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commit 8f7e09f4dbdb5c815a18b8285fbc5d5d7bc17d86
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Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
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Date: Thu Feb 11 11:29:23 2021 +0000
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x86_64: Avoid lazy relocation of tlsdesc [BZ #27137]
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Lazy tlsdesc relocation is racy because the static tls optimization and
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tlsdesc management operations are done without holding the dlopen lock.
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This similar to the commit b7cf203b5c17dd6d9878537d41e0c7cc3d270a67
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for aarch64, but it fixes a different race: bug 27137.
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Another issue is that ld auditing ignores DT_BIND_NOW and thus tries to
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relocate tlsdesc lazily, but that does not work in a BIND_NOW module
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due to missing DT_TLSDESC_PLT. Unconditionally relocating tlsdesc at
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load time fixes this bug 27721 too.
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diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
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index e308b662d245cc63..ef5740ba281c7282 100644
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--- a/sysdeps/x86_64/dl-machine.h
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+++ b/sysdeps/x86_64/dl-machine.h
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@@ -563,12 +563,21 @@ elf_machine_lazy_rel (struct link_map *map,
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}
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else if (__glibc_likely (r_type == R_X86_64_TLSDESC))
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{
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- struct tlsdesc volatile * __attribute__((__unused__)) td =
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- (struct tlsdesc volatile *)reloc_addr;
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+ const Elf_Symndx symndx = ELFW (R_SYM) (reloc->r_info);
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+ const ElfW (Sym) *symtab = (const void *)D_PTR (map, l_info[DT_SYMTAB]);
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+ const ElfW (Sym) *sym = &symtab[symndx];
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+ const struct r_found_version *version = NULL;
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- td->arg = (void*)reloc;
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- td->entry = (void*)(D_PTR (map, l_info[ADDRIDX (DT_TLSDESC_PLT)])
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- + map->l_addr);
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+ if (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
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+ {
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+ const ElfW (Half) *vernum =
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+ (const void *)D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
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+ version = &map->l_versions[vernum[symndx] & 0x7fff];
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+ }
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+
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+ /* Always initialize TLS descriptors completely at load time, in
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+ case static TLS is allocated for it that requires locking. */
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+ elf_machine_rela (map, reloc, sym, version, reloc_addr, skip_ifunc);
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}
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else if (__glibc_unlikely (r_type == R_X86_64_IRELATIVE))
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{
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