Now that we have our kfunc lifecycle expectations clearly documented,
and that KF_DEPRECATED is documented as an optional method for kfunc
developers and maintainers to provide a deprecation story to BPF users,
we need to actually implement the flag.
This patch adds KF_DEPRECATED, and updates the verifier to issue a
verifier log message if a deprecated kfunc is called. Currently, a BPF
program either has to fail to verify, or be loaded with log level 2 in
order to see the message. We could eventually enhance this to always
be logged regardless of log level or verification status, or we could
instead emit a warning to dmesg. This seems like the least controversial
option for now.
A subsequent patch will add a selftest that verifies this behavior.
Signed-off-by: David Vernet <void@xxxxxxxxxxxxx>
---
include/linux/btf.h | 1 +
kernel/bpf/verifier.c | 8 ++++++++
2 files changed, 9 insertions(+)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 49e0fe6d8274..a0ea788ee9b0 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -71,6 +71,7 @@
#define KF_SLEEPABLE (1 << 5) /* kfunc may sleep */
#define KF_DESTRUCTIVE (1 << 6) /* kfunc performs destructive actions */
#define KF_RCU (1 << 7) /* kfunc only takes rcu pointer arguments */
+#define KF_DEPRECATED (1 << 8) /* kfunc is slated to be removed or deprecated */
/*
* Tag marking a kernel function as a kfunc. This is meant to minimize the
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4cc0e70ee71e..22adcf24f9e1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8511,6 +8511,11 @@ static bool is_kfunc_rcu(struct bpf_kfunc_call_arg_meta *meta)
return meta->kfunc_flags & KF_RCU;
}
+static bool is_kfunc_deprecated(const struct bpf_kfunc_call_arg_meta *meta)
+{
+ return meta->kfunc_flags & KF_DEPRECATED;
+}
+
static bool is_kfunc_arg_kptr_get(struct bpf_kfunc_call_arg_meta *meta, int arg)
{
return arg == 0 && (meta->kfunc_flags & KF_KPTR_GET);
@@ -9646,6 +9651,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
mark_btf_func_reg_size(env, regno, t->size);
}
+ if (is_kfunc_deprecated(&meta))
+ verbose(env, "calling deprecated kfunc %s\n", func_name);
+
return 0;
}
--
2.39.0
