From mboxrd@z Thu Jan  1 00:00:00 1970
From: julien.grall@citrix.com (Julien Grall)
Date: Fri, 11 Sep 2015 15:56:38 +0100
Subject: [PATCH] arm/xen: Enable user access to the kernel before issuing
 a privcmd call
In-Reply-To: <1441983304.3549.73.camel@citrix.com>
References: <1441980963-9002-1-git-send-email-julien.grall@citrix.com>
 <1441981760.3549.57.camel@citrix.com> <55F2E909.70600@citrix.com>
 <1441983304.3549.73.camel@citrix.com>
Message-ID: <55F2EBA6.6060008@citrix.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 11/09/15 15:55, Ian Campbell wrote:
> On Fri, 2015-09-11 at 15:45 +0100, Julien Grall wrote:
>> On 11/09/15 15:29, Ian Campbell wrote:
>>> On Fri, 2015-09-11 at 15:16 +0100, Julien Grall wrote:
>>>> When Xen is copyin data to/from the guest it will check if the kernel
>>>
>>> "copying"
>>>
>>>> has the right to do the access. If not, the hypercall will return an
>>>> error.
>>>>
>>>> After the commit a5e090acbf545c0a3b04080f8a488b17ec41fe02 "ARM:
>>>> software-based priviledged-no-access support", the kernel can't
>>>> access
>>>
>>> "privileged"
>>>
>>>> anymore the user space by default. This will result to fail on every
>>>
>>> "any more" (or "any longer")
>>>
>>>> hypercall made by the userspace (i.e via privcmd).
>>>>
>>>> We have to enable the userspace access and then restore the correct
>>>> permission everytime the privmcd is used to made an hypercall.
>>>
>>> "every time" and "privcmd"
>>>
>>>>  HYPERCALL1(tmem_op);
>>>>  HYPERCALL2(multicall);
>>>>  
>>>> -ENTRY(privcmd_call)
>>>> +ENTRY(__privcmd_call)
>>>
>>> arch/arm/include/asm/assembler.h seems to contain uaccess_* macros
>>> which
>>> could be used right here directly I think? That would be preferable to
>>> wrapping I think.
>>
>> Looking to the uaccess_save macro:
> 
> I was thinking more about uaccess_enable/disable.

Well, we can't assume that the function will be called with uaccess
disabled.  So we have to save the state and restore it after issuing the
hypercall.

Regards,

-- 
Julien Grall