457 lines
13 KiB
C
457 lines
13 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2020 - Google LLC
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* Author: David Brazdil <dbrazdil@google.com>
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*
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* Generates relocation information used by the kernel to convert
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* absolute addresses in hyp data from kernel VAs to hyp VAs.
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*
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* This is necessary because hyp code is linked into the same binary
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* as the kernel but executes under different memory mappings.
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* If the compiler used absolute addressing, those addresses need to
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* be converted before they are used by hyp code.
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*
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* The input of this program is the relocatable ELF object containing
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* all hyp code/data, not yet linked into vmlinux. Hyp section names
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* should have been prefixed with `.hyp` at this point.
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*
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* The output (printed to stdout) is an assembly file containing
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* an array of 32-bit integers and static relocations that instruct
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* the linker of `vmlinux` to populate the array entries with offsets
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* to positions in the kernel binary containing VAs used by hyp code.
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*
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* Note that dynamic relocations could be used for the same purpose.
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* However, those are only generated if CONFIG_RELOCATABLE=y.
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*/
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#include <elf.h>
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#include <endian.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <stdbool.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/mman.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include <generated/autoconf.h>
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#define HYP_SECTION_PREFIX ".hyp"
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#define HYP_RELOC_SECTION ".hyp.reloc"
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#define HYP_SECTION_SYMBOL_PREFIX "__hyp_section_"
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/*
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* AArch64 relocation type constants.
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* Included in case these are not defined in the host toolchain.
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*/
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#ifndef R_AARCH64_ABS64
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#define R_AARCH64_ABS64 257
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#endif
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#ifndef R_AARCH64_PREL64
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#define R_AARCH64_PREL64 260
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#endif
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#ifndef R_AARCH64_PREL32
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#define R_AARCH64_PREL32 261
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#endif
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#ifndef R_AARCH64_PREL16
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#define R_AARCH64_PREL16 262
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#endif
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#ifndef R_AARCH64_PLT32
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#define R_AARCH64_PLT32 314
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#endif
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#ifndef R_AARCH64_LD_PREL_LO19
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#define R_AARCH64_LD_PREL_LO19 273
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#endif
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#ifndef R_AARCH64_ADR_PREL_LO21
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#define R_AARCH64_ADR_PREL_LO21 274
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#endif
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#ifndef R_AARCH64_ADR_PREL_PG_HI21
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#define R_AARCH64_ADR_PREL_PG_HI21 275
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#endif
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#ifndef R_AARCH64_ADR_PREL_PG_HI21_NC
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#define R_AARCH64_ADR_PREL_PG_HI21_NC 276
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#endif
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#ifndef R_AARCH64_ADD_ABS_LO12_NC
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#define R_AARCH64_ADD_ABS_LO12_NC 277
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#endif
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#ifndef R_AARCH64_LDST8_ABS_LO12_NC
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#define R_AARCH64_LDST8_ABS_LO12_NC 278
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#endif
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#ifndef R_AARCH64_TSTBR14
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#define R_AARCH64_TSTBR14 279
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#endif
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#ifndef R_AARCH64_CONDBR19
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#define R_AARCH64_CONDBR19 280
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#endif
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#ifndef R_AARCH64_JUMP26
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#define R_AARCH64_JUMP26 282
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#endif
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#ifndef R_AARCH64_CALL26
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#define R_AARCH64_CALL26 283
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#endif
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#ifndef R_AARCH64_LDST16_ABS_LO12_NC
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#define R_AARCH64_LDST16_ABS_LO12_NC 284
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#endif
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#ifndef R_AARCH64_LDST32_ABS_LO12_NC
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#define R_AARCH64_LDST32_ABS_LO12_NC 285
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#endif
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#ifndef R_AARCH64_LDST64_ABS_LO12_NC
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#define R_AARCH64_LDST64_ABS_LO12_NC 286
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#endif
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#ifndef R_AARCH64_MOVW_PREL_G0
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#define R_AARCH64_MOVW_PREL_G0 287
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#endif
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#ifndef R_AARCH64_MOVW_PREL_G0_NC
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#define R_AARCH64_MOVW_PREL_G0_NC 288
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#endif
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#ifndef R_AARCH64_MOVW_PREL_G1
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#define R_AARCH64_MOVW_PREL_G1 289
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#endif
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#ifndef R_AARCH64_MOVW_PREL_G1_NC
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#define R_AARCH64_MOVW_PREL_G1_NC 290
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#endif
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#ifndef R_AARCH64_MOVW_PREL_G2
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#define R_AARCH64_MOVW_PREL_G2 291
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#endif
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#ifndef R_AARCH64_MOVW_PREL_G2_NC
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#define R_AARCH64_MOVW_PREL_G2_NC 292
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#endif
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#ifndef R_AARCH64_MOVW_PREL_G3
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#define R_AARCH64_MOVW_PREL_G3 293
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#endif
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#ifndef R_AARCH64_LDST128_ABS_LO12_NC
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#define R_AARCH64_LDST128_ABS_LO12_NC 299
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#endif
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/* Global state of the processed ELF. */
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static struct {
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const char *path;
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char *begin;
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size_t size;
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Elf64_Ehdr *ehdr;
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Elf64_Shdr *sh_table;
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const char *sh_string;
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} elf;
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#if defined(CONFIG_CPU_LITTLE_ENDIAN)
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#define elf16toh(x) le16toh(x)
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#define elf32toh(x) le32toh(x)
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#define elf64toh(x) le64toh(x)
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#define ELFENDIAN ELFDATA2LSB
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#elif defined(CONFIG_CPU_BIG_ENDIAN)
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#define elf16toh(x) be16toh(x)
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#define elf32toh(x) be32toh(x)
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#define elf64toh(x) be64toh(x)
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#define ELFENDIAN ELFDATA2MSB
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#else
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#error PDP-endian sadly unsupported...
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#endif
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#define fatal_error(fmt, ...) \
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({ \
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fprintf(stderr, "error: %s: " fmt "\n", \
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elf.path, ## __VA_ARGS__); \
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exit(EXIT_FAILURE); \
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__builtin_unreachable(); \
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})
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#define fatal_perror(msg) \
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({ \
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fprintf(stderr, "error: %s: " msg ": %s\n", \
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elf.path, strerror(errno)); \
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exit(EXIT_FAILURE); \
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__builtin_unreachable(); \
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})
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#define assert_op(lhs, rhs, fmt, op) \
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({ \
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typeof(lhs) _lhs = (lhs); \
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typeof(rhs) _rhs = (rhs); \
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\
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if (!(_lhs op _rhs)) { \
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fatal_error("assertion " #lhs " " #op " " #rhs \
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" failed (lhs=" fmt ", rhs=" fmt \
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", line=%d)", _lhs, _rhs, __LINE__); \
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} \
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})
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#define assert_eq(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, ==)
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#define assert_ne(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, !=)
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#define assert_lt(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, <)
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#define assert_ge(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, >=)
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/*
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* Return a pointer of a given type at a given offset from
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* the beginning of the ELF file.
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*/
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#define elf_ptr(type, off) ((type *)(elf.begin + (off)))
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/* Iterate over all sections in the ELF. */
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#define for_each_section(var) \
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for (var = elf.sh_table; var < elf.sh_table + elf16toh(elf.ehdr->e_shnum); ++var)
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/* Iterate over all Elf64_Rela relocations in a given section. */
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#define for_each_rela(shdr, var) \
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for (var = elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset)); \
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var < elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset) + elf64toh(shdr->sh_size)); var++)
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/* True if a string starts with a given prefix. */
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static inline bool starts_with(const char *str, const char *prefix)
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{
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return memcmp(str, prefix, strlen(prefix)) == 0;
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}
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/* Returns a string containing the name of a given section. */
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static inline const char *section_name(Elf64_Shdr *shdr)
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{
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return elf.sh_string + elf32toh(shdr->sh_name);
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}
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/* Returns a pointer to the first byte of section data. */
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static inline const char *section_begin(Elf64_Shdr *shdr)
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{
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return elf_ptr(char, elf64toh(shdr->sh_offset));
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}
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/* Find a section by its offset from the beginning of the file. */
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static inline Elf64_Shdr *section_by_off(Elf64_Off off)
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{
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assert_ne(off, 0UL, "%lu");
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return elf_ptr(Elf64_Shdr, off);
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}
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/* Find a section by its index. */
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static inline Elf64_Shdr *section_by_idx(uint16_t idx)
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{
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assert_ne(idx, SHN_UNDEF, "%u");
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return &elf.sh_table[idx];
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}
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/*
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* Memory-map the given ELF file, perform sanity checks, and
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* populate global state.
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*/
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static void init_elf(const char *path)
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{
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int fd, ret;
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struct stat stat;
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/* Store path in the global struct for error printing. */
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elf.path = path;
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/* Open the ELF file. */
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fd = open(path, O_RDONLY);
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if (fd < 0)
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fatal_perror("Could not open ELF file");
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/* Get status of ELF file to obtain its size. */
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ret = fstat(fd, &stat);
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if (ret < 0) {
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close(fd);
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fatal_perror("Could not get status of ELF file");
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}
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/* mmap() the entire ELF file read-only at an arbitrary address. */
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elf.begin = mmap(0, stat.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
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if (elf.begin == MAP_FAILED) {
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close(fd);
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fatal_perror("Could not mmap ELF file");
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}
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/* mmap() was successful, close the FD. */
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close(fd);
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/* Get pointer to the ELF header. */
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assert_ge(stat.st_size, sizeof(*elf.ehdr), "%lu");
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elf.ehdr = elf_ptr(Elf64_Ehdr, 0);
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/* Check the ELF magic. */
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assert_eq(elf.ehdr->e_ident[EI_MAG0], ELFMAG0, "0x%x");
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assert_eq(elf.ehdr->e_ident[EI_MAG1], ELFMAG1, "0x%x");
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assert_eq(elf.ehdr->e_ident[EI_MAG2], ELFMAG2, "0x%x");
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assert_eq(elf.ehdr->e_ident[EI_MAG3], ELFMAG3, "0x%x");
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/* Sanity check that this is an ELF64 relocatable object for AArch64. */
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assert_eq(elf.ehdr->e_ident[EI_CLASS], ELFCLASS64, "%u");
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assert_eq(elf.ehdr->e_ident[EI_DATA], ELFENDIAN, "%u");
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assert_eq(elf16toh(elf.ehdr->e_type), ET_REL, "%u");
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assert_eq(elf16toh(elf.ehdr->e_machine), EM_AARCH64, "%u");
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/* Populate fields of the global struct. */
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elf.sh_table = section_by_off(elf64toh(elf.ehdr->e_shoff));
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elf.sh_string = section_begin(section_by_idx(elf16toh(elf.ehdr->e_shstrndx)));
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}
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/* Print the prologue of the output ASM file. */
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static void emit_prologue(void)
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{
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printf(".data\n"
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".pushsection " HYP_RELOC_SECTION ", \"a\"\n");
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}
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/* Print ASM statements needed as a prologue to a processed hyp section. */
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static void emit_section_prologue(const char *sh_orig_name)
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{
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/* Declare the hyp section symbol. */
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printf(".global %s%s\n", HYP_SECTION_SYMBOL_PREFIX, sh_orig_name);
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}
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/*
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* Print ASM statements to create a hyp relocation entry for a given
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* R_AARCH64_ABS64 relocation.
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*
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* The linker of vmlinux will populate the position given by `rela` with
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* an absolute 64-bit kernel VA. If the kernel is relocatable, it will
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* also generate a dynamic relocation entry so that the kernel can shift
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* the address at runtime for KASLR.
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*
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* Emit a 32-bit offset from the current address to the position given
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* by `rela`. This way the kernel can iterate over all kernel VAs used
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* by hyp at runtime and convert them to hyp VAs. However, that offset
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* will not be known until linking of `vmlinux`, so emit a PREL32
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* relocation referencing a symbol that the hyp linker script put at
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* the beginning of the relocated section + the offset from `rela`.
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*/
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static void emit_rela_abs64(Elf64_Rela *rela, const char *sh_orig_name)
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{
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/* Offset of this reloc from the beginning of HYP_RELOC_SECTION. */
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static size_t reloc_offset;
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/* Create storage for the 32-bit offset. */
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printf(".word 0\n");
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/*
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* Create a PREL32 relocation which instructs the linker of `vmlinux`
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* to insert offset to position <base> + <offset>, where <base> is
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* a symbol at the beginning of the relocated section, and <offset>
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* is `rela->r_offset`.
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*/
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printf(".reloc %lu, R_AARCH64_PREL32, %s%s + 0x%lx\n",
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reloc_offset, HYP_SECTION_SYMBOL_PREFIX, sh_orig_name,
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elf64toh(rela->r_offset));
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reloc_offset += 4;
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}
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/* Print the epilogue of the output ASM file. */
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static void emit_epilogue(void)
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{
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printf(".popsection\n");
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}
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/*
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* Iterate over all RELA relocations in a given section and emit
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* hyp relocation data for all absolute addresses in hyp code/data.
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*
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* Static relocations that generate PC-relative-addressing are ignored.
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* Failure is reported for unexpected relocation types.
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*/
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static void emit_rela_section(Elf64_Shdr *sh_rela)
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{
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Elf64_Shdr *sh_orig = &elf.sh_table[elf32toh(sh_rela->sh_info)];
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const char *sh_orig_name = section_name(sh_orig);
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Elf64_Rela *rela;
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/* Skip all non-hyp sections. */
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if (!starts_with(sh_orig_name, HYP_SECTION_PREFIX))
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return;
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emit_section_prologue(sh_orig_name);
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for_each_rela(sh_rela, rela) {
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uint32_t type = (uint32_t)elf64toh(rela->r_info);
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/* Check that rela points inside the relocated section. */
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assert_lt(elf64toh(rela->r_offset), elf64toh(sh_orig->sh_size), "0x%lx");
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switch (type) {
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/*
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* Data relocations to generate absolute addressing.
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* Emit a hyp relocation.
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*/
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case R_AARCH64_ABS64:
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emit_rela_abs64(rela, sh_orig_name);
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break;
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/* Allow position-relative data relocations. */
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case R_AARCH64_PREL64:
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case R_AARCH64_PREL32:
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case R_AARCH64_PREL16:
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case R_AARCH64_PLT32:
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break;
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/* Allow relocations to generate PC-relative addressing. */
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case R_AARCH64_LD_PREL_LO19:
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case R_AARCH64_ADR_PREL_LO21:
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case R_AARCH64_ADR_PREL_PG_HI21:
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case R_AARCH64_ADR_PREL_PG_HI21_NC:
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case R_AARCH64_ADD_ABS_LO12_NC:
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case R_AARCH64_LDST8_ABS_LO12_NC:
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case R_AARCH64_LDST16_ABS_LO12_NC:
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case R_AARCH64_LDST32_ABS_LO12_NC:
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case R_AARCH64_LDST64_ABS_LO12_NC:
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case R_AARCH64_LDST128_ABS_LO12_NC:
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break;
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/* Allow relative relocations for control-flow instructions. */
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case R_AARCH64_TSTBR14:
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case R_AARCH64_CONDBR19:
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case R_AARCH64_JUMP26:
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case R_AARCH64_CALL26:
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break;
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/* Allow group relocations to create PC-relative offset inline. */
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case R_AARCH64_MOVW_PREL_G0:
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case R_AARCH64_MOVW_PREL_G0_NC:
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case R_AARCH64_MOVW_PREL_G1:
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case R_AARCH64_MOVW_PREL_G1_NC:
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case R_AARCH64_MOVW_PREL_G2:
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case R_AARCH64_MOVW_PREL_G2_NC:
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case R_AARCH64_MOVW_PREL_G3:
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break;
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default:
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fatal_error("Unexpected RELA type %u", type);
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}
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}
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}
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/* Iterate over all sections and emit hyp relocation data for RELA sections. */
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static void emit_all_relocs(void)
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{
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Elf64_Shdr *shdr;
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for_each_section(shdr) {
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switch (elf32toh(shdr->sh_type)) {
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case SHT_REL:
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fatal_error("Unexpected SHT_REL section \"%s\"",
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section_name(shdr));
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case SHT_RELA:
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emit_rela_section(shdr);
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break;
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}
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}
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}
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int main(int argc, const char **argv)
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{
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if (argc != 2) {
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fprintf(stderr, "Usage: %s <elf_input>\n", argv[0]);
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return EXIT_FAILURE;
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}
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init_elf(argv[1]);
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emit_prologue();
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emit_all_relocs();
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emit_epilogue();
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return EXIT_SUCCESS;
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}
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