linux-kernel - Re: [PATCH 04/29] x86/livepatch: Validate __fentry_

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Date:   Wed, 23 Feb 2022 07:41:39 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 04/29] x86/livepatch: Validate __fentry__ location

On Wed, 23 Feb 2022 11:57:26 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1578,7 +1578,23 @@ unsigned long ftrace_location_range(unsi
>   */
>  unsigned long ftrace_location(unsigned long ip)
>  {
> -	return ftrace_location_range(ip, ip);
> +	struct dyn_ftrace *rec;
> +	unsigned long offset;
> +	unsigned long size;
> +
> +	rec = lookup_rec(ip, ip);
> +	if (!rec) {
> +		if (!kallsyms_lookup_size_offset(ip, &size, &offset))
> +			goto out;
> +
> +		rec = lookup_rec(ip - offset, (ip - offset) + size);
> +	}
> +

Please create a new function for this. Perhaps find_ftrace_location().

ftrace_location() is used to see if the address given is a ftrace
nop or not. This change will make it always return true.

-- Steve