Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] lkdtm: Test KUAP directional user access unlocks on
 powerpc
To:     Russell Currey <ruscur@russell.cc>, keescook@chromium.org,
        mpe@ellerman.id.au
Cc:     linux-kernel@vger.kernel.org, dja@axtens.net,
        kernel-hardening@lists.openwall.com, linuxppc-dev@lists.ozlabs.org
References: <20200131053157.22463-1-ruscur@russell.cc>
 <1b40cea6-0675-731a-58b1-bdc65f1e495e@c-s.fr>
 <0b016861756cbe27e66651b5c21229a06558cb57.camel@russell.cc>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <c05a4327-0c81-0e3e-d93a-9d62183b146c@c-s.fr>
Date:   Fri, 31 Jan 2020 07:58:16 +0100
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.4.2
MIME-Version: 1.0
In-Reply-To: <0b016861756cbe27e66651b5c21229a06558cb57.camel@russell.cc>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: fr
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


Le 31/01/2020 à 07:53, Russell Currey a écrit :
> On Fri, 2020-01-31 at 07:44 +0100, Christophe Leroy wrote:
>>
>> Le 31/01/2020 à 06:31, Russell Currey a écrit :
>>> +	pr_info("attempting bad read at %px with write allowed\n",
>>> ptr);
>>> +	tmp = *ptr;
>>> +	tmp += 0xc0dec0de;
>>> +	prevent_write_to_user(ptr, sizeof(unsigned long));
>>
>> Does it work ? I would have thought that if the read fails the
>> process
>> will die and the following test won't be performed.
> 
> Correct, the ACCESS_USERSPACE test does the same thing.  Splitting this
> into separate R and W tests makes sense, even if it is unlikely that
> one would be broken without the other.
> 

Or once we are using user_access_begin() stuff, we can use 
unsafe_put_user() and unsafe_get_user() which should return an error 
instead of killing the caller.

Christophe