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