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. Right now, on x86, you are exactly right: Both seccomp and ptrace take the slow path as part of _TIF_WORK_SYSCALL_ENTRY, and seccomp is only called in syscall_trace_enter. By adding a requirement for the slow-path in the form of ptrace_event(), the difficulty for making seccomp fast-path friendly is increased. (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.) 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, just say so, and I'll post the v12 with the docs updated to indicate that, at present, seccomp filters requires the slow path. However, if you see a nice way to avoid the dependency, I'd love to know! Thanks! will -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
