linux-kernel - Re: [PATCH v2 34/39] objtool: Validate IBT assumptions

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Message-ID: <20220228201007.GG11184@worktop.programming.kicks-ass.net>
Date:   Mon, 28 Feb 2022 21:10:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     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, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: Re: [PATCH v2 34/39] objtool: Validate IBT assumptions

On Mon, Feb 28, 2022 at 10:36:55AM -0800, Josh Poimboeuf wrote:
> On Mon, Feb 28, 2022 at 10:47:55AM +0100, Peter Zijlstra wrote:
> > On Sun, Feb 27, 2022 at 02:20:55PM -0800, Josh Poimboeuf wrote:
> > > On Sun, Feb 27, 2022 at 06:00:03PM +0100, Peter Zijlstra wrote:
> > > > > > @@ -3101,6 +3164,17 @@ static int validate_branch(struct objtoo
> > > > > >  
> > > > > >  		if (insn->hint) {
> > > > > >  			state.cfi = *insn->cfi;
> > > > > > +			if (ibt) {
> > > > > > +				struct symbol *sym;
> > > > > > +
> > > > > > +				if (insn->cfi->type == UNWIND_HINT_TYPE_REGS_PARTIAL &&
> > > > > > +				    (sym = find_symbol_by_offset(insn->sec, insn->offset)) &&
> > > > > > +				    insn->type != INSN_ENDBR && !insn->noendbr) {
> > > > > > +					WARN_FUNC("IRET_REGS hint without ENDBR: %s",
> > > > > > +						  insn->sec, insn->offset,
> > > > > > +						  sym->name);
> > > > > > +				}
> > > > > 
> > > > > No need to print sym->name here, WARN_FUNC() already does it?
> > > > 
> > > > Almost; perhaps the change to make is to either introduce WARN_SYM or
> > > > make WARN_FUNC also print !STT_FUNC symbols ?
> > > 
> > > In the case of no function, WARN_FUNC() falls back to printing sec+off.
> > > Is that not good enough?
> > 
> > I got really tired of doing the manual symbol lookup... I don't suppose
> > it matters too much now that I've more or less completed the triage, but
> > it was useful.
> 
> Maybe it would be reasonable to change WARN_FUNC to do that?  i.e. fall
> back from func+off to sym+off to sec+off.

I'll make it happen.