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glibc/glibc-nolink-libc.patch

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commit 624acf596c5074ffc63ff697850cad4c8ef2e7ff
Author: Florian Weimer <fweimer@redhat.com>
Date: Tue Nov 12 20:09:33 2024 +0100
elf: Second ld.so relocation only if libc.so has been loaded
Commit 8f8dd904c4a2207699bb666f30acceb5209c8d3f (“elf:
rtld_multiple_ref is always true”) removed some code that happened
to enable compatibility with programs that do not link against
libc.so. Such programs cannot call dlopen or any dynamic linker
functions (except __tls_get_addr), so this is not really useful.
Still ld.so should not crash with a null-pointer dereference
or undefined symbol reference in these cases.
Perform the final relocation for ld.so right before relocating
libc.so (which seems more correct anyway), but only if libc.so
has been loaded. In the main relocation loop, call
_dl_relocate_object unconditionally because it already checks
if the object has been relocated. Only call __rtld_mutex_init
and __rtld_malloc_init_real if libc.so has been loaded. Otherwise,
the full implementations are not available.
The previous concern regarding GOT updates through self-relocation
no longer applies because function pointers are updated
explicitly through __rtld_mutex_init and __rtld_malloc_init_real,
and not through relocation.
Fixes commit 8f8dd904c4a2207699bb666f30acceb5209c8d3f (“elf:
rtld_multiple_ref is always true”).
diff --git a/elf/Makefile b/elf/Makefile
index 3a1cb72955dc0eec..b044a2c2fa974905 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -3169,3 +3169,20 @@ tst-rtld-no-malloc-audit-ENV = LD_AUDIT=$(objpfx)tst-auditmod1.so
# Any shared object should do.
tst-rtld-no-malloc-preload-ENV = LD_PRELOAD=$(objpfx)tst-auditmod1.so
+
+# These rules link and run the special elf/tst-nolink-libc-* tests if
+# a port adds them to the tests variables. Neither test variant is
+# linked against libc.so, but tst-nolink-libc-1 is linked against
+# ld.so. The test is always run directly, not under the dynamic
+# linker.
+CFLAGS-tst-nolink-libc.c += $(no-stack-protector)
+$(objpfx)tst-nolink-libc-1: $(objpfx)tst-nolink-libc.o $(objpfx)ld.so
+ $(LINK.o) -nostdlib -nostartfiles -o $@ $< \
+ -Wl,--dynamic-linker=$(objpfx)ld.so,--no-as-needed $(objpfx)ld.so
+$(objpfx)tst-nolink-libc-1.out: $(objpfx)tst-nolink-libc-1 $(objpfx)ld.so
+ $< > $@ 2>&1; $(evaluate-test)
+$(objpfx)tst-nolink-libc-2: $(objpfx)tst-nolink-libc.o
+ $(LINK.o) -nostdlib -nostartfiles -o $@ $< \
+ -Wl,--dynamic-linker=$(objpfx)ld.so
+$(objpfx)tst-nolink-libc-2.out: $(objpfx)tst-nolink-libc-2 $(objpfx)ld.so
+ $< > $@ 2>&1; $(evaluate-test)
diff --git a/elf/rtld.c b/elf/rtld.c
index b8cc3f605f9e053c..f54b1829af20881a 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -2243,15 +2243,7 @@ dl_main (const ElfW(Phdr) *phdr,
_rtld_main_check (main_map, _dl_argv[0]);
- /* Now we have all the objects loaded. Relocate them all except for
- the dynamic linker itself. We do this in reverse order so that copy
- relocs of earlier objects overwrite the data written by later
- objects. We do not re-relocate the dynamic linker itself in this
- loop because that could result in the GOT entries for functions we
- call being changed, and that would break us. It is safe to relocate
- the dynamic linker out of order because it has no copy relocations.
- Likewise for libc, which is relocated early to ensure that IFUNC
- resolvers in libc work. */
+ /* Now we have all the objects loaded. */
int consider_profiling = GLRO(dl_profile) != NULL;
@@ -2259,9 +2251,19 @@ dl_main (const ElfW(Phdr) *phdr,
GLRO(dl_lazy) |= consider_profiling;
if (GL(dl_ns)[LM_ID_BASE].libc_map != NULL)
- _dl_relocate_object (GL(dl_ns)[LM_ID_BASE].libc_map,
- GL(dl_ns)[LM_ID_BASE].libc_map->l_scope,
- GLRO(dl_lazy) ? RTLD_LAZY : 0, consider_profiling);
+ {
+ /* If libc.so has been loaded, relocate it early, after the
+ dynamic loader itself. */
+ RTLD_TIMING_VAR (start);
+ rtld_timer_start (&start);
+
+ _dl_relocate_object_no_relro (&GL(dl_rtld_map), main_map->l_scope, 0, 0);
+ _dl_relocate_object (GL(dl_ns)[LM_ID_BASE].libc_map,
+ GL(dl_ns)[LM_ID_BASE].libc_map->l_scope,
+ GLRO(dl_lazy) ? RTLD_LAZY : 0, consider_profiling);
+
+ rtld_timer_accum (&relocate_time, start);
+ }
RTLD_TIMING_VAR (start);
rtld_timer_start (&start);
@@ -2284,9 +2286,8 @@ dl_main (const ElfW(Phdr) *phdr,
/* Also allocated with the fake malloc(). */
l->l_free_initfini = 0;
- if (l != &GL(dl_rtld_map))
- _dl_relocate_object (l, l->l_scope, GLRO(dl_lazy) ? RTLD_LAZY : 0,
- consider_profiling);
+ _dl_relocate_object (l, l->l_scope, GLRO(dl_lazy) ? RTLD_LAZY : 0,
+ consider_profiling);
/* Add object to slot information data if necessasy. */
if (l->l_tls_blocksize != 0 && __rtld_tls_init_tp_called)
@@ -2324,27 +2325,18 @@ dl_main (const ElfW(Phdr) *phdr,
/* Set up the object lookup structures. */
_dl_find_object_init ();
- /* Likewise for the locking implementation. */
- __rtld_mutex_init ();
-
- /* Re-relocate ourselves with user-controlled symbol definitions. */
-
- {
- RTLD_TIMING_VAR (start);
- rtld_timer_start (&start);
-
- _dl_relocate_object_no_relro (&GL(dl_rtld_map), main_map->l_scope, 0, 0);
-
- /* The malloc implementation has been relocated, so resolving
- its symbols (and potentially calling IFUNC resolvers) is safe
- at this point. */
- __rtld_malloc_init_real (main_map);
-
- if (GL(dl_rtld_map).l_relro_size != 0)
- _dl_protect_relro (&GL(dl_rtld_map));
+ /* If libc.so was loaded, ld.so has been fully relocated along with
+ it. Complete ld.so initialization with mutex symbols from
+ libc.so and malloc symbols from the global scope. */
+ if (GL(dl_ns)[LM_ID_BASE].libc_map != NULL)
+ {
+ __rtld_mutex_init ();
+ __rtld_malloc_init_real (main_map);
+ }
- rtld_timer_accum (&relocate_time, start);
- }
+ /* All ld.so initialization is complete. Apply RELRO. */
+ if (GL(dl_rtld_map).l_relro_size != 0)
+ _dl_protect_relro (&GL(dl_rtld_map));
/* Relocation is complete. Perform early libc initialization. This
is the initial libc, even if audit modules have been loaded with
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 527c7a5ae898acea..a3f7fc4054f5d54d 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -652,7 +652,12 @@ install-bin += \
# install-bin
$(objpfx)pldd: $(objpfx)xmalloc.o
+
+test-internal-extras += tst-nolink-libc
+ifeq ($(run-built-tests),yes)
+tests-special += $(objpfx)tst-nolink-libc-1.out $(objpfx)tst-nolink-libc-2.out
endif
+endif # $(subdir) == elf
ifeq ($(subdir),rt)
CFLAGS-mq_send.c += -fexceptions
diff --git a/sysdeps/unix/sysv/linux/arm/Makefile b/sysdeps/unix/sysv/linux/arm/Makefile
index a73c897f43c9a206..e73ce4f81114e789 100644
--- a/sysdeps/unix/sysv/linux/arm/Makefile
+++ b/sysdeps/unix/sysv/linux/arm/Makefile
@@ -1,5 +1,8 @@
ifeq ($(subdir),elf)
sysdep-rtld-routines += aeabi_read_tp libc-do-syscall
+# The test uses INTERNAL_SYSCALL_CALL. In thumb mode, this uses
+# an undefined reference to __libc_do_syscall.
+CFLAGS-tst-nolink-libc.c += -marm
endif
ifeq ($(subdir),misc)
diff --git a/sysdeps/unix/sysv/linux/tst-nolink-libc.c b/sysdeps/unix/sysv/linux/tst-nolink-libc.c
new file mode 100644
index 0000000000000000..817f37784b4080f9
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-nolink-libc.c
@@ -0,0 +1,25 @@
+/* Test program not linked against libc.so and not using any glibc functions.
+ Copyright (C) 2024 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <sysdep.h>
+
+void
+_start (void)
+{
+ INTERNAL_SYSCALL_CALL (exit_group, 0);
+}
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