Hi, Thomas - > Well, if you are not in thread context then the check is pointless: > __range_not_ok(addr, size, user_addr_max()) > and: > #define user_addr_max() (current->thread.addr_limit.seg) > > So what guarantees when you are not in context of current, i.e. in thread > context, that the addr/size which is checked against the limits of current > actually belongs to current?
We're probably in task context in that there is a valid current(), but running with preemption and/or interrupts and/or pagefaults disabled at that point, so in_task() objects. Think of it like from a kprobes handler callback, except maybe more temporary preemption blocking. > I assume this is about systemtap modules. Can you please explain > what you are trying to achieve? I guess you know that you actually > access current, but then we need a seperate special function and not > relaxing of the checks. This part is used in a part of the runtime that is a userspace analogue of probe_kernel_address(), where we're given a potential userspace address. We would like to quickly test whether it's even plausible as a userspace address, before doing a (pagefault-disabled) trial fetch/store to it. - FChE
