On 02/29, Will Drewry wrote: > On Wed, Feb 29, 2012 at 10:14 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > On 02/28, Will Drewry wrote: > >> > >> On Tue, Feb 28, 2012 at 11:04 AM, Will Drewry <wad@xxxxxxxxxxxx> wrote: > >> > On Tue, Feb 28, 2012 at 10:43 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > >> >> > >> >> 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? > > Early on in this patch series, I was urged away from regviews (for > many reasons), one of them was so that seccomp could, at some point, > be fast-path'd like audit is for x86. (It may be on arm already, I'd > need to check.) So I was hoping that I could avoid adding a slow-path > dependency to the seccomp code. Thanks, now I see what you meant. > By adding a requirement for the > slow-path in the form of ptrace_event(), the difficulty for making > seccomp fast-path friendly is increased. Yes. I do not know if this is really bad. I mean, I do not know how much do we want the fast-path'd seccomp. > (It could be possible to add > a return code, e.g., return NEEDS_SLOW_PATH, which tells the fast path > code to restart the handling at syscall_trace_enter, so maybe I am > making a big deal out of nothing.) Probably. Or SECCOMP_RET_TRACE can set TIF_NOTIFY_RESUME. (Btw there is another alternative although imho PTRACE_EVENT_SECCOMP looks better. SECCOMP_RET_TRACE can simply set TIF_SYSCALL_TRACE and return, syscall_trace_enter() will report the syscall. If we make it fast-path'ed, then TIF_NOTIFY_RESUME should trigger the slow path) > I was hoping to avoid having TIF_SECCOMP imply the slow-path, but if > that is the only sane way to integrate, then I can leave making it > fast-path friendly as a future exercise. > > If I'm over-optimizing, may be ;) but it is very possible I underestimate the problem. I'd like to know what Roland thinks. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
