[PATCH v1 bpf-next 7/7] selftests/bpf: Add tests for rbtree API interaction in sleepable progs

Dave Marchevsky
2023-08-01T20:36:54Z

Confirm that the following sleepable prog states fail verification:
* bpf_rcu_read_unlock before bpf_spin_unlock
* Breaks "spin_{lock,unlock} only allowed in RCU CS". Even if
bpf_rcu_read_lock is called again before bpf_spin_unlock this
should fail.
* bpf_spin_lock outside RCU critical section

Also confirm that correct usage passes verification.

None of the selftest progs actually attach to bpf_testmod's
bpf_testmod_test_read.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
---
.../selftests/bpf/progs/refcounted_kptr.c | 37 ++++++++++++++
.../bpf/progs/refcounted_kptr_fail.c | 48 +++++++++++++++++++
2 files changed, 85 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
index c55652fdc63a..f7ab2711fea8 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
@@ -8,6 +8,9 @@
#include "bpf_misc.h"
#include "bpf_experimental.h"

+extern void bpf_rcu_read_lock(void) __ksym;
+extern void bpf_rcu_read_unlock(void) __ksym;
+
struct node_data {
long key;
long list_data;
@@ -497,4 +500,38 @@ long rbtree_wrong_owner_remove_fail_a2(void *ctx)
return 0;
}

+SEC("?fentry.s/bpf_testmod_test_read")
+__success
+int BPF_PROG(rbtree_sleepable_rcu,
+ struct file *file, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+ struct bpf_rb_node *rb;
+ struct node_data *n, *m = NULL;
+
+ n = bpf_obj_new(typeof(*n));
+ if (!n)
+ return 0;
+
+ bpf_rcu_read_lock();
+ bpf_spin_lock(&lock);
+ bpf_rbtree_add(&root, &n->r, less);
+ rb = bpf_rbtree_first(&root);
+ if (!rb)
+ goto err_out;
+
+ rb = bpf_rbtree_remove(&root, rb);
+ if (!rb)
+ goto err_out;
+
+ m = container_of(rb, struct node_data, r);
+
+err_out:
+ bpf_spin_unlock(&lock);
+ bpf_rcu_read_unlock();
+ if (m)
+ bpf_obj_drop(m);
+ return 0;
+}
+
char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
index 0b09e5c915b1..0a75d914e0f9 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
@@ -13,6 +13,9 @@ struct node_acquire {
struct bpf_refcount refcount;
};

+extern void bpf_rcu_read_lock(void) __ksym;
+extern void bpf_rcu_read_unlock(void) __ksym;
+
#define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
private(A) struct bpf_spin_lock glock;
private(A) struct bpf_rb_root groot __contains(node_acquire, node);
@@ -71,4 +74,49 @@ long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)
return 0;
}

+SEC("?fentry.s/bpf_testmod_test_read")
+__failure __msg("sleepable progs may only spin_{lock,unlock} in RCU CS")
+int BPF_PROG(rbtree_fail_sleepable_lock_no_rcu,
+ struct file *file, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+ struct node_acquire *n;
+
+ n = bpf_obj_new(typeof(*n));
+ if (!n)
+ return 0;
+
+ /* no bpf_rcu_read_{lock,unlock} */
+ bpf_spin_lock(&glock);
+ bpf_rbtree_add(&groot, &n->node, less);
+ bpf_spin_unlock(&glock);
+
+ return 0;
+}
+
+SEC("?fentry.s/bpf_testmod_test_read")
+__failure __msg("function calls are not allowed while holding a lock")
+int BPF_PROG(rbtree_fail_sleepable_lock_across_rcu,
+ struct file *file, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+ struct node_acquire *n;
+
+ n = bpf_obj_new(typeof(*n));
+ if (!n)
+ return 0;
+
+ /* spin_{lock,unlock} are in different RCU CS */
+ bpf_rcu_read_lock();
+ bpf_spin_lock(&glock);
+ bpf_rbtree_add(&groot, &n->node, less);
+ bpf_rcu_read_unlock();
+
+ bpf_rcu_read_lock();
+ bpf_spin_unlock(&glock);
+ bpf_rcu_read_unlock();
+
+ return 0;
+}
+
char _license[] SEC("license") = "GPL";
--
2.34.1