Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault

[Masami Hiramatsu]

On Mon, 25 Feb 2019 11:40:18 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Mon, 25 Feb 2019 17:09:45 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> 
> > > This should probably go with whatever effort makes nmi_uaccess_ok()
> > > available on all architectures.  That being said, how about just
> > > making copy_from_user_nmi() work on all architectures, even if it just
> > > fails unconditionally on some of them?  
> > 
> > I think even if we have copy_from_user_nmi(), we need something like
> > nmi_uaccess_ok() because without it we can not correctly use
> > __copy_from_user_inatomic()...
> 
> But wouldn't that just be part of the implementation of
> "copy_from_user_nmi()" as being in an NMI just assumes being inatomic?

Yes for copy_from_user_nmi(). But there are some other fundamental
functions, like __get_user(). And when we optimize the loop in
strncpy/strnlen from user in atomic, I think one nmi_access_ok() at
entry is enough.

Thank you,

-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>