linux-kernel - Re: [PATCH 0/6] x86/alternatives: text

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Date:   Sun, 2 Sep 2018 16:46:46 +0000
From:   Nadav Amit <namit@...are.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 0/6] x86/alternatives: text_poke() fixes

at 9:49 PM, Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Fri, 31 Aug 2018 13:46:35 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
>> On Thu, 30 Aug 2018 10:32:12 -0700
>> Nadav Amit <namit@...are.com> 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).
>>> 
>>> 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.
>>> 
>>> The second issue is the missing lockdep assertion to ensure text_mutex
>>> is taken. It is actually not always taken, so fix the instances that
>>> were found not to take the lock (although they should be safe even
>>> without taking the lock).
>>> 
>>> Finally, try to be more conservative and to map a single page, instead
>>> of two, when possible. This helps both security and performance.
>>> 
>>> In addition, there is some cleanup of the patching code to make it more
>>> readable.
>> 
>> OK, this series looks good to me, and tested with ftracetest, kprobe testsets.
>> 
>> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
>> Tested-by: Masami Hiramatsu <mhiramat@...nel.org>
> 
> Oh, I missed a note.
> 
> To apply this series on -tip tree, we have to revert Jiri's text_mutex
> checker.
> 
> 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")

Thanks for the heads-up. I’ll add a revert for this patch and send v2.

Regards,
Nadav