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Message-ID: <Yv4dKABja9CxqcDS@worktop.programming.kicks-ass.net>
Date: Thu, 18 Aug 2022 13:06:16 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Pengfei Xu <pengfei.xu@...el.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>,
"Yang, Weijiang" <weijiang.yang@...el.com>,
"Su, Heng" <heng.su@...el.com>, linux-kernel@...r.kernel.org,
Josh Poimboeuf <jpoimboe@...hat.com>, pbonzini@...hat.com,
x86@...nel.org
Subject: Re: [PATCH] x86/kvm, objtool: Avoid fastop ENDBR from being sealed
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.
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