From: Mathias Krause <minipli@googlemail.com>
To: Andy Lutomirski <luto@amacapital.net>, Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>,
Mark Rutland <mark.rutland@arm.com>,
Hoeun Ryu <hoeun.ryu@gmail.com>, PaX Team <pageexec@freemail.hu>,
Emese Revfy <re.emese@gmail.com>,
Russell King <linux@armlinux.org.uk>, X86 ML <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()
Date: Fri, 7 Apr 2017 10:34:32 +0200 [thread overview]
Message-ID: <CA+rthh95rW95woiWvyeCcoJT-qRM18KCDGHGtH=bDHZdExmVmg@mail.gmail.com> (raw)
In-Reply-To: <CALCETrVErxE5P=V4LD=kFCBtnp2YYEGRsbxhTG0SXJjrw6Yk1A@mail.gmail.com>
On 6 April 2017 at 17:59, Andy Lutomirski <luto@amacapital.net> wrote:
> On Wed, Apr 5, 2017 at 5:14 PM, Kees Cook <keescook@chromium.org> wrote:
>> On Wed, Apr 5, 2017 at 4:57 PM, Andy Lutomirski <luto@kernel.org> wrote:
>>> On Wed, Mar 29, 2017 at 6:41 PM, Kees Cook <keescook@chromium.org> wrote:
>>>> On Wed, Mar 29, 2017 at 3:38 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>>> On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keescook@chromium.org> wrote:
>>>>>> Based on PaX's x86 pax_{open,close}_kernel() implementation, this
>>>>>> allows HAVE_ARCH_RARE_WRITE to work on x86.
>>>>>>
>>>>>> +
>>>>>> +static __always_inline unsigned long __arch_rare_write_begin(void)
>>>>>> +{
>>>>>> + unsigned long cr0;
>>>>>> +
>>>>>> + preempt_disable();
>>>>>
>>>>> This looks wrong. DEBUG_LOCKS_WARN_ON(!irqs_disabled()) would work,
>>>>> as would local_irq_disable(). There's no way that just disabling
>>>>> preemption is enough.
>>>>>
>>>>> (Also, how does this interact with perf nmis?)
>>>>
>>>> Do you mean preempt_disable() isn't strong enough here? I'm open to
>>>> suggestions. The goal would be to make sure nothing between _begin and
>>>> _end would get executed without interruption...
>>>>
>>>
>>> Sorry for the very slow response.
>>>
>>> preempt_disable() isn't strong enough to prevent interrupts, and an
>>> interrupt here would run with WP off, causing unknown havoc. I tend
>>> to think that the caller should be responsible for turning off
>>> interrupts.
>>
>> So, something like:
>>
>> Top-level functions:
>>
>> static __always_inline rare_write_begin(void)
>> {
>> preempt_disable();
>> local_irq_disable();
>> barrier();
>> __arch_rare_write_begin();
>> barrier();
>> }
>
> Looks good, except you don't need preempt_disable().
> local_irq_disable() also disables preemption. You might need to use
> local_irq_save(), though, depending on whether any callers already
> have IRQs off.
Well, doesn't look good to me. NMIs will still be able to interrupt
this code and will run with CR0.WP = 0.
Shouldn't you instead question yourself why PaX can do it "just" with
preempt_disable() instead?!
Cheers,
Mathias
next prev parent reply other threads:[~2017-04-07 8:34 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-29 18:15 [RFC v2] Introduce rare_write() infrastructure Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 01/11] " Kees Cook
2017-03-29 18:23 ` Kees Cook
2017-03-30 7:44 ` Ho-Eun Ryu
2017-03-30 17:02 ` Kees Cook
2017-04-07 8:09 ` Ho-Eun Ryu
2017-04-07 20:38 ` Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 02/11] lkdtm: add test for " Kees Cook
2017-03-30 9:34 ` [kernel-hardening] " Ian Campbell
2017-03-30 16:16 ` Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 03/11] net: switch sock_diag handlers to rare_write() Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook
2017-03-29 22:38 ` Andy Lutomirski
2017-03-30 1:41 ` Kees Cook
2017-04-05 23:57 ` Andy Lutomirski
2017-04-06 0:14 ` Kees Cook
2017-04-06 15:59 ` Andy Lutomirski
2017-04-07 8:34 ` Mathias Krause [this message]
2017-04-07 9:46 ` [kernel-hardening] " Thomas Gleixner
2017-04-07 10:51 ` Mathias Krause
2017-04-07 13:14 ` Thomas Gleixner
2017-04-07 13:30 ` Mathias Krause
2017-04-07 16:14 ` Andy Lutomirski
2017-04-07 16:22 ` Mark Rutland
2017-04-07 19:58 ` PaX Team
2017-04-08 4:58 ` Andy Lutomirski
2017-04-09 12:47 ` PaX Team
2017-04-10 0:10 ` Andy Lutomirski
2017-04-10 10:42 ` PaX Team
2017-04-10 16:01 ` Andy Lutomirski
2017-04-07 20:44 ` Thomas Gleixner
2017-04-07 21:20 ` Kees Cook
2017-04-08 4:12 ` Daniel Micay
2017-04-08 4:13 ` Daniel Micay
2017-04-08 4:21 ` Daniel Micay
2017-04-08 5:07 ` Andy Lutomirski
2017-04-08 7:33 ` Daniel Micay
2017-04-08 15:20 ` Andy Lutomirski
2017-04-09 10:53 ` Ingo Molnar
2017-04-10 10:22 ` Mark Rutland
2017-04-09 20:24 ` PaX Team
2017-04-10 0:31 ` Andy Lutomirski
2017-04-10 19:47 ` PaX Team
2017-04-10 20:27 ` Andy Lutomirski
2017-04-10 20:13 ` Kees Cook
2017-04-10 20:17 ` Andy Lutomirski
2017-04-07 19:25 ` Thomas Gleixner
2017-04-07 14:45 ` Peter Zijlstra
2017-04-10 10:29 ` Mark Rutland
2017-04-07 19:52 ` PaX Team
2017-04-10 8:26 ` Thomas Gleixner
2017-04-10 19:55 ` PaX Team
2017-04-07 9:37 ` Peter Zijlstra
2017-03-29 18:15 ` [RFC v2][PATCH 05/11] ARM: mm: dump: Add domain to output Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 06/11] ARM: domains: Extract common USER domain init Kees Cook
2017-03-29 18:15 ` [RFC v2][PATCH 07/11] ARM: mm: set DOMAIN_WR_RARE for rodata Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 08/11] ARM: Implement __arch_rare_write_begin/end() Kees Cook
2017-04-07 9:36 ` Peter Zijlstra
2017-03-29 18:16 ` [RFC v2][PATCH 09/11] list: add rare_write() list helpers Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 10/11] gcc-plugins: Add constify plugin Kees Cook
2017-03-29 18:16 ` [RFC v2][PATCH 11/11] cgroups: force all struct cftype const Kees Cook
2017-03-29 19:00 ` [RFC v2] Introduce rare_write() infrastructure Russell King - ARM Linux
2017-03-29 19:14 ` Kees Cook
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