[PATCH v2 bpf-next 5/5] bpf: trampoline: support FTRACE_OPS_FL_SHARE_IPMODIFY
From: Song Liu
Date: Thu Jun 02 2022 - 15:43:08 EST
This allows bpf trampoline to trace kernel functions with live patch.
Also, move bpf trampoline to *_ftrace_direct_multi APIs, which allows
setting different flags of ftrace_ops.
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
include/linux/bpf.h | 3 ++
kernel/bpf/trampoline.c | 109 +++++++++++++++++++++++++++++++++++-----
2 files changed, 99 insertions(+), 13 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a6e06f384e81..20a8ed600ca6 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -44,6 +44,7 @@ struct kobject;
struct mem_cgroup;
struct module;
struct bpf_func_state;
+struct ftrace_ops;
extern struct idr btf_idr;
extern spinlock_t btf_idr_lock;
@@ -816,6 +817,7 @@ struct bpf_tramp_image {
struct bpf_trampoline {
/* hlist for trampoline_table */
struct hlist_node hlist;
+ struct ftrace_ops *fops;
/* serializes access to fields of this trampoline */
struct mutex mutex;
refcount_t refcnt;
@@ -838,6 +840,7 @@ struct bpf_trampoline {
struct bpf_tramp_image *cur_image;
u64 selector;
struct module *mod;
+ bool indirect_call;
};
struct bpf_attach_target_info {
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 93c7675f0c9e..447c788c5520 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -27,6 +27,44 @@ static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
/* serializes access to trampoline_table */
static DEFINE_MUTEX(trampoline_mutex);
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex);
+
+static int bpf_tramp_ftrace_ops_func(struct ftrace_ops *ops, enum ftrace_ops_cmd cmd)
+{
+ struct bpf_trampoline *tr = ops->private;
+ int ret;
+
+ /*
+ * The normal locking order is
+ * tr->mutex => direct_mutex (ftrace.c) => ftrace_lock (ftrace.c)
+ *
+ * This is called from prepare_direct_functions_for_ipmodify, with
+ * direct_mutex locked. Use mutex_trylock() to avoid dead lock.
+ * Also, bpf_trampoline_update here should not lock direct_mutex.
+ */
+ if (!mutex_trylock(&tr->mutex))
+ return -EAGAIN;
+
+ switch (cmd) {
+ case FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY:
+ tr->indirect_call = true;
+ ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+ break;
+ case FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY:
+ tr->indirect_call = false;
+ tr->fops->flags &= ~FTRACE_OPS_FL_SHARE_IPMODIFY;
+ ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+ break;
+ default:
+ ret = -EINVAL;
+ break;
+ };
+ mutex_unlock(&tr->mutex);
+ return ret;
+}
+#endif
+
bool bpf_prog_has_trampoline(const struct bpf_prog *prog)
{
enum bpf_attach_type eatype = prog->expected_attach_type;
@@ -87,7 +125,16 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
tr = kzalloc(sizeof(*tr), GFP_KERNEL);
if (!tr)
goto out;
-
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+ tr->fops = kzalloc(sizeof(struct ftrace_ops), GFP_KERNEL);
+ if (!tr->fops) {
+ kfree(tr);
+ tr = NULL;
+ goto out;
+ }
+ tr->fops->private = tr;
+ tr->fops->ops_func = bpf_tramp_ftrace_ops_func;
+#endif
tr->key = key;
INIT_HLIST_NODE(&tr->hlist);
hlist_add_head(&tr->hlist, head);
@@ -126,7 +173,7 @@ static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
int ret;
if (tr->func.ftrace_managed)
- ret = unregister_ftrace_direct((long)ip, (long)old_addr);
+ ret = unregister_ftrace_direct_multi(tr->fops, (long)old_addr);
else
ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
@@ -135,15 +182,20 @@ static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
return ret;
}
-static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
+static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr,
+ bool lock_direct_mutex)
{
void *ip = tr->func.addr;
int ret;
- if (tr->func.ftrace_managed)
- ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
- else
+ if (tr->func.ftrace_managed) {
+ if (lock_direct_mutex)
+ ret = modify_ftrace_direct_multi(tr->fops, (long)new_addr);
+ else
+ ret = modify_ftrace_direct_multi_nolock(tr->fops, (long)new_addr);
+ } else {
ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
+ }
return ret;
}
@@ -161,10 +213,15 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
if (bpf_trampoline_module_get(tr))
return -ENOENT;
- if (tr->func.ftrace_managed)
- ret = register_ftrace_direct((long)ip, (long)new_addr);
- else
+ if (tr->func.ftrace_managed) {
+ ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 0, 0);
+ ret = register_ftrace_direct_multi(tr->fops, (long)new_addr);
+ if (ret)
+ ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 1, 0);
+
+ } else {
ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
+ }
if (ret)
bpf_trampoline_module_put(tr);
@@ -330,7 +387,7 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx)
return ERR_PTR(err);
}
-static int bpf_trampoline_update(struct bpf_trampoline *tr)
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
{
struct bpf_tramp_image *im;
struct bpf_tramp_links *tlinks;
@@ -363,20 +420,45 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
if (ip_arg)
flags |= BPF_TRAMP_F_IP_ARG;
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+again:
+ if (tr->indirect_call)
+ flags |= BPF_TRAMP_F_ORIG_STACK;
+#endif
+
err = arch_prepare_bpf_trampoline(im, im->image, im->image + PAGE_SIZE,
&tr->func.model, flags, tlinks,
tr->func.addr);
if (err < 0)
goto out;
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+ if (tr->indirect_call)
+ tr->fops->flags |= FTRACE_OPS_FL_SHARE_IPMODIFY;
+#endif
+
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, tr->cur_image->image, im->image);
+ err = modify_fentry(tr, tr->cur_image->image, im->image, lock_direct_mutex);
else
/* first time registering */
err = register_fentry(tr, im->image);
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+ if (err == -EAGAIN) {
+ if (WARN_ON_ONCE(tr->indirect_call))
+ goto out;
+ /* should only retry on the first register */
+ if (WARN_ON_ONCE(tr->cur_image))
+ goto out;
+ tr->indirect_call = true;
+ tr->fops->func = NULL;
+ tr->fops->trampoline = 0;
+ goto again;
+ }
+#endif
if (err)
goto out;
if (tr->cur_image)
@@ -460,7 +542,7 @@ int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline
hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
tr->progs_cnt[kind]++;
- err = bpf_trampoline_update(tr);
+ err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
if (err) {
hlist_del_init(&link->tramp_hlist);
tr->progs_cnt[kind]--;
@@ -487,7 +569,7 @@ int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampolin
}
hlist_del_init(&link->tramp_hlist);
tr->progs_cnt[kind]--;
- err = bpf_trampoline_update(tr);
+ err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
out:
mutex_unlock(&tr->mutex);
return err;
@@ -535,6 +617,7 @@ void bpf_trampoline_put(struct bpf_trampoline *tr)
* multiple rcu callbacks.
*/
hlist_del(&tr->hlist);
+ kfree(tr->fops);
kfree(tr);
out:
mutex_unlock(&trampoline_mutex);
--
2.30.2