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i386: Avoid lazy relocation of tlsdesc [BZ #27137]

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Lazy tlsdesc relocation is racy because the static tls optimization and
tlsdesc management operations are done without holding the dlopen lock.

This similar to the commit b7cf203b5c
for aarch64, but it fixes a different race: bug 27137.

On i386 the code is a bit more complicated than on x86_64 because both
rel and rela relocs are supported.
This commit is contained in:
Szabolcs Nagy 2021-02-11 11:40:11 +00:00
parent 8f7e09f4db
commit ddcacd91cc
1 changed files with 35 additions and 43 deletions
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78
sysdeps/i386/dl-machine.h
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@ -688,50 +688,32 @@ elf_machine_lazy_rel (struct link_map *map,
}
else if (__glibc_likely (r_type == R_386_TLS_DESC))
{
struct tlsdesc volatile * __attribute__((__unused__)) td =
(struct tlsdesc volatile *)reloc_addr;
/* Handle relocations that reference the local *ABS* in a simple
way, so as to preserve a potential addend. */
if (ELF32_R_SYM (reloc->r_info) == 0)
td->entry = _dl_tlsdesc_resolve_abs_plus_addend;
/* Given a known-zero addend, we can store a pointer to the
reloc in the arg position. */
else if (td->arg == 0)
{
td->arg = (void*)reloc;
td->entry = _dl_tlsdesc_resolve_rel;
}
else
{
/* We could handle non-*ABS* relocations with non-zero addends
by allocating dynamically an arg to hold a pointer to the
reloc, but that sounds pointless. */
const Elf32_Rel *const r = reloc;
/* The code below was borrowed from elf_dynamic_do_rel(). */
const ElfW(Sym) *const symtab =
(const void *) D_PTR (map, l_info[DT_SYMTAB]);
const Elf32_Rel *const r = reloc;
/* The code below was borrowed from elf_dynamic_do_rel(). */
const ElfW(Sym) *const symtab =
(const void *) D_PTR (map, l_info[DT_SYMTAB]);
/* Always initialize TLS descriptors completely at load time, in
case static TLS is allocated for it that requires locking. */
# ifdef RTLD_BOOTSTRAP
/* The dynamic linker always uses versioning. */
assert (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL);
/* The dynamic linker always uses versioning. */
assert (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL);
# else
if (map->l_info[VERSYMIDX (DT_VERSYM)])
# endif
{
const ElfW(Half) *const version =
(const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
ElfW(Half) ndx = version[ELFW(R_SYM) (r->r_info)] & 0x7fff;
elf_machine_rel (map, r, &symtab[ELFW(R_SYM) (r->r_info)],
&map->l_versions[ndx],
(void *) (l_addr + r->r_offset), skip_ifunc);
}
# ifndef RTLD_BOOTSTRAP
else
elf_machine_rel (map, r, &symtab[ELFW(R_SYM) (r->r_info)], NULL,
(void *) (l_addr + r->r_offset), skip_ifunc);
if (map->l_info[VERSYMIDX (DT_VERSYM)])
# endif
{
const ElfW(Half) *const version =
(const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
ElfW(Half) ndx = version[ELFW(R_SYM) (r->r_info)] & 0x7fff;
elf_machine_rel (map, r, &symtab[ELFW(R_SYM) (r->r_info)],
&map->l_versions[ndx],
(void *) (l_addr + r->r_offset), skip_ifunc);
}
# ifndef RTLD_BOOTSTRAP
else
elf_machine_rel (map, r, &symtab[ELFW(R_SYM) (r->r_info)], NULL,
(void *) (l_addr + r->r_offset), skip_ifunc);
# endif
}
else if (__glibc_unlikely (r_type == R_386_IRELATIVE))
{
@ -758,11 +740,21 @@ elf_machine_lazy_rela (struct link_map *map,
;
else if (__glibc_likely (r_type == R_386_TLS_DESC))
{
struct tlsdesc volatile * __attribute__((__unused__)) td =
(struct tlsdesc volatile *)reloc_addr;
const Elf_Symndx symndx = ELFW (R_SYM) (reloc->r_info);
const ElfW (Sym) *symtab = (const void *)D_PTR (map, l_info[DT_SYMTAB]);
const ElfW (Sym) *sym = &symtab[symndx];
const struct r_found_version *version = NULL;
td->arg = (void*)reloc;
td->entry = _dl_tlsdesc_resolve_rela;
if (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
{
const ElfW (Half) *vernum =
(const void *)D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
version = &map->l_versions[vernum[symndx] & 0x7fff];
}
/* Always initialize TLS descriptors completely at load time, in
case static TLS is allocated for it that requires locking. */
elf_machine_rela (map, reloc, sym, version, reloc_addr, skip_ifunc);
}
else if (__glibc_unlikely (r_type == R_386_IRELATIVE))
{