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

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Date:   Wed, 8 Apr 2020 17:54:53 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, 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,
        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

+++ Peter Zijlstra [08/04/20 17:44 +0200]:
>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.

The intention of the original patches was to do the text scan to catch
a handful of out-of-tree hypervisor modules - but now that
decode_module() is being generalized to more cases, I don't mind
scanning all modules.

Thanks,

Jessica