cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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trampoline.c (17469B)


      1// SPDX-License-Identifier: GPL-2.0-only
      2/* Copyright (c) 2019 Facebook */
      3#include <linux/hash.h>
      4#include <linux/bpf.h>
      5#include <linux/filter.h>
      6#include <linux/ftrace.h>
      7#include <linux/rbtree_latch.h>
      8#include <linux/perf_event.h>
      9#include <linux/btf.h>
     10#include <linux/rcupdate_trace.h>
     11#include <linux/rcupdate_wait.h>
     12#include <linux/module.h>
     13#include <linux/static_call.h>
     14
     15/* dummy _ops. The verifier will operate on target program's ops. */
     16const struct bpf_verifier_ops bpf_extension_verifier_ops = {
     17};
     18const struct bpf_prog_ops bpf_extension_prog_ops = {
     19};
     20
     21/* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */
     22#define TRAMPOLINE_HASH_BITS 10
     23#define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)
     24
     25static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
     26
     27/* serializes access to trampoline_table */
     28static DEFINE_MUTEX(trampoline_mutex);
     29
     30bool bpf_prog_has_trampoline(const struct bpf_prog *prog)
     31{
     32	enum bpf_attach_type eatype = prog->expected_attach_type;
     33	enum bpf_prog_type ptype = prog->type;
     34
     35	return (ptype == BPF_PROG_TYPE_TRACING &&
     36		(eatype == BPF_TRACE_FENTRY || eatype == BPF_TRACE_FEXIT ||
     37		 eatype == BPF_MODIFY_RETURN)) ||
     38		(ptype == BPF_PROG_TYPE_LSM && eatype == BPF_LSM_MAC);
     39}
     40
     41void *bpf_jit_alloc_exec_page(void)
     42{
     43	void *image;
     44
     45	image = bpf_jit_alloc_exec(PAGE_SIZE);
     46	if (!image)
     47		return NULL;
     48
     49	set_vm_flush_reset_perms(image);
     50	/* Keep image as writeable. The alternative is to keep flipping ro/rw
     51	 * every time new program is attached or detached.
     52	 */
     53	set_memory_x((long)image, 1);
     54	return image;
     55}
     56
     57void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym)
     58{
     59	ksym->start = (unsigned long) data;
     60	ksym->end = ksym->start + PAGE_SIZE;
     61	bpf_ksym_add(ksym);
     62	perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
     63			   PAGE_SIZE, false, ksym->name);
     64}
     65
     66void bpf_image_ksym_del(struct bpf_ksym *ksym)
     67{
     68	bpf_ksym_del(ksym);
     69	perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
     70			   PAGE_SIZE, true, ksym->name);
     71}
     72
     73static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
     74{
     75	struct bpf_trampoline *tr;
     76	struct hlist_head *head;
     77	int i;
     78
     79	mutex_lock(&trampoline_mutex);
     80	head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
     81	hlist_for_each_entry(tr, head, hlist) {
     82		if (tr->key == key) {
     83			refcount_inc(&tr->refcnt);
     84			goto out;
     85		}
     86	}
     87	tr = kzalloc(sizeof(*tr), GFP_KERNEL);
     88	if (!tr)
     89		goto out;
     90
     91	tr->key = key;
     92	INIT_HLIST_NODE(&tr->hlist);
     93	hlist_add_head(&tr->hlist, head);
     94	refcount_set(&tr->refcnt, 1);
     95	mutex_init(&tr->mutex);
     96	for (i = 0; i < BPF_TRAMP_MAX; i++)
     97		INIT_HLIST_HEAD(&tr->progs_hlist[i]);
     98out:
     99	mutex_unlock(&trampoline_mutex);
    100	return tr;
    101}
    102
    103static int bpf_trampoline_module_get(struct bpf_trampoline *tr)
    104{
    105	struct module *mod;
    106	int err = 0;
    107
    108	preempt_disable();
    109	mod = __module_text_address((unsigned long) tr->func.addr);
    110	if (mod && !try_module_get(mod))
    111		err = -ENOENT;
    112	preempt_enable();
    113	tr->mod = mod;
    114	return err;
    115}
    116
    117static void bpf_trampoline_module_put(struct bpf_trampoline *tr)
    118{
    119	module_put(tr->mod);
    120	tr->mod = NULL;
    121}
    122
    123static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
    124{
    125	void *ip = tr->func.addr;
    126	int ret;
    127
    128	if (tr->func.ftrace_managed)
    129		ret = unregister_ftrace_direct((long)ip, (long)old_addr);
    130	else
    131		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
    132
    133	if (!ret)
    134		bpf_trampoline_module_put(tr);
    135	return ret;
    136}
    137
    138static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
    139{
    140	void *ip = tr->func.addr;
    141	int ret;
    142
    143	if (tr->func.ftrace_managed)
    144		ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
    145	else
    146		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
    147	return ret;
    148}
    149
    150/* first time registering */
    151static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
    152{
    153	void *ip = tr->func.addr;
    154	unsigned long faddr;
    155	int ret;
    156
    157	faddr = ftrace_location((unsigned long)ip);
    158	if (faddr)
    159		tr->func.ftrace_managed = true;
    160
    161	if (bpf_trampoline_module_get(tr))
    162		return -ENOENT;
    163
    164	if (tr->func.ftrace_managed)
    165		ret = register_ftrace_direct((long)ip, (long)new_addr);
    166	else
    167		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
    168
    169	if (ret)
    170		bpf_trampoline_module_put(tr);
    171	return ret;
    172}
    173
    174static struct bpf_tramp_links *
    175bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_arg)
    176{
    177	struct bpf_tramp_link *link;
    178	struct bpf_tramp_links *tlinks;
    179	struct bpf_tramp_link **links;
    180	int kind;
    181
    182	*total = 0;
    183	tlinks = kcalloc(BPF_TRAMP_MAX, sizeof(*tlinks), GFP_KERNEL);
    184	if (!tlinks)
    185		return ERR_PTR(-ENOMEM);
    186
    187	for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
    188		tlinks[kind].nr_links = tr->progs_cnt[kind];
    189		*total += tr->progs_cnt[kind];
    190		links = tlinks[kind].links;
    191
    192		hlist_for_each_entry(link, &tr->progs_hlist[kind], tramp_hlist) {
    193			*ip_arg |= link->link.prog->call_get_func_ip;
    194			*links++ = link;
    195		}
    196	}
    197	return tlinks;
    198}
    199
    200static void __bpf_tramp_image_put_deferred(struct work_struct *work)
    201{
    202	struct bpf_tramp_image *im;
    203
    204	im = container_of(work, struct bpf_tramp_image, work);
    205	bpf_image_ksym_del(&im->ksym);
    206	bpf_jit_free_exec(im->image);
    207	bpf_jit_uncharge_modmem(PAGE_SIZE);
    208	percpu_ref_exit(&im->pcref);
    209	kfree_rcu(im, rcu);
    210}
    211
    212/* callback, fexit step 3 or fentry step 2 */
    213static void __bpf_tramp_image_put_rcu(struct rcu_head *rcu)
    214{
    215	struct bpf_tramp_image *im;
    216
    217	im = container_of(rcu, struct bpf_tramp_image, rcu);
    218	INIT_WORK(&im->work, __bpf_tramp_image_put_deferred);
    219	schedule_work(&im->work);
    220}
    221
    222/* callback, fexit step 2. Called after percpu_ref_kill confirms. */
    223static void __bpf_tramp_image_release(struct percpu_ref *pcref)
    224{
    225	struct bpf_tramp_image *im;
    226
    227	im = container_of(pcref, struct bpf_tramp_image, pcref);
    228	call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu);
    229}
    230
    231/* callback, fexit or fentry step 1 */
    232static void __bpf_tramp_image_put_rcu_tasks(struct rcu_head *rcu)
    233{
    234	struct bpf_tramp_image *im;
    235
    236	im = container_of(rcu, struct bpf_tramp_image, rcu);
    237	if (im->ip_after_call)
    238		/* the case of fmod_ret/fexit trampoline and CONFIG_PREEMPTION=y */
    239		percpu_ref_kill(&im->pcref);
    240	else
    241		/* the case of fentry trampoline */
    242		call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu);
    243}
    244
    245static void bpf_tramp_image_put(struct bpf_tramp_image *im)
    246{
    247	/* The trampoline image that calls original function is using:
    248	 * rcu_read_lock_trace to protect sleepable bpf progs
    249	 * rcu_read_lock to protect normal bpf progs
    250	 * percpu_ref to protect trampoline itself
    251	 * rcu tasks to protect trampoline asm not covered by percpu_ref
    252	 * (which are few asm insns before __bpf_tramp_enter and
    253	 *  after __bpf_tramp_exit)
    254	 *
    255	 * The trampoline is unreachable before bpf_tramp_image_put().
    256	 *
    257	 * First, patch the trampoline to avoid calling into fexit progs.
    258	 * The progs will be freed even if the original function is still
    259	 * executing or sleeping.
    260	 * In case of CONFIG_PREEMPT=y use call_rcu_tasks() to wait on
    261	 * first few asm instructions to execute and call into
    262	 * __bpf_tramp_enter->percpu_ref_get.
    263	 * Then use percpu_ref_kill to wait for the trampoline and the original
    264	 * function to finish.
    265	 * Then use call_rcu_tasks() to make sure few asm insns in
    266	 * the trampoline epilogue are done as well.
    267	 *
    268	 * In !PREEMPT case the task that got interrupted in the first asm
    269	 * insns won't go through an RCU quiescent state which the
    270	 * percpu_ref_kill will be waiting for. Hence the first
    271	 * call_rcu_tasks() is not necessary.
    272	 */
    273	if (im->ip_after_call) {
    274		int err = bpf_arch_text_poke(im->ip_after_call, BPF_MOD_JUMP,
    275					     NULL, im->ip_epilogue);
    276		WARN_ON(err);
    277		if (IS_ENABLED(CONFIG_PREEMPTION))
    278			call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
    279		else
    280			percpu_ref_kill(&im->pcref);
    281		return;
    282	}
    283
    284	/* The trampoline without fexit and fmod_ret progs doesn't call original
    285	 * function and doesn't use percpu_ref.
    286	 * Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
    287	 * Then use call_rcu_tasks() to wait for the rest of trampoline asm
    288	 * and normal progs.
    289	 */
    290	call_rcu_tasks_trace(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
    291}
    292
    293static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx)
    294{
    295	struct bpf_tramp_image *im;
    296	struct bpf_ksym *ksym;
    297	void *image;
    298	int err = -ENOMEM;
    299
    300	im = kzalloc(sizeof(*im), GFP_KERNEL);
    301	if (!im)
    302		goto out;
    303
    304	err = bpf_jit_charge_modmem(PAGE_SIZE);
    305	if (err)
    306		goto out_free_im;
    307
    308	err = -ENOMEM;
    309	im->image = image = bpf_jit_alloc_exec_page();
    310	if (!image)
    311		goto out_uncharge;
    312
    313	err = percpu_ref_init(&im->pcref, __bpf_tramp_image_release, 0, GFP_KERNEL);
    314	if (err)
    315		goto out_free_image;
    316
    317	ksym = &im->ksym;
    318	INIT_LIST_HEAD_RCU(&ksym->lnode);
    319	snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu_%u", key, idx);
    320	bpf_image_ksym_add(image, ksym);
    321	return im;
    322
    323out_free_image:
    324	bpf_jit_free_exec(im->image);
    325out_uncharge:
    326	bpf_jit_uncharge_modmem(PAGE_SIZE);
    327out_free_im:
    328	kfree(im);
    329out:
    330	return ERR_PTR(err);
    331}
    332
    333static int bpf_trampoline_update(struct bpf_trampoline *tr)
    334{
    335	struct bpf_tramp_image *im;
    336	struct bpf_tramp_links *tlinks;
    337	u32 flags = BPF_TRAMP_F_RESTORE_REGS;
    338	bool ip_arg = false;
    339	int err, total;
    340
    341	tlinks = bpf_trampoline_get_progs(tr, &total, &ip_arg);
    342	if (IS_ERR(tlinks))
    343		return PTR_ERR(tlinks);
    344
    345	if (total == 0) {
    346		err = unregister_fentry(tr, tr->cur_image->image);
    347		bpf_tramp_image_put(tr->cur_image);
    348		tr->cur_image = NULL;
    349		tr->selector = 0;
    350		goto out;
    351	}
    352
    353	im = bpf_tramp_image_alloc(tr->key, tr->selector);
    354	if (IS_ERR(im)) {
    355		err = PTR_ERR(im);
    356		goto out;
    357	}
    358
    359	if (tlinks[BPF_TRAMP_FEXIT].nr_links ||
    360	    tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)
    361		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
    362
    363	if (ip_arg)
    364		flags |= BPF_TRAMP_F_IP_ARG;
    365
    366	err = arch_prepare_bpf_trampoline(im, im->image, im->image + PAGE_SIZE,
    367					  &tr->func.model, flags, tlinks,
    368					  tr->func.addr);
    369	if (err < 0)
    370		goto out;
    371
    372	WARN_ON(tr->cur_image && tr->selector == 0);
    373	WARN_ON(!tr->cur_image && tr->selector);
    374	if (tr->cur_image)
    375		/* progs already running at this address */
    376		err = modify_fentry(tr, tr->cur_image->image, im->image);
    377	else
    378		/* first time registering */
    379		err = register_fentry(tr, im->image);
    380	if (err)
    381		goto out;
    382	if (tr->cur_image)
    383		bpf_tramp_image_put(tr->cur_image);
    384	tr->cur_image = im;
    385	tr->selector++;
    386out:
    387	kfree(tlinks);
    388	return err;
    389}
    390
    391static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
    392{
    393	switch (prog->expected_attach_type) {
    394	case BPF_TRACE_FENTRY:
    395		return BPF_TRAMP_FENTRY;
    396	case BPF_MODIFY_RETURN:
    397		return BPF_TRAMP_MODIFY_RETURN;
    398	case BPF_TRACE_FEXIT:
    399		return BPF_TRAMP_FEXIT;
    400	case BPF_LSM_MAC:
    401		if (!prog->aux->attach_func_proto->type)
    402			/* The function returns void, we cannot modify its
    403			 * return value.
    404			 */
    405			return BPF_TRAMP_FEXIT;
    406		else
    407			return BPF_TRAMP_MODIFY_RETURN;
    408	default:
    409		return BPF_TRAMP_REPLACE;
    410	}
    411}
    412
    413int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr)
    414{
    415	enum bpf_tramp_prog_type kind;
    416	struct bpf_tramp_link *link_exiting;
    417	int err = 0;
    418	int cnt = 0, i;
    419
    420	kind = bpf_attach_type_to_tramp(link->link.prog);
    421	mutex_lock(&tr->mutex);
    422	if (tr->extension_prog) {
    423		/* cannot attach fentry/fexit if extension prog is attached.
    424		 * cannot overwrite extension prog either.
    425		 */
    426		err = -EBUSY;
    427		goto out;
    428	}
    429
    430	for (i = 0; i < BPF_TRAMP_MAX; i++)
    431		cnt += tr->progs_cnt[i];
    432
    433	if (kind == BPF_TRAMP_REPLACE) {
    434		/* Cannot attach extension if fentry/fexit are in use. */
    435		if (cnt) {
    436			err = -EBUSY;
    437			goto out;
    438		}
    439		tr->extension_prog = link->link.prog;
    440		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL,
    441					 link->link.prog->bpf_func);
    442		goto out;
    443	}
    444	if (cnt >= BPF_MAX_TRAMP_LINKS) {
    445		err = -E2BIG;
    446		goto out;
    447	}
    448	if (!hlist_unhashed(&link->tramp_hlist)) {
    449		/* prog already linked */
    450		err = -EBUSY;
    451		goto out;
    452	}
    453	hlist_for_each_entry(link_exiting, &tr->progs_hlist[kind], tramp_hlist) {
    454		if (link_exiting->link.prog != link->link.prog)
    455			continue;
    456		/* prog already linked */
    457		err = -EBUSY;
    458		goto out;
    459	}
    460
    461	hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
    462	tr->progs_cnt[kind]++;
    463	err = bpf_trampoline_update(tr);
    464	if (err) {
    465		hlist_del_init(&link->tramp_hlist);
    466		tr->progs_cnt[kind]--;
    467	}
    468out:
    469	mutex_unlock(&tr->mutex);
    470	return err;
    471}
    472
    473/* bpf_trampoline_unlink_prog() should never fail. */
    474int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr)
    475{
    476	enum bpf_tramp_prog_type kind;
    477	int err;
    478
    479	kind = bpf_attach_type_to_tramp(link->link.prog);
    480	mutex_lock(&tr->mutex);
    481	if (kind == BPF_TRAMP_REPLACE) {
    482		WARN_ON_ONCE(!tr->extension_prog);
    483		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP,
    484					 tr->extension_prog->bpf_func, NULL);
    485		tr->extension_prog = NULL;
    486		goto out;
    487	}
    488	hlist_del_init(&link->tramp_hlist);
    489	tr->progs_cnt[kind]--;
    490	err = bpf_trampoline_update(tr);
    491out:
    492	mutex_unlock(&tr->mutex);
    493	return err;
    494}
    495
    496struct bpf_trampoline *bpf_trampoline_get(u64 key,
    497					  struct bpf_attach_target_info *tgt_info)
    498{
    499	struct bpf_trampoline *tr;
    500
    501	tr = bpf_trampoline_lookup(key);
    502	if (!tr)
    503		return NULL;
    504
    505	mutex_lock(&tr->mutex);
    506	if (tr->func.addr)
    507		goto out;
    508
    509	memcpy(&tr->func.model, &tgt_info->fmodel, sizeof(tgt_info->fmodel));
    510	tr->func.addr = (void *)tgt_info->tgt_addr;
    511out:
    512	mutex_unlock(&tr->mutex);
    513	return tr;
    514}
    515
    516void bpf_trampoline_put(struct bpf_trampoline *tr)
    517{
    518	int i;
    519
    520	if (!tr)
    521		return;
    522	mutex_lock(&trampoline_mutex);
    523	if (!refcount_dec_and_test(&tr->refcnt))
    524		goto out;
    525	WARN_ON_ONCE(mutex_is_locked(&tr->mutex));
    526
    527	for (i = 0; i < BPF_TRAMP_MAX; i++)
    528		if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[i])))
    529			goto out;
    530
    531	/* This code will be executed even when the last bpf_tramp_image
    532	 * is alive. All progs are detached from the trampoline and the
    533	 * trampoline image is patched with jmp into epilogue to skip
    534	 * fexit progs. The fentry-only trampoline will be freed via
    535	 * multiple rcu callbacks.
    536	 */
    537	hlist_del(&tr->hlist);
    538	kfree(tr);
    539out:
    540	mutex_unlock(&trampoline_mutex);
    541}
    542
    543#define NO_START_TIME 1
    544static __always_inline u64 notrace bpf_prog_start_time(void)
    545{
    546	u64 start = NO_START_TIME;
    547
    548	if (static_branch_unlikely(&bpf_stats_enabled_key)) {
    549		start = sched_clock();
    550		if (unlikely(!start))
    551			start = NO_START_TIME;
    552	}
    553	return start;
    554}
    555
    556static void notrace inc_misses_counter(struct bpf_prog *prog)
    557{
    558	struct bpf_prog_stats *stats;
    559	unsigned int flags;
    560
    561	stats = this_cpu_ptr(prog->stats);
    562	flags = u64_stats_update_begin_irqsave(&stats->syncp);
    563	u64_stats_inc(&stats->misses);
    564	u64_stats_update_end_irqrestore(&stats->syncp, flags);
    565}
    566
    567/* The logic is similar to bpf_prog_run(), but with an explicit
    568 * rcu_read_lock() and migrate_disable() which are required
    569 * for the trampoline. The macro is split into
    570 * call __bpf_prog_enter
    571 * call prog->bpf_func
    572 * call __bpf_prog_exit
    573 *
    574 * __bpf_prog_enter returns:
    575 * 0 - skip execution of the bpf prog
    576 * 1 - execute bpf prog
    577 * [2..MAX_U64] - execute bpf prog and record execution time.
    578 *     This is start time.
    579 */
    580u64 notrace __bpf_prog_enter(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx)
    581	__acquires(RCU)
    582{
    583	rcu_read_lock();
    584	migrate_disable();
    585
    586	run_ctx->saved_run_ctx = bpf_set_run_ctx(&run_ctx->run_ctx);
    587
    588	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
    589		inc_misses_counter(prog);
    590		return 0;
    591	}
    592	return bpf_prog_start_time();
    593}
    594
    595static void notrace update_prog_stats(struct bpf_prog *prog,
    596				      u64 start)
    597{
    598	struct bpf_prog_stats *stats;
    599
    600	if (static_branch_unlikely(&bpf_stats_enabled_key) &&
    601	    /* static_key could be enabled in __bpf_prog_enter*
    602	     * and disabled in __bpf_prog_exit*.
    603	     * And vice versa.
    604	     * Hence check that 'start' is valid.
    605	     */
    606	    start > NO_START_TIME) {
    607		unsigned long flags;
    608
    609		stats = this_cpu_ptr(prog->stats);
    610		flags = u64_stats_update_begin_irqsave(&stats->syncp);
    611		u64_stats_inc(&stats->cnt);
    612		u64_stats_add(&stats->nsecs, sched_clock() - start);
    613		u64_stats_update_end_irqrestore(&stats->syncp, flags);
    614	}
    615}
    616
    617void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start, struct bpf_tramp_run_ctx *run_ctx)
    618	__releases(RCU)
    619{
    620	bpf_reset_run_ctx(run_ctx->saved_run_ctx);
    621
    622	update_prog_stats(prog, start);
    623	__this_cpu_dec(*(prog->active));
    624	migrate_enable();
    625	rcu_read_unlock();
    626}
    627
    628u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx)
    629{
    630	rcu_read_lock_trace();
    631	migrate_disable();
    632	might_fault();
    633
    634	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
    635		inc_misses_counter(prog);
    636		return 0;
    637	}
    638
    639	run_ctx->saved_run_ctx = bpf_set_run_ctx(&run_ctx->run_ctx);
    640
    641	return bpf_prog_start_time();
    642}
    643
    644void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start,
    645				       struct bpf_tramp_run_ctx *run_ctx)
    646{
    647	bpf_reset_run_ctx(run_ctx->saved_run_ctx);
    648
    649	update_prog_stats(prog, start);
    650	__this_cpu_dec(*(prog->active));
    651	migrate_enable();
    652	rcu_read_unlock_trace();
    653}
    654
    655void notrace __bpf_tramp_enter(struct bpf_tramp_image *tr)
    656{
    657	percpu_ref_get(&tr->pcref);
    658}
    659
    660void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr)
    661{
    662	percpu_ref_put(&tr->pcref);
    663}
    664
    665int __weak
    666arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *image_end,
    667			    const struct btf_func_model *m, u32 flags,
    668			    struct bpf_tramp_links *tlinks,
    669			    void *orig_call)
    670{
    671	return -ENOTSUPP;
    672}
    673
    674static int __init init_trampolines(void)
    675{
    676	int i;
    677
    678	for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
    679		INIT_HLIST_HEAD(&trampoline_table[i]);
    680	return 0;
    681}
    682late_initcall(init_trampolines);