This was originally added to support binutils older than version
2.22:
<https://sourceware.org/ml/libc-alpha/2010-12/msg00051.html>
Since 2.22 is older than the minimum required binutils version
for building glibc, we no longer need this. (The changes do
not impact the statically linked startup code.)
This function is defined in libc.so, and the dynamic loader calls
right after relocation has been finished, before any ELF constructors
or the preinit function is invoked. It is also used in the static
build for initializing parts of the static libc.
To locate __libc_early_init, a direct symbol lookup function is used,
_dl_lookup_direct. It does not search the entire symbol scope and
consults merely a single link map. This function could also be used
to implement lookups in the vDSO (as an optimization).
A per-namespace variable (libc_map) is added for locating libc.so,
to avoid repeated traversals of the search scope. It is similar to
GL(dl_initfirst). An alternative would have been to thread a context
argument from _dl_open down to _dl_map_object_from_fd (where libc.so
is identified). This could have avoided the global variable, but
the change would be larger as a result. It would not have been
possible to use this to replace GL(dl_initfirst) because that global
variable is used to pass the function pointer past the stack switch
from dl_main to the main program. Replacing that requires adding
a new argument to _dl_init, which in turn needs changes to the
architecture-specific libc.so startup code written in assembler.
__libc_early_init should not be used to replace _dl_var_init (as
it exists today on some architectures). Instead, _dl_lookup_direct
should be used to look up a new variable symbol in libc.so, and
that should then be initialized from the dynamic loader, immediately
after the object has been loaded in _dl_map_object_from_fd (before
relocation is run). This way, more IFUNC resolvers which depend on
these variables will work.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
GNU ld and gold's -Map include a line like:
path/to/build/libc_pic.a(check_fds.os)
lld -Map does not have the archive member list, but we can still derive the
members from the following output
VMA LMA Size Align Out In Symbol
...
1a1c0 1a1c0 e2 16 path/to/build/libc_pic.a(check_fds.os):(.text)
binutils ld has supported --audit, --depaudit for a long time,
only support in glibc has been missing.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Writable, executable segments defeat security hardening. The
existing check for DT_TEXTREL does not catch this.
hppa and SPARC currently keep the PLT in an RWX load segment.
Exporting functions and relying on symbol interposition from libc.so
makes the choice of implementation dependent on DT_NEEDED order, which
is not what some compiler drivers expect.
This commit replaces one magic mechanism (symbol interposition) with
another one (preprocessor-/compiler-based redirection). This makes
the hand-over from the minimal malloc to the full malloc more
explicit.
Removing the ABI symbols is backwards-compatible because libc.so is
always in scope, and the dynamic loader will find the malloc-related
symbols there since commit f0b2132b35
("ld.so: Support moving versioned symbols between sonames
[BZ #24741]").
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This generalizes a mechanism used for stack-protector support, so
that it can be applied to other symbols if required.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
There are two fixes that are needed to be able to dlopen filter
objects. First _dl_map_object_deps cannot assume that map will be at
the beginning of l_searchlist.r_list[], as filtees are inserted before
map. Secondly dl_open_worker needs to ensure that filtees get
relocated.
In _dl_map_object_deps:
* avoiding removing relocation dependencies of map by setting
l_reserved to 0 and otherwise processing the rest of the search
list.
* ensure that map remains at the beginning of l_initfini - the list
of things that need initialisation (and destruction). Do this by
splitting the copy up. This may not be required, but matches the
initialization order without dlopen.
Modify dl_open_worker to relocate the objects in new->l_inifini.
new->l_initfini is constructed in _dl_map_object_deps, and lists the
objects that need initialization and destruction. Originally the list
of objects in new->l_next are relocated. All of these objects should
also be included in new->l_initfini (both lists are populated with
dependencies in _dl_map_object_deps). We can't use new->l_prev to pick
up filtees, as during a recursive dlopen from an interposed malloc
call, l->prev can contain objects that are not ready for relocation.
Add tests to verify that symbols resolve to the filtee implementation
when auxiliary and filter objects are used, both as a normal link and
when dlopen'd.
Tested by running the testsuite on x86_64.
As noted in
<https://sourceware.org/ml/libc-alpha/2019-06/msg00824.html>,
elf/tst-rtld-preload fails when cross-testing because it attempts to
run the test wrapper with itself. Unfortunately, that thread never
resulted in a complete and correct patch for that test.
This patch addresses the issues with that test more thoroughly. The
test is changed not to use the wrapper twice, including updating the
message it prints about the command it runs to be more complete and
accurate after the change; the Makefile is changed not to pass the
redundant '$(test-wrapper)' argument.
Tested for Arm that this fixes the failure seen for that test in
cross-testing.
The tests elf/tst-ifunc-fault-bindnow and elf/tst-ifunc-fault-lazy
fail in cross-testing because they run the dynamic linker directly
without using the test wrapper. This patch fixes them to use the test
wrapper instead.
Tested that this fixes the failure of those two tests for powerpc
soft-float.
Without CET, a jump into a newly loaded object through an overwritten
link map often does not crash, it just executes some random code.
CET detects this in some cases because the function pointer does not
point to the start of a function in the replacement shared object,
so there is no ENDBR instruction.
The new test uses a small shared object and the existing dangling
link map to trigger the bug.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Test ldconfig after /etc/ld.so.conf update and verify a running process
observes changes to /etc/ld.so.cache.
The test uses the test-in-container framework.
Reviewed-by: Arjun Shankar <arjun@redhat.com>
Previously, ld.so was invoked only with the elf subdirectory on the
library search path. Since the soname link for libc.so only exists in
the top-level build directory, this leaked the system libc into the
test.
The assumption behind the assert in activate_nodelete was wrong:
Inconsistency detected by ld.so: dl-open.c: 459: activate_nodelete:
Assertion `!imap->l_init_called || imap->l_type != lt_loaded' failed! (edit)
It can happen that an already-loaded object that is in the local
scope is promoted to NODELETE status, via binding to a unique
symbol.
Similarly, it is possible that such NODELETE promotion occurs to
an already-loaded object from the global scope. This is why the
loop in activate_nodelete has to cover all objects in the namespace
of the new object.
In do_lookup_unique, it could happen that the NODELETE status of
an already-loaded object was overwritten with a pending NODELETE
status. As a result, if dlopen fails, this could cause a loss of
the NODELETE status of the affected object, eventually resulting
in an incorrect unload.
Fixes commit f63b73814f ("Remove all
loaded objects if dlopen fails, ignoring NODELETE [BZ #20839]").
Since commit a3cc4f48e9 ("Remove
--as-needed configure test."), --as-needed support is no longer
optional.
The macros are not much shorter and do not provide documentary
value, either, so this commit removes them.
This commit adds missing skip_ifunc checks to aarch64, arm, i386,
sparc, and x86_64. A new test case ensures that IRELATIVE IFUNC
resolvers do not run in various diagnostic modes of the dynamic
loader.
Reviewed-By: Szabolcs Nagy <szabolcs.nagy@arm.com>
This introduces a “pending NODELETE” state in the link map, which is
flipped to the persistent NODELETE state late in dlopen, via
activate_nodelete. During initial relocation, symbol binding
records pending NODELETE state only. dlclose ignores pending NODELETE
state. Taken together, this results that a partially completed dlopen
is rolled back completely because new NODELETE mappings are unloaded.
Tested on x86_64-linux-gnu and i386-linux-gnu.
Change-Id: Ib2a3d86af6f92d75baca65431d74783ee0dbc292
If a lazy binding failure happens during the execution of an ELF
constructor or destructor, the dynamic loader catches the error
and reports it using the dlerror mechanism. This is undesirable
because there could be other constructors and destructors that
need processing (which are skipped), and the process is in an
inconsistent state at this point. Therefore, we have to issue
a fatal dynamic loader error error and terminate the process.
Note that the _dl_catch_exception in _dl_open is just an inner catch,
to roll back some state locally. If called from dlopen, there is
still an outer catch, which is why calling _dl_init via call_dl_init
and a no-exception is required and cannot be avoiding by moving the
_dl_init call directly into _dl_open.
_dl_fini does not need changes because it does not install an error
handler, so errors are already fatal there.
Change-Id: I6b1addfe2e30f50a1781595f046f44173db9491a
In GCC 10, the default at -O2 is now -ftree-loop-distribute-patterns.
This optimization causes GCC to "helpfully" convert the hand-written
loop in _dl_start into a call to memset, which is not available that
early in program startup. Similar problems in other places in GLIBC
have been addressed by explicitly building with
-fno-tree-loop-distribute-patterns, but this one may have been
overlooked previously because it only affects targets where
HAVE_BUILTIN_MEMSET is not defined.
This patch fixes a bug observed on nios2-linux-gnu target that caused
all programs to segv on startup.
From the beginning, elf/tst-dlopen-aout has exercised two different
bugs: (a) failure to report errors for a dlopen of the executable
itself in some cases (bug 24900) and (b) incorrect rollback of the
TLS modid allocation in case of a dlopen failure (bug 16634).
This commit replaces the test with elf/tst-dlopen-self for (a) and
elf/tst-dlopen-tlsmodid for (b). The latter tests use the
elf/tst-dlopen-self binaries (or iconv) with dlopen, so they are
no longer self-dlopen tests.
Tested on x86_64-linux-gnu and i686-linux-gnu, with a toolchain that
does not default to PIE.
Commit a42faf59d6 ("Fix BZ #16634.")
attempted to fix a TLS modid consistency issue by adding additional
checks to the open_verify function. However, this is fragile
because open_verify cannot reliably predict whether
_dl_map_object_from_fd will later fail in the more complex cases
(such as memory allocation failures). Therefore, this commit
assigns the TLS modid as late as possible. At that point, the link
map pointer will eventually be passed to _dl_close, which will undo
the TLS modid assignment.
Reviewed-by: Gabriel F. T. Gomes <gabrielftg@linux.ibm.com>
In case of an explicit loader invocation, ld.so essentially performs
a dlopen call to load the main executable. Since the pathname of
the executable is known at this point, it gets stored in the link
map. In regular mode, the pathname is not known and "" is used
instead.
As a result, if a program calls dlopen on the pathname of the main
program, the dlopen call succeeds and returns a handle for the main
map. This results in an unnecessary difference between glibc
testing (without --enable-hardcoded-path-in-tests) and production
usage.
This commit discards the names when building the link map in
_dl_new_object for the main executable, but it still determines
the origin at this point in case of an explict loader invocation.
The reason is that the specified pathname has to be used; the kernel
has a different notion of the main executable.
dlopen can no longer open PIE binaries, so it is not necessary
to link the executable as non-PIE to trigger a dlopen failure.
If we hard-code the path to the real executable, we can run the test
with and without hard-coded paths because the dlopen path will not
be recognized as the main program in both cases. (With an explict
loader invocation, the loader currently adds argv[0] to l_libname
for the main map and the dlopen call suceeds as a result; it does
not do that in standard mode.)
This change should be fully backwards-compatible because the old
code aborted the load if a soname mismatch was encountered
(instead of searching further for a matching symbol). This means
that no different symbols are found.
The soname check was explicitly disabled for the skip_map != NULL
case. However, this only happens with dl(v)sym and RTLD_NEXT,
and those lookups do not come with a verneed entry that could be used
for the check.
The error check was already explicitly disabled for the skip_map !=
NULL case, that is, when dl(v)sym was called with RTLD_NEXT. But
_dl_vsym always sets filename in the struct r_found_version argument
to NULL, so the check was not active anyway. This means that
symbol lookup results for the skip_map != NULL case do not change,
either.
This test corrupts /var/cache/ldconfig/aux-cache and executes ldconfig
to check it will not segfault using the corrupted aux_cache. The test
uses the test-in-container framework. Verified no regressions on
x86_64.
The audit module itself can be linked with BIND_NOW; it does not
affect its functionality.
This should complete the leftovers from commit
2d6ab5df3b ("Document and fix
--enable-bind-now [BZ #21015]").
Since 9182aa6799 (Fix vDSO l_name for GDB's, BZ#387) the initial link_map
for executable itself and loader will have both l_name and l_libname->name
holding the same value due:
elf/dl-object.c
95 new->l_name = *realname ? realname : (char *) newname->name + libname_len - 1;
Since newname->name points to new->l_libname->name.
This leads to pldd to an infinite call at:
elf/pldd-xx.c
203 again:
204 while (1)
205 {
206 ssize_t n = pread64 (memfd, tmpbuf.data, tmpbuf.length, name_offset);
228 /* Try the l_libname element. */
229 struct E(libname_list) ln;
230 if (pread64 (memfd, &ln, sizeof (ln), m.l_libname) == sizeof (ln))
231 {
232 name_offset = ln.name;
233 goto again;
234 }
Since the value at ln.name (l_libname->name) will be the same as previously
read. The straightforward fix is just avoid the check and read the new list
entry.
I checked also against binaries issues with old loaders with fix for BZ#387,
and pldd could dump the shared objects.
Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu, and
powerpc64le-linux-gnu.
[BZ #18035]
* elf/Makefile (tests-container): Add tst-pldd.
* elf/pldd-xx.c: Use _Static_assert in of pldd_assert.
(E(find_maps)): Avoid use alloca, use default read file operations
instead of explicit LFS names, and fix infinite loop.
* elf/pldd.c: Explicit set _FILE_OFFSET_BITS, cleanup headers.
(get_process_info): Use _Static_assert instead of assert, use default
directory operations instead of explicit LFS names, and free some
leadek pointers.
* elf/tst-pldd.c: New file.
It is possible that the link editor injects an allocated ABI tag note
before the artificial, allocated large note in the test. Note parsing
in open_verify stops when the first ABI tag note is encountered, so if
the ABI tag note comes first, the problematic code is not actually
exercised.
Also tweak the artificial note so that it is a syntactically valid
4-byte aligned note, in case the link editor tries to parse notes and
process them.
Improves the testing part of commit 0065aaaaae.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
The existing tests all use global symbols (but with different
visibility). Local symbols could be treated differently by the
compiler and linker (as was the case on POWER ELFv2, causing
bug 23937), and we did not have test coverage for this.
Tested on x86-64 and POWER ELFv2 little-endian, with and without
--disable-multi-arch. On POWER, the test cases elf/ifuncmain9,
elf/ifuncmain9pic, elf/ifuncmain9pie reproduce bug 23937 with older
binutils.
We should run IFUNC tests with --disable-multi-arch if the toolchain
supports IFUNCs. For correctness, --disable-multi-arch must not
remove IFUNC support from the loader.
Tested on x86-64, x32 and i686 with and without --disable-multi-arch.
* configure.ac (have-ifunc): New LIBC_CONFIG_VAR.
* configure: Regenerated.
* elf/Makefile: Run IFUNC tests if binutils supports IFUNC.
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
The clone.S patch fixes 2 elfutils testsuite unwind failures, where the
backtrace gets stuck repeating __thread_start until we hit the backtrace
limit. This was confirmed by building and installing a patched glibc and
then building elfutils and running its testsuite.
Unfortunately, the testcase isn't working as expected and I don't know why.
The testcase passes even when my clone.S patch is not installed. The testcase
looks logically similarly to the elfutils testcases that are failing. Maybe
there is a subtle difference in how the glibc unwinding works versus the
elfutils unwinding? I don't have good gdb pthread support yet, so I haven't
found a way to debug this. Anyways, I don't know if the testcase is useful or
not. If the testcase isn't useful then maybe the clone.S patch is OK without
a testcase?
Jim
[BZ #24040]
* elf/Makefile (CFLAGS-tst-unwind-main.c): Add -DUSE_PTHREADS=0.
* elf/tst-unwind-main.c: If USE_PTHEADS, include pthread.h and error.h
(func): New.
(main): If USE_PTHREADS, call pthread_create to run func. Otherwise
call func directly.
* nptl/Makefile (tests): Add tst-unwind-thread.
(CFLAGS-tst-unwind-thread.c): Define.
* nptl/tst-unwind-thread.c: New file.
* sysdeps/unix/sysv/linux/riscv/clone.S (__thread_start): Mark ra
as undefined.
Add support for %x, %lx and %zx to _dl_exception_create_format and pad
to the full width with 0.
* elf/Makefile (tests-internal): Add tst-create_format1.
* elf/dl-exception.c (_dl_exception_create_format): Support
%x, %lx and %zx.
* elf/tst-create_format1.c: New file.
Mark the ra register as undefined in _start, so that unwinding through
main works correctly. Also, don't use a tail call so that ra points after
the call to __libc_start_main, not after the previous call.
Currently, DT_TEXTREL is incompatible with IFUNC. When DT_TEXTREL or
DF_TEXTREL is seen, the dynamic linker calls __mprotect on the segments
with PROT_READ|PROT_WRITE before applying dynamic relocations. It leads
to segfault when performing IFUNC resolution (which requires PROT_EXEC
as well for the IFUNC resolver).
This patch makes it call __mprotect with extra PROT_WRITE bit, which
will keep the PROT_EXEC bit if exists, and thus fixes the segfault.
FreeBSD rtld libexec/rtld-elf/rtld.c (reloc_textrel_prot) does the same.
Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
sparc64-linux-gnu, sparcv9-linux-gnu, and armv8-linux-gnueabihf.
Adam J. Richte <adam_richter2004@yahoo.com>
Adhemerval Zanella <adhemerval.zanella@linaro.org>
Fangrui Song <maskray@google.com>
[BZ #20480]
* config.h.in (CAN_TEXTREL_IFUNC): New define.
* configure.ac: Add check if linker supports textrel relocation with
ifunc.
* elf/dl-reloc.c (_dl_relocate_object): Use all required flags on
DT_TEXTREL segments, not only PROT_READ and PROT_WRITE.
* elf/Makefile (ifunc-pie-tests): Add tst-ifunc-textrel.
(CFLAGS-tst-ifunc-textrel.c): New rule.
* elf/tst-ifunc-textrel.c: New file.
I'm testing a patch to let the compiler expand calls to floor in libm
as built-in function calls as much as possible, instead of calling
__floor, so that no architecture-specific __floor inlines are needed,
and then to arrange for non-inlined calls to end up calling __floor,
as done with sqrt and __ieee754_sqrt.
This shows up elf/tst-relsort1mod2.c calling floor, which must not be
converted to a call to __floor. Now, while an IS_IN (libm)
conditional could be added to the existing conditionals on such
redirections in include/math.h, the _ISOMAC conditional ought to
suffice (code in other glibc libraries shouldn't be calling floor or
sqrt anyway, as they aren't provided in libc and the other libraries
don't link with libm). But while tests are mostly now built with
_ISOMAC defined, test modules in modules-names aren't unless also
listed in modules-names-tests.
As far as I can see, all the modules in modules-names in elf/ are in
fact parts of tests and so listing them in modules-names-tests is
appropriate, so they get built with something closer to the headers
used for user code, except in a few cases that actually rely on
something from internal headers. This patch duly sets
modules-names-tests there accordingly (filtering out those tests that
fail to build without internal headers).
Tested for x86_64, and with build-many-glibcs.py.
* elf/Makefile (modules-names-tests): New variable.
* scripts/check-execstack.awk: Consider `xfail' variable containing a
list
of libraries whose stack executability is expected.
* elf/Makefile ($(objpfx)check-execstack.out): Pass
$(check-execstack-xfail) to check-execstack.awk through `xfail'
variable.
* sysdeps/mach/hurd/i386/Makefile (check-execstack-xfail): Set to ld.so
libc.so libpthread.so.
Intel Control-flow Enforcement Technology (CET) instructions:
https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-en
forcement-technology-preview.pdf
includes Indirect Branch Tracking (IBT) and Shadow Stack (SHSTK).
GNU_PROPERTY_X86_FEATURE_1_IBT is added to GNU program property to
indicate that all executable sections are compatible with IBT when
ENDBR instruction starts each valid target where an indirect branch
instruction can land. Linker sets GNU_PROPERTY_X86_FEATURE_1_IBT on
output only if it is set on all relocatable inputs.
On an IBT capable processor, the following steps should be taken:
1. When loading an executable without an interpreter, enable IBT and
lock IBT if GNU_PROPERTY_X86_FEATURE_1_IBT is set on the executable.
2. When loading an executable with an interpreter, enable IBT if
GNU_PROPERTY_X86_FEATURE_1_IBT is set on the interpreter.
a. If GNU_PROPERTY_X86_FEATURE_1_IBT isn't set on the executable,
disable IBT.
b. Lock IBT.
3. If IBT is enabled, when loading a shared object without
GNU_PROPERTY_X86_FEATURE_1_IBT:
a. If legacy interwork is allowed, then mark all pages in executable
PT_LOAD segments in legacy code page bitmap. Failure of legacy code
page bitmap allocation causes an error.
b. If legacy interwork isn't allowed, it causes an error.
GNU_PROPERTY_X86_FEATURE_1_SHSTK is added to GNU program property to
indicate that all executable sections are compatible with SHSTK where
return address popped from shadow stack always matches return address
popped from normal stack. Linker sets GNU_PROPERTY_X86_FEATURE_1_SHSTK
on output only if it is set on all relocatable inputs.
On a SHSTK capable processor, the following steps should be taken:
1. When loading an executable without an interpreter, enable SHSTK if
GNU_PROPERTY_X86_FEATURE_1_SHSTK is set on the executable.
2. When loading an executable with an interpreter, enable SHSTK if
GNU_PROPERTY_X86_FEATURE_1_SHSTK is set on interpreter.
a. If GNU_PROPERTY_X86_FEATURE_1_SHSTK isn't set on the executable
or any shared objects loaded via the DT_NEEDED tag, disable SHSTK.
b. Otherwise lock SHSTK.
3. After SHSTK is enabled, it is an error to load a shared object
without GNU_PROPERTY_X86_FEATURE_1_SHSTK.
To enable CET support in glibc, --enable-cet is required to configure
glibc. When CET is enabled, both compiler and assembler must support
CET. Otherwise, it is a configure-time error.
To support CET run-time control,
1. _dl_x86_feature_1 is added to the writable ld.so namespace to indicate
if IBT or SHSTK are enabled at run-time. It should be initialized by
init_cpu_features.
2. For dynamic executables:
a. A l_cet field is added to struct link_map to indicate if IBT or
SHSTK is enabled in an ELF module. _dl_process_pt_note or
_rtld_process_pt_note is called to process PT_NOTE segment for
GNU program property and set l_cet.
b. _dl_open_check is added to check IBT and SHSTK compatibilty when
dlopening a shared object.
3. Replace i386 _dl_runtime_resolve and _dl_runtime_profile with
_dl_runtime_resolve_shstk and _dl_runtime_profile_shstk, respectively if
SHSTK is enabled.
CET run-time control can be changed via GLIBC_TUNABLES with
$ export GLIBC_TUNABLES=glibc.tune.x86_shstk=[permissive|on|off]
$ export GLIBC_TUNABLES=glibc.tune.x86_ibt=[permissive|on|off]
1. permissive: SHSTK is disabled when dlopening a legacy ELF module.
2. on: IBT or SHSTK are always enabled, regardless if there are IBT or
SHSTK bits in GNU program property.
3. off: IBT or SHSTK are always disabled, regardless if there are IBT or
SHSTK bits in GNU program property.
<cet.h> from CET-enabled GCC is automatically included by assembly codes
to add GNU_PROPERTY_X86_FEATURE_1_IBT and GNU_PROPERTY_X86_FEATURE_1_SHSTK
to GNU program property. _CET_ENDBR is added at the entrance of all
assembly functions whose address may be taken. _CET_NOTRACK is used to
insert NOTRACK prefix with indirect jump table to support IBT. It is
defined as notrack when _CET_NOTRACK is defined in <cet.h>.
[BZ #21598]
* configure.ac: Add --enable-cet.
* configure: Regenerated.
* elf/Makefille (all-built-dso): Add a comment.
* elf/dl-load.c (filebuf): Moved before "dynamic-link.h".
Include <dl-prop.h>.
(_dl_map_object_from_fd): Call _dl_process_pt_note on PT_NOTE
segment.
* elf/dl-open.c: Include <dl-prop.h>.
(dl_open_worker): Call _dl_open_check.
* elf/rtld.c: Include <dl-prop.h>.
(dl_main): Call _rtld_process_pt_note on PT_NOTE segment. Call
_rtld_main_check.
* sysdeps/generic/dl-prop.h: New file.
* sysdeps/i386/dl-cet.c: Likewise.
* sysdeps/unix/sysv/linux/x86/cpu-features.c: Likewise.
* sysdeps/unix/sysv/linux/x86/dl-cet.h: Likewise.
* sysdeps/x86/cet-tunables.h: Likewise.
* sysdeps/x86/check-cet.awk: Likewise.
* sysdeps/x86/configure: Likewise.
* sysdeps/x86/configure.ac: Likewise.
* sysdeps/x86/dl-cet.c: Likewise.
* sysdeps/x86/dl-procruntime.c: Likewise.
* sysdeps/x86/dl-prop.h: Likewise.
* sysdeps/x86/libc-start.h: Likewise.
* sysdeps/x86/link_map.h: Likewise.
* sysdeps/i386/dl-trampoline.S (_dl_runtime_resolve): Add
_CET_ENDBR.
(_dl_runtime_profile): Likewise.
(_dl_runtime_resolve_shstk): New.
(_dl_runtime_profile_shstk): Likewise.
* sysdeps/linux/x86/Makefile (sysdep-dl-routines): Add dl-cet
if CET is enabled.
(CFLAGS-.o): Add -fcf-protection if CET is enabled.
(CFLAGS-.os): Likewise.
(CFLAGS-.op): Likewise.
(CFLAGS-.oS): Likewise.
(asm-CPPFLAGS): Add -fcf-protection -include cet.h if CET
is enabled.
(tests-special): Add $(objpfx)check-cet.out.
(cet-built-dso): New.
(+$(cet-built-dso:=.note)): Likewise.
(common-generated): Add $(cet-built-dso:$(common-objpfx)%=%.note).
($(objpfx)check-cet.out): New.
(generated): Add check-cet.out.
* sysdeps/x86/cpu-features.c: Include <dl-cet.h> and
<cet-tunables.h>.
(TUNABLE_CALLBACK (set_x86_ibt)): New prototype.
(TUNABLE_CALLBACK (set_x86_shstk)): Likewise.
(init_cpu_features): Call get_cet_status to check CET status
and update dl_x86_feature_1 with CET status. Call
TUNABLE_CALLBACK (set_x86_ibt) and TUNABLE_CALLBACK
(set_x86_shstk). Disable and lock CET in libc.a.
* sysdeps/x86/cpu-tunables.c: Include <cet-tunables.h>.
(TUNABLE_CALLBACK (set_x86_ibt)): New function.
(TUNABLE_CALLBACK (set_x86_shstk)): Likewise.
* sysdeps/x86/sysdep.h (_CET_NOTRACK): New.
(_CET_ENDBR): Define if not defined.
(ENTRY): Add _CET_ENDBR.
* sysdeps/x86/dl-tunables.list (glibc.tune): Add x86_ibt and
x86_shstk.
* sysdeps/x86_64/dl-trampoline.h (_dl_runtime_resolve): Add
_CET_ENDBR.
(_dl_runtime_profile): Likewise.
We have this condition in `check_match' (in elf/dl-lookup.c):
if (__glibc_unlikely ((sym->st_value == 0 /* No value. */
&& stt != STT_TLS)
|| ELF_MACHINE_SYM_NO_MATCH (sym)
|| (type_class & (sym->st_shndx == SHN_UNDEF))))
return NULL;
which causes all !STT_TLS symbols whose value is zero to be silently
ignored in lookup. This may make sense for regular symbols, however not
for absolute (SHN_ABS) ones, where zero is like any value, there's no
special meaning attached to it.
Consequently legitimate programs fail, for example taking the
`elf/tst-absolute-sym' test case, substituting 0 for 0x55aa in
`elf/tst-absolute-sym-lib.lds' and then trying to run the resulting
program we get this:
$ .../elf/tst-absolute-sym
.../elf/tst-absolute-sym: symbol lookup error: .../elf/tst-absolute-sym-lib.so: undefined symbol: absolute
$
even though the symbol clearly is there:
$ readelf --dyn-syms .../elf/tst-absolute-sym-lib.so | grep '\babsolute\b'
7: 00000000 0 NOTYPE GLOBAL DEFAULT ABS absolute
$
The check for the zero value has been there since forever or commit
d66e34cd4234/08162fa88891 ("Implemented runtime dynamic linker to
support ELF shared libraries.") dating back to May 2nd 1995, and the
problem triggers regardless of commit e7feec374c ("elf: Correct
absolute (SHN_ABS) symbol run-time calculation [BZ #19818]") being
present or not.
Fix the issue then, by permitting `sym->st_value' to be 0 for SHN_ABS
symbols in lookup.
[BZ #23307]
* elf/dl-lookup.c (check_match): Do not reject a symbol whose
`st_value' is 0 if `st_shndx' is SHN_ABS.
* elf/tst-absolute-zero.c: New file.
* elf/tst-absolute-zero-lib.c: New file.
* elf/tst-absolute-zero-lib.lds: New file.
* elf/Makefile (tests): Add `tst-absolute-zero'.
(modules-names): Add `tst-absolute-zero-lib'.
(LDLIBS-tst-absolute-zero-lib.so): New variable.
($(objpfx)tst-absolute-zero-lib.so): New dependency.
($(objpfx)tst-absolute-zero: New dependency.
