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![Alexei Starovoitov](/assets/img/avatar_default.png)
Add per-program counter for number of times recursion prevention mechanism was triggered and expose it via show_fdinfo and bpf_prog_info. Teach bpftool to print it. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20210210033634.62081-7-alexei.starovoitov@gmail.com
498 lines
12 KiB
C
498 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2019 Facebook */
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#include <linux/hash.h>
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#include <linux/bpf.h>
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#include <linux/filter.h>
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#include <linux/ftrace.h>
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#include <linux/rbtree_latch.h>
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#include <linux/perf_event.h>
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#include <linux/btf.h>
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#include <linux/rcupdate_trace.h>
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#include <linux/rcupdate_wait.h>
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/* dummy _ops. The verifier will operate on target program's ops. */
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const struct bpf_verifier_ops bpf_extension_verifier_ops = {
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};
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const struct bpf_prog_ops bpf_extension_prog_ops = {
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};
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/* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */
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#define TRAMPOLINE_HASH_BITS 10
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#define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)
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static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
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/* serializes access to trampoline_table */
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static DEFINE_MUTEX(trampoline_mutex);
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void *bpf_jit_alloc_exec_page(void)
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{
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void *image;
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image = bpf_jit_alloc_exec(PAGE_SIZE);
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if (!image)
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return NULL;
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set_vm_flush_reset_perms(image);
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/* Keep image as writeable. The alternative is to keep flipping ro/rw
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* everytime new program is attached or detached.
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*/
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set_memory_x((long)image, 1);
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return image;
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}
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void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym)
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{
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ksym->start = (unsigned long) data;
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ksym->end = ksym->start + PAGE_SIZE;
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bpf_ksym_add(ksym);
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perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
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PAGE_SIZE, false, ksym->name);
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}
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void bpf_image_ksym_del(struct bpf_ksym *ksym)
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{
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bpf_ksym_del(ksym);
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perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
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PAGE_SIZE, true, ksym->name);
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}
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static void bpf_trampoline_ksym_add(struct bpf_trampoline *tr)
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{
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struct bpf_ksym *ksym = &tr->ksym;
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snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu", tr->key);
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bpf_image_ksym_add(tr->image, ksym);
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}
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static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
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{
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struct bpf_trampoline *tr;
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struct hlist_head *head;
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void *image;
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int i;
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mutex_lock(&trampoline_mutex);
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head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
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hlist_for_each_entry(tr, head, hlist) {
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if (tr->key == key) {
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refcount_inc(&tr->refcnt);
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goto out;
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}
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}
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tr = kzalloc(sizeof(*tr), GFP_KERNEL);
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if (!tr)
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goto out;
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/* is_root was checked earlier. No need for bpf_jit_charge_modmem() */
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image = bpf_jit_alloc_exec_page();
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if (!image) {
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kfree(tr);
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tr = NULL;
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goto out;
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}
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tr->key = key;
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INIT_HLIST_NODE(&tr->hlist);
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hlist_add_head(&tr->hlist, head);
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refcount_set(&tr->refcnt, 1);
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mutex_init(&tr->mutex);
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for (i = 0; i < BPF_TRAMP_MAX; i++)
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INIT_HLIST_HEAD(&tr->progs_hlist[i]);
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tr->image = image;
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INIT_LIST_HEAD_RCU(&tr->ksym.lnode);
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bpf_trampoline_ksym_add(tr);
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out:
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mutex_unlock(&trampoline_mutex);
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return tr;
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}
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static int is_ftrace_location(void *ip)
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{
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long addr;
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addr = ftrace_location((long)ip);
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if (!addr)
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return 0;
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if (WARN_ON_ONCE(addr != (long)ip))
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return -EFAULT;
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return 1;
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}
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static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
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{
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void *ip = tr->func.addr;
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int ret;
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if (tr->func.ftrace_managed)
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ret = unregister_ftrace_direct((long)ip, (long)old_addr);
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else
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ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
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return ret;
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}
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static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
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{
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void *ip = tr->func.addr;
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int ret;
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if (tr->func.ftrace_managed)
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ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
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else
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ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
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return ret;
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}
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/* first time registering */
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static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
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{
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void *ip = tr->func.addr;
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int ret;
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ret = is_ftrace_location(ip);
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if (ret < 0)
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return ret;
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tr->func.ftrace_managed = ret;
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if (tr->func.ftrace_managed)
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ret = register_ftrace_direct((long)ip, (long)new_addr);
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else
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ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
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return ret;
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}
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static struct bpf_tramp_progs *
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bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total)
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{
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const struct bpf_prog_aux *aux;
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struct bpf_tramp_progs *tprogs;
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struct bpf_prog **progs;
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int kind;
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*total = 0;
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tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
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if (!tprogs)
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return ERR_PTR(-ENOMEM);
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for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
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tprogs[kind].nr_progs = tr->progs_cnt[kind];
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*total += tr->progs_cnt[kind];
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progs = tprogs[kind].progs;
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hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist)
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*progs++ = aux->prog;
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}
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return tprogs;
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}
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static int bpf_trampoline_update(struct bpf_trampoline *tr)
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{
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void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
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void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
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struct bpf_tramp_progs *tprogs;
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u32 flags = BPF_TRAMP_F_RESTORE_REGS;
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int err, total;
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tprogs = bpf_trampoline_get_progs(tr, &total);
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if (IS_ERR(tprogs))
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return PTR_ERR(tprogs);
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if (total == 0) {
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err = unregister_fentry(tr, old_image);
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tr->selector = 0;
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goto out;
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}
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if (tprogs[BPF_TRAMP_FEXIT].nr_progs ||
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tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs)
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flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
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/* Though the second half of trampoline page is unused a task could be
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* preempted in the middle of the first half of trampoline and two
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* updates to trampoline would change the code from underneath the
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* preempted task. Hence wait for tasks to voluntarily schedule or go
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* to userspace.
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* The same trampoline can hold both sleepable and non-sleepable progs.
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* synchronize_rcu_tasks_trace() is needed to make sure all sleepable
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* programs finish executing.
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* Wait for these two grace periods together.
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*/
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synchronize_rcu_mult(call_rcu_tasks, call_rcu_tasks_trace);
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err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2,
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&tr->func.model, flags, tprogs,
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tr->func.addr);
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if (err < 0)
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goto out;
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if (tr->selector)
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/* progs already running at this address */
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err = modify_fentry(tr, old_image, new_image);
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else
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/* first time registering */
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err = register_fentry(tr, new_image);
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if (err)
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goto out;
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tr->selector++;
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out:
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kfree(tprogs);
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return err;
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}
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static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
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{
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switch (prog->expected_attach_type) {
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case BPF_TRACE_FENTRY:
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return BPF_TRAMP_FENTRY;
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case BPF_MODIFY_RETURN:
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return BPF_TRAMP_MODIFY_RETURN;
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case BPF_TRACE_FEXIT:
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return BPF_TRAMP_FEXIT;
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case BPF_LSM_MAC:
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if (!prog->aux->attach_func_proto->type)
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/* The function returns void, we cannot modify its
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* return value.
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*/
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return BPF_TRAMP_FEXIT;
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else
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return BPF_TRAMP_MODIFY_RETURN;
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default:
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return BPF_TRAMP_REPLACE;
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}
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}
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int bpf_trampoline_link_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
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{
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enum bpf_tramp_prog_type kind;
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int err = 0;
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int cnt;
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kind = bpf_attach_type_to_tramp(prog);
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mutex_lock(&tr->mutex);
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if (tr->extension_prog) {
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/* cannot attach fentry/fexit if extension prog is attached.
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* cannot overwrite extension prog either.
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*/
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err = -EBUSY;
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goto out;
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}
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cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT];
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if (kind == BPF_TRAMP_REPLACE) {
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/* Cannot attach extension if fentry/fexit are in use. */
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if (cnt) {
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err = -EBUSY;
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goto out;
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}
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tr->extension_prog = prog;
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err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL,
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prog->bpf_func);
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goto out;
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}
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if (cnt >= BPF_MAX_TRAMP_PROGS) {
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err = -E2BIG;
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goto out;
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}
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if (!hlist_unhashed(&prog->aux->tramp_hlist)) {
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/* prog already linked */
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err = -EBUSY;
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goto out;
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}
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hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]);
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tr->progs_cnt[kind]++;
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err = bpf_trampoline_update(tr);
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if (err) {
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hlist_del(&prog->aux->tramp_hlist);
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tr->progs_cnt[kind]--;
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}
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out:
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mutex_unlock(&tr->mutex);
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return err;
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}
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/* bpf_trampoline_unlink_prog() should never fail. */
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int bpf_trampoline_unlink_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
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{
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enum bpf_tramp_prog_type kind;
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int err;
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kind = bpf_attach_type_to_tramp(prog);
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mutex_lock(&tr->mutex);
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if (kind == BPF_TRAMP_REPLACE) {
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WARN_ON_ONCE(!tr->extension_prog);
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err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP,
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tr->extension_prog->bpf_func, NULL);
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tr->extension_prog = NULL;
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goto out;
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}
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hlist_del(&prog->aux->tramp_hlist);
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tr->progs_cnt[kind]--;
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err = bpf_trampoline_update(tr);
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out:
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mutex_unlock(&tr->mutex);
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return err;
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}
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struct bpf_trampoline *bpf_trampoline_get(u64 key,
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struct bpf_attach_target_info *tgt_info)
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{
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struct bpf_trampoline *tr;
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tr = bpf_trampoline_lookup(key);
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if (!tr)
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return NULL;
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mutex_lock(&tr->mutex);
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if (tr->func.addr)
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goto out;
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memcpy(&tr->func.model, &tgt_info->fmodel, sizeof(tgt_info->fmodel));
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tr->func.addr = (void *)tgt_info->tgt_addr;
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out:
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mutex_unlock(&tr->mutex);
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return tr;
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}
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void bpf_trampoline_put(struct bpf_trampoline *tr)
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{
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if (!tr)
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return;
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mutex_lock(&trampoline_mutex);
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if (!refcount_dec_and_test(&tr->refcnt))
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goto out;
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WARN_ON_ONCE(mutex_is_locked(&tr->mutex));
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if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY])))
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goto out;
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if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
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goto out;
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bpf_image_ksym_del(&tr->ksym);
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/* This code will be executed when all bpf progs (both sleepable and
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* non-sleepable) went through
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* bpf_prog_put()->call_rcu[_tasks_trace]()->bpf_prog_free_deferred().
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* Hence no need for another synchronize_rcu_tasks_trace() here,
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* but synchronize_rcu_tasks() is still needed, since trampoline
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* may not have had any sleepable programs and we need to wait
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* for tasks to get out of trampoline code before freeing it.
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*/
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synchronize_rcu_tasks();
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bpf_jit_free_exec(tr->image);
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hlist_del(&tr->hlist);
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kfree(tr);
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out:
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mutex_unlock(&trampoline_mutex);
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}
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#define NO_START_TIME 1
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static u64 notrace bpf_prog_start_time(void)
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{
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u64 start = NO_START_TIME;
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if (static_branch_unlikely(&bpf_stats_enabled_key)) {
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start = sched_clock();
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if (unlikely(!start))
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start = NO_START_TIME;
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}
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return start;
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}
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static void notrace inc_misses_counter(struct bpf_prog *prog)
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{
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struct bpf_prog_stats *stats;
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stats = this_cpu_ptr(prog->stats);
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u64_stats_update_begin(&stats->syncp);
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stats->misses++;
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u64_stats_update_end(&stats->syncp);
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}
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/* The logic is similar to BPF_PROG_RUN, but with an explicit
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* rcu_read_lock() and migrate_disable() which are required
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* for the trampoline. The macro is split into
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* call __bpf_prog_enter
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* call prog->bpf_func
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* call __bpf_prog_exit
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*
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* __bpf_prog_enter returns:
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* 0 - skip execution of the bpf prog
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* 1 - execute bpf prog
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* [2..MAX_U64] - excute bpf prog and record execution time.
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* This is start time.
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*/
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u64 notrace __bpf_prog_enter(struct bpf_prog *prog)
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__acquires(RCU)
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{
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rcu_read_lock();
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migrate_disable();
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if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
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inc_misses_counter(prog);
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return 0;
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}
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return bpf_prog_start_time();
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}
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static void notrace update_prog_stats(struct bpf_prog *prog,
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u64 start)
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{
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struct bpf_prog_stats *stats;
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if (static_branch_unlikely(&bpf_stats_enabled_key) &&
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/* static_key could be enabled in __bpf_prog_enter*
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* and disabled in __bpf_prog_exit*.
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* And vice versa.
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* Hence check that 'start' is valid.
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*/
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start > NO_START_TIME) {
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stats = this_cpu_ptr(prog->stats);
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u64_stats_update_begin(&stats->syncp);
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stats->cnt++;
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stats->nsecs += sched_clock() - start;
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u64_stats_update_end(&stats->syncp);
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}
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}
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void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start)
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__releases(RCU)
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{
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update_prog_stats(prog, start);
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__this_cpu_dec(*(prog->active));
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migrate_enable();
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rcu_read_unlock();
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}
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u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog)
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{
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rcu_read_lock_trace();
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migrate_disable();
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might_fault();
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if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
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inc_misses_counter(prog);
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return 0;
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}
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return bpf_prog_start_time();
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}
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void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start)
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{
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update_prog_stats(prog, start);
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__this_cpu_dec(*(prog->active));
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migrate_enable();
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rcu_read_unlock_trace();
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}
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int __weak
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arch_prepare_bpf_trampoline(void *image, void *image_end,
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const struct btf_func_model *m, u32 flags,
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struct bpf_tramp_progs *tprogs,
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void *orig_call)
|
|
{
|
|
return -ENOTSUPP;
|
|
}
|
|
|
|
static int __init init_trampolines(void)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
|
|
INIT_HLIST_HEAD(&trampoline_table[i]);
|
|
return 0;
|
|
}
|
|
late_initcall(init_trampolines);
|