On 8/21/23 12:33 PM, Dave Marchevsky wrote:
Confirm that the following sleepable prog states fail verification:
* bpf_rcu_read_unlock before bpf_spin_unlock
* RCU CS will last at least as long as spin_lock CS
I think the reason is bpf_spin_lock() does not allow any functions
in spin lock region except some graph api kfunc's.
Also confirm that correct usage passes verification, specifically:
* Explicit use of bpf_rcu_read_{lock, unlock} in sleepable test prog
* Implied RCU CS due to spin_lock CS
None of the selftest progs actually attach to bpf_testmod's
bpf_testmod_test_read.
Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
---
.../selftests/bpf/progs/refcounted_kptr.c | 71 +++++++++++++++++++
.../bpf/progs/refcounted_kptr_fail.c | 28 ++++++++
2 files changed, 99 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
index c55652fdc63a..893a4fdb4b6e 100644
[...]
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
index 0b09e5c915b1..1ef07f6ee580 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 +74,29 @@ long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)
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";
