From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
Joao Moreira <joao@overdrivepizza.com>, X86 ML <x86@kernel.org>,
hjl.tools@gmail.com, Josh Poimboeuf <jpoimboe@redhat.com>,
andrew.cooper3@citrix.com, LKML <linux-kernel@vger.kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
llvm@lists.linux.dev
Subject: Re: [RFC][PATCH 6/6] objtool: Add IBT validation / fixups
Date: Wed, 16 Feb 2022 13:24:29 +0100 [thread overview]
Message-ID: <20220216122429.GB86719@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20220215210550.GD23216@worktop.programming.kicks-ass.net>
On Tue, Feb 15, 2022 at 10:05:50PM +0100, Peter Zijlstra wrote:
> > Peter, is there a reason you want things in the specific order of:
> >
> > cmp, je-to-call, trap, call
> >
> > Isn't it more run-time efficient to have an out-of-line failure of
> > the form:
> >
> > cmp, jne-to-trap, call, ...code..., trap, jmp-to-call
> >
> > I thought the static label stuff allowed the "default out of line"
> > option, as far as pessimizing certain states, etc? The former is certainly
> > code-size smaller, though, yes, but doesn't it waste space in the cache
> > line for the unlikely case, etc?
>
> Mostly so that we can deduce the address of the trap from the retpoline
> site, also the above has a fairly high chance of using jcc.d32 which is
> actually larger than jcc.d8+ud2.
Also; and I think I mentioned this a few emails back, by having the
whole CFI thing as a single range of bytes it becomes easier to patch.
next prev parent reply other threads:[~2022-02-16 12:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20211122170301.764232470@infradead.org>
[not found] ` <20211122170805.338489412@infradead.org>
[not found] ` <6ebb0ab131c522f20c094294d49091fc@overdrivepizza.com>
[not found] ` <202202081541.900F9E1B@keescook>
[not found] ` <ad6c2633f39e39583bc5c5eaf7ccbe52@overdrivepizza.com>
2022-02-09 4:05 ` [RFC][PATCH 6/6] objtool: Add IBT validation / fixups Kees Cook
2022-02-09 5:18 ` Joao Moreira
2022-02-11 13:38 ` Peter Zijlstra
2022-02-14 21:38 ` Sami Tolvanen
2022-02-14 22:25 ` Peter Zijlstra
2022-02-15 16:56 ` Sami Tolvanen
2022-02-15 20:03 ` Kees Cook
2022-02-15 21:05 ` Peter Zijlstra
2022-02-15 23:05 ` Kees Cook
2022-02-15 23:38 ` Joao Moreira
2022-02-16 12:24 ` Peter Zijlstra [this message]
2022-02-15 20:53 ` Peter Zijlstra
2022-02-15 22:45 ` Joao Moreira
2022-02-16 0:57 ` Andrew Cooper
2022-03-02 3:06 ` Peter Collingbourne
2022-03-02 3:32 ` Joao Moreira
2022-06-08 17:53 ` Fāng-ruì Sòng
2022-06-09 0:05 ` Sami Tolvanen
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