linux-kernel - Re: [PATCH v14 03/19] function_graph: Pass ftrace

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Message-ID: <20240917082624.GC27290@willie-the-truck>
Date: Tue, 17 Sep 2024 09:26:25 +0100
From: Will Deacon <will@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org,
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
	Florent Revest <revest@...omium.org>,
	linux-trace-kernel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alan Maguire <alan.maguire@...cle.com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v14 03/19] function_graph: Pass ftrace_regs to entryfunc

On Sun, Sep 15, 2024 at 04:46:14AM -0400, Steven Rostedt wrote:
> Can I get an Acked-by from the AARCH64 maintainers for this patch?

Sorry, I wasn't CC'd on the thread, so I missed this.

> On Fri, 13 Sep 2024 00:08:40 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > 
> > Pass ftrace_regs to the fgraph_ops::entryfunc(). If ftrace_regs is not
> > available, it passes a NULL instead. User callback function can access
> > some registers (including return address) via this ftrace_regs.

Under which circumstances is 'ftrace_regs' NULL?

The arm64 implementation of ftrace_graph_func() is:

> > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> > index a650f5e11fc5..bc647b725e6a 100644
> > --- a/arch/arm64/kernel/ftrace.c
> > +++ b/arch/arm64/kernel/ftrace.c
> > @@ -481,7 +481,25 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
> >  void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
> >  		       struct ftrace_ops *op, struct ftrace_regs *fregs)
> >  {
> > -	prepare_ftrace_return(ip, &fregs->lr, fregs->fp);
> > +	unsigned long return_hooker = (unsigned long)&return_to_handler;
> > +	unsigned long frame_pointer = fregs->fp;

Which dereferences the unchecked pointer here ^^.

Will