> On Feb 22, 2019, at 10:28 AM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > >> On Fri, Feb 22, 2019 at 9:48 AM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> >>> On Feb 22, 2019, at 9:43 AM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> 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. > > Hmm. I misunderstood you. I thought you wanted the oops. We’d have to check that we don’t trip the “SMAP violation, egads!” check.
