From: Kees Cook <email@example.com> To: "Reshetova, Elena" <firstname.lastname@example.org> Cc: "Perla, Enrico" <email@example.com>, Andy Lutomirski <firstname.lastname@example.org>, Jann Horn <email@example.com>, Andy Lutomirski <firstname.lastname@example.org>, Peter Zijlstra <email@example.com>, "firstname.lastname@example.org" <email@example.com>, "firstname.lastname@example.org" <email@example.com>, "firstname.lastname@example.org" <email@example.com>, "firstname.lastname@example.org" <email@example.com>, "firstname.lastname@example.org" <email@example.com> Subject: Re: [RFC PATCH] x86/entry/64: randomize kernel stack offset upon system call Date: Wed, 20 Feb 2019 14:20:17 -0800 [thread overview] Message-ID: <CAGXu5jLbR0Tk6XEdCg+27bsc4+SKGwzNsV12imwjHnLmmpV0mA@mail.gmail.com> (raw) In-Reply-To: <2236FBA76BA1254E88B949DDB74E612BA4BC57C1@IRSMSX102.ger.corp.intel.com> On Wed, Feb 13, 2019 at 11:52 PM Reshetova, Elena <firstname.lastname@example.org> wrote: > Now back to our proposed countermeasures given that attacker has found a way to do > a crafted overflow and overwrite: > > 1) pt_regs is not predictable, but can be discovered in ptrace-style scenario or cache-probing. > If discovered, then attack succeeds as of now. > 2) relative stack offset is not predictable and randomized, cannot be probed very easily via > cache or ptrace. So, this is an additional hurdle on the attacker's way since stack is non- > deterministic now. > 3) nothing changed for this type of attack, given that attacker's goal is not to overwrite CS > in adjusted pt_regs. If it is his goal, then it helps with that. > > > Now summary: > > It would seem to me that: > > - regs->cs |= 3 on exit is a thing worth doing anyway, just because it is cheap, as Andy said, and it > might make a positive difference in two out of three attack scenarios. Objections? I would agree, let's just do this. > - randomization of stack top is only worth doing in ptrace-blocked scenario. > Do we have such scenarios left that people care about? > Because if we do, then we know that there is a real attack vector that we close this way, otherwise not. > This is actually interesting, because we need to remember to take ptrace into our overall > kernel hardening threat model (smth that at least I haven't quite realized before) and evaluate every new > feature (especially randomization ones) being robust against ptrace probing. > > - randomization after pt_regs only would make a difference in attack scenario "c", for which > we don't yet have a proof of concept exploit or technique that would work (does not guarantee that > attackers don't have the exploits ready through :( ). > So, if we implement this, the "justification part" for the feature would be smth like "to make it > harder for future possible stack-based exploits that utilize overflows", if/when someone find a new > 'ala VLA' way of doing the controlled overflow. > How do people feel about it? Is it worth having? I can work on the POC for this in direction that Andy > outlined and can provide performance impact/etc., but it is good that we understand that we cannot > provide a better justification for this feature at the moment unless someone is ready to share some > new exploit technique with us. I think this make sense. I do think, however, the work should be done at syscall entry, though. Thoughts? -- Kees Cook
next prev parent reply other threads:[~2019-02-20 22:20 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 [this message] 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 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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