linux-kernel - Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

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Message-ID: <20200408154419.GP20730@hirez.programming.kicks-ass.net>
Date:   Wed, 8 Apr 2020 17:44:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        hch@...radead.org, sean.j.christopherson@...el.com,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        kenny@...ix.com, jeyu@...nel.org, rasmus.villemoes@...vas.dk,
        pbonzini@...hat.com, fenghua.yu@...el.com, xiaoyao.li@...el.com,
        nadav.amit@...il.com, thellstrom@...are.com, tony.luck@...el.com,
        gregkh@...uxfoundation.org, jannh@...gle.com,
        keescook@...omium.org, David.Laight@...lab.com,
        dcovelli@...are.com, mhiramat@...nel.org
Subject: Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

On Wed, Apr 08, 2020 at 09:27:26AM -0400, Steven Rostedt wrote:
> On Tue, 07 Apr 2020 13:02:40 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:

> > +		if (insn_is_mov_CRn(&insn) || insn_is_mov_DRn(&insn)) {
> > +			pr_err("Module writes to CRn or DRn, please use the proper accessors: %s\n", mod->name);
> > +			return -ENOEXEC;
> > +		}
> > +
> 
> Something like this should be done for all modules, not just out of tree
> modules.

I'm all for it; but people were worried scanning all modules was too
expensive (I don't really believe it is, module loading just can't be a
hot-path). Also, in-tree modules are audited a lot more than out of tree
magic voodoo crap.