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Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules
 loading
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <20190211190108.GP19618@zn.tnic>
Date:   Mon, 11 Feb 2019 11:09:25 -0800
Cc:     Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Damian Tometzki <linux_dti@icloud.com>,
        linux-integrity <linux-integrity@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Linux-MM <linux-mm@kvack.org>, Will Deacon <will.deacon@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Kristen Carlson Accardi <kristen@linux.intel.com>,
        "Dock, Deneen T" <deneen.t.dock@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>
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References: <20190129003422.9328-1-rick.p.edgecombe@intel.com>
 <20190129003422.9328-11-rick.p.edgecombe@intel.com>
 <20190211182956.GN19618@zn.tnic>
 <1533F2BB-2284-499B-9912-6D74D0B87BC1@gmail.com>
 <20190211190108.GP19618@zn.tnic>
To:     Borislav Petkov <bp@alien8.de>
Sender: linux-kernel-owner@vger.kernel.org
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> On Feb 11, 2019, at 11:01 AM, Borislav Petkov <bp@alien8.de> wrote:
>=20
> 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.
>=20
> 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=E2=80=99ll use boot_cpu_has() as you said.=