Re: [PATCH v11 10/12] ptrace,seccomp: Add PTRACE_SECCOMP support

On 02/28, Will Drewry wrote:

On Tue, Feb 28, 2012 at 11:04 AM, Will Drewry [off-list ref] wrote:

quoted

On Tue, Feb 28, 2012 at 10:43 AM, Oleg Nesterov [off-list ref] wrote:

quoted

Great. In this case this patch becomes really trivial. Just 2 defines
in ptrace.h and the unconditional ptrace_event() under SECCOMP_RET_TRACE.

hrm the only snag is that I can't then rely on TIF_SYSCALL_TRACE to
ensure seccomp is in the slow-path.  Right now, on x86, seccomp is
slow-path, but it doesn't have to be to have the syscall and args.
However, for ptrace to behavior properly, I believed it did need to be
in the slow path.  If SECCOMP_RET_TRACE doesn't rely on
PTRACE_SYSCALL, then it introduces a need for seccomp to always be in
the slow path or to flag (somehow) when it needs slow path.

My understanding of this magic is very limited, and I'm afraid
I misunderstood... So please correct me.

But what is the problem? system_call checks _TIF_WORK_SYSCALL_ENTRY
which includes _TIF_SECCOMP | _TIF_SYSCALL_TRACE, and jumps to
tracesys which does SAVE_REST.

Anyway. secure_computing() is called by syscall_trace_enter() which
also calls tracehook_report_syscall_entry(). If SECCOMP_RET_TRACE
can't do ptrace_event() then why tracehook_report_syscall_entry() is
fine?

Oleg.