Commit 00963a2e authored by Song Liu's avatar Song Liu Committed by Daniel Borkmann
Browse files

bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch) 



When tracing a function with IPMODIFY ftrace_ops (livepatch), the bpf
trampoline must follow the instruction pointer saved on stack. This needs
extra handling for bpf trampolines with BPF_TRAMP_F_CALL_ORIG flag.

Implement bpf_tramp_ftrace_ops_func and use it for the ftrace_ops used
by BPF trampoline. This enables tracing functions with livepatch.

This also requires moving bpf trampoline to *_ftrace_direct_mult APIs.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/all/20220602193706.2607681-2-song@kernel.org/
Link: https://lore.kernel.org/bpf/20220720002126.803253-5-song@kernel.org
parent 316cba62

include/linux/bpf.h

+8 −0
Original line number Diff line number Diff line
@@ -47,6 +47,7 @@ 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;
@@ -756,6 +757,11 @@ struct btf_func_model { 
 */

#define BPF_TRAMP_F_ORIG_STACK		BIT(5)



/* This trampoline is on a function with another ftrace_ops with IPMODIFY,

 * e.g., a live patch. This flag is set and cleared by ftrace call backs,

 */

#define BPF_TRAMP_F_SHARE_IPMODIFY	BIT(6)



/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50

 * bytes on x86.

 */
@@ -838,9 +844,11 @@ 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;

	u32 flags;

	u64 key;

	struct {

		struct btf_func_model model;

kernel/bpf/trampoline.c

+141 −17
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 
#include <linux/static_call.h>

#include <linux/bpf_verifier.h>

#include <linux/bpf_lsm.h>

#include <linux/delay.h>



/* dummy _ops. The verifier will operate on target program's ops. */

const struct bpf_verifier_ops bpf_extension_verifier_ops = {
@@ -29,6 +30,81 @@ 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 = 0;



	if (cmd == FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_SELF) {

		/* This is called inside register_ftrace_direct_multi(), so

		 * tr->mutex is already locked.

		 */

		lockdep_assert_held_once(&tr->mutex);



		/* Instead of updating the trampoline here, we propagate

		 * -EAGAIN to register_ftrace_direct_multi(). Then we can

		 * retry register_ftrace_direct_multi() after updating the

		 * trampoline.

		 */

		if ((tr->flags & BPF_TRAMP_F_CALL_ORIG) &&

		    !(tr->flags & BPF_TRAMP_F_ORIG_STACK)) {

			if (WARN_ON_ONCE(tr->flags & BPF_TRAMP_F_SHARE_IPMODIFY))

				return -EBUSY;



			tr->flags |= BPF_TRAMP_F_SHARE_IPMODIFY;

			return -EAGAIN;

		}



		return 0;

	}



	/* The normal locking order is

	 *    tr->mutex => direct_mutex (ftrace.c) => ftrace_lock (ftrace.c)

	 *

	 * The following two commands are called from

	 *

	 *   prepare_direct_functions_for_ipmodify

	 *   cleanup_direct_functions_after_ipmodify

	 *

	 * In both cases, direct_mutex is already locked. Use

	 * mutex_trylock(&tr->mutex) to avoid deadlock in race condition

	 * (something else is making changes to this same trampoline).

	 */

	if (!mutex_trylock(&tr->mutex)) {

		/* sleep 1 ms to make sure whatever holding tr->mutex makes

		 * some progress.

		 */

		msleep(1);

		return -EAGAIN;

	}



	switch (cmd) {

	case FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_PEER:

		tr->flags |= BPF_TRAMP_F_SHARE_IPMODIFY;



		if ((tr->flags & BPF_TRAMP_F_CALL_ORIG) &&

		    !(tr->flags & BPF_TRAMP_F_ORIG_STACK))

			ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);

		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 */);

		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;
@@ -89,6 +165,16 @@ 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);
@@ -128,7 +214,7 @@ 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);
@@ -137,15 +223,20 @@ 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);

	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;

}
@@ -163,10 +254,12 @@ 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);

	} else {

		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);

	}



	if (ret)

		bpf_trampoline_module_put(tr);
@@ -332,11 +425,11 @@ 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;

	u32 flags = BPF_TRAMP_F_RESTORE_REGS;

	u32 orig_flags = tr->flags;

	bool ip_arg = false;

	int err, total;
@@ -358,18 +451,31 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr) 
		goto out;

	}



	/* clear all bits except SHARE_IPMODIFY */

	tr->flags &= BPF_TRAMP_F_SHARE_IPMODIFY;



	if (tlinks[BPF_TRAMP_FEXIT].nr_links ||

	    tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)

	    tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links) {

		/* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME

		 * should not be set together.

		 */

		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

		tr->flags |= BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

	} else {

		tr->flags |= BPF_TRAMP_F_RESTORE_REGS;

	}



	if (ip_arg)

		flags |= BPF_TRAMP_F_IP_ARG;

		tr->flags |= BPF_TRAMP_F_IP_ARG;



#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS

again:

	if ((tr->flags & BPF_TRAMP_F_SHARE_IPMODIFY) &&

	    (tr->flags & BPF_TRAMP_F_CALL_ORIG))

		tr->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.model, tr->flags, tlinks,

					  tr->func.addr);

	if (err < 0)

		goto out;
@@ -378,17 +484,34 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr) 
	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) {

		/* -EAGAIN from bpf_tramp_ftrace_ops_func. Now

		 * BPF_TRAMP_F_SHARE_IPMODIFY is set, we can generate the

		 * trampoline again, and retry register.

		 */

		/* reset fops->func and fops->trampoline for re-register */

		tr->fops->func = NULL;

		tr->fops->trampoline = 0;

		goto again;

	}

#endif

	if (err)

		goto out;



	if (tr->cur_image)

		bpf_tramp_image_put(tr->cur_image);

	tr->cur_image = im;

	tr->selector++;

out:

	/* If any error happens, restore previous flags */

	if (err)

		tr->flags = orig_flags;

	kfree(tlinks);

	return err;

}
@@ -454,7 +577,7 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr 


	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 +610,7 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_ 
	}

	hlist_del_init(&link->tramp_hlist);

	tr->progs_cnt[kind]--;

	return bpf_trampoline_update(tr);

	return bpf_trampoline_update(tr, true /* lock_direct_mutex */);

}



/* bpf_trampoline_unlink_prog() should never fail. */
@@ -715,6 +838,7 @@ 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);