linux-kernel - Re: [PATCH v2 16/19] objtool: Implement noinstr validation

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Date:   Tue, 17 Mar 2020 16:00:08 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org, x86@...nel.org,
        mhiramat@...nel.org, mbenes@...e.cz, brgerst@...il.com
Subject: Re: [PATCH v2 16/19] objtool: Implement noinstr validation

On Tue, Mar 17, 2020 at 06:02:50PM +0100, Peter Zijlstra wrote:
> Validate that any call out of .noinstr.text is in between
> instr_begin() and instr_end() annotations.
> 
> This annotation is useful to ensure correct behaviour wrt tracing
> sensitive code like entry/exit and idle code. When we run code in a
> sensitive context we want a guarantee no unknown code is ran.
> 
> Since this validation relies on knowing the section of call
> destination symbols, we must run it on vmlinux.o instead of on
> individual object files.
> 
> Add two options:
> 
>  -d/--duplicate "duplicate validation for vmlinux"
>  -l/--vmlinux "vmlinux.o validation"

I'm not sure I see the point of the --vmlinux option, when it will be
autodetected anyway?

> @@ -46,5 +49,9 @@ int cmd_check(int argc, const char **arg
>  
>  	objname = argv[0];
>  
> +	s = strstr(objname, "vmlinux.o");
> +	if (s && !s[9])
> +		vmlinux = true;
> +

I think this would be slightly cleaner:

	if (!strcmp(basename(objname), "vmlinux.o"))
		vmlinux = true;

-- 
Josh