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

Jessica Yu
2020-04-08T15:55:02Z

+++ 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@infradead.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