From: Andi Kleen <ak@linux.intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Woodhouse <dwmw2@infradead.org>,
David Woodhouse <dwmw@amazon.co.uk>, Paul Turner <pjt@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Kees Cook <keescook@google.com>, Rik van Riel <riel@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>,
Jiri Kosina <jikos@kernel.org>,
One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH v6 11/10] x86/retpoline: Avoid return buffer underflows on context switch
Date: Mon, 8 Jan 2018 16:06:26 -0800 [thread overview]
Message-ID: <20180109000626.GE6718@tassilo.jf.intel.com> (raw)
In-Reply-To: <CA+55aFwJLjNTDXBo-OkBhJ7ddrY+30MZY_HiY6TAc_tJNaL9-A@mail.gmail.com>
On Mon, Jan 08, 2018 at 03:56:30PM -0800, Linus Torvalds wrote:
> On Mon, Jan 8, 2018 at 3:44 PM, David Woodhouse <dwmw2@infradead.org> wrote:
> >
> > To guard against this fill the return buffer with controlled
> > content during context switch. This prevents any underflows.
>
> Ugh. I really dislike this patch. Everything else in the retpoline
> patches makes me go "ok, that's reasonable". This one makes me go
> "Eww".
>
> It's hacky, it's ugly, and it looks pretty expensive too.
Modern cores are quite fast at executing calls.
>
> Is there really nothing more clever we can do?
We could be a cleverer in selecting how many dummy calls to do.
But that would likely be fragile and hard to maintain
and likely be more complicated, and I doubt it would buy that much.
Don't really have a better proposal, sorry.
-Andi
prev parent reply other threads:[~2018-01-09 0:06 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-07 22:11 [PATCH v6 00/10] Retpoline: Avoid speculative indirect calls in kernel David Woodhouse
2018-01-07 22:11 ` [PATCH v6 01/10] x86/retpoline: Add initial retpoline support David Woodhouse
2018-01-08 10:45 ` Peter Zijlstra
2018-01-08 10:53 ` David Woodhouse
2018-01-08 11:03 ` Peter Zijlstra
2018-01-08 12:45 ` David Woodhouse
2018-01-08 13:42 ` Josh Poimboeuf
2018-01-08 13:46 ` Thomas Gleixner
2018-01-08 13:53 ` Josh Poimboeuf
2018-01-08 14:26 ` David Woodhouse
2018-01-08 21:20 ` Josh Poimboeuf
2018-01-09 12:36 ` Peter Zijlstra
2018-01-09 13:35 ` Thomas Gleixner
2018-01-09 13:40 ` Woodhouse, David
2018-01-07 22:11 ` [PATCH v6 02/10] x86/retpoline/crypto: Convert crypto assembler indirect jumps David Woodhouse
2018-01-08 13:49 ` Josh Poimboeuf
2018-01-07 22:11 ` [PATCH v6 03/10] x86/retpoline/entry: Convert entry " David Woodhouse
2018-01-07 22:11 ` [PATCH v6 04/10] x86/retpoline/ftrace: Convert ftrace " David Woodhouse
2018-01-07 22:11 ` [PATCH v6 05/10] x86/retpoline/hyperv: Convert " David Woodhouse
2018-01-07 22:11 ` [PATCH v6 06/10] x86/retpoline/xen: Convert Xen hypercall " David Woodhouse
2018-01-07 22:11 ` [PATCH v6 07/10] x86/retpoline/checksum32: Convert assembler " David Woodhouse
2018-01-07 22:11 ` [PATCH v6 08/10] x86/retpoline/irq32: " David Woodhouse
2018-01-07 22:11 ` [PATCH v6 09/10] x86/retpoline: Add boot time option to disable retpoline David Woodhouse
2018-01-07 22:11 ` [PATCH v6 10/10] x86/retpoline: Exclude objtool with retpoline David Woodhouse
2018-01-08 10:25 ` Thomas Gleixner
2018-01-08 10:34 ` Woodhouse, David
2018-01-08 13:20 ` Josh Poimboeuf
2018-01-07 22:22 ` [PATCH v6 00/10] Retpoline: Avoid speculative indirect calls in kernel Linus Torvalds
2018-01-08 10:01 ` Thomas Gleixner
2018-01-08 17:54 ` Ingo Molnar
2018-01-08 21:10 ` Thomas Gleixner
2018-01-08 10:34 ` Paul Turner
2018-01-08 10:38 ` Jiri Kosina
2018-01-08 10:45 ` Paul Turner
2018-01-08 10:42 ` Paul Turner
2018-01-08 11:16 ` Andrew Cooper
2018-01-08 11:25 ` Paul Turner
2018-01-08 16:13 ` Alexei Starovoitov
2018-01-10 15:20 ` Woodhouse, David
2018-01-10 15:31 ` Dr. David Alan Gilbert
2018-01-08 10:45 ` David Woodhouse
2018-01-08 10:53 ` Paul Turner
2018-01-08 12:49 ` David Woodhouse
2018-01-08 23:44 ` [PATCH v6 11/10] x86/retpoline: Avoid return buffer underflows on context switch David Woodhouse
2018-01-08 23:56 ` Linus Torvalds
2018-01-08 23:58 ` Woodhouse, David
2018-01-09 0:35 ` Linus Torvalds
2018-01-09 0:42 ` David Woodhouse
2018-01-09 0:48 ` Linus Torvalds
2018-01-09 0:55 ` David Woodhouse
2018-01-09 0:44 ` Andi Kleen
2018-01-09 0:58 ` Linus Torvalds
2018-01-09 1:15 ` Andrew Cooper
2018-01-09 3:27 ` Andy Lutomirski
2018-01-09 13:04 ` David Woodhouse
2018-01-09 13:10 ` Peter Zijlstra
2018-01-09 17:53 ` Kees Cook
2018-01-09 18:09 ` Linus Torvalds
2018-02-16 8:58 ` Pavel Machek
2018-01-09 1:16 ` Andi Kleen
2018-01-09 1:21 ` [PATCH v6 11/10] x86/retpoline: Avoid return buffer underflows on context switch II Andi Kleen
2018-01-09 1:23 ` Woodhouse, David
2018-01-09 1:49 ` Andi Kleen
2018-01-09 1:53 ` Paul Turner
2018-01-09 1:18 ` [PATCH v6 11/10] x86/retpoline: Avoid return buffer underflows on context switch Woodhouse, David
2018-01-09 0:06 ` Andi Kleen [this message]
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