On Fri, Feb 22, 2019 at 09:43:14AM -0800, Linus Torvalds 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. On bpf side the bpf_probe_read() helper just calls probe_kernel_read() and users pass both user and kernel addresses into it and expect that the helper will actually try to read from that address. If __probe_kernel_read will suddenly start failing on all user addresses it will break the expectations. How do we solve it in bpf_probe_read? Call probe_kernel_read and if that fails call unsafe_get_user byte-by-byte in the loop? That's doable, but people already complain that bpf_probe_read() is slow and shows up in their perf report.
