[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CALCETrW7nN8Ja=r9k4ANpekKovC_wsYrGrge1WNoGsAjZZvqHQ@mail.gmail.com>
Date: Wed, 5 Apr 2017 16:57:35 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Mark Rutland <mark.rutland@....com>, Andy Lutomirski <luto@...nel.org>, Hoeun Ryu <hoeun.ryu@...il.com>,
PaX Team <pageexec@...email.hu>, Emese Revfy <re.emese@...il.com>,
Russell King <linux@...linux.org.uk>, X86 ML <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()
On Wed, Mar 29, 2017 at 6:41 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Mar 29, 2017 at 3:38 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Wed, Mar 29, 2017 at 11:15 AM, Kees Cook <keescook@...omium.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.
--Andy
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
