| /* |
| ;* Copyright (C) 2014 Google, Inc. |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; version 2 of the License. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| * GNU General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License |
| * along with this program; if not, write to the Free Software |
| * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA, 02110-1301 USA |
| */ |
| |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| |
| #include "elfparsing.h" |
| #include "rmodule.h" |
| #include "../../src/include/rmodule-defs.h" |
| |
| struct rmod_context; |
| |
| struct arch_ops { |
| int arch; |
| /* Determine if relocation is a valid type for the architecture. */ |
| int (*valid_type)(struct rmod_context *ctx, Elf64_Rela *rel); |
| /* Determine if relocation should be emitted. */ |
| int (*should_emit)(struct rmod_context *ctx, Elf64_Rela *rel); |
| }; |
| |
| struct rmod_context { |
| /* Ops to process relocations. */ |
| struct arch_ops *ops; |
| |
| /* endian conversion ops */ |
| struct xdr *xdr; |
| |
| /* Parsed ELF sturcture. */ |
| struct parsed_elf pelf; |
| /* Program segment. */ |
| Elf64_Phdr *phdr; |
| |
| /* Collection of relocation addresses fixup in the module. */ |
| Elf64_Xword nrelocs; |
| Elf64_Addr *emitted_relocs; |
| |
| /* The following fields are addresses within the linked program. */ |
| Elf64_Addr link_addr; |
| Elf64_Addr entry; |
| Elf64_Addr parameters_begin; |
| Elf64_Addr parameters_end; |
| Elf64_Addr bss_begin; |
| Elf64_Addr bss_end; |
| Elf64_Xword size; |
| }; |
| |
| /* |
| * Architecture specific support operations. |
| */ |
| static int valid_reloc_386(struct rmod_context *ctx, Elf64_Rela *rel) |
| { |
| int type; |
| |
| type = ELF64_R_TYPE(rel->r_info); |
| |
| /* Only these 2 relocations are expected to be found. */ |
| return (type == R_386_32 || type == R_386_PC32); |
| } |
| |
| static int should_emit_386(struct rmod_context *ctx, Elf64_Rela *rel) |
| { |
| int type; |
| |
| type = ELF64_R_TYPE(rel->r_info); |
| |
| /* R_386_32 relocations are absolute. Must emit these. */ |
| return (type == R_386_32); |
| } |
| |
| static struct arch_ops reloc_ops[] = { |
| { |
| .arch = EM_386, |
| .valid_type = valid_reloc_386, |
| .should_emit = should_emit_386, |
| }, |
| }; |
| |
| /* |
| * Relocation processing loops. |
| */ |
| |
| static int for_each_reloc(struct rmod_context *ctx, int do_emit) |
| { |
| Elf64_Half i; |
| struct parsed_elf *pelf = &ctx->pelf; |
| |
| for (i = 0; i < pelf->ehdr.e_shnum; i++) { |
| Elf64_Shdr *shdr; |
| Elf64_Rela *relocs; |
| Elf64_Xword nrelocs; |
| Elf64_Xword j; |
| |
| relocs = pelf->relocs[i]; |
| |
| /* No relocations in this section. */ |
| if (relocs == NULL) |
| continue; |
| |
| shdr = &pelf->shdr[i]; |
| nrelocs = shdr->sh_size / shdr->sh_entsize; |
| |
| for (j = 0; j < nrelocs; j++) { |
| Elf64_Rela *r = &relocs[j]; |
| |
| if (!ctx->ops->valid_type(ctx, r)) { |
| ERROR("Invalid reloc type: %u\n", |
| (unsigned int)ELF64_R_TYPE(r->r_info)); |
| return -1; |
| } |
| |
| if (ctx->ops->should_emit(ctx, r)) { |
| int n = ctx->nrelocs; |
| if (do_emit) |
| ctx->emitted_relocs[n] = r->r_offset; |
| ctx->nrelocs++; |
| } |
| } |
| } |
| |
| return 0; |
| } |
| |
| static int find_program_segment(struct rmod_context *ctx) |
| { |
| int i; |
| int nsegments; |
| struct parsed_elf *pelf; |
| Elf64_Phdr *phdr; |
| |
| pelf = &ctx->pelf; |
| |
| /* There should only be a single loadable segment. */ |
| nsegments = 0; |
| for (i = 0; i < pelf->ehdr.e_phnum; i++) { |
| if (pelf->phdr[i].p_type != PT_LOAD) |
| continue; |
| phdr = &pelf->phdr[i]; |
| nsegments++; |
| } |
| |
| if (nsegments != 1) { |
| ERROR("Unexepcted number of loadable segments: %d.\n", |
| nsegments); |
| return -1; |
| } |
| |
| INFO("Segment at 0x%0llx, file size 0x%0llx, mem size 0x%0llx.\n", |
| (long long)phdr->p_vaddr, (long long)phdr->p_filesz, |
| (long long)phdr->p_memsz); |
| |
| ctx->phdr = phdr; |
| |
| return 0; |
| } |
| |
| static int |
| filter_relocation_sections(struct rmod_context *ctx) |
| { |
| int i; |
| const char *shstrtab; |
| struct parsed_elf *pelf; |
| const Elf64_Phdr *phdr; |
| |
| pelf = &ctx->pelf; |
| phdr = ctx->phdr; |
| shstrtab = buffer_get(pelf->strtabs[pelf->ehdr.e_shstrndx]); |
| |
| /* |
| * Find all relocation sections that contain relocation entries |
| * for sections that fall within the bounds of the segment. For |
| * easier processing the pointer to the relocation array for the |
| * sections that don't fall within the loadable program are NULL'd |
| * out. |
| */ |
| for (i = 0; i < pelf->ehdr.e_shnum; i++) { |
| Elf64_Shdr *shdr; |
| Elf64_Word sh_info; |
| const char *section_name; |
| |
| shdr = &pelf->shdr[i]; |
| |
| /* Ignore non-relocation sections. */ |
| if (shdr->sh_type != SHT_RELA && shdr->sh_type != SHT_REL) |
| continue; |
| |
| /* Obtain section which relocations apply. */ |
| sh_info = shdr->sh_info; |
| shdr = &pelf->shdr[sh_info]; |
| |
| section_name = &shstrtab[shdr->sh_name]; |
| DEBUG("Relocation section found for '%s' section.\n", |
| section_name); |
| |
| /* Do not process relocations for debug sections. */ |
| if (strstr(section_name, ".debug") != NULL) { |
| pelf->relocs[i] = NULL; |
| continue; |
| } |
| |
| /* |
| * If relocations apply to a non program section ignore the |
| * relocations for future processing. |
| */ |
| if (shdr->sh_type != SHT_PROGBITS) { |
| pelf->relocs[i] = NULL; |
| continue; |
| } |
| |
| if (shdr->sh_addr < phdr->p_vaddr || |
| ((shdr->sh_addr + shdr->sh_size) > |
| (phdr->p_vaddr + phdr->p_memsz))) { |
| ERROR("Relocations being applied to section %d not " |
| "within segment region.\n", sh_info); |
| return -1; |
| } |
| } |
| |
| return 0; |
| } |
| |
| static int vaddr_cmp(const void *a, const void *b) |
| { |
| const Elf64_Addr *pa = a; |
| const Elf64_Addr *pb = b; |
| |
| if (*pa < *pb) |
| return -1; |
| if (*pa > *pb) |
| return 1; |
| return 0; |
| } |
| |
| static int collect_relocations(struct rmod_context *ctx) |
| { |
| int nrelocs; |
| |
| /* |
| * The relocs array in the pelf should only contain relocations that |
| * apply to the program. Count the number relocations. Then collect |
| * them into the allocated buffer. |
| */ |
| if (for_each_reloc(ctx, 0)) |
| return -1; |
| |
| nrelocs = ctx->nrelocs; |
| INFO("%d relocations to be emitted.\n", nrelocs); |
| if (!nrelocs) { |
| ERROR("No valid relocations in file.\n"); |
| return -1; |
| } |
| |
| /* Reset the counter for indexing into the array. */ |
| ctx->nrelocs = 0; |
| ctx->emitted_relocs = calloc(nrelocs, sizeof(Elf64_Addr)); |
| /* Write out the relocations into the emitted_relocs array. */ |
| if (for_each_reloc(ctx, 1)) |
| return -1; |
| |
| if (ctx->nrelocs != nrelocs) { |
| ERROR("Mismatch counted and emitted relocations: %zu vs %zu.\n", |
| (size_t)nrelocs, (size_t)ctx->nrelocs); |
| return -1; |
| } |
| |
| /* Sort the relocations by their address. */ |
| qsort(ctx->emitted_relocs, nrelocs, sizeof(Elf64_Addr), vaddr_cmp); |
| |
| return 0; |
| } |
| |
| static int |
| populate_sym(struct rmod_context *ctx, const char *sym_name, Elf64_Addr *addr, |
| int nsyms, const char *strtab) |
| { |
| int i; |
| Elf64_Sym *syms; |
| |
| syms = ctx->pelf.syms; |
| |
| for (i = 0; i < nsyms; i++) { |
| if (syms[i].st_name == 0) |
| continue; |
| if (strcmp(sym_name, &strtab[syms[i].st_name])) |
| continue; |
| DEBUG("%s -> 0x%llx\n", sym_name, (long long)syms[i].st_value); |
| *addr = syms[i].st_value; |
| return 0; |
| } |
| ERROR("symbol '%s' not found.\n", sym_name); |
| return -1; |
| } |
| |
| static int populate_program_info(struct rmod_context *ctx) |
| { |
| int i; |
| const char *strtab; |
| struct parsed_elf *pelf; |
| Elf64_Ehdr *ehdr; |
| int nsyms; |
| |
| pelf = &ctx->pelf; |
| ehdr = &pelf->ehdr; |
| |
| /* Obtain the string table. */ |
| strtab = NULL; |
| for (i = 0; i < ehdr->e_shnum; i++) { |
| if (ctx->pelf.strtabs[i] == NULL) |
| continue; |
| /* Don't use the section headers' string table. */ |
| if (i == ehdr->e_shstrndx) |
| continue; |
| strtab = buffer_get(ctx->pelf.strtabs[i]); |
| break; |
| } |
| |
| if (strtab == NULL) { |
| ERROR("No string table found.\n"); |
| return -1; |
| } |
| |
| /* Determine number of symbols. */ |
| nsyms = 0; |
| for (i = 0; i < ehdr->e_shnum; i++) { |
| if (pelf->shdr[i].sh_type != SHT_SYMTAB) |
| continue; |
| |
| nsyms = pelf->shdr[i].sh_size / pelf->shdr[i].sh_entsize; |
| break; |
| } |
| |
| if (populate_sym(ctx, "_module_params_begin", &ctx->parameters_begin, |
| nsyms, strtab)) |
| return -1; |
| |
| if (populate_sym(ctx, "_module_params_end", &ctx->parameters_end, |
| nsyms, strtab)) |
| return -1; |
| |
| if (populate_sym(ctx, "_bss", &ctx->bss_begin, nsyms, strtab)) |
| return -1; |
| |
| if (populate_sym(ctx, "_ebss", &ctx->bss_end, nsyms, strtab)) |
| return -1; |
| |
| if (populate_sym(ctx, "__rmodule_entry", &ctx->entry, nsyms, strtab)) |
| return -1; |
| |
| /* Link address is the virtual address of the program segment. */ |
| ctx->link_addr = ctx->phdr->p_vaddr; |
| |
| /* The program size is the memsz of the program segment. */ |
| ctx->size = ctx->phdr->p_memsz; |
| |
| return 0; |
| } |
| |
| static int |
| add_section(struct elf_writer *ew, struct buffer *data, const char *name, |
| Elf64_Addr addr, Elf64_Word size) |
| { |
| Elf64_Shdr shdr; |
| int ret; |
| |
| memset(&shdr, 0, sizeof(shdr)); |
| if (data != NULL) { |
| shdr.sh_type = SHT_PROGBITS; |
| shdr.sh_flags = SHF_ALLOC | SHF_WRITE | SHF_EXECINSTR; |
| } else { |
| shdr.sh_type = SHT_NOBITS; |
| shdr.sh_flags = SHF_ALLOC; |
| } |
| shdr.sh_addr = addr; |
| shdr.sh_offset = addr; |
| shdr.sh_size = size; |
| |
| ret = elf_writer_add_section(ew, &shdr, data, name); |
| |
| if (ret) |
| ERROR("Could not add '%s' section.\n", name); |
| |
| return ret; |
| } |
| |
| static int |
| write_elf(const struct rmod_context *ctx, const struct buffer *in, |
| struct buffer *out) |
| { |
| int i; |
| int ret; |
| int bit64; |
| size_t loc; |
| size_t rmod_data_size; |
| struct elf_writer *ew; |
| struct buffer rmod_data; |
| struct buffer rmod_header; |
| struct buffer program; |
| struct buffer relocs; |
| Elf64_Xword total_size; |
| Elf64_Addr addr; |
| Elf64_Ehdr ehdr; |
| |
| bit64 = ctx->pelf.ehdr.e_ident[EI_CLASS] == ELFCLASS64; |
| |
| /* |
| * 3 sections will be added to the ELF file. |
| * +------------------+ |
| * | rmodule header | |
| * +------------------+ |
| * | program | |
| * +------------------+ |
| * | relocations | |
| * +------------------+ |
| */ |
| |
| /* Create buffer for header and relocations. */ |
| rmod_data_size = sizeof(struct rmodule_header); |
| if (bit64) |
| rmod_data_size += ctx->nrelocs * sizeof(Elf64_Addr); |
| else |
| rmod_data_size += ctx->nrelocs * sizeof(Elf32_Addr); |
| |
| if (buffer_create(&rmod_data, rmod_data_size, "rmod")) |
| return -1; |
| |
| buffer_splice(&rmod_header, &rmod_data, |
| 0, sizeof(struct rmodule_header)); |
| buffer_clone(&relocs, &rmod_data); |
| buffer_seek(&relocs, sizeof(struct rmodule_header)); |
| |
| /* Reset current location. */ |
| buffer_set_size(&rmod_header, 0); |
| buffer_set_size(&relocs, 0); |
| |
| /* Program contents. */ |
| buffer_splice(&program, in, ctx->phdr->p_offset, ctx->phdr->p_filesz); |
| |
| /* Create ELF writer with modified entry point. */ |
| memcpy(&ehdr, &ctx->pelf.ehdr, sizeof(ehdr)); |
| ehdr.e_entry = ctx->entry; |
| ew = elf_writer_init(&ehdr); |
| |
| if (ew == NULL) { |
| ERROR("Failed to create ELF writer.\n"); |
| buffer_delete(&rmod_data); |
| return -1; |
| } |
| |
| /* Write out rmodule_header. */ |
| ctx->xdr->put16(&rmod_header, RMODULE_MAGIC); |
| ctx->xdr->put8(&rmod_header, RMODULE_VERSION_1); |
| ctx->xdr->put8(&rmod_header, 0); |
| /* payload_begin_offset */ |
| loc = sizeof(struct rmodule_header); |
| ctx->xdr->put32(&rmod_header, loc); |
| /* payload_end_offset */ |
| loc += ctx->phdr->p_filesz; |
| ctx->xdr->put32(&rmod_header, loc); |
| /* relocations_begin_offset */ |
| ctx->xdr->put32(&rmod_header, loc); |
| /* relocations_end_offset */ |
| if (bit64) |
| loc += ctx->nrelocs * sizeof(Elf64_Addr); |
| else |
| loc += ctx->nrelocs * sizeof(Elf32_Addr); |
| ctx->xdr->put32(&rmod_header, loc); |
| /* module_link_start_address */ |
| ctx->xdr->put32(&rmod_header, ctx->link_addr); |
| /* module_program_size */ |
| ctx->xdr->put32(&rmod_header, ctx->size); |
| /* module_entry_point */ |
| ctx->xdr->put32(&rmod_header, ctx->entry); |
| /* parameters_begin */ |
| ctx->xdr->put32(&rmod_header, ctx->parameters_begin); |
| /* parameters_end */ |
| ctx->xdr->put32(&rmod_header, ctx->parameters_end); |
| /* bss_begin */ |
| ctx->xdr->put32(&rmod_header, ctx->bss_begin); |
| /* bss_end */ |
| ctx->xdr->put32(&rmod_header, ctx->bss_end); |
| /* padding[4] */ |
| ctx->xdr->put32(&rmod_header, 0); |
| ctx->xdr->put32(&rmod_header, 0); |
| ctx->xdr->put32(&rmod_header, 0); |
| ctx->xdr->put32(&rmod_header, 0); |
| |
| /* Write the relocations. */ |
| for (i = 0; i < ctx->nrelocs; i++) { |
| if (bit64) |
| ctx->xdr->put64(&relocs, ctx->emitted_relocs[i]); |
| else |
| ctx->xdr->put32(&relocs, ctx->emitted_relocs[i]); |
| } |
| |
| total_size = 0; |
| addr = 0; |
| |
| /* |
| * There are 2 cases to deal with. The program has a large NOBITS |
| * section and the relocations can fit entirely within occupied memory |
| * region for the program. The other is that the relocations increase |
| * the memory footprint of the program if it was loaded directly into |
| * the region it would run. The rmdoule header is a fixed cost that |
| * is considered a part of the program. |
| */ |
| total_size += buffer_size(&rmod_header); |
| total_size += ctx->phdr->p_memsz; |
| if (buffer_size(&relocs) + ctx->phdr->p_filesz > total_size) { |
| total_size -= ctx->phdr->p_memsz; |
| total_size += buffer_size(&relocs); |
| total_size += ctx->phdr->p_filesz; |
| } |
| |
| ret = add_section(ew, &rmod_header, ".header", addr, |
| buffer_size(&rmod_header)); |
| if (ret < 0) |
| goto out; |
| addr += buffer_size(&rmod_header); |
| |
| ret = add_section(ew, &program, ".program", addr, ctx->phdr->p_filesz); |
| if (ret < 0) |
| goto out; |
| addr += ctx->phdr->p_filesz; |
| |
| ret = add_section(ew, &relocs, ".relocs", addr, buffer_size(&relocs)); |
| if (ret < 0) |
| goto out; |
| addr += buffer_size(&relocs); |
| |
| if (total_size != addr) { |
| ret = add_section(ew, NULL, ".empty", addr, total_size - addr); |
| if (ret < 0) |
| goto out; |
| } |
| |
| /* |
| * Ensure last section has a memory usage that meets the required |
| * total size of the program in memory. |
| */ |
| |
| ret = elf_writer_serialize(ew, out); |
| if (ret < 0) |
| ERROR("Failed to serialize ELF to buffer.\n"); |
| |
| out: |
| buffer_delete(&rmod_data); |
| elf_writer_destroy(ew); |
| |
| return ret; |
| } |
| |
| int rmodule_create(const struct buffer *elfin, struct buffer *elfout) |
| { |
| struct rmod_context ctx; |
| struct parsed_elf *pelf; |
| int i; |
| int ret; |
| |
| ret = -1; |
| memset(&ctx, 0, sizeof(ctx)); |
| pelf = &ctx.pelf; |
| |
| if (parse_elf(elfin, pelf, ELF_PARSE_ALL)) { |
| ERROR("Couldn't parse ELF!\n"); |
| return -1; |
| } |
| |
| /* Only allow executables to be turned into rmodules. */ |
| if (pelf->ehdr.e_type != ET_EXEC) { |
| ERROR("ELF is not an executable: %u.\n", pelf->ehdr.e_type); |
| goto out; |
| } |
| |
| /* Determine if architecture is supported. */ |
| for (i = 0; i < ARRAY_SIZE(reloc_ops); i++) { |
| if (reloc_ops[i].arch == pelf->ehdr.e_machine) { |
| ctx.ops = &reloc_ops[i]; |
| break; |
| } |
| } |
| |
| if (ctx.ops == NULL) { |
| ERROR("ELF is unsupported arch: %u.\n", pelf->ehdr.e_machine); |
| goto out; |
| } |
| |
| /* Set the endian ops. */ |
| if (ctx.pelf.ehdr.e_ident[EI_DATA] == ELFDATA2MSB) |
| ctx.xdr = &xdr_be; |
| else |
| ctx.xdr = &xdr_le; |
| |
| if (find_program_segment(&ctx)) |
| goto out; |
| |
| if (filter_relocation_sections(&ctx)) |
| goto out; |
| |
| if (collect_relocations(&ctx)) |
| goto out; |
| |
| if (populate_program_info(&ctx)) |
| goto out; |
| |
| if (write_elf(&ctx, elfin, elfout)) |
| goto out; |
| |
| ret = 0; |
| |
| out: |
| free(ctx.emitted_relocs); |
| parsed_elf_destroy(pelf); |
| return ret; |
| } |