[11/15] x86_64: Avoid lazy relocation of tlsdesc [BZ #27137]

Message ID 8c6dae9ee45f9af51ce70cb8422582096dbf7ffc.1613390045.git.szabolcs.nagy@arm.com
State New
Headers show
Series
  • Dynamic TLS related data race fixes
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Commit Message

Mike Frysinger via Libc-alpha Feb. 15, 2021, 12:02 p.m.
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 b7cf203b5c17dd6d9878537d41e0c7cc3d270a67
for aarch64, but it fixes a different race: bug 27137.
---
 sysdeps/x86_64/dl-machine.h | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

-- 
2.17.1

Patch

diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index 103eee6c3f..9a876a371e 100644
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -570,12 +570,21 @@  elf_machine_lazy_rel (struct link_map *map,
     }
   else if (__glibc_likely (r_type == R_X86_64_TLSDESC))
     {
-      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 = (void*)(D_PTR (map, l_info[ADDRIDX (DT_TLSDESC_PLT)])
-			  + map->l_addr);
+      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_X86_64_IRELATIVE))
     {