On Mon, Dec 04, 2023 at 07:16:14PM +0100, Peter Zijlstra wrote: > On Mon, Dec 04, 2023 at 06:25:34PM +0100, Jiri Olsa wrote: > > > that boots properly for me but gives crash below when running bpf tests > > OK, more funnies.. > > > [ 482.145182][ T699] RIP: 0010:bpf_for_each_array_elem+0xbb/0x120 > > [ 482.145672][ T699] Code: 4c 01 f5 89 5c 24 04 4c 89 e7 48 8d 74 24 04 48 89 ea 4c 89 fd 4c 89 f9 45 31 c0 4d 89 eb 41 ba ef 86 cd 67 45 03 53 f1 74 02 <0f> 0b 41 ff d3 0f 1f 00 48 85 c0 75 0e 48 8d 43 01 41 8b 4c 24 24 > > [ 482.147221][ T699] RSP: 0018:ffffc900017e3e88 EFLAGS: 00010217 > > [ 482.147702][ T699] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc900017e3ed8 > > [ 482.152162][ T699] RDX: ffff888152eb0210 RSI: ffffc900017e3e8c RDI: ffff888152eb0000 > > [ 482.152770][ T699] RBP: ffffc900017e3ed8 R08: 0000000000000000 R09: 0000000000000000 > > [ 482.153350][ T699] R10: 000000004704ef28 R11: ffffffffa0012774 R12: ffff888152eb0000 > > [ 482.153951][ T699] R13: ffffffffa0012774 R14: ffff888152eb0210 R15: ffffc900017e3ed8 > > [ 482.154554][ T699] FS: 00007fa60d4fdd00(0000) GS:ffff88846d200000(0000) knlGS:0000000000000000 > > [ 482.155138][ T699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 482.155564][ T699] CR2: 00007fa60d7d8000 CR3: 00000001502a2005 CR4: 0000000000770ef0 > > [ 482.156095][ T699] PKRU: 55555554 > > [ 482.156349][ T699] Call Trace: > > [ 482.156596][ T699] <TASK> > > [ 482.156816][ T699] ? __die_body+0x68/0xb0 > > [ 482.157138][ T699] ? die+0xba/0xe0 > > [ 482.157456][ T699] ? do_trap+0xa5/0x180 > > [ 482.157826][ T699] ? bpf_for_each_array_elem+0xbb/0x120 > > [ 482.158277][ T699] ? bpf_for_each_array_elem+0xbb/0x120 > > [ 482.158711][ T699] ? do_error_trap+0xc4/0x140 > > [ 482.159052][ T699] ? bpf_for_each_array_elem+0xbb/0x120 > > [ 482.159506][ T699] ? handle_invalid_op+0x2c/0x40 > > [ 482.159906][ T699] ? bpf_for_each_array_elem+0xbb/0x120 > > [ 482.160990][ T699] ? exc_invalid_op+0x38/0x60 > > [ 482.161375][ T699] ? asm_exc_invalid_op+0x1a/0x20 > > [ 482.161788][ T699] ? 0xffffffffa0012774 > > [ 482.162149][ T699] ? 0xffffffffa0012774 > > [ 482.162513][ T699] ? bpf_for_each_array_elem+0xbb/0x120 > > [ 482.162905][ T699] bpf_prog_ca45ea7f9cb8ac1a_inner_map+0x94/0x98 > > [ 482.163471][ T699] bpf_trampoline_6442549234+0x47/0x1000 > > Looks like this trips an #UD, I'll go try and figure out what this > bpf_for_each_array_elem() does to cause this. Looks like it has an > indirect call, could be the callback_fn thing has a CFI mis-match. So afaict this is used through bpf_for_each_map_elem(), where the argument still is properly callback_fn. However, in the desriptor bpf_for_each_map_elem_proto the argument gets described as: ARG_PTR_TO_FUNC, which in turn has a comment like: ARG_PTR_TO_FUNC, /* pointer to a bpf program function */ Which to me sounds like there is definite type punning involved. The call in bpf_for_each_array_elem() is a regular C indirect call, which gets adorned with the kCFI magic. But I doubt the BPF function that gets used gets the correct matching bits on. TL;DR, I think this is a pre-existing problem with kCFI + eBPF and not caused by my patches. Could any of you bpf knowledgeable folks please explain me exactly what gets used as the function pointer in this case? -- I'm not sure I can follow along well enough to begin looking for a solution at this point :/
