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Date: Thu, 28 Jan 2016 18:33:01 -0800
From: Andy Lutomirski <>
To: Kees Cook <>
Cc: "" <>,, 
	Oleg Nesterov <>, Will Drewry <>, 
	"" <>, Linux API <>, 
	LSM List <>, 
	"" <>
Subject: Re: [RFC][PATCH] seccomp: add SECCOMP_RET_ACK for non-fatal SIGSYS

On Thu, Jan 28, 2016 at 5:06 PM, Kees Cook <> 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 <>

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


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