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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Read the intermediate KLP reloc/symbol representations created by klp diff
* and convert them to the proper format required by livepatch. This needs to
* run last to avoid linker wreckage. Linkers don't tend to handle the "two
* rela sections for a single base section" case very well, nor do they like
* SHN_LIVEPATCH.
*
* This is the final tool in the livepatch module generation pipeline:
*
* kernel builds -> objtool klp diff -> module link -> objtool klp post-link
*/
#include <fcntl.h>
#include <gelf.h>
#include <objtool/objtool.h>
#include <objtool/warn.h>
#include <objtool/klp.h>
#include <objtool/util.h>
#include <linux/livepatch_external.h>
static int fix_klp_relocs(struct elf *elf)
{
struct section *symtab, *klp_relocs;
klp_relocs = find_section_by_name(elf, KLP_RELOCS_SEC);
if (!klp_relocs)
return 0;
symtab = find_section_by_name(elf, ".symtab");
if (!symtab) {
ERROR("missing .symtab");
return -1;
}
for (int i = 0; i < sec_size(klp_relocs) / sizeof(struct klp_reloc); i++) {
struct klp_reloc *klp_reloc;
unsigned long klp_reloc_off;
struct section *sec, *tmp, *klp_rsec;
unsigned long offset;
struct reloc *reloc;
char sym_modname[64];
char rsec_name[SEC_NAME_LEN];
u64 addend;
struct symbol *sym, *klp_sym;
klp_reloc_off = i * sizeof(*klp_reloc);
klp_reloc = klp_relocs->data->d_buf + klp_reloc_off;
/*
* Read __klp_relocs[i]:
*/
/* klp_reloc.sec_offset */
reloc = find_reloc_by_dest(elf, klp_relocs,
klp_reloc_off + offsetof(struct klp_reloc, offset));
if (!reloc) {
ERROR("malformed " KLP_RELOCS_SEC " section");
return -1;
}
sec = reloc->sym->sec;
offset = reloc_addend(reloc);
/* klp_reloc.sym */
reloc = find_reloc_by_dest(elf, klp_relocs,
klp_reloc_off + offsetof(struct klp_reloc, sym));
if (!reloc) {
ERROR("malformed " KLP_RELOCS_SEC " section");
return -1;
}
klp_sym = reloc->sym;
addend = reloc_addend(reloc);
/* symbol format: .klp.sym.modname.sym_name,sympos */
if (sscanf(klp_sym->name + strlen(KLP_SYM_PREFIX), "%55[^.]", sym_modname) != 1)
ERROR("can't find modname in klp symbol '%s'", klp_sym->name);
/*
* Create the KLP rela:
*/
/* section format: .klp.rela.sec_objname.section_name */
if (snprintf_check(rsec_name, SEC_NAME_LEN,
KLP_RELOC_SEC_PREFIX "%s.%s",
sym_modname, sec->name))
return -1;
klp_rsec = find_section_by_name(elf, rsec_name);
if (!klp_rsec) {
klp_rsec = elf_create_section(elf, rsec_name, 0,
elf_rela_size(elf),
SHT_RELA, elf_addr_size(elf),
SHF_ALLOC | SHF_INFO_LINK | SHF_RELA_LIVEPATCH);
if (!klp_rsec)
return -1;
klp_rsec->sh.sh_link = symtab->idx;
klp_rsec->sh.sh_info = sec->idx;
klp_rsec->base = sec;
}
tmp = sec->rsec;
sec->rsec = klp_rsec;
if (!elf_create_reloc(elf, sec, offset, klp_sym, addend, klp_reloc->type))
return -1;
sec->rsec = tmp;
/*
* Fix up the corresponding KLP symbol:
*/
klp_sym->sym.st_shndx = SHN_LIVEPATCH;
if (!gelf_update_sym(symtab->data, klp_sym->idx, &klp_sym->sym)) {
ERROR_ELF("gelf_update_sym");
return -1;
}
/*
* Disable the original non-KLP reloc by converting it to R_*_NONE:
*/
reloc = find_reloc_by_dest(elf, sec, offset);
sym = reloc->sym;
sym->sym.st_shndx = SHN_LIVEPATCH;
set_reloc_type(elf, reloc, 0);
if (!gelf_update_sym(symtab->data, sym->idx, &sym->sym)) {
ERROR_ELF("gelf_update_sym");
return -1;
}
}
return 0;
}
/*
* This runs on the livepatch module after all other linking has been done. It
* converts the intermediate __klp_relocs section into proper KLP relocs to be
* processed by livepatch. This needs to run last to avoid linker wreckage.
* Linkers don't tend to handle the "two rela sections for a single base
* section" case very well, nor do they appreciate SHN_LIVEPATCH.
*/
int cmd_klp_post_link(int argc, const char **argv)
{
struct elf *elf;
argc--;
argv++;
if (argc != 1) {
fprintf(stderr, "%d\n", argc);
fprintf(stderr, "usage: objtool link <file.ko>\n");
return -1;
}
elf = elf_open_read(argv[0], O_RDWR);
if (!elf)
return -1;
if (fix_klp_relocs(elf))
return -1;
if (elf_write(elf))
return -1;
return elf_close(elf);
}
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