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d8eca5bbb2
This generic extension to BPF maps allows for directly loading an address residing inside a BPF map value as a single BPF ldimm64 instruction! The idea is similar to what BPF_PSEUDO_MAP_FD does today, which is a special src_reg flag for ldimm64 instruction that indicates that inside the first part of the double insns's imm field is a file descriptor which the verifier then replaces as a full 64bit address of the map into both imm parts. For the newly added BPF_PSEUDO_MAP_VALUE src_reg flag, the idea is the following: the first part of the double insns's imm field is again a file descriptor corresponding to the map, and the second part of the imm field is an offset into the value. The verifier will then replace both imm parts with an address that points into the BPF map value at the given value offset for maps that support this operation. Currently supported is array map with single entry. It is possible to support more than just single map element by reusing both 16bit off fields of the insns as a map index, so full array map lookup could be expressed that way. It hasn't been implemented here due to lack of concrete use case, but could easily be done so in future in a compatible way, since both off fields right now have to be 0 and would correctly denote a map index 0. The BPF_PSEUDO_MAP_VALUE is a distinct flag as otherwise with BPF_PSEUDO_MAP_FD we could not differ offset 0 between load of map pointer versus load of map's value at offset 0, and changing BPF_PSEUDO_MAP_FD's encoding into off by one to differ between regular map pointer and map value pointer would add unnecessary complexity and increases barrier for debugability thus less suitable. Using the second part of the imm field as an offset into the value does /not/ come with limitations since maximum possible value size is in u32 universe anyway. This optimization allows for efficiently retrieving an address to a map value memory area without having to issue a helper call which needs to prepare registers according to calling convention, etc, without needing the extra NULL test, and without having to add the offset in an additional instruction to the value base pointer. The verifier then treats the destination register as PTR_TO_MAP_VALUE with constant reg->off from the user passed offset from the second imm field, and guarantees that this is within bounds of the map value. Any subsequent operations are normally treated as typical map value handling without anything extra needed from verification side. The two map operations for direct value access have been added to array map for now. In future other types could be supported as well depending on the use case. The main use case for this commit is to allow for BPF loader support for global variables that reside in .data/.rodata/.bss sections such that we can directly load the address of them with minimal additional infrastructure required. Loader support has been added in subsequent commits for libbpf library. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
376 lines
8.8 KiB
C
376 lines
8.8 KiB
C
// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
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/* Copyright (C) 2018 Netronome Systems, Inc. */
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#define _GNU_SOURCE
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#include <stdarg.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/types.h>
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#include <libbpf.h>
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#include "disasm.h"
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#include "json_writer.h"
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#include "main.h"
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#include "xlated_dumper.h"
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static int kernel_syms_cmp(const void *sym_a, const void *sym_b)
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{
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return ((struct kernel_sym *)sym_a)->address -
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((struct kernel_sym *)sym_b)->address;
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}
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void kernel_syms_load(struct dump_data *dd)
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{
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struct kernel_sym *sym;
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char buff[256];
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void *tmp, *address;
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FILE *fp;
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fp = fopen("/proc/kallsyms", "r");
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if (!fp)
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return;
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while (!feof(fp)) {
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if (!fgets(buff, sizeof(buff), fp))
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break;
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tmp = reallocarray(dd->sym_mapping, dd->sym_count + 1,
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sizeof(*dd->sym_mapping));
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if (!tmp) {
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out:
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free(dd->sym_mapping);
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dd->sym_mapping = NULL;
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fclose(fp);
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return;
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}
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dd->sym_mapping = tmp;
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sym = &dd->sym_mapping[dd->sym_count];
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if (sscanf(buff, "%p %*c %s", &address, sym->name) != 2)
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continue;
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sym->address = (unsigned long)address;
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if (!strcmp(sym->name, "__bpf_call_base")) {
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dd->address_call_base = sym->address;
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/* sysctl kernel.kptr_restrict was set */
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if (!sym->address)
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goto out;
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}
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if (sym->address)
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dd->sym_count++;
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}
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fclose(fp);
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qsort(dd->sym_mapping, dd->sym_count,
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sizeof(*dd->sym_mapping), kernel_syms_cmp);
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}
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void kernel_syms_destroy(struct dump_data *dd)
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{
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free(dd->sym_mapping);
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}
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struct kernel_sym *kernel_syms_search(struct dump_data *dd,
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unsigned long key)
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{
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struct kernel_sym sym = {
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.address = key,
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};
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return dd->sym_mapping ?
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bsearch(&sym, dd->sym_mapping, dd->sym_count,
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sizeof(*dd->sym_mapping), kernel_syms_cmp) : NULL;
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}
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static void __printf(2, 3) print_insn(void *private_data, const char *fmt, ...)
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{
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va_list args;
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va_start(args, fmt);
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vprintf(fmt, args);
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va_end(args);
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}
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static void __printf(2, 3)
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print_insn_for_graph(void *private_data, const char *fmt, ...)
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{
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char buf[64], *p;
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va_list args;
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va_start(args, fmt);
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vsnprintf(buf, sizeof(buf), fmt, args);
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va_end(args);
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p = buf;
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while (*p != '\0') {
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if (*p == '\n') {
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memmove(p + 3, p, strlen(buf) + 1 - (p - buf));
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/* Align each instruction dump row left. */
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*p++ = '\\';
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*p++ = 'l';
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/* Output multiline concatenation. */
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*p++ = '\\';
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} else if (*p == '<' || *p == '>' || *p == '|' || *p == '&') {
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memmove(p + 1, p, strlen(buf) + 1 - (p - buf));
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/* Escape special character. */
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*p++ = '\\';
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}
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p++;
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}
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printf("%s", buf);
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}
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static void __printf(2, 3)
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print_insn_json(void *private_data, const char *fmt, ...)
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{
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unsigned int l = strlen(fmt);
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char chomped_fmt[l];
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va_list args;
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va_start(args, fmt);
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if (l > 0) {
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strncpy(chomped_fmt, fmt, l - 1);
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chomped_fmt[l - 1] = '\0';
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}
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jsonw_vprintf_enquote(json_wtr, chomped_fmt, args);
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va_end(args);
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}
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static const char *print_call_pcrel(struct dump_data *dd,
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struct kernel_sym *sym,
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unsigned long address,
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const struct bpf_insn *insn)
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{
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if (!dd->nr_jited_ksyms)
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/* Do not show address for interpreted programs */
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"%+d", insn->off);
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else if (sym)
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"%+d#%s", insn->off, sym->name);
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else
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"%+d#0x%lx", insn->off, address);
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return dd->scratch_buff;
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}
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static const char *print_call_helper(struct dump_data *dd,
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struct kernel_sym *sym,
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unsigned long address)
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{
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if (sym)
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"%s", sym->name);
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else
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"0x%lx", address);
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return dd->scratch_buff;
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}
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static const char *print_call(void *private_data,
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const struct bpf_insn *insn)
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{
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struct dump_data *dd = private_data;
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unsigned long address = dd->address_call_base + insn->imm;
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struct kernel_sym *sym;
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if (insn->src_reg == BPF_PSEUDO_CALL &&
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(__u32) insn->imm < dd->nr_jited_ksyms)
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address = dd->jited_ksyms[insn->imm];
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sym = kernel_syms_search(dd, address);
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if (insn->src_reg == BPF_PSEUDO_CALL)
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return print_call_pcrel(dd, sym, address, insn);
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else
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return print_call_helper(dd, sym, address);
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}
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static const char *print_imm(void *private_data,
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const struct bpf_insn *insn,
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__u64 full_imm)
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{
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struct dump_data *dd = private_data;
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if (insn->src_reg == BPF_PSEUDO_MAP_FD)
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"map[id:%u]", insn->imm);
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else if (insn->src_reg == BPF_PSEUDO_MAP_VALUE)
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"map[id:%u][0]+%u", insn->imm, (insn + 1)->imm);
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else
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snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
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"0x%llx", (unsigned long long)full_imm);
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return dd->scratch_buff;
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}
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void dump_xlated_json(struct dump_data *dd, void *buf, unsigned int len,
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bool opcodes, bool linum)
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{
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const struct bpf_prog_linfo *prog_linfo = dd->prog_linfo;
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const struct bpf_insn_cbs cbs = {
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.cb_print = print_insn_json,
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.cb_call = print_call,
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.cb_imm = print_imm,
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.private_data = dd,
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};
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struct bpf_func_info *record;
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struct bpf_insn *insn = buf;
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struct btf *btf = dd->btf;
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bool double_insn = false;
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unsigned int nr_skip = 0;
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char func_sig[1024];
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unsigned int i;
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jsonw_start_array(json_wtr);
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record = dd->func_info;
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for (i = 0; i < len / sizeof(*insn); i++) {
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if (double_insn) {
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double_insn = false;
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continue;
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}
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double_insn = insn[i].code == (BPF_LD | BPF_IMM | BPF_DW);
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jsonw_start_object(json_wtr);
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if (btf && record) {
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if (record->insn_off == i) {
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btf_dumper_type_only(btf, record->type_id,
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func_sig,
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sizeof(func_sig));
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if (func_sig[0] != '\0') {
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jsonw_name(json_wtr, "proto");
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jsonw_string(json_wtr, func_sig);
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}
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record = (void *)record + dd->finfo_rec_size;
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}
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}
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if (prog_linfo) {
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const struct bpf_line_info *linfo;
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linfo = bpf_prog_linfo__lfind(prog_linfo, i, nr_skip);
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if (linfo) {
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btf_dump_linfo_json(btf, linfo, linum);
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nr_skip++;
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}
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}
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jsonw_name(json_wtr, "disasm");
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print_bpf_insn(&cbs, insn + i, true);
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if (opcodes) {
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jsonw_name(json_wtr, "opcodes");
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jsonw_start_object(json_wtr);
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jsonw_name(json_wtr, "code");
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jsonw_printf(json_wtr, "\"0x%02hhx\"", insn[i].code);
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jsonw_name(json_wtr, "src_reg");
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jsonw_printf(json_wtr, "\"0x%hhx\"", insn[i].src_reg);
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jsonw_name(json_wtr, "dst_reg");
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jsonw_printf(json_wtr, "\"0x%hhx\"", insn[i].dst_reg);
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jsonw_name(json_wtr, "off");
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print_hex_data_json((uint8_t *)(&insn[i].off), 2);
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jsonw_name(json_wtr, "imm");
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if (double_insn && i < len - 1)
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print_hex_data_json((uint8_t *)(&insn[i].imm),
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12);
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else
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print_hex_data_json((uint8_t *)(&insn[i].imm),
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4);
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jsonw_end_object(json_wtr);
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}
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jsonw_end_object(json_wtr);
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}
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jsonw_end_array(json_wtr);
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}
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void dump_xlated_plain(struct dump_data *dd, void *buf, unsigned int len,
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bool opcodes, bool linum)
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{
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const struct bpf_prog_linfo *prog_linfo = dd->prog_linfo;
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const struct bpf_insn_cbs cbs = {
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.cb_print = print_insn,
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.cb_call = print_call,
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.cb_imm = print_imm,
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.private_data = dd,
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};
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struct bpf_func_info *record;
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struct bpf_insn *insn = buf;
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struct btf *btf = dd->btf;
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unsigned int nr_skip = 0;
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bool double_insn = false;
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char func_sig[1024];
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unsigned int i;
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record = dd->func_info;
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for (i = 0; i < len / sizeof(*insn); i++) {
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if (double_insn) {
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double_insn = false;
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continue;
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}
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if (btf && record) {
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if (record->insn_off == i) {
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btf_dumper_type_only(btf, record->type_id,
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func_sig,
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sizeof(func_sig));
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if (func_sig[0] != '\0')
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printf("%s:\n", func_sig);
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record = (void *)record + dd->finfo_rec_size;
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}
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}
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if (prog_linfo) {
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const struct bpf_line_info *linfo;
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linfo = bpf_prog_linfo__lfind(prog_linfo, i, nr_skip);
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if (linfo) {
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btf_dump_linfo_plain(btf, linfo, "; ",
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linum);
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nr_skip++;
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}
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}
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double_insn = insn[i].code == (BPF_LD | BPF_IMM | BPF_DW);
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printf("% 4d: ", i);
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print_bpf_insn(&cbs, insn + i, true);
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if (opcodes) {
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printf(" ");
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fprint_hex(stdout, insn + i, 8, " ");
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if (double_insn && i < len - 1) {
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printf(" ");
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fprint_hex(stdout, insn + i + 1, 8, " ");
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}
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printf("\n");
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}
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}
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}
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void dump_xlated_for_graph(struct dump_data *dd, void *buf_start, void *buf_end,
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unsigned int start_idx)
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{
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const struct bpf_insn_cbs cbs = {
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.cb_print = print_insn_for_graph,
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.cb_call = print_call,
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.cb_imm = print_imm,
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.private_data = dd,
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};
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struct bpf_insn *insn_start = buf_start;
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struct bpf_insn *insn_end = buf_end;
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struct bpf_insn *cur = insn_start;
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for (; cur <= insn_end; cur++) {
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printf("% 4d: ", (int)(cur - insn_start + start_idx));
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print_bpf_insn(&cbs, cur, true);
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if (cur != insn_end)
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printf(" | ");
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}
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}
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