From: Amery Hung <ameryhung@gmail.com>
To: bpf@vger.kernel.org
Cc: alexei.starovoitov@gmail.com, andrii@kernel.org,
daniel@iogearbox.net, eddyz87@gmail.com, memxor@gmail.com,
ameryhung@gmail.com, kernel-team@meta.com
Subject: [PATCH bpf-next v2 22/23] selftests/bpf: Test nullable per-CPU kptr identity after exchange
Date: Fri, 11 Sep 2026 15:04:14 -0700 [thread overview]
Message-ID: <20260911220415.1396439-23-ameryhung@gmail.com> (raw)
In-Reply-To: <20260911220415.1396439-1-ameryhung@gmail.com>
Pass two unchecked bpf_percpu_obj_new() results to bpf_kptr_xchg()
inside an RCU critical section. The exchanges consume ownership and
leave nullable RCU-protected aliases.
Checking the first alias must not make the second non-NULL. Verify that
bpf_this_cpu_ptr() still rejects the unchecked second alias.
Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
.../selftests/bpf/progs/percpu_alloc_fail.c | 35 +++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c b/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c
index 3701f4ea58c7..57615b0f0c25 100644
--- a/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c
+++ b/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c
@@ -24,6 +24,7 @@ struct val_600b_t {
struct elem {
long sum;
struct val_t __percpu_kptr *pc;
+ struct val_t __percpu_kptr *pc2;
};
struct {
@@ -46,6 +47,8 @@ struct {
struct task_struct *bpf_task_from_pid(s32 pid) __ksym;
void bpf_task_release(struct task_struct *p) __ksym;
+void bpf_rcu_read_lock(void) __ksym;
+void bpf_rcu_read_unlock(void) __ksym;
long ret;
@@ -123,6 +126,38 @@ int BPF_PROG(test_array_map_3)
return 0;
}
+SEC("?fentry.s/bpf_fentry_test1")
+__failure __msg("Possibly NULL pointer passed to trusted R1")
+int BPF_PROG(reject_nullable_percpu_xchg_alias)
+{
+ struct val_t __percpu_kptr *p1, *p2, *old;
+ struct val_t *v;
+ struct elem *e;
+ int index = 0;
+
+ e = bpf_map_lookup_elem(&array, &index);
+ if (!e)
+ return 0;
+
+ p1 = bpf_percpu_obj_new(struct val_t);
+ p2 = bpf_percpu_obj_new(struct val_t);
+
+ bpf_rcu_read_lock();
+ old = bpf_kptr_xchg(&e->pc, p1);
+ if (old)
+ bpf_percpu_obj_drop(old);
+ old = bpf_kptr_xchg(&e->pc2, p2);
+ if (old)
+ bpf_percpu_obj_drop(old);
+
+ if (p1) {
+ v = bpf_this_cpu_ptr(p2);
+ v->b = 1;
+ }
+ bpf_rcu_read_unlock();
+ return 0;
+}
+
SEC("?fentry.s/bpf_fentry_test1")
__failure __msg("R1 expected for bpf_percpu_obj_drop()")
int BPF_PROG(test_array_map_4)
--
2.52.0
next prev parent reply other threads:[~2026-09-11 22:04 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-11 22:03 [PATCH bpf-next v2 00/23] Unify helper and kfunc argument checks Amery Hung
2026-09-11 22:03 ` [PATCH bpf-next v2 01/23] bpf: Pass call metadata through shared " Amery Hung
2026-09-11 22:03 ` [PATCH bpf-next v2 02/23] bpf: Address check_func_arg() arguments by argno Amery Hung
2026-09-11 22:03 ` [PATCH bpf-next v2 03/23] bpf: Only compare func_id against BPF_FUNC_* for helper calls Amery Hung
2026-09-11 22:03 ` [PATCH bpf-next v2 04/23] bpf: Only compare func_id against kfunc BTF IDs for kfunc calls Amery Hung
2026-09-11 22:03 ` [PATCH bpf-next v2 05/23] bpf: Clarify unused and scalar function argument types Amery Hung
2026-09-11 22:19 ` sashiko-bot
2026-09-11 22:03 ` [PATCH bpf-next v2 06/23] bpf: Unify kfunc argument kinds with enum bpf_arg_type Amery Hung
2026-09-11 22:26 ` sashiko-bot
2026-09-11 22:03 ` [PATCH bpf-next v2 07/23] bpf: Classify kfunc arguments the verifier ignores Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 08/23] bpf: Align helper and kfunc ARG_PTR_TO_PROG_AUX handling Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 09/23] bpf: Set OBJ_RELEASE when generating kfunc argument types Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 10/23] bpf: Set MEM_UNINIT and dynptr subtypes when generating kfunc arg types Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 11/23] bpf: Set MEM_RCU when generating kfunc argument types Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 12/23] bpf: Resolve BTF ID of ARG_PTR_TO_BTF_ID in kfunc bpf_func_proto Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 13/23] bpf: Resolve ARG_PTR_TO_MEM | MEM_FIXED_SIZE size " Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 14/23] bpf: Consolidate runtime argument type resolution Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 15/23] bpf: Consolidate nullable argument validation Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 16/23] bpf: Drop redundant BTF pointer helper write rejection Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 17/23] bpf: Consolidate helper and kfunc PTR_TO_BTF_ID argument matching Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 18/23] bpf: Admit kfunc argument registers through check_reg_type() Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 19/23] bpf: Consolidate function call pkt_access validation Amery Hung
2026-09-11 22:04 ` [PATCH bpf-next v2 20/23] selftests/bpf: Test kfunc packet memory direct writes Amery Hung
2026-09-11 22:36 ` sashiko-bot
2026-09-11 22:04 ` [PATCH bpf-next v2 21/23] bpf: Consolidate release argument validation Amery Hung
2026-09-11 22:04 ` Amery Hung [this message]
2026-09-11 22:04 ` [PATCH bpf-next v2 23/23] bpf: Check helper and kfunc arguments in one path Amery Hung
2026-09-12 3:20 ` [PATCH bpf-next v2 00/23] Unify helper and kfunc argument checks patchwork-bot+netdevbpf
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