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

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Date:   Wed, 18 Mar 2020 10:03:09 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
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 04:00:08PM -0500, Josh Poimboeuf wrote:
> 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?

Ah, I sometimes do stuff like:

 cp vmlinux.o vmlinux.o.orig
 quilt push; make -j$lots
 cp vmlinux.o vmlinux.o.1
 quilt push; make -j$lots
 ...

And then it is nice to force the mode.

> > @@ -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;

Ah, indeed. I totally forgot userspace coding it seems..