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Diffstat (limited to 'kernel/bpf/trampoline.c')
-rw-r--r--kernel/bpf/trampoline.c218
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)