On 01/20, Kees Cook wrote:
The only difference is that sys_uretprobe() is new and existing setups doesn't know about it. Suppose you have
int func(void) { return 123; }
int main(void) { seccomp(SECCOMP_SET_MODE_STRICT, 0,0); for (;;) func(); }
and it runs with func() uretprobed.
If you install the new kernel, this application will crash immediately.
I understand your objections, but what do you think we can do instead? I don't think a new "try_to_speedup_uretprobes_at_your_own_risk" sysctl makes sense, it will be almost never enabled...
This seems like a uretprobes design problem. If it's going to use syscalls, it must take things like seccomp into account.
True. I reviewed that patch, and I forgot about seccomp too.
SECCOMP_SET_MODE_STRICT will also crash in the face of syscall_restart...
Yes, I guess SECCOMP_SET_MODE_STRICT assumes that read/write can't return ERESTART_RESTARTBLOCK.
But again, what can we do right now?
I do not like the idea to revert the patch which adds sys_uretprobe(). Don't get me wrong, I do not use uprobes, so personally I don't really care about the performance improvements it adds. Not to mention FRED, although I have no idea when it will be available.
Lets forget about sys_uretprobe(). Lets suppose the kernel doesn't have ERESTART_RESTARTBLOCK/sys_restart_syscall and we want to add this feature today.
How do you think we can do this without breaking the existing setups which use seccomp ?
Oleg.