linux-kernel - Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write

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Message-ID: <CALCETrWkrpuJkcgiwMdc61Vv5U2u39FiWgzWfA_85nziK0pZsg@mail.gmail.com>
Date:   Wed, 29 Mar 2017 15:38:43 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Kees Cook <keescook@...omium.org>
Cc:     "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Mark Rutland <mark.rutland@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Hoeun Ryu <hoeun.ryu@...il.com>,
        PaX Team <pageexec@...email.hu>,
        Emese Revfy <re.emese@...il.com>,
        Russell King <linux@...linux.org.uk>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()

On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keescook@...omium.org> wrote:
> Based on PaX's x86 pax_{open,close}_kernel() implementation, this
> allows HAVE_ARCH_RARE_WRITE to work on x86.
>

> +
> +static __always_inline unsigned long __arch_rare_write_begin(void)
> +{
> +       unsigned long cr0;
> +
> +       preempt_disable();

This looks wrong.  DEBUG_LOCKS_WARN_ON(!irqs_disabled()) would work,
as would local_irq_disable().  There's no way that just disabling
preemption is enough.

(Also, how does this interact with perf nmis?)

--Andy