linux-kernel - Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules loading

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Message-Id: <A671F14F-3E03-4A97-9F54-426533077E0C@gmail.com>
Date:   Mon, 11 Feb 2019 11:09:25 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Damian Tometzki <linux_dti@...oud.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux-MM <linux-mm@...ck.org>, Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        "Dock, Deneen T" <deneen.t.dock@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules
 loading

> On Feb 11, 2019, at 11:01 AM, Borislav Petkov <bp@...en8.de> wrote:
> 
> On Mon, Feb 11, 2019 at 10:45:26AM -0800, Nadav Amit wrote:
>> Are you sure about that? This path is still used when modules are loaded.
> 
> Yes, I'm sure. Loading a module does a gazillion things so saving a
> couple of insns - yes, boot_cpu_has() is usually a RIP-relative MOV and a
> TEST - doesn't show even as a blip on any radar.

I fully agree, if that is the standard.

It is just that I find the use of static_cpu_has()/boot_cpu_has() to be very
inconsistent. I doubt that show_cpuinfo_misc(), copy_fpstate_to_sigframe(),
or i915_memcpy_init_early() that use static_cpu_has() are any hotter than
text_poke_early().

Anyhow, I’ll use boot_cpu_has() as you said.