Re: [PATCH v3 bpf-next 14/18] bpf: Compare BTF types of functions arguments with actual types
From: Alexei Starovoitov <hidden>
Date: 2019-11-08 17:57:33
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bpf
On 11/8/19 9:32 AM, Song Liu wrote:
quoted
On Nov 8, 2019, at 9:28 AM, Song Liu [off-list ref] wrote:quoted
On Nov 7, 2019, at 10:40 PM, Alexei Starovoitov [off-list ref] wrote: Make the verifier check that BTF types of function arguments match actual types passed into top-level BPF program and into BPF-to-BPF calls. If types match such BPF programs and sub-programs will have full support of BPF trampoline. If types mismatch the trampoline has to be conservative. It has to save/restore all 5 program arguments and assume 64-bit scalars. If FENTRY/FEXIT program is attached to this program in the future such FENTRY/FEXIT program will be able to follow pointers only via bpf_probe_read_kernel(). Signed-off-by: Alexei Starovoitov <ast@kernel.org>Acked-by: Song Liu <redacted>One nit though: maybe use "reliable" instead of "unreliable" +struct bpf_func_info_aux { + bool reliable; +}; + + bool func_proto_reliable; So the default value 0, is not reliable.
I don't see how this can work. Once particular func proto was found unreliable the verifier won't keep checking. If we start with 'bool reliable = false' how do you see the whole mechanism working ? Say the first time the verifier analyzed the subroutine and everything matches. Can it do reliable = true ? No. It has to check all other callsites. Then it would need another variable and extra pass ?