From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <tglx@linutronix.de>
X-Google-Smtp-Source: AH8x227SdZdwKRbcMwUpltrd/RdHn2nr7ukLqG3Psh4gke8s8QylyaK5KCACJCfUXtM6QHguiN6K
ARC-Seal: i=1; a=rsa-sha256; t=1516914307; cv=none;
        d=google.com; s=arc-20160816;
        b=YfXv8knLFgly9N6D9xxYvIg9K3eBXAqIOCFiHtiV7a2NrOzQ4/kiCheN074Ii0aYlv
         9XwJTYtAodJc1CSFPTcvigEW71abIHB0EjNcKbOCdVMZ9H6raIM1LZbT5vlEB3JV00NG
         SHI572FytdSIv1yj47ANt+PFuOsWjKG4NHd8QHG4VvoGjJW9K6rE/AoKg4tDV5yrJMF0
         35mVXp7ZGeON+Tx5vSSkFKPKP2whE2kLmH7Occ7SLCORdY/WVFcbRxxB3J4FU4J/mxUL
         VkQiGuGh43LDCniBLYsuipRdxvsNnhGVmFnUFkUXigIgr3lS6rRPuabzTjxIDdPq0pKn
         KnUQ==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
        h=mime-version:user-agent:references:message-id:in-reply-to:subject
         :cc:to:from:date:arc-authentication-results;
        bh=UtCW8eiHDqTO9nLN194NZIdt/W902/aWPRXS3cBGByc=;
        b=Nkjuz9HaO77n8BH8zHufEWuKucQT8Th7Gqnv2aa0vEqQagn3A5R+nd4IEil7BlsdUo
         PwwLucD6TdMOPQ5AFpi1yeVwrqG0BGJkyXC6ZZ2aAtoCj7S8AUFNdM6ir0QczJpTGPaX
         RPpSJYpa3rAXCUwiCPBVHHLBiJxXK6skXSZOBKV4Do6HC2WUyxtQsF19QdyJuo1/pG9n
         Qwrd0j7B7PmAyb3AnkvFxvpesxEs95WaUveZCp1b5Pam2GwCsmRc7VGNbA4i1fNFmYDY
         Ld3K8BAcfTFTkd+BGZ9kXylTb70qlQQkbFloXGXJk9rCFZKerS8Td6Ohx2gDO2U8/npG
         tl2Q==
ARC-Authentication-Results: i=1; mx.google.com;
       spf=pass (google.com: best guess record for domain of tglx@linutronix.de designates 146.0.238.70 as permitted sender) smtp.mailfrom=tglx@linutronix.de
Authentication-Results: mx.google.com;
       spf=pass (google.com: best guess record for domain of tglx@linutronix.de designates 146.0.238.70 as permitted sender) smtp.mailfrom=tglx@linutronix.de
Date: Thu, 25 Jan 2018 22:05:05 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@kernel.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
    the arch/x86 maintainers <x86@kernel.org>,
    LKML <linux-kernel@vger.kernel.org>,
    Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
    Alan Cox <alan@linux.intel.com>, Jann Horn <jannh@google.com>,
    Samuel Neves <samuel.c.p.neves@gmail.com>,
    Dan Williams <dan.j.williams@intel.com>,
    Kernel Hardening <kernel-hardening@lists.openwall.com>,
    Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH] x86/retpoline/entry: Disable the entire SYSCALL64 fast
 path with retpolines on
In-Reply-To: <CALCETrVUY9p9jMNhuBgM3mWATsr1Fc_ZWc=bjidBkLw7bq5Vdg@mail.gmail.com>
Message-ID: <alpine.DEB.2.20.1801252204250.2203@nanos>
References: <503224b776b9513885453756e44bab235221124e.1516644136.git.luto@kernel.org> <CA+55aFwcU_hHz+S9ZDphBDRQLw6pMsd+6Yp_=mQA8kTcmTzWcQ@mail.gmail.com> <CA+55aFyONQeyHit6LcQz_JM5+C9pr61fcWFSpdn=7K_2mZN+oA@mail.gmail.com>
 <CALCETrVUY9p9jMNhuBgM3mWATsr1Fc_ZWc=bjidBkLw7bq5Vdg@mail.gmail.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
X-getmail-retrieved-from-mailbox: INBOX
X-GMAIL-THRID: =?utf-8?q?1590316784671066673?=
X-GMAIL-MSGID: =?utf-8?q?1590599937285781041?=
X-Mailing-List: linux-kernel@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>

On Thu, 25 Jan 2018, Andy Lutomirski wrote:
> On Thu, Jan 25, 2018 at 10:48 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> > On Mon, Jan 22, 2018 at 10:55 AM, Linus Torvalds
> > <torvalds@linux-foundation.org> 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 <luto@kernel.org> that patch.
> 
> Or I can grab it and send it to -tip.

That would be nice, so we can route it through x86/pti which provides it
for backporting cleanly.

Thanks,

	tglx