160 lines
3.6 KiB
C
160 lines
3.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright(c) 2019 Intel Corporation. */
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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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/* The BPF dispatcher is a multiway branch code generator. The
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* dispatcher is a mechanism to avoid the performance penalty of an
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* indirect call, which is expensive when retpolines are enabled. A
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* dispatch client registers a BPF program into the dispatcher, and if
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* there is available room in the dispatcher a direct call to the BPF
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* program will be generated. All calls to the BPF programs called via
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* the dispatcher will then be a direct call, instead of an
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* indirect. The dispatcher hijacks a trampoline function it via the
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* __fentry__ of the trampoline. The trampoline function has the
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* following signature:
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*
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* unsigned int trampoline(const void *ctx, const struct bpf_insn *insnsi,
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* unsigned int (*bpf_func)(const void *,
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* const struct bpf_insn *));
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*/
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static struct bpf_dispatcher_prog *bpf_dispatcher_find_prog(
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struct bpf_dispatcher *d, struct bpf_prog *prog)
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{
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int i;
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for (i = 0; i < BPF_DISPATCHER_MAX; i++) {
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if (prog == d->progs[i].prog)
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return &d->progs[i];
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}
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return NULL;
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}
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static struct bpf_dispatcher_prog *bpf_dispatcher_find_free(
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struct bpf_dispatcher *d)
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{
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return bpf_dispatcher_find_prog(d, NULL);
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}
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static bool bpf_dispatcher_add_prog(struct bpf_dispatcher *d,
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struct bpf_prog *prog)
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{
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struct bpf_dispatcher_prog *entry;
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if (!prog)
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return false;
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entry = bpf_dispatcher_find_prog(d, prog);
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if (entry) {
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refcount_inc(&entry->users);
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return false;
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}
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entry = bpf_dispatcher_find_free(d);
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if (!entry)
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return false;
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bpf_prog_inc(prog);
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entry->prog = prog;
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refcount_set(&entry->users, 1);
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d->num_progs++;
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return true;
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}
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static bool bpf_dispatcher_remove_prog(struct bpf_dispatcher *d,
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struct bpf_prog *prog)
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{
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struct bpf_dispatcher_prog *entry;
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if (!prog)
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return false;
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entry = bpf_dispatcher_find_prog(d, prog);
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if (!entry)
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return false;
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if (refcount_dec_and_test(&entry->users)) {
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entry->prog = NULL;
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bpf_prog_put(prog);
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d->num_progs--;
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return true;
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}
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return false;
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}
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int __weak arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs)
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{
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return -ENOTSUPP;
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}
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static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image)
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{
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s64 ips[BPF_DISPATCHER_MAX] = {}, *ipsp = &ips[0];
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int i;
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for (i = 0; i < BPF_DISPATCHER_MAX; i++) {
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if (d->progs[i].prog)
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*ipsp++ = (s64)(uintptr_t)d->progs[i].prog->bpf_func;
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}
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return arch_prepare_bpf_dispatcher(image, &ips[0], d->num_progs);
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}
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static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
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{
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void *old, *new;
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u32 noff;
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int err;
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if (!prev_num_progs) {
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old = NULL;
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noff = 0;
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} else {
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old = d->image + d->image_off;
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noff = d->image_off ^ (PAGE_SIZE / 2);
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}
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new = d->num_progs ? d->image + noff : NULL;
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if (new) {
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if (bpf_dispatcher_prepare(d, new))
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return;
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}
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err = bpf_arch_text_poke(d->func, BPF_MOD_JUMP, old, new);
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if (err || !new)
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return;
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d->image_off = noff;
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}
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void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,
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struct bpf_prog *to)
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{
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bool changed = false;
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int prev_num_progs;
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if (from == to)
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return;
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mutex_lock(&d->mutex);
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if (!d->image) {
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d->image = bpf_jit_alloc_exec_page();
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if (!d->image)
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goto out;
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bpf_image_ksym_add(d->image, &d->ksym);
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}
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prev_num_progs = d->num_progs;
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changed |= bpf_dispatcher_remove_prog(d, from);
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changed |= bpf_dispatcher_add_prog(d, to);
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if (!changed)
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goto out;
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bpf_dispatcher_update(d, prev_num_progs);
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out:
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mutex_unlock(&d->mutex);
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}
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