linux-kernel - Re: [PATCH] ftrace,kcfi: Separate ftrace_stub() and ftrace_stub

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Message-ID: <Y06pb6NseR0YxFir@lakrids>
Date:   Tue, 18 Oct 2022 14:26:07 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH] ftrace,kcfi: Separate ftrace_stub() and
 ftrace_stub_graph()

On Tue, Oct 18, 2022 at 03:18:46PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 18, 2022 at 02:35:16PM +0200, Peter Zijlstra wrote:
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -162,6 +162,16 @@
> >  #define PATCHABLE_DISCARDS	*(__patchable_function_entries)
> >  #endif
> >  
> > +#ifndef ARCH_SUPPORTS_CFI_CLANG
> 
> #ifndef CONFIG_ARCH_..
> 
> works much better as we found.
> 
> > +/*
> > + * Simply points to ftrace_stub, but with the proper protocol.
> > + * Defined by the linker script in linux/vmlinux.lds.h
> > + */
> > +#define	FTRACE_STUB_HACK	ftrace_stub_graph = ftrace_stub;
> > +#else
> > +#define FTRACE_STUB_HACK
> > +#endif
> 
> Fixed up version available at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git x86/urgent

Thanks for this!

I've just tested that branch, (HEAD commit 586edc9c16e747ce). With kCFI
enabled I can run the ftrace boot tests and ftrace selftests without
issues.

FWIW:

  Reviewed-by: Mark Rutland <mark.rutland@....com>
  Tested-by: Mark Rutland <mark.rutland@....com>

Mark.