Florian Weimer <fw@xxxxxxxxxxxxx> writes: > * Gabriel Krisman Bertazi: > >> +Interface >> +--------- >> + >> +A process can setup this mechanism on supported kernels >> +CONFIG_SYSCALL_USER_DISPATCH) by executing the following prctl: >> + >> + prctl(PR_SET_SYSCALL_USER_DISPATCH, <op>, <offset>, <length>, [selector]) >> + >> +<op> is either PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF, to enable and >> +disable the mechanism globally for that thread. When >> +PR_SYS_DISPATCH_OFF is used, the other fields must be zero. >> + >> +<offset> and <offset+length> delimit a closed memory region interval >> +from which syscalls are always executed directly, regardless of the >> +userspace selector. This provides a fast path for the C library, which >> +includes the most common syscall dispatchers in the native code >> +applications, and also provides a way for the signal handler to return >> +without triggering a nested SIGSYS on (rt_)sigreturn. Users of this >> +interface should make sure that at least the signal trampoline code is >> +included in this region. In addition, for syscalls that implement the >> +trampoline code on the vDSO, that trampoline is never intercepted. >> + >> +[selector] is a pointer to a char-sized region in the process memory >> +region, that provides a quick way to enable disable syscall redirection >> +thread-wide, without the need to invoke the kernel directly. selector >> +can be set to PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF. Any other >> +value should terminate the program with a SIGSYS. > > Is this a process property or a task/thread property? The last > paragraph says “thread-wide”, but the first paragraph says “process”. It is per-thread, as it doesn't survive across clone/fork syscalls. I will fix the first paragraph of this text. -- Gabriel Krisman Bertazi
