From: Nadav Amit <namit@vmware.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch <linux-arch@vger.kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Jiri Kosina <jkosina@suse.cz>, 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
Date: Wed, 5 Sep 2018 19:10:46 +0000 [thread overview]
Message-ID: <6B256AB7-0158-47DF-B2D5-4C835579F3A3@vmware.com> (raw)
In-Reply-To: <8D3CE999-6D3A-4984-934A-634BDD8AC25A@vmware.com>
at 12:02 PM, Nadav Amit <namit@vmware.com> wrote:
> 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).
>>>
>>> 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.
>>
>> 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?
Oh.. I misunderstood you. You mean: why not to make the fixmap mappings that
are used for text_poke() as private ones.
Well, the main reason is that it can require synchronizations of the
different page-tables whenever a module is loaded/unloaded. The fixmap
region shares a PGD and PUD with the modules area in x86-64.
In contrast, the proposed solution uses a different PGD, so no
synchronization between page-tables is needed when modules are loaded.
Remember that module memory is allocated even when BPF programs are
installed, which can be rather common scenario.
next prev parent reply other threads:[~2018-09-05 19:10 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-02 17:32 [PATCH v2 0/6] x86/alternatives: text_poke() fixes Nadav Amit
2018-09-02 17:32 ` [PATCH v2 1/6] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-09-06 19:40 ` Peter Zijlstra
2018-09-06 19:42 ` Nadav Amit
2018-09-06 19:53 ` Peter Zijlstra
2018-09-06 19:58 ` Nadav Amit
2018-09-06 20:25 ` Peter Zijlstra
2018-09-06 20:57 ` Nadav Amit
2018-09-06 21:41 ` Peter Zijlstra
2018-09-02 17:32 ` [PATCH v2 2/6] x86/mm: temporary mm struct Nadav Amit
2018-09-02 17:32 ` [PATCH v2 3/6] fork: provide a function for copying init_mm Nadav Amit
2018-09-02 17:32 ` [PATCH v2 4/6] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-09-06 9:01 ` Peter Zijlstra
2018-09-07 20:52 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 5/6] x86/alternatives: use temporary mm for text poking Nadav Amit
2018-09-02 17:32 ` [PATCH v2 6/6] x86/alternatives: remove text_poke() return value Nadav Amit
2018-09-05 18:56 ` [PATCH v2 0/6] x86/alternatives: text_poke() fixes Peter Zijlstra
2018-09-05 19:02 ` Nadav Amit
2018-09-05 19:10 ` Nadav Amit [this message]
2018-09-06 8:13 ` Peter Zijlstra
2018-09-06 8:42 ` Peter Zijlstra
2018-09-06 9:18 ` Peter Zijlstra
2018-09-06 10:16 ` Peter Zijlstra
2018-09-06 17:01 ` Nadav Amit
2018-09-06 17:17 ` Peter Zijlstra
2018-09-06 17:58 ` Nadav Amit
2018-09-06 18:09 ` Andy Lutomirski
2018-09-06 18:31 ` Peter Zijlstra
2018-09-06 18:38 ` Nadav Amit
2018-09-06 19:19 ` Peter Zijlstra
2018-09-06 17:23 ` Peter Zijlstra
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