[PATCH bpf v1 1/2] bpf: Fix exception exit lock checking for subprogs

[Ihor Solodrai <ihor.solodrai@linux.dev>]

process_bpf_exit_full() passes check_lock = !curframe to
check_resource_leak(), which is false in cases when bpf_throw() is
called from a static subprog. This makes check_resource_leak() to skip
validation of active_rcu_locks, active_preempt_locks, and
active_irq_id on exception exits from subprogs.

At runtime bpf_throw() unwinds the stack via ORC without releasing any
user-acquired locks, which may cause various issues as the result.

Fix by setting check_lock = true for exception exits regardless of
curframe, since exceptions bypass all intermediate frame
cleanup. Update the error message prefix to "bpf_throw" for exception
exits to distinguish them from normal BPF_EXIT. Update relevant
existing selftests to match the new message.

The spin_lock case is not affected because they are already checked [1]
at the call site in do_check_insn() before bpf_throw can run.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/bpf/verifier.c?h=v7.0-rc4#n21098

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>

---

This bug was discovered by an AI bot. You can find the original
AI-generated investigation here:
https://github.com/theihor/bpf/commits/ai-tinkering-20260310-0745/

---
 kernel/bpf/verifier.c                               | 3 ++-
 tools/testing/selftests/bpf/progs/exceptions_fail.c | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index df22bfc572e2..5c0e6809024f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20911,7 +20911,8 @@ static int process_bpf_exit_full(struct bpf_verifier_env *env,
 	 * state when it exits.
 	 */
 	int err = check_resource_leak(env, exception_exit,
-				      !env->cur_state->curframe,
+				      exception_exit || !env->cur_state->curframe,
+				      exception_exit ? "bpf_throw" :
 				      "BPF_EXIT instruction in main prog");
 	if (err)
 		return err;
diff --git a/tools/testing/selftests/bpf/progs/exceptions_fail.c b/tools/testing/selftests/bpf/progs/exceptions_fail.c
index 8a0fdff89927..1dd2703c7676 100644
--- a/tools/testing/selftests/bpf/progs/exceptions_fail.c
+++ b/tools/testing/selftests/bpf/progs/exceptions_fail.c
@@ -131,7 +131,7 @@ int reject_subprog_with_lock(void *ctx)
 }
 
 SEC("?tc")
-__failure __msg("BPF_EXIT instruction in main prog cannot be used inside bpf_rcu_read_lock-ed region")
+__failure __msg("bpf_throw cannot be used inside bpf_rcu_read_lock-ed region")
 int reject_with_rcu_read_lock(void *ctx)
 {
 	bpf_rcu_read_lock();
@@ -147,7 +147,7 @@ __noinline static int throwing_subprog(struct __sk_buff *ctx)
 }
 
 SEC("?tc")
-__failure __msg("BPF_EXIT instruction in main prog cannot be used inside bpf_rcu_read_lock-ed region")
+__failure __msg("bpf_throw cannot be used inside bpf_rcu_read_lock-ed region")
 int reject_subprog_with_rcu_read_lock(void *ctx)
 {
 	bpf_rcu_read_lock();
-- 
2.53.0