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bpf: Prepare bpf_prog_put() to be called from irq context.

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Currently bpf_prog_put() is called from the task context only.
With addition of bpf timers the timer related helpers will start calling
bpf_prog_put() from irq-saved region and in rare cases might drop
the refcnt to zero.
To address this case, first, convert bpf_prog_free_id() to be irq-save
(this is similar to bpf_map_free_id), and, second, defer non irq
appropriate calls into work queue.
For example:
bpf_audit_prog() is calling kmalloc and wake_up_interruptible,
bpf_prog_kallsyms_del_all()->bpf_ksym_del()->spin_unlock_bh().
They are not safe with irqs disabled.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210715005417.78572-2-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2021-07-14 17:54:07 -07:00 committed by Daniel Borkmann
parent de587d564f
commit d809e134be
1 changed files with 26 additions and 6 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

32
kernel/bpf/syscall.c
View file

@ -1699,6 +1699,8 @@ static int bpf_prog_alloc_id(struct bpf_prog *prog)
void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock)
{
unsigned long flags;
/* cBPF to eBPF migrations are currently not in the idr store.
* Offloaded programs are removed from the store when their device
* disappears - even if someone grabs an fd to them they are unusable,
@ -1708,7 +1710,7 @@ void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock)
return;
if (do_idr_lock)
spin_lock_bh(&prog_idr_lock);
spin_lock_irqsave(&prog_idr_lock, flags);
else
__acquire(&prog_idr_lock);
@ -1716,7 +1718,7 @@ void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock)
prog->aux->id = 0;
if (do_idr_lock)
spin_unlock_bh(&prog_idr_lock);
spin_unlock_irqrestore(&prog_idr_lock, flags);
else
__release(&prog_idr_lock);
}
@ -1752,14 +1754,32 @@ static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred)
}
}
static void bpf_prog_put_deferred(struct work_struct *work)
{
struct bpf_prog_aux *aux;
struct bpf_prog *prog;
aux = container_of(work, struct bpf_prog_aux, work);
prog = aux->prog;
perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0);
bpf_audit_prog(prog, BPF_AUDIT_UNLOAD);
__bpf_prog_put_noref(prog, true);
}
static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock)
{
if (atomic64_dec_and_test(&prog->aux->refcnt)) {
perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0);
bpf_audit_prog(prog, BPF_AUDIT_UNLOAD);
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);
__bpf_prog_put_noref(prog, true);
if (in_irq() || irqs_disabled()) {
INIT_WORK(&aux->work, bpf_prog_put_deferred);
schedule_work(&aux->work);
} else {
bpf_prog_put_deferred(&aux->work);
}
}
}