selftests/bpf: Add tests for rbtree API interaction in sleepable progs

Confirm that the following sleepable prog states fail verification:
* bpf_rcu_read_unlock before bpf_spin_unlock
* RCU C

selftests/bpf: Add tests for rbtree API interaction in sleepable progs

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

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@fb.com>
Link: https://lore.kernel.org/r/20230821193311.3290257-8-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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bpf: Make bpf_refcount_acquire fallible for non-owning refs

This patch fixes an incorrect assumption made in the original
bpf_refcount series [0], specifically that the BPF program calling
bpf_refco

bpf: Make bpf_refcount_acquire fallible for non-owning refs

This patch fixes an incorrect assumption made in the original
bpf_refcount series [0], specifically that the BPF program calling
bpf_refcount_acquire on some node can always guarantee that the node is
alive. In that series, the patch adding failure behavior to rbtree_add
and list_push_{front, back} breaks this assumption for non-owning
references.

Consider the following program:

n = bpf_kptr_xchg(&mapval, NULL);
/* skip error checking */

bpf_spin_lock(&l);
if(bpf_rbtree_add(&t, &n->rb, less)) {
bpf_refcount_acquire(n);
/* Failed to add, do something else with the node */
}
bpf_spin_unlock(&l);

It's incorrect to assume that bpf_refcount_acquire will always succeed in this
scenario. bpf_refcount_acquire is being called in a critical section
here, but the lock being held is associated with rbtree t, which isn't
necessarily the lock associated with the tree that the node is already
in. So after bpf_rbtree_add fails to add the node and calls bpf_obj_drop
in it, the program has no ownership of the node's lifetime. Therefore
the node's refcount can be decr'd to 0 at any time after the failing
rbtree_add. If this happens before the refcount_acquire above, the node
might be free'd, and regardless refcount_acquire will be incrementing a
0 refcount.

Later patches in the series exercise this scenario, resulting in the
expected complaint from the kernel (without this patch's changes):

refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 207 at lib/refcount.c:25 refcount_warn_saturate+0xbc/0x110
Modules linked in: bpf_testmod(O)
CPU: 1 PID: 207 Comm: test_progs Tainted: G O 6.3.0-rc7-02231-g723de1a718a2-dirty #371
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
RIP: 0010:refcount_warn_saturate+0xbc/0x110
Code: 6f 64 f6 02 01 e8 84 a3 5c ff 0f 0b eb 9d 80 3d 5e 64 f6 02 00 75 94 48 c7 c7 e0 13 d2 82 c6 05 4e 64 f6 02 01 e8 64 a3 5c ff <0f> 0b e9 7a ff ff ff 80 3d 38 64 f6 02 00 0f 85 6d ff ff ff 48 c7
RSP: 0018:ffff88810b9179b0 EFLAGS: 00010082
RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: 0000000000000202 RSI: 0000000000000008 RDI: ffffffff857c3680
RBP: ffff88810027d3c0 R08: ffffffff8125f2a4 R09: ffff88810b9176e7
R10: ffffed1021722edc R11: 746e756f63666572 R12: ffff88810027d388
R13: ffff88810027d3c0 R14: ffffc900005fe030 R15: ffffc900005fe048
FS: 00007fee0584a700(0000) GS:ffff88811b280000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005634a96f6c58 CR3: 0000000108ce9002 CR4: 0000000000770ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
bpf_refcount_acquire_impl+0xb5/0xc0

(rest of output snipped)

The patch addresses this by changing bpf_refcount_acquire_impl to use
refcount_inc_not_zero instead of refcount_inc and marking
bpf_refcount_acquire KF_RET_NULL.

For owning references, though, we know the above scenario is not possible
and thus that bpf_refcount_acquire will always succeed. Some verifier
bookkeeping is added to track "is input owning ref?" for bpf_refcount_acquire
calls and return false from is_kfunc_ret_null for bpf_refcount_acquire on
owning refs despite it being marked KF_RET_NULL.

Existing selftests using bpf_refcount_acquire are modified where
necessary to NULL-check its return value.

[0]: https://lore.kernel.org/bpf/20230415201811.343116-1-davemarchevsky@fb.com/

Fixes: d2dcc67df910 ("bpf: Migrate bpf_rbtree_add and bpf_list_push_{front,back} to possibly fail")
Reported-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230602022647.1571784-5-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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selftests/bpf: Add refcounted_kptr tests

Test refcounted local kptr functionality added in previous patches in
the series.

Usecases which pass verification:

* Add refcounted local kptr to both tre

selftests/bpf: Add refcounted_kptr tests

Test refcounted local kptr functionality added in previous patches in
the series.

Usecases which pass verification:

* Add refcounted local kptr to both tree and list. Then, read and -
possibly, depending on test variant - delete from tree, then list.
* Also test doing read-and-maybe-delete in opposite order
* Stash a refcounted local kptr in a map_value, then add it to a
rbtree. Read from both, possibly deleting after tree read.
* Add refcounted local kptr to both tree and list. Then, try reading and
deleting twice from one of the collections.
* bpf_refcount_acquire of just-added non-owning ref should work, as
should bpf_refcount_acquire of owning ref just out of bpf_obj_new

Usecases which fail verification:

* The simple successful bpf_refcount_acquire cases from above should
both fail to verify if the newly-acquired owning ref is not dropped

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230415201811.343116-10-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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