linux-kernel - Re: [RFC PATCH 1/2] kprobes: Prohibit probing on CFI preamble symbol

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Date:   Tue, 11 Jul 2023 08:50:21 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Petr Pavlu <petr.pavlu@...e.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, samitolvanen@...gle.com, x86@...nel.org,
        linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] kprobes: Prohibit probing on CFI preamble
 symbol

On Mon, 10 Jul 2023 17:37:24 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, Jul 10, 2023 at 09:14:24PM +0900, Masami Hiramatsu (Google) wrote:
> 
> 
> > +#ifdef CONFIG_CFI_CLANG
> > +static bool is_cfi_preamble_symbol(unsigned long addr)
> > +{
> > +	char symbuf[KSYM_NAME_LEN];
> > +
> > +	if (lookup_symbol_name(addr, symbuf))
> > +		return false;
> > +
> > +	return str_has_prefix("__cfi_", symbuf)
> 		|| str_has_prefix("__pfx_", symbol);
> 
> The __pfx_ symbols can happen when !CFI_CLANG but still having
> FUNCTION_PADDING_BYTES.

Indeed. Currently __pfx is not probed via tracefs interface because it is
notrace function but kprobe itself should also prohibit that.

> 
> > +}
> > +#else
> > +#define is_cfi_preamble_symbol(addr)	(0)
> > +#endif
> 
> As such I think we can do the above unconditionally, without either
> there should not be any matching symbols.

OK.

Thank you!

> 


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