From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@intel.com>,
Mike Rapoport <rppt@linux.ibm.com>,
linux-kernel@vger.kernel.org,
Alexandre Chartre <alexandre.chartre@oracle.com>,
Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Jonathan Adams <jwadams@google.com>,
Kees Cook <keescook@chromium.org>, Paul Turner <pjt@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-mm@kvack.org, linux-security-module@vger.kernel.org,
x86@kernel.org
Subject: Re: [RFC PATCH 2/7] x86/sci: add core implementation for system call isolation
Date: Fri, 26 Apr 2019 11:49:27 -0700 [thread overview]
Message-ID: <1556304567.2833.62.camel@HansenPartnership.com> (raw)
In-Reply-To: <8E695557-1CD2-431A-99CC-49A4E8247BAE@amacapital.net>
On Fri, 2019-04-26 at 10:40 -0700, Andy Lutomirski wrote:
> > On Apr 26, 2019, at 8:19 AM, James Bottomley <James.Bottomley@hanse
> > npartnership.com> wrote:
> >
> > On Fri, 2019-04-26 at 08:07 -0700, Andy Lutomirski wrote:
> > > > On Apr 26, 2019, at 7:57 AM, James Bottomley
> > > > <James.Bottomley@hansenpartnership.com> wrote:
> > > >
> > > > > > On Fri, 2019-04-26 at 07:46 -0700, Dave Hansen wrote:
> > > > > > On 4/25/19 2:45 PM, Mike Rapoport wrote:
> > > > > > After the isolated system call finishes, the mappings
> > > > > > created during its execution are cleared.
> > > > >
> > > > > Yikes. I guess that stops someone from calling write() a
> > > > > bunch of times on every filesystem using every block device
> > > > > driver and all the DM code to get a lot of code/data faulted
> > > > > in. But, it also means not even long-running processes will
> > > > > ever have a chance of behaving anything close to normally.
> > > > >
> > > > > Is this something you think can be rectified or is there
> > > > > something fundamental that would keep SCI page tables from
> > > > > being cached across different invocations of the same
> > > > > syscall?
> > > >
> > > > There is some work being done to look at pre-populating the
> > > > isolated address space with the expected execution footprint of
> > > > the system call, yes. It lessens the ROP gadget protection
> > > > slightly because you might find a gadget in the pre-populated
> > > > code, but it solves a lot of the overhead problem.
> > >
> > > I’m not even remotely a ROP expert, but: what stops a ROP payload
> > > from using all the “fault-in” gadgets that exist — any function
> > > that can return on an error without doing to much will fault in
> > > the whole page containing the function.
> >
> > The address space pre-population is still per syscall, so you don't
> > get access to the code footprint of a different syscall. So the
> > isolated address space is created anew for every system call, it's
> > just pre-populated with that system call's expected footprint.
>
> That’s not what I mean. Suppose I want to use a ROP gadget in
> vmalloc(), but vmalloc isn’t in the page tables. Then first push
> vmalloc itself into the stack. As long as RDI contains a sufficiently
> ridiculous value, it should just return without doing anything. And
> it can return right back into the ROP gadget, which is now available.
Yes, it's not perfect, but stack space for a smashing attack is at a
premium and now you need two stack frames for every gadget you chain
instead of one so we've halved your ability to chain gadgets.
> > > To improve this, we would want some thing that would try to check
> > > whether the caller is actually supposed to call the callee, which
> > > is more or less the hard part of CFI. So can’t we just do CFI
> > > and call it a day?
> >
> > By CFI you mean control flow integrity? In theory I believe so,
> > yes, but in practice doesn't it require a lot of semantic object
> > information which is easy to get from higher level languages like
> > java but a bit more difficult for plain C.
>
> Yes. As I understand it, grsecurity instruments gcc to create some
> kind of hash of all function signatures. Then any indirect call can
> effectively verify that it’s calling a function of the right type.
> And every return verified a cookie.
>
> On CET CPUs, RET gets checked directly, and I don’t see the benefit
> of SCI.
Presumably you know something I don't but I thought CET CPUs had been
planned for release for ages, but not actually released yet?
> > > On top of that, a robust, maintainable implementation of this
> > > thing seems very complicated — for example, what happens if
> > > vfree() gets called?
> >
> > Address space Local vs global object tracking is another thing on
> > our list. What we'd probably do is verify the global object was
> > allowed to be freed and then hand it off safely to the main kernel
> > address space.
>
> This seems exceedingly complicated.
It's a research project: we're exploring what's possible so we can
choose the techniques that give the best security improvement for the
additional overhead.
James
next prev parent reply other threads:[~2019-04-26 18:49 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-25 21:45 [RFC PATCH 0/7] x86: introduce system calls addess space isolation Mike Rapoport
2019-04-25 21:45 ` [RFC PATCH 1/7] x86/cpufeatures: add X86_FEATURE_SCI Mike Rapoport
2019-04-25 21:45 ` [RFC PATCH 2/7] x86/sci: add core implementation for system call isolation Mike Rapoport
2019-04-26 7:49 ` Peter Zijlstra
2019-04-28 5:45 ` Mike Rapoport
2019-04-26 8:31 ` Ingo Molnar
2019-04-26 9:58 ` Ingo Molnar
2019-04-26 21:26 ` Andy Lutomirski
2019-04-27 8:47 ` Ingo Molnar
2019-04-27 10:46 ` Ingo Molnar
2019-04-29 18:26 ` James Morris
2019-04-29 18:43 ` Andy Lutomirski
2019-04-29 18:46 ` Andy Lutomirski
2019-04-30 5:03 ` Ingo Molnar
2019-04-30 9:38 ` Peter Zijlstra
2019-04-30 11:05 ` Ingo Molnar
2019-05-02 11:35 ` Robert O'Callahan
2019-05-02 15:20 ` Ingo Molnar
2019-05-02 21:07 ` Robert O'Callahan
2019-04-26 14:44 ` James Bottomley
2019-04-26 14:46 ` Dave Hansen
2019-04-26 14:57 ` James Bottomley
2019-04-26 15:07 ` Andy Lutomirski
2019-04-26 15:19 ` James Bottomley
2019-04-26 17:40 ` Andy Lutomirski
2019-04-26 18:49 ` James Bottomley [this message]
2019-04-26 19:22 ` Andy Lutomirski
2019-04-25 21:45 ` [RFC PATCH 3/7] x86/entry/64: add infrastructure for switching to isolated syscall context Mike Rapoport
2019-04-25 21:45 ` [RFC PATCH 4/7] x86/sci: hook up isolated system call entry and exit Mike Rapoport
2019-04-25 21:45 ` [RFC PATCH 5/7] x86/mm/fault: hook up SCI verification Mike Rapoport
2019-04-26 7:42 ` Peter Zijlstra
2019-04-28 5:47 ` Mike Rapoport
2019-04-30 16:44 ` Andy Lutomirski
2019-05-01 5:39 ` Mike Rapoport
2019-04-25 21:45 ` [RFC PATCH 6/7] security: enable system call isolation in kernel config Mike Rapoport
2019-04-25 21:45 ` [RFC PATCH 7/7] sci: add example system calls to exercse SCI Mike Rapoport
2019-04-26 0:30 ` [RFC PATCH 0/7] x86: introduce system calls addess space isolation Andy Lutomirski
2019-04-26 8:07 ` Jiri Kosina
2019-04-28 6:01 ` Mike Rapoport
2019-04-26 14:41 ` Dave Hansen
2019-04-28 6:08 ` Mike Rapoport
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