linux-kernel - Re: [PATCH] mm: Add new vma flag VM_LOCAL

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Message-ID: <de0384c7-23a0-fb92-3672-d89b364c5597@netapp.com>
Date:   Tue, 15 May 2018 15:31:02 +0300
From:   Boaz Harrosh <boazh@...app.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Matthew Wilcox <willy@...radead.org>,
        Jeff Moyer <jmoyer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Amit Golander <Amit.Golander@...app.com>
Subject: Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU

On 15/05/18 15:09, Peter Zijlstra wrote:
> On Tue, May 15, 2018 at 02:41:41PM +0300, Boaz Harrosh wrote:
>> On 15/05/18 14:11, Matthew Wilcox wrote:
> 
>>> You're still thinking about this from the wrong perspective.  If you
>>> were writing a program to attack this facility, how would you do it?
>>> It's not exactly hard to leak one pointer's worth of information.
>>>
>>
>> That would be very hard. Because that program would:
>> - need to be root
>> - need to start and pretend it is zus Server with the all mount
>>   thread thing, register new filesystem, grab some pmem devices.
>> - Mount the said filesystem on said pmem. Create core-pinned ZT threads
>>   for all CPUs, start accepting IO.
>> - And only then it can start leaking the pointer and do bad things.
>>   The bad things it can do to the application, not to the Kernel.
> 
> No I think you can do bad things to the kernel at that point. Consider
> it populating the TLBs on the 'wrong' CPU by 'inadvertenly' touching
> 'random' memory.
> 
> Then cause an invalidation and get the page re-used for kernel bits.
> 
> Then access that page through the 'stale' TLB entry we still have on the
> 'wrong' CPU and corrupt kernel data.
> 

Yes a BAD filesystem Server can do bad things I agree. But a filesystem can
do very bad things in any case. through the front door, No? and we trust
it with our data. So there is some trust we already put in a filesystem i think.

I will try to look at this deeper, see if I can actually enforce this policy.
Do you have any ideas? can I force page_faults on the other cores?

Thank you for looking
Boaz