From: Oscar Carter <oscar.carter@gmx.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Oscar Carter <oscar.carter@gmx.com>,
Ingo Molnar <mingo@redhat.com>, Kees Cook <keescook@chromium.org>,
linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com, Jann Horn <jannh@google.com>
Subject: Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts
Date: Sat, 25 Jul 2020 17:09:14 +0200 [thread overview]
Message-ID: <20200725150914.GA3362@ubuntu> (raw)
In-Reply-To: <20200724143457.27755412@oasis.local.home>
Hi Steven,
On Fri, Jul 24, 2020 at 02:34:57PM -0400, Steven Rostedt wrote:
> On Fri, 24 Jul 2020 19:55:00 +0200
> Oscar Carter <oscar.carter@gmx.com> wrote:
>
> > > Which one of the above is this patch set for?
> >
> > This patch is the result of a warning obtained with the following:
> >
> > make allmodconfig ARCH=powerpc
> > make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- -j4
> >
> > And with the -Wcast-function-type enabled in the top level makefile.
>
> Looking into powerpc I found this:
>
> arch/powerpc/include/asm/ftrace.h:
>
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> #define ARCH_SUPPORTS_FTRACE_OPS 1
> #endif
>
>
> arch/powerpc/Kconfig:
>
> select HAVE_DYNAMIC_FTRACE_WITH_REGS if MPROFILE_KERNEL
> [..]
>
> config MPROFILE_KERNEL
> depends on PPC64 && CPU_LITTLE_ENDIAN && FUNCTION_TRACER
> def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-mprofile-kernel.sh $(CC) -I$(srctree)/include -D__KERNEL__)
>
> So, it looks like you need to be 64bit PowerPC, Little Endian, and gcc
> needs to support -mprofile.
>
> Otherwise, it falls back to the old way that does the type casting.
>
> If you are really concerned about this, I would recommend adding
> support to the architecture you care about, and then this will no
> longer be an issue.
>
> The funny part is, you can still add support for ftrace_ops, without
> adding support for DYNAMIC_FTRACE_WITH_REGS, if you only care about not
> having to do that typecast.
I agree with you. I will try to add the support for ftrace_ops without
adding support for DYNAMIC_FTRACE_WITH_REGS to the powerpc architecture.
It's a great solution to allow a clean CFI build and so, protect this
arch (powerpc) against attacks that try to modify the normal control
flow.
I take a look at the kernel documentation about port ftrace to other
architectures [1] but it is out of date.
If I try to do this I will need some help. Some info that point me to the
right direction would be greatly appreciated. Some advice about what
functions I will need to implement would be really helpfull. Or point me
to the right piece of code that I can pick as base point.
> My NAK still stands. I wont let an intrusive patch be added to the
> ftrace core code to deal with an unsupported feature in an architecture.
Don't worry. I agree with you and thanks for finding a better way to
accomplish the initial purpose.
> I would be will to add that linker trick to remove the warning. Or we
> just use that warning as incentive to get architecture developers to
> implement this feature ;-)
In my opinion it would be better to leave the code as it an make the warning
visible until this feature has been added.
> -- Steve
[1] https://www.kernel.org/doc/html/latest/trace/ftrace-design.html
Thanks again,
Oscar Carter
next prev parent reply other threads:[~2020-07-25 15:10 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-19 15:50 [PATCH v2 0/2] kernel/trace: Remove function callback casts Oscar Carter
2020-07-19 15:50 ` [PATCH v2 1/2] kernel/trace: Prepare to remove " Oscar Carter
2020-07-19 15:50 ` [PATCH v2 2/2] kernel/trace: Remove " Oscar Carter
2020-07-21 18:05 ` Steven Rostedt
2020-07-24 16:19 ` Oscar Carter
2020-07-24 16:35 ` Steven Rostedt
2020-07-24 17:14 ` Oscar Carter
2020-07-24 17:24 ` Oscar Carter
2020-07-24 17:36 ` Steven Rostedt
2020-07-24 17:40 ` Steven Rostedt
2020-07-24 17:48 ` Steven Rostedt
2020-07-24 17:55 ` Oscar Carter
2020-07-24 18:34 ` Steven Rostedt
2020-07-25 15:09 ` Oscar Carter [this message]
2020-07-25 15:19 ` Oscar Carter
2020-07-26 15:52 ` Oscar Carter
2020-07-27 13:53 ` Steven Rostedt
2020-07-31 14:41 ` Oscar Carter
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