linux-kernel - Re: [RFC][PATCH] seccomp: add SECCOMP_RET

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Message-ID: <CALCETrVpa1zxVXOJoYKZ0zLCdH07dBKbw0Yo-BSJRH0eP_RBvQ@mail.gmail.com>
Date:	Thu, 28 Jan 2016 18:33:01 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Kees Cook <keescook@...omium.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	jeffv@...gle.com, Oleg Nesterov <oleg@...hat.com>,
	Will Drewry <wad@...omium.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC][PATCH] seccomp: add SECCOMP_RET_ACK for non-fatal SIGSYS

On Thu, Jan 28, 2016 at 5:06 PM, Kees Cook <keescook@...omium.org> wrote:
> Tracing processes for syscall usage can be done one step at a time with
> SECCOMP_RET_TRAP, but this will block the syscall. Alternatively, using
> a ptrace manager to handle SECCOMP_RET_TRACE returns can be used but is
> heavy weight and depends on the ptrace infrastructure. A light-weight
> method to learn syscalls is needed, which can reuse the existing delivery
> of SIGSYS but without skipping the syscall. This is implemented as
> SECCOMP_RET_ACK which is as permissive as SECCOMP_RET_ALLOW but delivers
> SIGSYS after syscall completion, as long as the SECCOMP_RET_DATA is
> non-zero. A signal handler can install a new rule for each syscall as
> they are signaled with SECCOMP_RET_DATA set to 0 to disable reporting
> for that syscall in the future (which is required for restarting syscalls
> that are signal-sensitive like nanosleep).
>
> Registers from the signal will reflect registers after the syscall returns
> rather than before. Signal-sensitive syscalls will trigger EINTR, so they
> must be whitelisted before they are resumed. Not allowing the sigreturn
> syscall (and likely prctl to whitelist) will make using SECCOMP_RET_ACK
> useless.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Could this use task_work to queue the signal on return to user mode
instead?  Would that solve the EINTR issues?

--Andy