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From:   Nadav Amit <namit@vmware.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
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        Andy Lutomirski <luto@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v2 0/6] x86/alternatives: text_poke() fixes
Thread-Topic: [PATCH v2 0/6] x86/alternatives: text_poke() fixes
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Date:   Wed, 5 Sep 2018 19:02:16 +0000
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at 11:56 AM, Peter Zijlstra <peterz@infradead.org> wrote:

> On Sun, Sep 02, 2018 at 10:32:18AM -0700, Nadav Amit wrote:
>> This patch-set addresses some issues that were raised in a recent
>> correspondence and might affect the security and the correctness of code
>> patching. (Note that patching performance is not addressed by this
>> patch-set).
>>=20
>> The main issue that the patches deal with is the fact that the fixmap
>> PTEs that are used for patching are available for access from other
>> cores and might be exploited. They are not even flushed from the TLB in
>> remote cores, so the risk is even higher. Address this issue by
>> introducing a temporary mm that is only used during patching.
>> Unfortunately, due to init ordering, fixmap is still used during
>> boot-time patching. Future patches can eliminate the need for it.
>=20
> Remind me; why are we doing it like this instead of fixing fixmap?
> Because while this fixes the text_poke crud, it does leave fixmap
> broken.

Do you have other fixmap mappings in mind that are modified after boot?