Re: [PATCH v3 1/2] bpf: restore the ebpf program ID for BPF_AUDIT_UNLOAD and PERF_BPF_EVENT_PROG_UNLOAD

When changing the ebpf program put() routines to support being called from within IRQ context the program ID was reset to zero prior to calling the perf event and audit UNLOAD record generators, which resulted in problems as the ebpf program ID was bogus (always zero). This patch addresses this problem by removing an unnecessary call to bpf_prog_free_id() in __bpf_prog_offload_destroy() and adjusting __bpf_prog_put() to only call bpf_prog_free_id() after audit and perf have finished their bpf program unload tasks in bpf_prog_put_deferred(). For the record, no one can determine, or remember, why it was necessary to free the program ID, and remove it from the IDR, prior to executing bpf_prog_put_deferred(); regardless, both Stanislav and Alexei agree that the approach in this patch should be safe. It is worth noting that when moving the bpf_prog_free_id() call, the do_idr_lock parameter was forced to true as the ebpf devs determined this was the correct as the do_idr_lock should always be true. The do_idr_lock parameter will be removed in a follow-up patch, but it was kept here to keep the patch small in an effort to ease any stable backports. I also modified the bpf_audit_prog() logic used to associate the AUDIT_BPF record with other associated records, e.g. @ctx != NULL. Instead of keying off the operation, it now keys off the execution context, e.g. '!in_irg && !irqs_disabled()', which is much more appropriate and should help better connect the UNLOAD operations with the associated audit state (other audit records). Cc: stable(a)vger.kernel.org Fixes: d809e134be7a ("bpf: Prepare bpf_prog_put() to be called from irq context.") Reported-by: Burn Alting <burn.alting(a)iinet.net.au&gt; Reported-by: Jiri Olsa <olsajiri(a)gmail.com&gt; Suggested-by: Stanislav Fomichev <sdf(a)google.com&gt; Suggested-by: Alexei Starovoitov <alexei.starovoitov(a)gmail.com&gt; Signed-off-by: Paul Moore <paul(a)paul-moore.com&gt; --- * v3 - abandon most of the changes in v2 - move bpf_prog_free_id() after the audit/perf unload hooks - remove bpf_prog_free_id() from __bpf_prog_offload_destroy() - added stable tag

* v2 - change subj - add mention of the perf regression - drop the dedicated program audit ID - add the bpf_prog::valid_id flag, bpf_prog_get_id() getter - convert prog ID users to new ID getter * v1 - subj was: "bpf: restore the ebpf audit UNLOAD id field" - initial draft --- kernel/bpf/offload.c | 3 --- kernel/bpf/syscall.c | 6 ++---- 2 files changed, 2 insertions(+), 7 deletions(-) diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c index 13e4efc971e6..190d9f9dc987 100644 --- a/kernel/bpf/offload.c +++ b/kernel/bpf/offload.c @@ -216,9 +216,6 @@ static void __bpf_prog_offload_destroy(struct bpf_prog *prog) if (offload->dev_state) offload->offdev->ops->destroy(prog); - /* Make sure BPF_PROG_GET_NEXT_ID can't find this dead program */ - bpf_prog_free_id(prog, true); - list_del_init(&offload->offloads); kfree(offload); prog->aux->offload = NULL; diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 64131f88c553..61bb19e81b9c 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1972,7 +1972,7 @@ static void bpf_audit_prog(const struct bpf_prog *prog, unsigned int op) return; if (audit_enabled == AUDIT_OFF) return; - if (op == BPF_AUDIT_LOAD) + if (!in_irq() && !irqs_disabled()) ctx = audit_context(); ab = audit_log_start(ctx, GFP_ATOMIC, AUDIT_BPF); if (unlikely(!ab)) @@ -2067,6 +2067,7 @@ static void bpf_prog_put_deferred(struct work_struct *work) prog = aux->prog; perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0); bpf_audit_prog(prog, BPF_AUDIT_UNLOAD); + bpf_prog_free_id(prog, true); __bpf_prog_put_noref(prog, true); } @@ -2075,9 +2076,6 @@ static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock) struct bpf_prog_aux *aux = prog->aux; if (atomic64_dec_and_test(&aux->refcnt)) { - /* bpf_prog_free_id() must be called first */ - bpf_prog_free_id(prog, do_idr_lock); - if (in_irq() || irqs_disabled()) { INIT_WORK(&aux->work, bpf_prog_put_deferred); schedule_work(&aux->work); -- 2.39.0