From: Matthew Wilcox <willy@infradead.org>
To: Boaz Harrosh <boazh@netapp.com>
Cc: Jeff Moyer <jmoyer@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Rik van Riel <riel@redhat.com>, Jan Kara <jack@suse.cz>,
Matthew Wilcox <mawilcox@microsoft.com>,
Amit Golander <Amit.Golander@netapp.com>
Subject: Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU
Date: Tue, 15 May 2018 04:11:59 -0700 [thread overview]
Message-ID: <20180515111159.GA31599@bombadil.infradead.org> (raw)
In-Reply-To: <f3a66d8b-b9dc-b110-08aa-a63f0c309fb2@netapp.com>
On Tue, May 15, 2018 at 01:43:23PM +0300, Boaz Harrosh wrote:
> On 15/05/18 03:41, Matthew Wilcox wrote:
> > On Mon, May 14, 2018 at 10:37:38PM +0300, Boaz Harrosh wrote:
> >> On 14/05/18 22:15, Matthew Wilcox wrote:
> >>> On Mon, May 14, 2018 at 08:28:01PM +0300, Boaz Harrosh wrote:
> >>>> On a call to mmap an mmap provider (like an FS) can put
> >>>> this flag on vma->vm_flags.
> >>>>
> >>>> The VM_LOCAL_CPU flag tells the Kernel that the vma will be used
> >>>> from a single-core only, and therefore invalidation (flush_tlb) of
> >>>> PTE(s) need not be a wide CPU scheduling.
> >>>
> >>> I still don't get this. You're opening the kernel up to being exploited
> >>> by any application which can persuade it to set this flag on a VMA.
> >>>
> >>
> >> No No this is not an application accessible flag this can only be set
> >> by the mmap implementor at ->mmap() time (Say same as VM_VM_MIXEDMAP).
> >>
> >> Please see the zuf patches for usage (Again apologise for pushing before
> >> a user)
> >>
> >> The mmap provider has all the facilities to know that this can not be
> >> abused, not even by a trusted Server.
> >
> > I don't think page tables work the way you think they work.
> >
> > + err = vm_insert_pfn_prot(zt->vma, zt_addr, pfn, prot);
> >
> > That doesn't just insert it into the local CPU's page table. Any CPU
> > which directly accesses or even prefetches that address will also get
> > the translation into its cache.
>
> Yes I know, but that is exactly the point of this flag. I know that this
> address is only ever accessed from a single core. Because it is an mmap (vma)
> of an O_TMPFILE-exclusive file created in a core-pinned thread and I allow
> only that thread any kind of access to this vma. Both the filehandle and the
> mmaped pointer are kept on the thread stack and have no access from outside.
>
> So the all point of this flag is the kernel driver telling mm that this
> address is enforced to only be accessed from one core-pinned thread.
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.
next prev parent reply other threads:[~2018-05-15 11:11 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-14 17:28 [PATCH] mm: Add new vma flag VM_LOCAL_CPU Boaz Harrosh
2018-05-14 18:26 ` Boaz Harrosh
2018-05-15 7:08 ` Christoph Hellwig
2018-05-15 10:45 ` Boaz Harrosh
2018-05-14 19:15 ` Matthew Wilcox
2018-05-14 19:37 ` Boaz Harrosh
2018-05-15 0:41 ` Matthew Wilcox
2018-05-15 10:43 ` Boaz Harrosh
2018-05-15 11:11 ` Matthew Wilcox [this message]
2018-05-15 11:41 ` Boaz Harrosh
2018-05-15 12:03 ` Matthew Wilcox
2018-05-15 13:29 ` Boaz Harrosh
2018-05-15 13:50 ` Matthew Wilcox
2018-05-15 14:10 ` Boaz Harrosh
2018-05-15 14:18 ` Matthew Wilcox
2018-05-15 14:30 ` Boaz Harrosh
2018-05-15 12:09 ` Peter Zijlstra
2018-05-15 12:31 ` Boaz Harrosh
2018-05-15 11:47 ` Peter Zijlstra
2018-05-15 12:01 ` Boaz Harrosh
2018-05-15 12:07 ` Mark Rutland
2018-05-15 12:35 ` Peter Zijlstra
2018-05-15 13:19 ` Boaz Harrosh
2018-05-18 14:14 ` Christopher Lameter
2018-05-22 16:05 ` Boaz Harrosh
2018-05-22 16:18 ` Dave Hansen
2018-05-22 16:46 ` Christopher Lameter
2018-05-22 16:56 ` Peter Zijlstra
2018-05-22 17:03 ` Dave Hansen
2018-05-22 17:35 ` Christopher Lameter
2018-05-22 17:51 ` Matthew Wilcox
2018-05-23 17:30 ` Dave Hansen
2018-05-23 17:46 ` Nadav Amit
2018-05-23 18:10 ` Mark Rutland
2018-05-14 21:49 ` Andrew Morton
2018-05-15 0:44 ` Matthew Wilcox
2018-05-15 11:54 ` Boaz Harrosh
2018-05-15 13:24 ` Boaz Harrosh
2018-05-15 14:17 ` Peter Zijlstra
2018-05-15 14:36 ` Boaz Harrosh
2018-05-15 14:19 ` Dave Hansen
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