From: Kees Cook <email@example.com> To: Andy Lutomirski <firstname.lastname@example.org> Cc: Elena Reshetova <email@example.com>, Josh Poimboeuf <firstname.lastname@example.org>, Kernel Hardening <email@example.com>, Andy Lutomirski <firstname.lastname@example.org>, Thomas Gleixner <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, Borislav Petkov <email@example.com>, Peter Zijlstra <firstname.lastname@example.org> Subject: Re: [RFC PATCH] x86/entry/64: randomize kernel stack offset upon system call Date: Wed, 20 Feb 2019 14:03:13 -0800 [thread overview] Message-ID: <CAGXu5jL1Bx6_JfS9ei7dZA=9Hk4wBBQXRLtYPpqOAhRUoYDbuQ@mail.gmail.com> (raw) In-Reply-To: <1D62D311-DD73-43BD-9ED1-8B9450842B89@amacapital.net> On Fri, Feb 8, 2019 at 8:34 AM Andy Lutomirski <email@example.com> wrote: > > On Feb 8, 2019, at 4:15 AM, Elena Reshetova <firstname.lastname@example.org> wrote: > > This feature should make considerably harder various > > stack-based attacks that are based upon overflowing > > a kernel stack into adjusted kernel stack with a > > possibility to jump over a guard page. > > Since the stack offset is randomized upon each > > system call, it is very hard for attacker to reliably > > land in any particular place on the adjusted stack. > > > > I think we need a better justification. With VLAs gone, it should be statically impossible to overflow past a guard page. I do agree, that the stack is a much more well-defended area right now, and that the urgency for this feature is lower, but if it's easy to implement, I think we should do it. With VLAs universally gone, we can't get unbounded allocations that lead to both linear overflows and indexed overflows. But this doesn't mean a counter or index can't still go crazy -- it just means the expected stack layout will no longer be attached to it. With VMAP_STACK we stop linear overflows of the stack since we'll hit a guard page. However, this does not stop indexed overflows where we can jump the guard page. It is harder to control an indexed overflow vs a linear overflow, but it's still possible. Adding more variability to this, I think, has value in making attacks less reliable. Also, I'd note that while this is currently an x86-only implementation, it's not hard to extend to other architectures that don't already have VMAP_STACK. (And while it is the default, not all x86 builds have CONFIG_VMAP_STACK=y, though why you'd turn that off and turn this on, I'm not sure.) -- Kees Cook
next prev parent reply other threads:[~2019-02-20 22:03 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-02-08 12:15 [RFC PATCH] Early version of thread stack randomization Elena Reshetova 2019-02-08 12:15 ` [RFC PATCH] x86/entry/64: randomize kernel stack offset upon system call Elena Reshetova 2019-02-08 13:05 ` Peter Zijlstra 2019-02-08 13:20 ` Reshetova, Elena 2019-02-08 14:26 ` Peter Zijlstra 2019-02-09 11:13 ` Reshetova, Elena 2019-02-09 18:25 ` Andy Lutomirski 2019-02-11 6:39 ` Reshetova, Elena 2019-02-11 15:54 ` Andy Lutomirski 2019-02-12 10:16 ` Perla, Enrico 2019-02-14 7:52 ` Reshetova, Elena 2019-02-19 14:47 ` Jann Horn 2019-02-20 22:20 ` Kees Cook 2019-02-21 6:37 ` Andy Lutomirski 2019-02-21 13:20 ` Jann Horn 2019-02-21 15:49 ` Andy Lutomirski 2019-02-20 22:15 ` Kees Cook 2019-02-20 22:53 ` Kees Cook 2019-02-21 23:29 ` Kees Cook 2019-02-27 11:03 ` Reshetova, Elena 2019-02-21 9:35 ` Perla, Enrico 2019-02-21 17:23 ` Kees Cook 2019-02-21 17:48 ` Perla, Enrico 2019-02-21 19:18 ` Kees Cook 2019-02-20 21:51 ` Kees Cook 2019-02-08 15:15 ` Peter Zijlstra 2019-02-09 11:38 ` Reshetova, Elena 2019-02-09 12:09 ` Greg KH 2019-02-11 6:05 ` Reshetova, Elena 2019-02-08 16:34 ` Andy Lutomirski 2019-02-20 22:03 ` Kees Cook [this message] 2019-02-08 21:28 ` Kees Cook 2019-02-11 12:47 ` Reshetova, Elena 2019-02-20 22:04 ` Kees Cook
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