The second argument of the bpf_kptr_xchg() helper function is ARG_PTR_TO_BTF_ID_OR_NULL. A recent patch fixed a bug whereby the verifier would fail with an internal error message if a program invoked the helper with a PTR_TO_BTF_ID | PTR_MAYBE_NULL register. This testcase adds some testcases to ensure that it fails gracefully moving forward. Before the fix, these testcases would have failed an error resembling the following: ; p = bpf_kfunc_call_test_acquire(&(unsigned long){0}); 99: (7b) *(u64 *)(r10 -16) = r7 ; frame1: ... 100: (bf) r1 = r10 ; frame1: ... 101: (07) r1 += -16 ; frame1: ... ; p = bpf_kfunc_call_test_acquire(&(unsigned long){0}); 102: (85) call bpf_kfunc_call_test_acquire#13908 ; frame1: R0_w=ptr_or_null_prog_test_ref_kfunc... ; p = bpf_kptr_xchg(&v->ref_ptr, p); 103: (bf) r1 = r6 ; frame1: ... 104: (bf) r2 = r0 ; frame1: R0_w=ptr_or_null_prog_test_ref_kfunc... 105: (85) call bpf_kptr_xchg#194 verifier internal error: invalid PTR_TO_BTF_ID register for type match Signed-off-by: David Vernet <void@xxxxxxxxxxxxx> --- .../selftests/bpf/progs/cpumask_failure.c | 25 +++++++++++++++++++ .../selftests/bpf/progs/map_kptr_fail.c | 23 +++++++++++++++++ 2 files changed, 48 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/cpumask_failure.c b/tools/testing/selftests/bpf/progs/cpumask_failure.c index db4f94e72b61..a9bf6ea336cf 100644 --- a/tools/testing/selftests/bpf/progs/cpumask_failure.c +++ b/tools/testing/selftests/bpf/progs/cpumask_failure.c @@ -165,3 +165,28 @@ int BPF_PROG(test_global_mask_no_null_check, struct task_struct *task, u64 clone return 0; } + +SEC("tp_btf/task_newtask") +__failure __msg("Possibly NULL pointer passed to helper arg2") +int BPF_PROG(test_global_mask_rcu_no_null_check, struct task_struct *task, u64 clone_flags) +{ + struct bpf_cpumask *prev, *curr; + + curr = bpf_cpumask_create(); + if (!curr) + return 0; + + prev = bpf_kptr_xchg(&global_mask, curr); + if (prev) + bpf_cpumask_release(prev); + + bpf_rcu_read_lock(); + curr = global_mask; + /* PTR_TO_BTF_ID | PTR_MAYBE_NULL | MEM_RCU passed to bpf_kptr_xchg() */ + prev = bpf_kptr_xchg(&global_mask, curr); + bpf_rcu_read_unlock(); + if (prev) + bpf_cpumask_release(prev); + + return 0; +} diff --git a/tools/testing/selftests/bpf/progs/map_kptr_fail.c b/tools/testing/selftests/bpf/progs/map_kptr_fail.c index 08f9ec18c345..15bf3127dba3 100644 --- a/tools/testing/selftests/bpf/progs/map_kptr_fail.c +++ b/tools/testing/selftests/bpf/progs/map_kptr_fail.c @@ -20,6 +20,7 @@ struct array_map { } array_map SEC(".maps"); extern struct prog_test_ref_kfunc *bpf_kfunc_call_test_acquire(unsigned long *sp) __ksym; +extern void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p) __ksym; extern struct prog_test_ref_kfunc * bpf_kfunc_call_test_kptr_get(struct prog_test_ref_kfunc **p, int a, int b) __ksym; @@ -442,4 +443,26 @@ int kptr_get_ref_state(struct __sk_buff *ctx) return 0; } +SEC("?tc") +__failure __msg("Possibly NULL pointer passed to helper arg2") +int kptr_xchg_possibly_null(struct __sk_buff *ctx) +{ + struct prog_test_ref_kfunc *p; + struct map_value *v; + int key = 0; + + v = bpf_map_lookup_elem(&array_map, &key); + if (!v) + return 0; + + p = bpf_kfunc_call_test_acquire(&(unsigned long){0}); + + /* PTR_TO_BTF_ID | PTR_MAYBE_NULL passed to bpf_kptr_xchg() */ + p = bpf_kptr_xchg(&v->ref_ptr, p); + if (p) + bpf_kfunc_call_test_release(p); + + return 0; +} + char _license[] SEC("license") = "GPL"; -- 2.39.0