Re: [PATCH] x86/kvm, objtool: Avoid fastop ENDBR from being sealed

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Aug 18, 2022 at 03:38:45PM +0800, Pengfei Xu wrote:
>   And this "Missing ENDBR: andw_ax_dx+0x0/0x10 [kvm]" issue was
>   reproduced again after ran syzkaller 5min on ADL-P.

Ha, indeed :/

> > > +/*
> > > + * Create a dummy function pointer reference to prevent objtool from marking
> > > + * the function as needing to be "sealed" (i.e. ENDBR converted to NOP by
> > > + * apply_ibt_endbr()).
> > > + */
> > > +#define IBT_NOSEAL(fname)				\
> > > +	".pushsection .discard.endbr.noseal\n\t"	\
> > > +	_ASM_PTR fname "\n\t"				\
> > > +	".popsection\n\t"
> > > +

objtool/check.c:validate_ibt():

                if (!strncmp(sec->name, ".discard", 8)                  ||
		    ...)
		    continue;

So yeah, that'll just get ignored. So at the very least we need to
special case this section.