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elf: Use PHDRs instead of sections for resolving relocations 

Co-authored-by: Connor Horman <chorman64@gmail.com>
This commit is contained in:
mintsuki 2022-03-08 21:05:48 +01:00
parent 08547c0d8f
commit f3ffa8723f
1 changed files with 67 additions and 25 deletions
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92
common/lib/elf.c
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@ -9,9 +9,16 @@
#include <fs/file.h>
#define PT_LOAD 0x00000001
#define PT_DYNAMIC 0x00000002
#define PT_INTERP 0x00000003
#define PT_PHDR 0x00000006
#define DT_NULL 0x00000000
#define DT_NEEDED 0x00000001
#define DT_RELA 0x00000007
#define DT_RELASZ 0x00000008
#define DT_RELAENT 0x00000009
#define ABI_SYSV 0x00
#define ARCH_X86_64 0x3e
#define ARCH_X86_32 0x03
@ -26,7 +33,6 @@
#define EI_VERSION 6
#define EI_OSABI 7
struct elf32_hdr {
uint8_t ident[16];
uint16_t type;
@ -86,6 +92,11 @@ struct elf64_rela {
uint64_t r_addend;
};
struct elf64_dyn {
uint64_t d_tag;
uint64_t d_un;
};
int elf_bits(uint8_t *elf) {
struct elf64_hdr hdr;
memcpy(&hdr, elf + (0), 20);
@ -106,46 +117,75 @@ int elf_bits(uint8_t *elf) {
}
static bool elf64_is_relocatable(uint8_t *elf, struct elf64_hdr *hdr) {
// Find RELA sections
for (uint16_t i = 0; i < hdr->sh_num; i++) {
struct elf64_shdr section;
memcpy(&section, elf + (hdr->shoff + i * sizeof(struct elf64_shdr)),
sizeof(struct elf64_shdr));
if (section.sh_type != SHT_RELA)
continue;
if (section.sh_entsize != sizeof(struct elf64_rela)) {
print("elf: Unknown sh_entsize for RELA section!\n");
continue;
}
return true;
// Find DYN segment
for (uint16_t i = 0; i < hdr->ph_num; i++) {
struct elf64_phdr phdr;
memcpy(&phdr, elf + (hdr->phoff + i * sizeof(struct elf64_phdr)),
sizeof(struct elf64_phdr));
if (phdr.p_type == PT_DYNAMIC)
return true;
}
return false;
}
static int elf64_apply_relocations(uint8_t *elf, struct elf64_hdr *hdr, void *buffer, uint64_t vaddr, size_t size, uint64_t slide) {
// Find RELA sections
for (uint16_t i = 0; i < hdr->sh_num; i++) {
struct elf64_shdr section;
memcpy(&section, elf + (hdr->shoff + i * sizeof(struct elf64_shdr)),
sizeof(struct elf64_shdr));
// Find DYN segment
for (uint16_t i = 0; i < hdr->ph_num; i++) {
struct elf64_phdr phdr;
memcpy(&phdr, elf + (hdr->phoff + i * sizeof(struct elf64_phdr)),
sizeof(struct elf64_phdr));
if (section.sh_type != SHT_RELA)
if (phdr.p_type != PT_DYNAMIC)
continue;
if (section.sh_entsize != sizeof(struct elf64_rela)) {
uint64_t rela_offset = 0;
uint64_t rela_size = 0;
uint64_t rela_ent = 0;
for (uint16_t j = 0; j < phdr.p_filesz / sizeof(struct elf64_dyn); j++) {
struct elf64_dyn dyn;
memcpy(&dyn, elf + (phdr.p_offset + j * sizeof(struct elf64_dyn)),
sizeof(struct elf64_dyn));
switch (dyn.d_tag) {
case DT_RELA:
rela_offset = dyn.d_un;
break;
case DT_RELAENT:
rela_ent = dyn.d_un;
break;
case DT_RELASZ:
rela_size = dyn.d_un;
break;
}
}
if (rela_offset == 0) {
break;
}
if (rela_ent != sizeof(struct elf64_rela)) {
print("elf: Unknown sh_entsize for RELA section!\n");
return 1;
}
for (uint16_t j = 0; j < hdr->ph_num; j++) {
struct elf64_phdr _phdr;
memcpy(&_phdr, elf + (hdr->phoff + j * sizeof(struct elf64_phdr)),
sizeof(struct elf64_phdr));
if (_phdr.p_vaddr <= rela_offset && _phdr.p_vaddr + _phdr.p_filesz > rela_offset) {
rela_offset -= _phdr.p_vaddr;
rela_offset += _phdr.p_offset;
break;
}
}
// This is a RELA header, get and apply all relocations
for (uint64_t offset = 0; offset < section.sh_size; offset += section.sh_entsize) {
for (uint64_t offset = 0; offset < rela_size; offset += rela_ent) {
struct elf64_rela relocation;
memcpy(&relocation, elf + (section.sh_offset + offset), sizeof(relocation));
memcpy(&relocation, elf + (rela_offset + offset), sizeof(struct elf64_rela));
switch (relocation.r_info) {
case R_X86_64_RELATIVE: {
@ -169,6 +209,8 @@ static int elf64_apply_relocations(uint8_t *elf, struct elf64_hdr *hdr, void *bu
return 1;
}
}
break;
}
return 0;