On Fri, Feb 22, 2019 at 02:30:26PM -0500, Steven Rostedt wrote:
On Fri, 22 Feb 2019 11:27:05 -0800 Alexei Starovoitov alexei.starovoitov@gmail.com wrote:
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.
We're changing kprobes to add a specific flag to say that we want to differentiate between kernel or user reads. Can this be done with bpf_probe_read()? If it's showing up in perf report, I doubt a single
so you're saying you will break existing kprobe scripts? I don't think it's a good idea. It's not acceptable to break bpf_probe_read uapi.