From: Tycho Andersen <tycho@tycho.ws>
To: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: Mike Rapoport <rppt@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
James Bottomley <jejb@linux.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"x86@kernel.org" <x86@kernel.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Alan Cox <alan@linux.intel.com>
Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings
Date: Tue, 29 Oct 2019 09:13:43 -0600 [thread overview]
Message-ID: <20191029151343.GE32132@cisco> (raw)
In-Reply-To: <2236FBA76BA1254E88B949DDB74E612BA4EEC0CE@IRSMSX102.ger.corp.intel.com>
Hi Elena, Mike,
On Tue, Oct 29, 2019 at 11:25:12AM +0000, Reshetova, Elena wrote:
> > The patch below aims to allow applications to create mappins that have
> > pages visible only to the owning process. Such mappings could be used to
> > store secrets so that these secrets are not visible neither to other
> > processes nor to the kernel.
>
> Hi Mike,
>
> I have actually been looking into the closely related problem for the past
> couple of weeks (on and off). What is common here is the need for userspace
> to indicate to kernel that some pages contain secrets. And then there are
> actually a number of things that kernel can do to try to protect these secrets
> better. Unmap from direct map is one of them. Another thing is to map such
> pages as non-cached, which can help us to prevent or considerably restrict
> speculation on such pages. The initial proof of concept for marking pages as
> "UNCACHED" that I got from Dave Hansen was actually based on mlock2()
> and a new flag for it for this purpose. Since then I have been thinking on what
> interface suits the use case better and actually selected going with new madvise()
> flag instead because of all possible implications for fragmentation and performance.
> My logic was that we better allocate the secret data explicitly (using mmap())
> to make sure that no other process data accidentally gets to suffer.
> Imagine I would allocate a buffer to hold a secret key, signal with mlock
> to protect it and suddenly my other high throughput non-secret buffer
> (which happened to live on the same page by chance) became very slow
> and I don't even have an easy way (apart from mmap()ing it!) to guarantee
> that it won't be affected.
>
> So, I ended up towards smth like:
>
> secret_buffer = mmap(NULL, PAGE_SIZE, ...)
> madvise(secret_buffer, size, MADV_SECRET)
>
> I have work in progress code here:
> https://github.com/ereshetova/linux/commits/madvise
>
> I haven't sent it for review, because it is not ready yet and I am now working
> on trying to add the page wiping functionality. Otherwise it would be useless
> to protect the page during the time it is used in userspace, but then allow it
> to get reused by a different process later after it has been released back and
> userspace was stupid enough not to wipe the contents (or was crashed on
> purpose before it was able to wipe anything out).
I was looking at this and thinking that wiping during do_exit() might
be a nice place, but I haven't tried anything yet.
> We have also had some discussions with Tycho that XPFO can be also
> applied selectively for such "SECRET" marked pages and I know that he has also
> did some initial prototyping on this, so I think it would be great to decide
> on userspace interface first and then see how we can assemble together all
> these features.
Yep! Here's my tree with the direct un-mapping bits ported from XPFO:
https://github.com/tych0/linux/commits/madvise
As noted in one of the commit messages I think the bit math for page
prot flags needs a bit of work, but the test passes, so :)
In any case, I'll try to look at Mike's patches later today.
Cheers,
Tycho
next prev parent reply other threads:[~2019-10-29 15:13 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-27 10:17 [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Mike Rapoport
2019-10-27 10:17 ` Mike Rapoport
2019-10-28 12:31 ` Kirill A. Shutemov
2019-10-28 13:00 ` Mike Rapoport
2019-10-28 13:16 ` Kirill A. Shutemov
2019-10-28 13:55 ` Peter Zijlstra
2019-10-28 19:59 ` Edgecombe, Rick P
2019-10-28 21:00 ` Peter Zijlstra
2019-10-29 17:27 ` Edgecombe, Rick P
2019-10-30 10:04 ` Peter Zijlstra
2019-10-30 15:35 ` Alexei Starovoitov
2019-10-30 18:39 ` Peter Zijlstra
2019-10-30 18:52 ` Alexei Starovoitov
2019-10-30 17:48 ` Edgecombe, Rick P
2019-10-30 17:58 ` Dave Hansen
2019-10-30 18:01 ` Dave Hansen
2019-10-29 5:43 ` Dan Williams
2019-10-29 6:43 ` Kirill A. Shutemov
2019-10-29 8:56 ` Peter Zijlstra
2019-10-29 11:00 ` Kirill A. Shutemov
2019-10-29 12:39 ` AMD TLB errata, (Was: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings) Peter Zijlstra
2019-11-15 14:12 ` Tom Lendacky
2019-11-15 14:31 ` Peter Zijlstra
2019-10-29 19:43 ` [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Dan Williams
2019-10-29 20:07 ` Dave Hansen
2019-10-29 7:08 ` Christopher Lameter
2019-10-29 8:55 ` Mike Rapoport
2019-10-29 10:12 ` Christopher Lameter
2019-10-30 7:11 ` Mike Rapoport
2019-10-30 12:09 ` Christopher Lameter
2019-10-28 14:55 ` David Hildenbrand
2019-10-28 17:12 ` Dave Hansen
2019-10-28 17:32 ` Sean Christopherson
2019-10-28 18:08 ` Matthew Wilcox
2019-10-29 9:28 ` Mike Rapoport
2019-10-29 9:19 ` Mike Rapoport
2019-10-28 18:02 ` Andy Lutomirski
2019-10-29 11:02 ` David Hildenbrand
2019-10-30 8:15 ` Mike Rapoport
2019-10-30 8:19 ` David Hildenbrand
2019-10-31 19:16 ` Mike Rapoport
2019-10-31 21:52 ` Dan Williams
2019-10-27 10:30 ` Florian Weimer
2019-10-27 11:00 ` Mike Rapoport
2019-10-28 20:23 ` Florian Weimer
2019-10-29 9:01 ` Mike Rapoport
2019-10-28 20:44 ` Andy Lutomirski
2019-10-29 9:32 ` Mike Rapoport
2019-10-29 17:00 ` Andy Lutomirski
2019-10-30 8:40 ` Mike Rapoport
2019-10-30 21:28 ` Andy Lutomirski
2019-10-31 7:21 ` Mike Rapoport
2019-12-05 15:34 ` Mike Rapoport
2019-12-08 14:10 ` [PATCH] mm: extend memfd with ability to create secret memory kbuild test robot
2019-10-29 11:25 ` [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Reshetova, Elena
2019-10-29 15:13 ` Tycho Andersen [this message]
2019-10-29 17:03 ` Andy Lutomirski
2019-10-29 17:37 ` Alan Cox
2019-10-29 17:43 ` James Bottomley
2019-10-29 18:10 ` Andy Lutomirski
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