linux-kernel - Re: [PATCH v5 11/34] function_graph: Have the instances use their own ftrace

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Date: Tue, 26 Dec 2023 09:20:23 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Steven Rostedt
 <rostedt@...dmis.org>, Florent Revest <revest@...omium.org>,
 linux-trace-kernel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, bpf <bpf@...r.kernel.org>, Sven
 Schnelle <svens@...ux.ibm.com>, 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>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH v5 11/34] function_graph: Have the instances use their
 own ftrace_ops for filtering

Hi,

On Mon, 18 Dec 2023 22:13:46 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> @@ -408,15 +395,51 @@ int function_graph_enter(unsigned long ret, unsigned long func,
>  	return -EBUSY;
>  }
>  
> +/* This is called from ftrace_graph_func() via ftrace */
> +int function_graph_enter_ops(unsigned long ret, unsigned long func,
> +			     unsigned long frame_pointer, unsigned long *retp,
> +			     struct fgraph_ops *gops)
> +{
> +	struct ftrace_graph_ent trace;
> +	int index;
> +	int type;
> +

Here,  I found that this needs to check whether the fgraph_array[gops->idx]
is still valid or not. When unregistering the fgraph, fgraph_array[idx] is
cleared (with fgraph_stub) and disable ftrace. So there is a chance to hit
this and it will mess up the shadow stack because gops->idx is already invalid.

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>