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

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Date:   Mon, 10 Jul 2023 17:37:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.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, 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.

> +}
> +#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.