where it would be available while still in the
trampoline?