linux-kernel - Re: [RFC PATCH] x86/split_lock: Disable SLD if an unaware (out-of-tree) module enables VMX

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Date:   Mon, 6 Apr 2020 18:01:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org,
        "Kenneth R. Crudup" <kenny@...ix.com>,
        Jessica Yu <jeyu@...nel.org>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Tony Luck <tony.luck@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        David Laight <David.Laight@...lab.com>,
        Doug Covelli <dcovelli@...are.com>
Subject: Re: [RFC PATCH] x86/split_lock: Disable SLD if an unaware
 (out-of-tree) module enables VMX

On Mon, Apr 06, 2020 at 08:39:02AM -0700, Christoph Hellwig wrote:
> On Mon, Apr 06, 2020 at 08:24:11AM -0700, Christoph Hellwig wrote:
> > > and this
> > > removes __get_vm_area() and with the ability to custom ranges. It also
> > > removes map_vm_area() and replaces it with map_vm_area_nx() which kills
> > > adding executable maps.
> 
> Also there seems to be various other ways to create exectuable mappings,
> pretty much everything in vmalloc.c that gets a pgprot_t..

Please feel free to use my pgprot_nx() and apply liberally on any
exported function.

But crucially, I don't think any of the still exported functions allows
getting memory in the text range, and if you want to run code outside of
the text range, things become _much_ harder. That said, modules
shouldn't be able to create executable code, full-stop (IMO).