diff options
Diffstat (limited to 'kernel/bpf/trampoline.c')
| -rw-r--r-- | kernel/bpf/trampoline.c | 218 |
1 files changed, 168 insertions, 50 deletions
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 7bc3b3209224..1f3a4be4b175 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -57,19 +57,10 @@ void bpf_image_ksym_del(struct bpf_ksym *ksym) PAGE_SIZE, true, ksym->name); } -static void bpf_trampoline_ksym_add(struct bpf_trampoline *tr) -{ - struct bpf_ksym *ksym = &tr->ksym; - - snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu", tr->key); - bpf_image_ksym_add(tr->image, ksym); -} - static struct bpf_trampoline *bpf_trampoline_lookup(u64 key) { struct bpf_trampoline *tr; struct hlist_head *head; - void *image; int i; mutex_lock(&trampoline_mutex); @@ -84,14 +75,6 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key) if (!tr) goto out; - /* is_root was checked earlier. No need for bpf_jit_charge_modmem() */ - image = bpf_jit_alloc_exec_page(); - if (!image) { - kfree(tr); - tr = NULL; - goto out; - } - tr->key = key; INIT_HLIST_NODE(&tr->hlist); hlist_add_head(&tr->hlist, head); @@ -99,9 +82,6 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key) mutex_init(&tr->mutex); for (i = 0; i < BPF_TRAMP_MAX; i++) INIT_HLIST_HEAD(&tr->progs_hlist[i]); - tr->image = image; - INIT_LIST_HEAD_RCU(&tr->ksym.lnode); - bpf_trampoline_ksym_add(tr); out: mutex_unlock(&trampoline_mutex); return tr; @@ -185,10 +165,142 @@ bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total) return tprogs; } +static void __bpf_tramp_image_put_deferred(struct work_struct *work) +{ + struct bpf_tramp_image *im; + + im = container_of(work, struct bpf_tramp_image, work); + bpf_image_ksym_del(&im->ksym); + bpf_jit_free_exec(im->image); + bpf_jit_uncharge_modmem(1); + percpu_ref_exit(&im->pcref); + kfree_rcu(im, rcu); +} + +/* callback, fexit step 3 or fentry step 2 */ +static void __bpf_tramp_image_put_rcu(struct rcu_head *rcu) +{ + struct bpf_tramp_image *im; + + im = container_of(rcu, struct bpf_tramp_image, rcu); + INIT_WORK(&im->work, __bpf_tramp_image_put_deferred); + schedule_work(&im->work); +} + +/* callback, fexit step 2. Called after percpu_ref_kill confirms. */ +static void __bpf_tramp_image_release(struct percpu_ref *pcref) +{ + struct bpf_tramp_image *im; + + im = container_of(pcref, struct bpf_tramp_image, pcref); + call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu); +} + +/* callback, fexit or fentry step 1 */ +static void __bpf_tramp_image_put_rcu_tasks(struct rcu_head *rcu) +{ + struct bpf_tramp_image *im; + + im = container_of(rcu, struct bpf_tramp_image, rcu); + if (im->ip_after_call) + /* the case of fmod_ret/fexit trampoline and CONFIG_PREEMPTION=y */ + percpu_ref_kill(&im->pcref); + else + /* the case of fentry trampoline */ + call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu); +} + +static void bpf_tramp_image_put(struct bpf_tramp_image *im) +{ + /* The trampoline image that calls original function is using: + * rcu_read_lock_trace to protect sleepable bpf progs + * rcu_read_lock to protect normal bpf progs + * percpu_ref to protect trampoline itself + * rcu tasks to protect trampoline asm not covered by percpu_ref + * (which are few asm insns before __bpf_tramp_enter and + * after __bpf_tramp_exit) + * + * The trampoline is unreachable before bpf_tramp_image_put(). + * + * First, patch the trampoline to avoid calling into fexit progs. + * The progs will be freed even if the original function is still + * executing or sleeping. + * In case of CONFIG_PREEMPT=y use call_rcu_tasks() to wait on + * first few asm instructions to execute and call into + * __bpf_tramp_enter->percpu_ref_get. + * Then use percpu_ref_kill to wait for the trampoline and the original + * function to finish. + * Then use call_rcu_tasks() to make sure few asm insns in + * the trampoline epilogue are done as well. + * + * In !PREEMPT case the task that got interrupted in the first asm + * insns won't go through an RCU quiescent state which the + * percpu_ref_kill will be waiting for. Hence the first + * call_rcu_tasks() is not necessary. + */ + if (im->ip_after_call) { + int err = bpf_arch_text_poke(im->ip_after_call, BPF_MOD_JUMP, + NULL, im->ip_epilogue); + WARN_ON(err); + if (IS_ENABLED(CONFIG_PREEMPTION)) + call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu_tasks); + else + percpu_ref_kill(&im->pcref); + return; + } + + /* The trampoline without fexit and fmod_ret progs doesn't call original + * function and doesn't use percpu_ref. + * Use call_rcu_tasks_trace() to wait for sleepable progs to finish. + * Then use call_rcu_tasks() to wait for the rest of trampoline asm + * and normal progs. + */ + call_rcu_tasks_trace(&im->rcu, __bpf_tramp_image_put_rcu_tasks); +} + +static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx) +{ + struct bpf_tramp_image *im; + struct bpf_ksym *ksym; + void *image; + int err = -ENOMEM; + + im = kzalloc(sizeof(*im), GFP_KERNEL); + if (!im) + goto out; + + err = bpf_jit_charge_modmem(1); + if (err) + goto out_free_im; + + err = -ENOMEM; + im->image = image = bpf_jit_alloc_exec_page(); + if (!image) + goto out_uncharge; + + err = percpu_ref_init(&im->pcref, __bpf_tramp_image_release, 0, GFP_KERNEL); + if (err) + goto out_free_image; + + ksym = &im->ksym; + INIT_LIST_HEAD_RCU(&ksym->lnode); + snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu_%u", key, idx); + bpf_image_ksym_add(image, ksym); + return im; + +out_free_image: + bpf_jit_free_exec(im->image); +out_uncharge: + bpf_jit_uncharge_modmem(1); +out_free_im: + kfree(im); +out: + return ERR_PTR(err); +} + static int bpf_trampoline_update(struct bpf_trampoline *tr) { - void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2; - void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2; + struct bpf_tramp_image *im; struct bpf_tramp_progs *tprogs; u32 flags = BPF_TRAMP_F_RESTORE_REGS; int err, total; @@ -198,41 +310,42 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr) return PTR_ERR(tprogs); if (total == 0) { - err = unregister_fentry(tr, old_image); + err = unregister_fentry(tr, tr->cur_image->image); + bpf_tramp_image_put(tr->cur_image); + tr->cur_image = NULL; tr->selector = 0; goto out; } + im = bpf_tramp_image_alloc(tr->key, tr->selector); + if (IS_ERR(im)) { + err = PTR_ERR(im); + goto out; + } + if (tprogs[BPF_TRAMP_FEXIT].nr_progs || tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs) flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME; - /* Though the second half of trampoline page is unused a task could be - * preempted in the middle of the first half of trampoline and two - * updates to trampoline would change the code from underneath the - * preempted task. Hence wait for tasks to voluntarily schedule or go - * to userspace. - * The same trampoline can hold both sleepable and non-sleepable progs. - * synchronize_rcu_tasks_trace() is needed to make sure all sleepable - * programs finish executing. - * Wait for these two grace periods together. - */ - synchronize_rcu_mult(call_rcu_tasks, call_rcu_tasks_trace); - - err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2, + err = arch_prepare_bpf_trampoline(im, im->image, im->image + PAGE_SIZE, &tr->func.model, flags, tprogs, tr->func.addr); if (err < 0) goto out; - if (tr->selector) + WARN_ON(tr->cur_image && tr->selector == 0); + WARN_ON(!tr->cur_image && tr->selector); + if (tr->cur_image) /* progs already running at this address */ - err = modify_fentry(tr, old_image, new_image); + err = modify_fentry(tr, tr->cur_image->image, im->image); else /* first time registering */ - err = register_fentry(tr, new_image); + err = register_fentry(tr, im->image); if (err) goto out; + if (tr->cur_image) + bpf_tramp_image_put(tr->cur_image); + tr->cur_image = im; tr->selector++; out: kfree(tprogs); @@ -364,17 +477,12 @@ void bpf_trampoline_put(struct bpf_trampoline *tr) goto out; if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT]))) goto out; - bpf_image_ksym_del(&tr->ksym); - /* This code will be executed when all bpf progs (both sleepable and - * non-sleepable) went through - * bpf_prog_put()->call_rcu[_tasks_trace]()->bpf_prog_free_deferred(). - * Hence no need for another synchronize_rcu_tasks_trace() here, - * but synchronize_rcu_tasks() is still needed, since trampoline - * may not have had any sleepable programs and we need to wait - * for tasks to get out of trampoline code before freeing it. + /* This code will be executed even when the last bpf_tramp_image + * is alive. All progs are detached from the trampoline and the + * trampoline image is patched with jmp into epilogue to skip + * fexit progs. The fentry-only trampoline will be freed via + * multiple rcu callbacks. */ - synchronize_rcu_tasks(); - bpf_jit_free_exec(tr->image); hlist_del(&tr->hlist); kfree(tr); out: @@ -478,8 +586,18 @@ void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start) rcu_read_unlock_trace(); } +void notrace __bpf_tramp_enter(struct bpf_tramp_image *tr) +{ + percpu_ref_get(&tr->pcref); +} + +void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr) +{ + percpu_ref_put(&tr->pcref); +} + int __weak -arch_prepare_bpf_trampoline(void *image, void *image_end, +arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *image_end, const struct btf_func_model *m, u32 flags, struct bpf_tramp_progs *tprogs, void *orig_call) |