linux-kernel - Re: [PATCH v2 05/28] objtool: Add a pass for generating __mcount

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Message-ID: <202009101127.28B4414D2A@keescook>
Date:   Thu, 10 Sep 2020 11:29:38 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>, peterz@...radead.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH v2 05/28] objtool: Add a pass for generating __mcount_loc

On Fri, Sep 04, 2020 at 11:31:04AM +0200, peterz@...radead.org wrote:
> On Thu, Sep 03, 2020 at 03:03:30PM -0700, Sami Tolvanen wrote:
> > On Thu, Sep 3, 2020 at 2:51 PM Kees Cook <keescook@...omium.org> wrote:
> > >
> > > On Thu, Sep 03, 2020 at 01:30:30PM -0700, Sami Tolvanen wrote:
> > > > From: Peter Zijlstra <peterz@...radead.org>
> > > >
> > > > Add the --mcount option for generating __mcount_loc sections
> > > > needed for dynamic ftrace. Using this pass requires the kernel to
> > > > be compiled with -mfentry and CC_USING_NOP_MCOUNT to be defined
> > > > in Makefile.
> > > >
> > > > Link: https://lore.kernel.org/lkml/20200625200235.GQ4781@hirez.programming.kicks-ass.net/
> > > > Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> > >
> > > Hmm, I'm not sure why this hasn't gotten picked up yet. Is this expected
> > > to go through -tip or something else?
> > 
> > Note that I picked up this patch from Peter's original email, to which
> > I included a link in the commit message, but it wasn't officially
> > submitted as a patch. However, the previous discussion seems to have
> > died, so I included the patch in this series, as it cleanly solves the
> > problem of whitelisting non-call references to __fentry__. I was
> > hoping for Peter and Steven to comment on how they prefer to proceed
> > here.
> 
> Right; so I'm obviously fine with this patch and I suppose I can pick it
> (and the next) into tip/objtool/core, provided Steve is okay with this
> approach.

Hello Steven-of-the-future-after-4000-emails![1] ;)

Getting your Ack on this would be very welcome, and would unblock a
portion of this series.

Thanks! :)

[1] https://twitter.com/srostedt/status/1303697650592755712

-- 
Kees Cook