[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <CAJcbSZGOYsoaYJBMPrLx4AffRRdaWCzGXNAPTRgP1DWeAkBkWA@mail.gmail.com>
Date: Thu, 5 Oct 2017 09:14:25 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Herbert Xu <herbert@...dor.apana.org.au>, "David S . Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
Matthias Kaehlcke <mka@...omium.org>, Tom Lendacky <thomas.lendacky@....com>,
Andy Lutomirski <luto@...nel.org>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Borislav Petkov <bp@...e.de>, "Rafael J . Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>,
Pavel Machek <pavel@....cz>, Juergen Gross <jgross@...e.com>, Chris Wright <chrisw@...s-sol.org>,
Alok Kataria <akataria@...are.com>, Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo <tj@...nel.org>,
Christoph Lameter <cl@...ux.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Alexey Dobriyan <adobriyan@...il.com>, Andrew Morton <akpm@...ux-foundation.org>,
Paul Gortmaker <paul.gortmaker@...driver.com>, Chris Metcalf <cmetcalf@...lanox.com>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Nicolas Pitre <nicolas.pitre@...aro.org>,
Borislav Petkov <bp@...en8.de>, "Luis R . Rodriguez" <mcgrof@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Christopher Li <sparse@...isli.org>,
Jason Baron <jbaron@...mai.com>, Dou Liyang <douly.fnst@...fujitsu.com>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Mika Westerberg <mika.westerberg@...ux.intel.com>, Lukas Wunner <lukas@...ner.de>,
Masahiro Yamada <yamada.masahiro@...ionext.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Markus Trippelsdorf <markus@...ppelsdorf.de>,
Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>,
Joerg Roedel <joro@...tes.org>, Rik van Riel <riel@...hat.com>, David Howells <dhowells@...hat.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Waiman Long <longman@...hat.com>,
Kyle Huey <me@...ehuey.com>, Andrey Ryabinin <aryabinin@...tuozzo.com>,
Jonathan Corbet <corbet@....net>, Matthew Wilcox <mawilcox@...rosoft.com>, Michal Hocko <mhocko@...e.com>,
Peter Foley <pefoley2@...oley.com>, Paul Bolle <pebolle@...cali.nl>, Jiri Kosina <jkosina@...e.cz>,
Rob Landley <rob@...dley.net>, "H . J . Lu" <hjl.tools@...il.com>, Baoquan He <bhe@...hat.com>,
Jan H . Schönherr <jschoenh@...zon.de>,
Daniel Micay <danielmicay@...il.com>, "the arch/x86 maintainers" <x86@...nel.org>,
Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
Linux PM list <linux-pm@...r.kernel.org>, virtualization@...ts.linux-foundation.org,
xen-devel <xen-devel@...ts.xenproject.org>, linux-arch <linux-arch@...r.kernel.org>,
Sparse Mailing-list <linux-sparse@...r.kernel.org>, kvm list <kvm@...r.kernel.org>,
linux-doc@...r.kernel.org,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC v3 20/27] x86/ftrace: Adapt function tracing for PIE support
On Thu, Oct 5, 2017 at 9:11 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Thu, 5 Oct 2017 09:01:14 -0700
> Thomas Garnier <thgarnie@...gle.com> wrote:
>
>> On Thu, Oct 5, 2017 at 6:06 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>> > On Wed, 4 Oct 2017 14:19:56 -0700
>> > Thomas Garnier <thgarnie@...gle.com> wrote:
>> >
>> >> When using -fPIE/PIC with function tracing, the compiler generates a
>> >> call through the GOT (call *__fentry__@...PCREL). This instruction
>> >> takes 6 bytes instead of 5 on the usual relative call.
>> >>
>> >> With this change, function tracing supports 6 bytes on traceable
>> >> function and can still replace relative calls on the ftrace assembly
>> >> functions.
>> >>
>> >> Position Independent Executable (PIE) support will allow to extended the
>> >> KASLR randomization range below the -2G memory limit.
>> >
>> > Question: This 6 bytes is only the initial call that gcc creates. When
>> > function tracing is enabled, the calls are back to the normal call to
>> > the ftrace trampoline?
>>
>> That is correct.
>>
>
> Then I think a better idea is to simply nop them out at compile time,
> and have the code that updates them to nops to know about it.
>
> See scripts/recordmcount.c
>
> Could we simply add a 5 byte nop followed by a 1 byte nop, and treat it
> the same as if it didn't exist? This code can be a little complex, and
> can cause really nasty side effects if things go wrong. I would like to
> keep from adding more variables to the changes here.
Sure, I will simplify it for the next iteration.
Thanks for the feedback.
>
> -- Steve
--
Thomas
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
