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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 | // SPDX-License-Identifier: GPL-2.0-only /* Copyright(c) 2019 Intel Corporation. */ #include <linux/hash.h> #include <linux/bpf.h> #include <linux/filter.h> #include <linux/static_call.h> /* The BPF dispatcher is a multiway branch code generator. The * dispatcher is a mechanism to avoid the performance penalty of an * indirect call, which is expensive when retpolines are enabled. A * dispatch client registers a BPF program into the dispatcher, and if * there is available room in the dispatcher a direct call to the BPF * program will be generated. All calls to the BPF programs called via * the dispatcher will then be a direct call, instead of an * indirect. The dispatcher hijacks a trampoline function it via the * __fentry__ of the trampoline. The trampoline function has the * following signature: * * unsigned int trampoline(const void *ctx, const struct bpf_insn *insnsi, * unsigned int (*bpf_func)(const void *, * const struct bpf_insn *)); */ static struct bpf_dispatcher_prog *bpf_dispatcher_find_prog( struct bpf_dispatcher *d, struct bpf_prog *prog) { int i; for (i = 0; i < BPF_DISPATCHER_MAX; i++) { if (prog == d->progs[i].prog) return &d->progs[i]; } return NULL; } static struct bpf_dispatcher_prog *bpf_dispatcher_find_free( struct bpf_dispatcher *d) { return bpf_dispatcher_find_prog(d, NULL); } static bool bpf_dispatcher_add_prog(struct bpf_dispatcher *d, struct bpf_prog *prog) { struct bpf_dispatcher_prog *entry; if (!prog) return false; entry = bpf_dispatcher_find_prog(d, prog); if (entry) { refcount_inc(&entry->users); return false; } entry = bpf_dispatcher_find_free(d); if (!entry) return false; bpf_prog_inc(prog); entry->prog = prog; refcount_set(&entry->users, 1); d->num_progs++; return true; } static bool bpf_dispatcher_remove_prog(struct bpf_dispatcher *d, struct bpf_prog *prog) { struct bpf_dispatcher_prog *entry; if (!prog) return false; entry = bpf_dispatcher_find_prog(d, prog); if (!entry) return false; if (refcount_dec_and_test(&entry->users)) { entry->prog = NULL; bpf_prog_put(prog); d->num_progs--; return true; } return false; } int __weak arch_prepare_bpf_dispatcher(void *image, void *buf, s64 *funcs, int num_funcs) { return -ENOTSUPP; } static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image, void *buf) { s64 ips[BPF_DISPATCHER_MAX] = {}, *ipsp = &ips[0]; int i; for (i = 0; i < BPF_DISPATCHER_MAX; i++) { if (d->progs[i].prog) *ipsp++ = (s64)(uintptr_t)d->progs[i].prog->bpf_func; } return arch_prepare_bpf_dispatcher(image, buf, &ips[0], d->num_progs); } static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs) { void *new, *tmp; u32 noff = 0; if (prev_num_progs) noff = d->image_off ^ (PAGE_SIZE / 2); new = d->num_progs ? d->image + noff : NULL; tmp = d->num_progs ? d->rw_image + noff : NULL; if (new) { /* Prepare the dispatcher in d->rw_image. Then use * bpf_arch_text_copy to update d->image, which is RO+X. */ if (bpf_dispatcher_prepare(d, new, tmp)) return; if (IS_ERR(bpf_arch_text_copy(new, tmp, PAGE_SIZE / 2))) return; } __BPF_DISPATCHER_UPDATE(d, new ?: (void *)&bpf_dispatcher_nop_func); /* Make sure all the callers executing the previous/old half of the * image leave it, so following update call can modify it safely. */ synchronize_rcu(); if (new) d->image_off = noff; } void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from, struct bpf_prog *to) { bool changed = false; int prev_num_progs; if (from == to) return; mutex_lock(&d->mutex); if (!d->image) { d->image = bpf_prog_pack_alloc(PAGE_SIZE, bpf_jit_fill_hole_with_zero); if (!d->image) goto out; d->rw_image = bpf_jit_alloc_exec(PAGE_SIZE); if (!d->rw_image) { bpf_prog_pack_free(d->image, PAGE_SIZE); d->image = NULL; goto out; } bpf_image_ksym_add(d->image, PAGE_SIZE, &d->ksym); } prev_num_progs = d->num_progs; changed |= bpf_dispatcher_remove_prog(d, from); changed |= bpf_dispatcher_add_prog(d, to); if (!changed) goto out; bpf_dispatcher_update(d, prev_num_progs); out: mutex_unlock(&d->mutex); } |