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From 8f7e09f4dbdb5c815a18b8285fbc5d5d7bc17d86 Mon Sep 17 00:00:00 2001
From: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date: Thu, 11 Feb 2021 11:29:23 +0000
Subject: [PATCH] x86_64: Avoid lazy relocation of tlsdesc [BZ #27137]
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.
Another issue is that ld auditing ignores DT_BIND_NOW and thus tries to
relocate tlsdesc lazily, but that does not work in a BIND_NOW module
due to missing DT_TLSDESC_PLT. Unconditionally relocating tlsdesc at
load time fixes this bug 27721 too.
---
sysdeps/x86_64/dl-machine.h | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
---
Upstream-Status: Backport [https://sourceware.org/git/?p=glibc.git;a=patch;h=8f7e09f4dbdb5c815a18b8285fbc5d5d7bc17d86]
Signed-off-by: Akash Hadke <akash.hadke@kpit.com>
Signed-off-by: Akash Hadke <hadkeakash4@gmail.com>
---
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))
{
--
2.27.0
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