Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 22 Feb 2019 10:28:49 -0800 | Subject | Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault |
| |
On Fri, Feb 22, 2019 at 9:48 AM Andy Lutomirski <luto@amacapital.net> wrote: > > > On Feb 22, 2019, at 9:43 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > > Then we should still probably fix up "__probe_kernel_read()" to not > > allow user accesses. The easiest way to do that is actually likely to > > use the "unsafe_get_user()" functions *without* doing a > > uaccess_begin(), which will mean that modern CPU's will simply fault > > on a kernel access to user space. > > > > The nice thing about that is that usually developers will have access > > to exactly those modern boxes, so the people who notice that it > > doesn't work are the right people. > > We use probe_kernel_read() from oops code. I’d rather it return -EFAULT than oops harder and kill the first oops.
It would still do that.
Using the unsafe_get_user() macros doesn't remove the exception handling, and we wouldn't remove the whole "pagefault_disable()" either. So it would work exactly the same way it does now, except on a modern CPU it would return -EFAULT for a user space access due to AC not being set.
So no "oops harder", only "safer accesses".
Linus
| |