linux-kernel - Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

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Date:   Wed, 8 May 2019 07:42:48 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>,
        linux-kselftest@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

On Wed, May 08, 2019 at 02:04:16PM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 06:54:16AM -0500, Josh Poimboeuf wrote:
> > On Wed, May 08, 2019 at 09:49:03AM +0200, Peter Zijlstra wrote:
> > > The kprobe trampolines have a FRAME_POINTER annotation that makes no
> > > sense. It marks the frame in the middle of pt_regs, at the place of
> > > saving BP.
> > > 
> > > Change it to mark the pt_regs frame as per the ENCODE_FRAME_POINTER
> > > from the respective entry_*.S.
> > > 
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > ---
> > >  arch/x86/kernel/kprobes/common.h |   32 +++++++++++++++++++++++---------
> > >  1 file changed, 23 insertions(+), 9 deletions(-)
> > > 
> > > --- a/arch/x86/kernel/kprobes/common.h
> > > +++ b/arch/x86/kernel/kprobes/common.h
> > > @@ -6,14 +6,15 @@
> > >  
> > >  #include <asm/asm.h>
> > >  
> > > +#ifdef CONFIG_X86_64
> > > +
> > >  #ifdef CONFIG_FRAME_POINTER
> > > -# define SAVE_RBP_STRING "	push %" _ASM_BP "\n" \
> > > -			 "	mov  %" _ASM_SP ", %" _ASM_BP "\n"
> > > +#define ENCODE_FRAME_POINTER			\
> > > +	"	leaq 1(%rsp), %rbp\n"
> > >  #else
> > > -# define SAVE_RBP_STRING "	push %" _ASM_BP "\n"
> > > +#define ENCODE_FRAME_POINTER
> > >  #endif
> > 
> > > +#ifdef CONFIG_FRAME_POINTER
> > > +#define ENCODE_FRAME_POINTER			\
> > > +	"	movl %esp, %ebp\n"		\
> > > +	"	andl $0x7fffffff, %ebp\n"
> > > +#else
> > > +#define ENCODE_FRAME_POINTER
> > > +#endif
> > 
> > We should put these macros in a header file somewhere (including
> > stringified versions).
> 
> Probably a good idea. I'll frob them into asm/frame.h.
> 
> Do the x86_64 variants also want some ORC annotation?

Maybe so.  Though it looks like regs->ip isn't saved.  The saved
registers might need to be tweaked.  I'll need to look into it.

-- 
Josh