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: fec56f5890d9 ("bpf: Introduce BPF trampoline")
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
kernel/bpf/verifier.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
bpf-next Commit 15d83c4d7cef ("bpf: Allow loading of a bpf
iter program") contains the following change:
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7101,6 +7101,10 @@ static int check_return_code(struct bpf_verifier_env *env)
return 0;
range = tnum_const(0);
break;
+ case BPF_PROG_TYPE_TRACING:
+ if (env->prog->expected_attach_type != BPF_TRACE_ITER)
+ return 0;
+ break;
default:
return 0;
}
If this patch is accepted, it will have a merge conflict when syncing the change
back to net-next/bpf-next, To resolve it, we can change to something like below:
case BPF_TRACE_RAW_TP:
case BPF_MODIFY_RETURN:
return 0;
case BPF_TRACE_ITER:
break;
default:
return -ENOTSUPP;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fa1d8245b925..2d80cce0a28a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7059,6 +7059,24 @@ 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;
}
--
2.24.1
