From: Peter Zijlstra <peterz@infradead.org>
To: Nadav Amit <namit@vmware.com>
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: Thu, 6 Sep 2018 10:13:00 +0200 [thread overview]
Message-ID: <20180906081300.GF24082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <6B256AB7-0158-47DF-B2D5-4C835579F3A3@vmware.com>
On Wed, Sep 05, 2018 at 07:10:46PM +0000, Nadav Amit wrote:
> 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.
No, you got it the first time. There are in fact more fixmap abusers;
see drivers/acpi/apei/ghes.c. Also, as long as set_fixmap() allows
overwriting a _PAGE_PRESENT pte and has that dodgy
__flush_tlb_one_kernel() in it, the broken remains (and can return).
So we need to fix fixmap, to either disallow overwriting a _PAGE_PRESENT
pte, or to issue a full TLB invalidate.
Either fix will terminally break GHES, but that's OK, they've known
about this issue since 2015 and haven't cared, so I can't be bothered
about them.
next prev parent reply other threads:[~2018-09-06 8:13 UTC|newest]
Thread overview: 62+ 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 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 1/6] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-06 19:40 ` Peter Zijlstra
2018-09-06 19:40 ` Peter Zijlstra
2018-09-06 19:42 ` Nadav Amit
2018-09-06 19:42 ` Nadav Amit
2018-09-06 19:53 ` Peter Zijlstra
2018-09-06 19:53 ` Peter Zijlstra
2018-09-06 19:58 ` Nadav Amit
2018-09-06 19:58 ` Nadav Amit
2018-09-06 20:25 ` Peter Zijlstra
2018-09-06 20:25 ` Peter Zijlstra
2018-09-06 20:57 ` Nadav Amit
2018-09-06 20:57 ` Nadav Amit
2018-09-06 21:41 ` Peter Zijlstra
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 ` 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 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 4/6] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-06 9:01 ` Peter Zijlstra
2018-09-06 9:01 ` Peter Zijlstra
2018-09-07 20:52 ` Nadav Amit
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 ` Nadav Amit
2018-09-02 17:32 ` [PATCH v2 6/6] x86/alternatives: remove text_poke() return value Nadav Amit
2018-09-02 17:32 ` Nadav Amit
2018-09-05 18:56 ` [PATCH v2 0/6] x86/alternatives: text_poke() fixes Peter Zijlstra
2018-09-05 18:56 ` Peter Zijlstra
2018-09-05 19:02 ` Nadav Amit
2018-09-05 19:02 ` Nadav Amit
2018-09-05 19:10 ` Nadav Amit
2018-09-05 19:10 ` Nadav Amit
2018-09-06 8:13 ` Peter Zijlstra [this message]
2018-09-06 8:13 ` Peter Zijlstra
2018-09-06 8:42 ` Peter Zijlstra
2018-09-06 8:42 ` Peter Zijlstra
2018-09-06 9:18 ` Peter Zijlstra
2018-09-06 9:18 ` Peter Zijlstra
2018-09-06 10:16 ` Peter Zijlstra
2018-09-06 10:16 ` Peter Zijlstra
2018-09-06 17:01 ` Nadav Amit
2018-09-06 17:01 ` Nadav Amit
2018-09-06 17:17 ` Peter Zijlstra
2018-09-06 17:17 ` Peter Zijlstra
2018-09-06 17:58 ` Nadav Amit
2018-09-06 17:58 ` Nadav Amit
2018-09-06 18:09 ` Andy Lutomirski
2018-09-06 18:09 ` Andy Lutomirski
2018-09-06 18:31 ` Peter Zijlstra
2018-09-06 18:31 ` Peter Zijlstra
2018-09-06 18:38 ` Nadav Amit
2018-09-06 18:38 ` Nadav Amit
2018-09-06 19:19 ` Peter Zijlstra
2018-09-06 19:19 ` Peter Zijlstra
2018-09-06 17:23 ` Peter Zijlstra
2018-09-06 17:23 ` Peter Zijlstra
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