[RFC PATCH bpf-next 07/17] bpf: Add support to postpone trampoline update

Jiri Olsa
2022-08-08T14:07:54Z

Adding support to postpone the trampoline update and record
it to the update list. If the update list is provided, all
the reg/unreg/modify functions only add trampoline to the
update list and stores the requested update information/data
to the trampoline.

It will bed used in following changes where we need to do the
actual trampoline update at the end of the attachment.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
include/linux/bpf.h | 31 ++++++++++++-----
kernel/bpf/trampoline.c | 76 +++++++++++++++++++++++++++++------------
2 files changed, 78 insertions(+), 29 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a5738d57f6bd..a23ff5b8d14c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -768,6 +768,28 @@ struct btf_func_model {
*/
#define BPF_MAX_TRAMP_LINKS 38

+enum bpf_tramp_update_action {
+ BPF_TRAMP_UPDATE_REG,
+ BPF_TRAMP_UPDATE_UNREG,
+ BPF_TRAMP_UPDATE_MODIFY,
+};
+
+enum bpf_tramp_prog_type {
+ BPF_TRAMP_FENTRY,
+ BPF_TRAMP_FEXIT,
+ BPF_TRAMP_MODIFY_RETURN,
+ BPF_TRAMP_MAX,
+ BPF_TRAMP_REPLACE, /* more than MAX */
+};
+
+struct bpf_tramp_update {
+ enum bpf_tramp_update_action action;
+ struct bpf_tramp_image *im;
+ enum bpf_tramp_prog_type kind;
+ struct bpf_prog_array *old_array;
+ struct list_head list;
+};
+
struct bpf_tramp_prog {
struct bpf_prog *prog;
u64 cookie;
@@ -827,14 +849,6 @@ struct bpf_ksym {
bool prog;
};

-enum bpf_tramp_prog_type {
- BPF_TRAMP_FENTRY,
- BPF_TRAMP_FEXIT,
- BPF_TRAMP_MODIFY_RETURN,
- BPF_TRAMP_MAX,
- BPF_TRAMP_REPLACE, /* more than MAX */
-};
-
struct bpf_tramp_image {
void *image;
struct bpf_ksym ksym;
@@ -886,6 +900,7 @@ struct bpf_trampoline {
u64 selector;
struct module *mod;
struct bpf_shim_tramp_link *shim_link;
+ struct bpf_tramp_update update;
};

struct bpf_attach_target_info {
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index d28070247fa3..e926692ded85 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -31,7 +31,8 @@ static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
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_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex,
+ struct list_head *upd);

static int bpf_tramp_ftrace_ops_func(struct ftrace_ops *ops, enum ftrace_ops_cmd cmd)
{
@@ -87,13 +88,13 @@ static int bpf_tramp_ftrace_ops_func(struct ftrace_ops *ops, enum ftrace_ops_cmd

if ((tr->flags & BPF_TRAMP_F_CALL_ORIG) &&
!(tr->flags & BPF_TRAMP_F_ORIG_STACK))
- ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+ ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */, NULL);
break;
case FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY_PEER:
tr->flags &= ~BPF_TRAMP_F_SHARE_IPMODIFY;

if (tr->flags & BPF_TRAMP_F_ORIG_STACK)
- ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+ ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */, NULL);
break;
default:
ret = -EINVAL;
@@ -244,12 +245,20 @@ static void bpf_trampoline_module_put(struct bpf_trampoline *tr)
tr->mod = NULL;
}

-static int unregister_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im)
+static int unregister_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im,
+ struct list_head *upd)
{
void *old_addr = im->image;
void *ip = tr->func.addr;
int ret;

+ if (upd) {
+ tr->update.action = BPF_TRAMP_UPDATE_UNREG;
+ tr->update.im = NULL;
+ list_add_tail(&tr->update.list, upd);
+ return 0;
+ }
+
if (tr->func.ftrace_managed)
ret = unregister_ftrace_direct_multi(tr->fops, (long)old_addr);
else
@@ -257,17 +266,24 @@ static int unregister_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *

if (!ret)
bpf_trampoline_module_put(tr);
+
return ret;
}

static int modify_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im,
- bool lock_direct_mutex)
+ bool lock_direct_mutex, struct list_head *upd)
{
void *old_addr = tr->cur_image->image;
void *new_addr = im->image;
void *ip = tr->func.addr;
int ret;

+ if (upd) {
+ tr->update.action = BPF_TRAMP_UPDATE_MODIFY;
+ tr->update.im = im;
+ list_add_tail(&tr->update.list, upd);
+ return 0;
+ }
if (tr->func.ftrace_managed) {
if (lock_direct_mutex)
ret = modify_ftrace_direct_multi(tr->fops, (long)new_addr);
@@ -280,7 +296,8 @@ static int modify_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im,
}

/* first time registering */
-static int register_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im)
+static int register_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im,
+ struct list_head *upd)
{
void *new_addr = im->image;
void *ip = tr->func.addr;
@@ -294,6 +311,15 @@ static int register_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im
tr->func.ftrace_managed = true;
}

+ if (upd) {
+ if (ip && !tr->func.ftrace_managed)
+ return -ENOTSUPP;
+ tr->update.action = BPF_TRAMP_UPDATE_REG;
+ tr->update.im = im;
+ list_add_tail(&tr->update.list, upd);
+ return 0;
+ }
+
if (bpf_trampoline_module_get(tr))
return -ENOENT;

@@ -477,7 +503,8 @@ 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, bool lock_direct_mutex)
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex,
+ struct list_head *upd)
{
struct bpf_tramp_image *im;
struct bpf_tramp_progs *tprogs;
@@ -490,10 +517,12 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
return PTR_ERR(tprogs);

if (total == 0) {
- err = unregister_fentry(tr, tr->cur_image);
- bpf_tramp_image_put(tr->cur_image);
- tr->cur_image = NULL;
- tr->selector = 0;
+ err = unregister_fentry(tr, tr->cur_image, upd);
+ if (!upd) {
+ bpf_tramp_image_put(tr->cur_image);
+ tr->cur_image = NULL;
+ tr->selector = 0;
+ }
goto out;
}

@@ -536,10 +565,10 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
WARN_ON(!tr->cur_image && tr->selector);
if (tr->cur_image)
/* progs already running at this address */
- err = modify_fentry(tr, im, lock_direct_mutex);
+ err = modify_fentry(tr, im, lock_direct_mutex, upd);
else
/* first time registering */
- err = register_fentry(tr, im);
+ err = register_fentry(tr, im, upd);

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
if (err == -EAGAIN) {
@@ -553,7 +582,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
goto again;
}
#endif
- if (err)
+ if (err || upd)
goto out;

if (tr->cur_image)
@@ -592,7 +621,8 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
}
}

-static int __bpf_trampoline_link_prog(struct bpf_tramp_prog *tp, struct bpf_trampoline *tr)
+static int __bpf_trampoline_link_prog(struct bpf_tramp_prog *tp, struct bpf_trampoline *tr,
+ struct list_head *upd)
{
struct bpf_prog_array *old_array, *new_array;
const struct bpf_prog_array_item *item;
@@ -638,11 +668,14 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_prog *tp, struct bpf_tram
return -ENOMEM;
tr->progs_array[kind] = new_array;
tr->progs_cnt[kind]++;
- err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
+ err = bpf_trampoline_update(tr, true /* lock_direct_mutex */, upd);
if (err) {
tr->progs_array[kind] = old_array;
tr->progs_cnt[kind]--;
bpf_prog_array_free(new_array);
+ } else if (upd) {
+ tr->update.kind = kind;
+ tr->update.old_array = old_array;
} else {
bpf_prog_array_free(old_array);
}
@@ -654,12 +687,13 @@ int bpf_trampoline_link_prog(struct bpf_tramp_prog *tp, struct bpf_trampoline *t
int err;

mutex_lock(&tr->mutex);
- err = __bpf_trampoline_link_prog(tp, tr);
+ err = __bpf_trampoline_link_prog(tp, tr, NULL);
mutex_unlock(&tr->mutex);
return err;
}

-static int __bpf_trampoline_unlink_prog(struct bpf_tramp_prog *tp, struct bpf_trampoline *tr)
+static int __bpf_trampoline_unlink_prog(struct bpf_tramp_prog *tp, struct bpf_trampoline *tr,
+ struct list_head *upd)
{
struct bpf_prog_array *old_array, *new_array;
enum bpf_tramp_prog_type kind;
@@ -683,7 +717,7 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_prog *tp, struct bpf_tr
tr->progs_cnt[kind]--;
tr->progs_array[kind] = new_array;
bpf_prog_array_free(old_array);
- return bpf_trampoline_update(tr, true /* lock_direct_mutex */);
+ return bpf_trampoline_update(tr, true /* lock_direct_mutex */, upd);
}

/* bpf_trampoline_unlink_prog() should never fail. */
@@ -692,7 +726,7 @@ int bpf_trampoline_unlink_prog(struct bpf_tramp_prog *tp, struct bpf_trampoline
int err;

mutex_lock(&tr->mutex);
- err = __bpf_trampoline_unlink_prog(tp, tr);
+ err = __bpf_trampoline_unlink_prog(tp, tr, NULL);
mutex_unlock(&tr->mutex);
return err;
}
@@ -804,7 +838,7 @@ int bpf_trampoline_link_cgroup_shim(struct bpf_prog *prog,
goto err;
}

- err = __bpf_trampoline_link_prog(&shim_link->tp, tr);
+ err = __bpf_trampoline_link_prog(&shim_link->tp, tr, NULL);
if (err)
goto err;

--
2.37.1