From: Christian Brauner <christian.brauner@ubuntu.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Gabriel Krisman Bertazi <krisman@collabora.com>,
luto@kernel.org, tglx@linutronix.de, keescook@chromium.org,
x86@kernel.org, linux-kernel@vger.kernel.org,
linux-api@vger.kernel.org, willy@infradead.org,
linux-kselftest@vger.kernel.org, shuah@kernel.org,
kernel@collabora.com
Subject: Re: [PATCH v6 6/9] kernel: entry: Support Syscall User Dispatch for common syscall entry
Date: Mon, 7 Sep 2020 16:25:10 +0200 [thread overview]
Message-ID: <20200907142510.klojh2urwyui23ox@wittgenstein> (raw)
In-Reply-To: <0639209E-B6C6-4F86-84F4-04B91E1CC8AA@amacapital.net>
On Mon, Sep 07, 2020 at 07:15:52AM -0700, Andy Lutomirski wrote:
>
>
> > On Sep 7, 2020, at 3:15 AM, Christian Brauner <christian.brauner@ubuntu.com> wrote:
> >
> > On Fri, Sep 04, 2020 at 04:31:44PM -0400, Gabriel Krisman Bertazi wrote:
> >> Syscall User Dispatch (SUD) must take precedence over seccomp, since the
> >> use case is emulation (it can be invoked with a different ABI) such that
> >> seccomp filtering by syscall number doesn't make sense in the first
> >> place. In addition, either the syscall is dispatched back to userspace,
> >> in which case there is no resource for seccomp to protect, or the
> >
> > Tbh, I'm torn here. I'm not a super clever attacker but it feels to me
> > that this is still at least a clever way to circumvent a seccomp
> > sandbox.
> > If I'd be confined by a seccomp profile that would cause me to be
> > SIGKILLed when I try do open() I could prctl() myself to do user
> > dispatch to prevent that from happening, no?
> >
>
> Not really, I think. The idea is that you didn’t actually do open().
> You did a SYSCALL instruction which meant something else, and the
> syscall dispatch correctly prevented the kernel from misinterpreting
> it as open().
Right, for the case where you're e.g. emulating windows syscalls that's
true. I was thinking when you're running natively on Linux: couldn't I
first load a seccomp profile "kill me if someone does an open()", then
I exec() the target binary and that binary is setup to do
prctl(USER_DISPATCH) first thing. I guess, it's ok because as far as I
had time to read it this is a nothing or all mechanism, i.e. _all_
system calls are re-routed in contrast to e.g. seccomp where I could do
this per-syscall. So for user-dispatch it wouldn't make sense to use it
on Linux per se. Still makes me a little uneasy. :)
Christian
next prev parent reply other threads:[~2020-09-07 16:31 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 20:31 [PATCH v6 0/9] Syscall User Dispatch Gabriel Krisman Bertazi
2020-09-04 20:31 ` [PATCH v6 1/9] kernel: Support TIF_SYSCALL_INTERCEPT flag Gabriel Krisman Bertazi
2020-09-07 10:16 ` Christian Brauner
2020-09-08 4:59 ` Gabriel Krisman Bertazi
2020-09-22 19:42 ` Kees Cook
2020-09-23 20:28 ` Gabriel Krisman Bertazi
2020-09-11 9:32 ` peterz
2020-09-11 20:08 ` Gabriel Krisman Bertazi
2020-09-24 11:24 ` Peter Zijlstra
2020-09-22 19:44 ` Kees Cook
2020-09-23 20:18 ` Gabriel Krisman Bertazi
2020-09-23 20:49 ` Kees Cook
2020-09-25 8:00 ` Thomas Gleixner
2020-09-25 16:15 ` Gabriel Krisman Bertazi
2020-09-25 20:30 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 2/9] kernel: entry: Support TIF_SYSCAL_INTERCEPT on common entry code Gabriel Krisman Bertazi
2020-09-07 10:16 ` Christian Brauner
2020-09-11 9:35 ` peterz
2020-09-11 20:11 ` Gabriel Krisman Bertazi
2020-09-04 20:31 ` [PATCH v6 3/9] x86: vdso: Expose sigreturn address on vdso to the kernel Gabriel Krisman Bertazi
2020-09-22 19:40 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 4/9] signal: Expose SYS_USER_DISPATCH si_code type Gabriel Krisman Bertazi
2020-09-07 10:15 ` Christian Brauner
2020-09-22 19:39 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 5/9] kernel: Implement selective syscall userspace redirection Gabriel Krisman Bertazi
2020-09-05 11:24 ` Matthew Wilcox
2020-09-11 9:44 ` peterz
2020-09-04 20:31 ` [PATCH v6 6/9] kernel: entry: Support Syscall User Dispatch for common syscall entry Gabriel Krisman Bertazi
2020-09-07 10:15 ` Christian Brauner
2020-09-07 14:15 ` Andy Lutomirski
2020-09-07 14:25 ` Christian Brauner [this message]
2020-09-07 20:20 ` Andy Lutomirski
2020-09-11 9:46 ` peterz
2020-09-04 20:31 ` [PATCH v6 7/9] x86: Enable Syscall User Dispatch Gabriel Krisman Bertazi
2020-09-22 19:37 ` Kees Cook
2020-09-23 20:23 ` Gabriel Krisman Bertazi
2020-09-04 20:31 ` [PATCH v6 8/9] selftests: Add kselftest for syscall user dispatch Gabriel Krisman Bertazi
2020-09-22 19:35 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 9/9] doc: Document Syscall User Dispatch Gabriel Krisman Bertazi
2020-09-22 19:35 ` Kees Cook
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