From: Ingo Molnar <mingo@kernel.org>
To: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: "luto@kernel.org" <luto@kernel.org>,
"luto@amacapital.net" <luto@amacapital.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jpoimboe@redhat.com" <jpoimboe@redhat.com>,
"keescook@chromium.org" <keescook@chromium.org>,
"jannh@google.com" <jannh@google.com>,
"Perla, Enrico" <enrico.perla@intel.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"peterz@infradead.org" <peterz@infradead.org>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall
Date: Tue, 16 Apr 2019 09:34:44 +0200 [thread overview]
Message-ID: <20190416073444.GC127769@gmail.com> (raw)
In-Reply-To: <2236FBA76BA1254E88B949DDB74E612BA4C4F90F@IRSMSX102.ger.corp.intel.com>
* Reshetova, Elena <elena.reshetova@intel.com> wrote:
> > 4)
> >
> > But before you tweak the patch, a more fundamental question:
> >
> > Does the stack offset have to be per *syscall execution* randomized?
> > Which threats does this protect against that a simpler per task syscall
> > random offset wouldn't protect against?
>
> We *really* need it per syscall. If you take a look on the recent stack attacks
> [1],[2],[3],[4], they all do some initial probing on syscalls first to discover stack addresses
> or leftover data on the stack (or pre-populate stack with some attacker-controlled data),
> and then in the following syscall execute the actual attack (leak data, use
> pre-populated data for execution, etc.). If the offset stays the same during
> task life time, it can be easily recovered during this initial probing phase, and
> then nothing changes for the attacker.
>
> [1] Kernel Exploitation Via Uninitialized Stack, 2011
> https://www.defcon.org/images/defcon-19/dc-19-presentations/Cook/DEFCON-19-Cook-Kernel-Exploitation.pdf
> [2] Stackjacking, 2011, https://jon.oberheide.org/files/stackjacking-infiltrate11.pdf
> [3] The Stack is Back, 2012, https://jon.oberheide.org/files/infiltrate12-thestackisback.pdf
> [4] Exploiting Recursion in the Linux Kernel, 2016,
> https://googleprojectzero.blogspot.com/2016/06/exploiting-recursion-in-linux-kernel_20.html
Yeah, so if there's an information leak from the kernel stack, don't we
now effectively store 5 PRNG bits there for every syscall, allowing the
systematic probing of the generic PRNG?
The kernel can execute millions of syscalls per second, I'm pretty sure
there's a statistical attack against:
* This is a maximally equidistributed combined Tausworthe generator
* based on code from GNU Scientific Library 1.5 (30 Jun 2004)
*
* lfsr113 version:
*
* x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n)
*
* s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n << 6) ^ s1_n) >> 13))
* s2_{n+1} = (((s2_n & 4294967288) << 2) ^ (((s2_n << 2) ^ s2_n) >> 27))
* s3_{n+1} = (((s3_n & 4294967280) << 7) ^ (((s3_n << 13) ^ s3_n) >> 21))
* s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n << 3) ^ s4_n) >> 12))
*
* The period of this generator is about 2^113 (see erratum paper).
... which recovers the real PRNG state much faster than the ~60 seconds
seeding interval and allows the prediction of the next stack offset?
I.e. I don't see how kernel stack PRNG randomization protects against
information leaks from the kernel stack. By putting PRNG information into
the kernel stack for *every* system call we add a broad attack surface:
any obscure ioctl information leak can now be escalated into an attack
against the net_rand_state PRNG, right?
> No the above numbers are with CONFIG_PAGE_TABLE_ISOLATION=y for x86_64,
> I will test with CONFIG_PAGE_TABLE_ISOLATION turned off from now on
> also.
Thanks!
Ingo
next prev parent reply other threads:[~2019-04-16 7:34 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-15 6:09 [PATCH] x86/entry/64: randomize kernel stack offset upon syscall Elena Reshetova
2019-04-15 7:25 ` Ingo Molnar
2019-04-15 8:44 ` Reshetova, Elena
2019-04-16 7:34 ` Ingo Molnar [this message]
2019-04-16 11:10 ` Reshetova, Elena
2019-04-16 12:08 ` Peter Zijlstra
2019-04-16 12:45 ` David Laight
2019-04-16 15:43 ` Theodore Ts'o
2019-04-16 16:07 ` Peter Zijlstra
2019-04-16 16:47 ` Reshetova, Elena
2019-04-17 9:28 ` David Laight
2019-04-17 15:15 ` Theodore Ts'o
2019-04-17 15:40 ` Kees Cook
2019-04-17 15:53 ` David Laight
2019-04-24 11:42 ` Reshetova, Elena
2019-04-24 13:33 ` David Laight
2019-04-25 11:23 ` Reshetova, Elena
2019-04-26 11:33 ` Reshetova, Elena
2019-04-26 14:01 ` Theodore Ts'o
2019-04-26 17:44 ` Eric Biggers
2019-04-26 18:02 ` Theodore Ts'o
2019-04-27 13:59 ` Andy Lutomirski
2019-04-29 8:04 ` Reshetova, Elena
2019-04-26 18:34 ` Andy Lutomirski
2019-04-29 7:46 ` Reshetova, Elena
2019-04-29 16:08 ` Andy Lutomirski
2019-04-30 17:51 ` Reshetova, Elena
2019-04-30 18:01 ` Kees Cook
2019-05-01 8:23 ` David Laight
2019-05-02 8:07 ` Reshetova, Elena
2019-05-01 8:41 ` David Laight
2019-05-01 23:33 ` Andy Lutomirski
2019-05-02 8:15 ` Reshetova, Elena
2019-05-02 9:23 ` David Laight
2019-05-02 14:47 ` Andy Lutomirski
2019-05-02 15:08 ` Ingo Molnar
2019-05-02 16:32 ` Andy Lutomirski
2019-05-02 16:43 ` Ingo Molnar
2019-05-03 16:40 ` Andy Lutomirski
2019-05-02 16:34 ` David Laight
2019-05-02 16:45 ` Ingo Molnar
2019-05-03 16:17 ` Reshetova, Elena
2019-05-03 16:40 ` David Laight
2019-05-03 19:10 ` Linus Torvalds
2019-05-06 6:47 ` Reshetova, Elena
2019-05-06 7:01 ` Reshetova, Elena
2019-05-08 11:18 ` Reshetova, Elena
2019-05-08 11:32 ` Ingo Molnar
2019-05-08 13:22 ` Reshetova, Elena
2019-05-09 5:59 ` Ingo Molnar
2019-05-09 7:01 ` Reshetova, Elena
2019-05-09 8:43 ` Ingo Molnar
2019-05-11 22:45 ` Andy Lutomirski
2019-05-12 0:12 ` Kees Cook
2019-05-12 8:02 ` Ingo Molnar
2019-05-12 14:33 ` Kees Cook
2019-05-28 12:28 ` Reshetova, Elena
2019-05-28 13:33 ` Theodore Ts'o
2019-05-29 10:13 ` Reshetova, Elena
2019-05-29 10:51 ` David Laight
2019-05-29 18:35 ` Kees Cook
2019-05-29 18:37 ` Kees Cook
2019-07-29 11:41 ` Reshetova, Elena
2019-07-30 18:07 ` Kees Cook
2019-08-01 6:35 ` Reshetova, Elena
2019-05-09 7:03 ` Reshetova, Elena
2019-05-06 7:32 ` Reshetova, Elena
2019-04-29 7:49 ` Reshetova, Elena
2019-04-26 17:37 ` Edgecombe, Rick P
2019-04-17 6:24 ` Ingo Molnar
2019-04-16 18:19 ` Reshetova, Elena
[not found] <20190408061358.21288-1-elena.reshetova@intel.com>
2019-04-08 12:49 ` Josh Poimboeuf
2019-04-08 13:30 ` Reshetova, Elena
2019-04-08 16:21 ` Kees Cook
2019-04-10 8:26 ` Ingo Molnar
2019-04-10 9:00 ` Reshetova, Elena
2019-04-10 10:17 ` Ingo Molnar
2019-04-10 10:24 ` Reshetova, Elena
2019-04-10 14:52 ` Andy Lutomirski
2019-04-12 5:36 ` Reshetova, Elena
2019-04-12 21:16 ` Andy Lutomirski
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