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: Thu, 6 Sep 2018 17:58:46 +0000 [thread overview]
Message-ID: <9AF220A3-D783-442E-8E5B-AD0150628347@vmware.com> (raw)
Message-ID: <20180906175846.oMHZir3sP-3c-kjcQcj5umAo2qna69dfrJX3miKpWUU@z> (raw)
In-Reply-To: <20180906171754.GJ24106@hirez.programming.kicks-ass.net>
at 10:17 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Sep 06, 2018 at 05:01:25PM +0000, Nadav Amit wrote:
>> In addition, there might be a couple of issues with your fix:
>
> It boots on my box ;-)
>
>> 1. __set_pte_vaddr() is not used exclusive by set_fixmap(). This means
>> the warning might be wrong, but also means that these code patches (Xen’s
>> set_pte_mfn(), CPU-entry-area setup) needs to be checked. And as you said
>> before, someone might use this function for other purposes as well.
>
> CEA is fine, that actually needs it too.
>
> The one thing I missed out on earlier is the below chunk, that is no
> longer needed now that cea_set_pte() actually does the right thing.
>
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index b7b01d762d32..14ad97fa0749 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -293,12 +293,6 @@ static void ds_update_cea(void *cea, void *addr, size_t size, pgprot_t prot)
> preempt_disable();
> for (; msz < size; msz += PAGE_SIZE, pa += PAGE_SIZE, cea += PAGE_SIZE)
> cea_set_pte(cea, pa, prot);
> -
> - /*
> - * This is a cross-CPU update of the cpu_entry_area, we must shoot down
> - * all TLB entries for it.
> - */
> - flush_tlb_kernel_range(start, start + size);
> preempt_enable();
> }
>
> @@ -310,8 +304,6 @@ static void ds_clear_cea(void *cea, size_t size)
> preempt_disable();
> for (; msz < size; msz += PAGE_SIZE, cea += PAGE_SIZE)
> cea_set_pte(cea, 0, PAGE_NONE);
> -
> - flush_tlb_kernel_range(start, start + size);
> preempt_enable();
> }
>
>
>> 2. Printing the virtual address can break KASLR.
>
> Local KASLR is a myth.. but sure, we can fix the print.
>
>> 3. The WARN() can introduce some overhead since checking if IRQs are
>> disabled takes considerably long time. Perhaps VM_WARN() or something is
>> better. I realize this code-path is not on the hot-path though...
>
> Yeah, if it triggers you have bigger problems. We can make it
> WARN_ONCE() I suppose.
>
>> 4. I guess flush_tlb_kernel_range() should also have something like
>> VM_WARN_ON(irqs_disabled()), just as an additional general sanity check.
>
> It has, it's hidden in kernel/smp.c:smp_call_function_many().
Right. Thanks.
>
>> Let me know if you want me to make these changes and include your patch in
>> the set.
>
> The set is no longer needed. text_poke() is fine and correct with this
> one patch.
It depends what security you want. Some may consider even the short
time-window in which the kernel code is writable from other cores as
insufficient for security.
In addition, the set removes the need for remote TLB shootdowns that
text_poke() - with this fix - requires.
next prev parent reply other threads:[~2018-09-06 22:35 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
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 [this message]
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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