Commit e92888c7 authored May 13, 2020 by Yonghong Song Committed by Alexei Starovoitov May 14, 2020

bpf: Enforce returning 0 for fentry/fexit progs



Currently, tracing/fentry and tracing/fexit prog
return values are not enforced. In trampoline codes,
the fentry/fexit prog return values are ignored.
Let us enforce it to be 0 to avoid confusion and
allows potential future extension.

This patch also explicitly added return value
checking for tracing/raw_tp, tracing/fmod_ret,
and freplace programs such that these program
return values can be anything. The purpose are
two folds:
 1. to make it explicit about return value expectations
    for these programs in verifier.
 2. for tracing prog_type, if a future attach type
    is added, the default is -ENOTSUPP which will
    enforce to specify return value ranges explicitly.

Fixes: fec56f58 ("bpf: Introduce BPF trampoline")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200514053206.1298415-1-yhs@fb.com

parent 625236ba

kernel/bpf/verifier.c

+17 −0

Original line number	Diff line number	Diff line
		@@ -7059,6 +7059,23 @@ static int check_return_code(struct bpf_verifier_env *env)
		return 0;
		range = tnum_const(0);
		break;
		case BPF_PROG_TYPE_TRACING:
		switch (env->prog->expected_attach_type) {
		case BPF_TRACE_FENTRY:
		case BPF_TRACE_FEXIT:
		range = tnum_const(0);
		break;
		case BPF_TRACE_RAW_TP:
		case BPF_MODIFY_RETURN:
		return 0;
		default:
		return -ENOTSUPP;
		}
		break;
		case BPF_PROG_TYPE_EXT:
		/* freplace program can return anything as its return value
		* depends on the to-be-replaced kernel func or bpf program.
		*/
		default:
		return 0;
		}

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